Exploring Prokaryotic Communities in the Guts and Mucus of Nudibranchs, and Their Similarity to Sediment and Seawater Microbiomes.

In the present study, we compared mucus and gut-associated prokaryotic communities from seven nudibranch species with sediment and seawater from Thai coral reefs using high-throughput 16S rRNA gene sequencing. The nudibranch species were identified as Doriprismatica atromarginata (family Chromodorididae), Jorunna funebris (family Discodorididae), Phyllidiella nigra, Phyllidiella pustulosa, Phyllidia carlsonhoffi, Phyllidia elegans, and Phyllidia picta (all family Phyllidiidae). The most abundant bacterial phyla in the dataset were Proteobacteria, Tenericutes, Chloroflexi, Thaumarchaeota, and Cyanobacteria. Mucus and gut-associated communities differed from one another and from sediment and seawater communities. Host phylogeny was, furthermore, a significant predictor of differences in mucus and gut-associated prokaryotic community composition. With respect to higher taxon abundance, the order Rhizobiales (Proteobacteria) was more abundant in Phyllidia species (mucus and gut), whereas the order Mycoplasmatales (Tenericutes) was more abundant in D. atromarginata and J. funebris. Mucus samples were, furthermore, associated with greater abundances of certain phyla including Chloroflexi, Poribacteria, and Gemmatimonadetes, taxa considered to be indicators for high microbial abundance (HMA) sponge species. Overall, our results indicated that nudibranch microbiomes consisted of a number of abundant prokaryotic members with high sequence similarities to organisms previously detected in sponges.

Spatial and environmental variables structure sponge symbiont communities.

Understanding the maintenance and origin of beta diversity is a central topic in ecology. However, the factors that drive diversity patterns and underlying processes remain unclear, particularly for host-prokaryotic associations. Here, beta diversity patterns were studied in five prokaryotic biotopes, namely, two high microbial abundance (HMA) sponge taxa (Xestospongia spp. and Hyrtios erectus), one low microbial abundance (LMA) sponge taxon (Stylissa carteri), sediment and seawater sampled across thousands of kilometres. Using multiple regression on distance matrices (MRM), spatial (geographic distance) and environmental (sea surface temperature and chlorophyll α concentrations) variables proved significant predictors of beta diversity in all five biotopes and together explained from 54% to 82% of variation in dissimilarity of both HMA species, 27% to 43% of variation in sediment and seawater, but only 20% of variation of the LMA S. carteri. Variance partitioning was subsequently used to partition the variation into purely spatial, purely environmental and spatially-structured environmental components. The amount of variation in dissimilarity explained by the purely spatial component was lowest for S. carteri at 11% and highest for H. erectus at 55%. The purely environmental component, in turn, only explained from 0.15% to 2.83% of variation in all biotopes. In addition to spatial and environmental variables, a matrix of genetic differences between pairs of sponge individuals also proved a significant predictor of variation in prokaryotic dissimilarity of the Xestospongia species complex. We discuss the implications of these results for the HMA-LMA dichotomy and compare the MRM results with results obtained using constrained ordination and zeta diversity.

Marine Sponge and Octocoral-Associated Bacteria Show Versatile Secondary Metabolite Biosynthesis Potential and Antimicrobial Activities against Human Pathogens.

Marine microbiomes are prolific sources of bioactive natural products of potential pharmaceutical value. This study inspected two culture collections comprising 919 host-associated marine bacteria belonging to 55 genera and several thus-far unclassified lineages to identify isolates with potentially rich secondary metabolism and antimicrobial activities. Seventy representative isolates had their genomes mined for secondary metabolite biosynthetic gene clusters (SM-BGCs) and were screened for antimicrobial activities against four pathogenic bacteria and five pathogenic Candida strains. In total, 466 SM-BGCs were identified, with antimicrobial peptide- and polyketide synthase-related SM-BGCs being frequently detected. Only 38 SM-BGCs had similarities greater than 70% to SM-BGCs encoding known compounds, highlighting the potential biosynthetic novelty encoded by these genomes. Cross-streak assays showed that 33 of the 70 genome-sequenced isolates were active against at least one Candida species, while 44 isolates showed activity against at least one bacterial pathogen. Taxon-specific differences in antimicrobial activity among isolates suggested distinct molecules involved in antagonism against bacterial versus Candida pathogens. The here reported culture collections and genome-sequenced isolates constitute a valuable resource of understudied marine bacteria displaying antimicrobial activities and potential for the biosynthesis of novel secondary metabolites, holding promise for a future sustainable production of marine drug leads.

Compositional variation between high and low prokaryotic diversity coral reef biotopes translates to different predicted metagenomic gene content.

In a previous study, we identified host species that housed high and low diversity prokaryotic communities. In the present study, we expand on this and assessed the prokaryotic communities associated with seawater, sediment and 11 host species from 7 different phyla in a Taiwanese coral reef setting. The host taxa sampled included hard, octo- and black corals, molluscs, bryozoans, flatworms, fish and sea urchins. There were highly significant differences in composition among host species and all host species housed distinct communities from those found in seawater and sediment. In a hierarchical clustering analysis, samples from all host species, with the exception of the coral Galaxea astreata, formed significantly supported clusters. In addition to this, the coral G. astreata and the bryozoan Triphyllozoon inornatum on the one hand and the coral Tubastraea coccinea, the hermit crab Calcinus laevimanus and the flatworm Thysanozoon nigropapillosum on the other formed significantly supported clusters. In addition to composition, there were highly pronounced differences in richness and evenness among host species from the most diverse species, the bryozoan T. inornatum at 2518 ± 240 OTUs per 10,000 sequences to the least diverse species, the octocoral Cladiella sp. at 142 ± 14 OTUs per 10,000 sequences. In line with the differences in composition, there were significant differences in predicted metagenomic gene counts among host species. Furthermore, there were pronounced compositional and predicted functional differences between high diversity hosts (Liolophura japonica, G. astreata, T. coccinea, C. laevimanus, T. inornatum) and low diversity hosts (Antipathes sp., Pomacentrus coelestis, Modiolus auriculatus, T. nigropapillosum, Cladiella sp. and Diadema savigny). In particular, we found that all tested low diversity hosts were predicted to be enriched for the phosphotransferase system compared to high diversity hosts.

Bacterial Communities Inhabiting the Sponge Biemna fortis, Sediment and Water in Marine Lakes and the Open Sea.

Marine lakes are small bodies of landlocked seawater that are isolated from the open sea and have been shown to house numerous rare and unique taxa. The environmental conditions of the lakes are also characterised by lower pH and salinity and higher temperatures than generally found in the open sea. In the present study, we used a 16S rRNA gene barcoded pyrosequencing approach and a predictive metagenomic approach (PICRUSt) to examine bacterial composition and function in three distinct biotopes (sediment, water and the sponge species Biemna fortis) in three habitats (two marine lakes and the open sea) of the Berau reef system, Indonesia. Both biotope and habitat were significant predictors of higher taxon abundance and compositional variation. Most of the variation in operational taxonomic unit (OTU) composition was related to the biotope (42% for biotope alone versus 9% for habitat alone and 15% combined). Most OTUs were also restricted to a single biotope (1047 for B. fortis, 6120 for sediment and 471 for water). Only 98 OTUs were shared across all three biotopes. Bacterial communities from B. fortis, sediment and water samples were, however, also distinct in marine lake and open sea habitats. This was evident in the abundance of higher bacterial taxa. For example, the phylum Cyanobacteria was significantly more abundant in samples from marine lakes than from the open sea. This difference was most pronounced in the sponge B. fortis. In line with the compositional differences, there were pronounced differences in predicted relative gene count abundance among biotopes and habitats. Of particular interest was the predicted enrichment in B. fortis from the marine lakes for pathways including DNA replication and repair and the glutathione metabolism. This may facilitate adaptation of host and microbes to life in 'stressful' low pH, low salinity and/or high temperature environments such as those encountered in marine lakes.

Multitaxon activity profiling reveals differential microbial response to reduced seawater pH and oil pollution.

There is growing concern that predicted changes to global ocean chemistry will interact with anthropogenic pollution to significantly alter marine microbial composition and function. However, knowledge of the compounding effects of climate change stressors and anthropogenic pollution is limited. Here, we used 16S and 18S rRNA (cDNA)-based activity profiling to investigate the differential responses of selected microbial taxa to ocean acidification and oil hydrocarbon contamination under controlled laboratory conditions. Our results revealed that a lower relative abundance of sulphate-reducing bacteria (Desulfosarcina/Desulfococcus clade) due to an adverse effect of seawater acidification and oil hydrocarbon contamination (reduced pH-oil treatment) may be coupled to changes in sediment archaeal communities. In particular, we observed a pronounced compositional shift and marked reduction in the prevalence of otherwise abundant operational taxonomic units (OTUs) belonging to the archaeal Marine Benthic Group B and Marine Hydrothermal Vent Group (MHVG) in the reduced pH-oil treatment. Conversely, the abundance of several putative hydrocarbonoclastic fungal OTUs was higher in the reduced pH-oil treatment. Sediment hydrocarbon profiling, furthermore, revealed higher concentrations of several alkanes in the reduced pH-oil treatment, corroborating the functional implications of the structural changes to microbial community composition. Collectively, our results advance the understanding of the response of a complex microbial community to the interaction between reduced pH and anthropogenic pollution. In future acidified marine environments, oil hydrocarbon contamination may alter the typical mixotrophic and k-/r-strategist composition of surface sediment microbiomes towards a more heterotrophic state with lower doubling rates, thereby impairing the ability of the ecosystem to recover from acute oil contamination events.

The putative functional ecology and distribution of archaeal communities in sponges, sediment and seawater in a coral reef environment.

Archaea play crucial roles in a number of key ecological processes including nitrification and methanogenesis. Although several studies have been conducted on these organisms, the roles and dynamics of coral reef archaeal communities are still poorly understood, particularly in host and nonhost biotopes and in high (HMA) and low microbial abundance (LMA) sponges. Here, archaeal communities detected in six distinct biotopes, namely, sediment, seawater and four different sponge species Stylissa carteri, Stylissa massa, Xestospongia testudinaria and Hyrtios erectus from the Spermonde Archipelago, SW Sulawesi, Indonesia were investigated using 454-pyrosequencing of 16S rRNA genes (OTU cut-off 97%). Archaeal communities from sediment and sponges were dominated by Crenarchaeota, while the seawater community was dominated by Euryarchaeota. The biotope explained almost 75% of the variation in archaeal composition, with clear separation between microbial assemblages from sediment, X. testudinaria and H. erectus (HMA). In contrast, samples from seawater and both Stylissa species (LMA) showed considerable overlap in the ordination and, furthermore, shared most abundant OTUs with the exception of a single dominant OTU specifically enriched in both Stylissa species. Predicted functional gene content in archaeal assemblages also revealed significant differences among biotopes. Different ammonia assimilation strategies were exhibited by the archaeal communities: X. testudinaria, H. erectus and sediment archaeal communities were enriched for glutamate dehydrogenase with mixed specificity (NAD(P)(+) ) pathways, while archaeal planktonic communities were enriched for specific glutamate dehydrogenase (NADP(+) ) and glutamate synthase pathways. Archaeal communities in Stylissa had intermediate levels of enrichment. Our results indicate that archaeal communities in different biotopes have distinct ecophysiological roles.

Unraveling the interactive effects of climate change and oil contamination on laboratory-simulated estuarine benthic communities.

There is growing concern that modifications to the global environment such as ocean acidification and increased ultraviolet radiation may interact with anthropogenic pollutants to adversely affect the future marine environment. Despite this, little is known about the nature of the potential risks posed by such interactions. Here, we performed a multifactorial microcosm experiment to assess the impact of ocean acidification, ultraviolet B (UV-B) radiation and oil hydrocarbon contamination on sediment chemistry, the microbial community (composition and function) and biochemical marker response of selected indicator species. We found that increased ocean acidification and oil contamination in the absence of UV-B will significantly alter bacterial composition by, among other things, greatly reducing the relative abundance of Desulfobacterales, known to be important oil hydrocarbon degraders. Along with changes in bacterial composition, we identified concomitant shifts in the composition of oil hydrocarbons in the sediment and an increase in oxidative stress effects on our indicator species. Interestingly, our study identifies UV-B as a critical component in the interaction between these factors, as its presence alleviates harmful effects caused by the combination of reduced pH and oil pollution. The model system used here shows that the interactive effect of reduced pH and oil contamination can adversely affect the structure and functioning of sediment benthic communities, with the potential to exacerbate the toxicity of oil hydrocarbons in marine ecosystems.

Composition and Predictive Functional Analysis of Bacterial Communities in Seawater, Sediment and Sponges in the Spermonde Archipelago, Indonesia.

In this study, we used a 16S rRNA gene barcoded pyrosequencing approach to sample bacterial communities from six biotopes, namely, seawater, sediment and four sponge species (Stylissa carteri, Stylissa massa, Xestospongia testudinaria and Hyrtios erectus) inhabiting coral reefs of the Spermonde Archipelago, South Sulawesi, Indonesia. Samples were collected along a pronounced onshore to offshore environmental gradient. Our goals were to (1) compare higher taxon abundance among biotopes, (2) test to what extent variation in bacterial composition can be explained by the biotope versus environment, (3) identify dominant (>300 sequences) bacterial operational taxonomic units (OTUs) and their closest known relatives and (4) assign putative functions to the sponge bacterial communities using a recently developed predictive metagenomic approach. We observed marked differences in bacterial composition and the relative abundance of the most abundant phyla, classes and orders among sponge species, seawater and sediment. Although all biotopes housed compositionally distinct bacterial communities, there were three prominent clusters. These included (1) both Stylissa species and seawater, (2) X. testudinaria and H. erectus and (3) sediment. Bacterial communities sampled from the same biotope, but different environments (based on proximity to the coast) were much more similar than bacterial communities from different biotopes in the same environment. The biotope thus appears to be a much more important structuring force than the surrounding environment. There were concomitant differences in the predicted counts of KEGG orthologs (KOs) suggesting that bacterial communities housed in different sponge species, sediment and seawater perform distinct functions. In particular, the bacterial communities of both Stylissa species were predicted to be enriched for KOs related to chemotaxis, nitrification and denitrification whereas bacterial communities in X. testudinaria and H. erectus were predicted to be enriched for KOs related to the toxin-antitoxin (TA) system, nutrient starvation and heavy metal export.

Composition and predicted functional ecology of mussel-associated bacteria in Indonesian marine lakes.

In the present study, we sampled bacterial communities associated with mussels inhabiting two distinct coastal marine ecosystems in Kalimantan, Indonesia, namely, marine lakes and coastal mangroves. We used 16S rRNA gene pyrosequencing and predicted metagenomic analysis to compare microbial composition and function. Marine lakes are small landlocked bodies of seawater isolated to varying degrees from the open sea environment. They contain numerous endemic taxa and represent natural laboratories of speciation. Our primary goals were to (1) use BLAST search to identify closely related organisms to dominant bacterial OTUs in our mussel dataset and (2) to compare bacterial communities and enrichment in the predicted bacterial metagenome among lakes. Our sequencing effort yielded 3553 OTUs belonging to 44 phyla, 99 classes and 121 orders. Mussels in the largest marine lake (Kakaban) and the coastal mangrove habitat were dominated by bacteria belonging to the phylum Proteobacteria whereas smaller lakes, located on the island of Maratua, were dominated by bacteria belonging to the phyla Firmicutes and Tenericutes. The single most abundant OTU overall was assigned to the genus Mycoplasma. There were several significant differences among locations with respect to metabolic pathways. These included enrichment of xenobiotic biodegradation pathways in the largest marine lake and coastal mangrove. These locations were also the most enriched with respect to nitrogen metabolism. The presence of genes related to isoquinoline alkaloids, polyketides, hydrolases, mono and dioxygenases in the predicted analysis of functional pathways is an indication that the bacterial communities of Brachidontes mussels may be potentially important sources of new marine medicines and enzymes of industrial interest. Future work should focus on measuring how mussel microbial communities influence nutrient dynamics within the marine lake environment and isolating microbes with potential biotechnological applications.

Composition of Archaea in seawater, sediment, and sponges in the Kepulauan Seribu reef system, Indonesia.

Coral reefs are among the most diverse and productive ecosystems in the world. Most research has, however, focused on eukaryotes such as corals and fishes. Recently, there has been increasing interest in the composition of prokaryotes, particularly those inhabiting corals and sponges, but these have mainly focused on bacteria. There have been very few studies of coral reef Archaea, despite the fact that Archaea have been shown to play crucial roles in nutrient dynamics, including nitrification and methanogenesis, of oligotrophic environments such as coral reefs. Here, we present the first study to assess Archaea in four different coral reef biotopes (seawater, sediment, and two sponge species, Stylissa massa and Xestospongia testudinaria). The archaeal community of both sponge species and sediment was dominated by Crenarchaeota, while the seawater community was dominated by Euryarchaeota. The biotope explained more than 72% of the variation in archaeal composition. The number of operational taxonomic units (OTUs) was highest in sediment and seawater biotopes and substantially lower in both sponge hosts. No "sponge-specific" archaeal OTUs were found, i.e., OTUs found in both sponge species but absent from nonhost biotopes. Despite both sponge species hosting phylogenetically distinct microbial assemblages, there were only minor differences in Kyoto Encyclopedia of Genes and Genomes (KEGG) functional pathways. In contrast, most functional pathways differed significantly between microbiomes from sponges and nonhost biotopes including all energy metabolic pathways. With the exception of the methane and nitrogen metabolic pathway, all energy metabolic pathways were enriched in sponges when compared to nonhost biotopes.

Impacts of humic substances, elevated temperature, and UVB radiation on bacterial communities of the marine sponge Chondrilla sp.

Sponges are abundant components of coral reefs known for their filtration capabilities and intricate interactions with microbes. They play a crucial role in maintaining the ecological balance of coral reefs. Humic substances (HS) affect bacterial communities across terrestrial, freshwater, and marine ecosystems. However, the specific effects of HS on sponge-associated microbial symbionts have largely been neglected. Here, we used a randomized-controlled microcosm setup to investigate the independent and interactive effects of HS, elevated temperature, and UVB radiation on bacterial communities associated with the sponge Chondrilla sp. Our results indicated the presence of a core bacterial community consisting of relatively abundant members, apparently resilient to the tested environmental perturbations, alongside a variable bacterial community. Elevated temperature positively affected the relative abundances of ASVs related to Planctomycetales and members of the families Pseudohongiellaceae and Hyphomonadaceae. HS increased the relative abundances of several ASVs potentially involved in recalcitrant organic matter degradation (e.g., the BD2-11 terrestrial group, Saccharimonadales, and SAR202 clade). There was no significant independent effect of UVB and there were no significant interactive effects of HS, heat, and UVB on bacterial diversity and composition. The significant, independent impact of HS on the composition of sponge bacterial communities suggests that alterations to HS inputs may have cascading effects on adjacent marine ecosystems.

Assessing the Effects of Rotifer Feed Enrichments on Turbot (Scophthalmus maximus) Larvae and Post-Larvae Gut-Associated Bacterial Communities.

Live feed enrichments are often used in fish larvicultures as an optimized source of essential nutrients to improve larval growth and survival. In addition to this, they may also play an important role in structuring larval-associated microbial communities and may help improve their resistance to diseases. However, there is limited information available on how larval microbial communities and larviculture water are influenced by different live feed enrichments. In the present study, we investigated the effects of two commercial rotifer enrichments (ER) on turbot (Scophthalmus maximus) larval and post-larval gut-associated bacterial communities during larviculture production. We evaluated their effects on bacterial populations related to known pathogens and beneficial bacteria and their potential influence on the composition of bacterioplankton communities during larval rearing. High-throughput 16S rRNA gene sequencing was used to assess the effects of different rotifer enrichments (ER1 and ER2) on the structural diversity of bacterial communities of the whole turbot larvae 10 days after hatching (DAH), the post-larval gut 30 DAH, and the larviculture water. Our results showed that different rotifer feed enrichments were associated with significant differences in bacterial composition of turbot larvae 10 DAH, but not with the composition of larval gut communities 30 DAH or bacterioplankton communities 10 and 30 DAH. However, a more in-depth taxonomic analysis showed that there were significant differences in the abundance of Vibrionales in both 10 DAH larvae and in the 30 DAH post-larval gut fed different RE diets. Interestingly, the ER1 diet had a higher relative abundance of specific amplicon sequence variants (ASVs) related to potential Vibrio-antagonists belonging to the Roseobacter clade (e.g., Phaeobacter and Ruegeria at 10 DAH and Sulfitobacter at 30 DAH). In line with this, the diet was also associated with a lower relative abundance of Vibrio and a lower mortality. These results suggest that rotifer diets can affect colonization by Vibrio members in the guts of post-larval turbot. Overall, this study indicates that live feed enrichments can have modulatory effects on fish bacterial communities during the early stages of development, which includes the relative abundances of pathogenic and antagonist taxa in larviculture systems.

Denaturing gradient gel electrophoresis and barcoded pyrosequencing reveal unprecedented archaeal diversity in mangrove sediment and rhizosphere samples.

Mangroves are complex ecosystems that regulate nutrient and sediment fluxes to the open sea. The importance of bacteria and fungi in regulating nutrient cycles has led to an interest in their diversity and composition in mangroves. However, very few studies have assessed Archaea in mangroves, and virtually nothing is known about whether mangrove rhizospheres affect archaeal diversity and composition. Here, we studied the diversity and composition of Archaea in mangrove bulk sediment and the rhizospheres of two mangrove trees, Rhizophora mangle and Laguncularia racemosa, using denaturing gradient gel electrophoresis (DGGE) and pyrosequencing of archaeal 16S rRNA genes with a nested-amplification approach. DGGE profiles revealed significant structural differences between bulk sediment and rhizosphere samples, suggesting that roots of both mangrove species influence the sediment archaeal community. Nearly all of the detected sequences obtained with pyrosequencing were identified as Archaea, but most were unclassified at the level of phylum or below. Archaeal richness was, furthermore, the highest in the L. racemosa rhizosphere, intermediate in bulk sediment, and the lowest in the R. mangle rhizosphere. This study shows that rhizosphere microhabitats of R. mangle and L. racemosa, common plants in subtropical mangroves located in Rio de Janeiro, Brazil, hosted distinct archaeal assemblages.

Draft Genome Sequence of Vibrio mediterranei Strain CyArs1.

Here, we report on the draft genome sequence of Vibrio mediterranei strain CyArs1, isolated from the marine sponge Cinachyrella sp. Genome annotation revealed multiple genomic features, including eukaryotic-like repeat protein- and multidrug resistance-encoding genes, potentially involved in symbiotic relationships with the sponge host.

Assessing the genomic composition, putative ecological relevance and biotechnological potential of plasmids from sponge bacterial symbionts.

Plasmid-mediated transfer of genes can have direct consequences in several biological processes within sponge microbial communities. However, very few studies have attempted genomic and functional characterization of plasmids from marine host-associated microbial communities in general and those of sponges in particular. In the present study, we used an endogenous plasmid isolation method to obtain plasmids from bacterial symbionts of the marine sponges Stylissa carteri and Paratetilla sp. and investigated the genomic composition, putative ecological relevance and biotechnological potential of these plasmids. In total, we isolated and characterized three complete plasmids, three plasmid prophages and one incomplete plasmid. Our results highlight the importance of plasmids to transfer relevant genetic traits putatively involved in microbial symbiont adaptation and host-microbe and microbe-microbe interactions. For example, putative genes involved in bacterial response to chemical stress, competition, metabolic versatility and mediation of bacterial colonization and pathogenicity were detected. Genes coding for enzymes and toxins of biotechnological potential were also detected. Most plasmid prophage coding sequences were, however, hypothetical proteins with unknown functions. Overall, this study highlights the ecological relevance of plasmids in the marine sponge microbiome and provides evidence that plasmids of sponge bacterial symbionts may represent an untapped resource of genes of biotechnological interest.

The effect of natural disturbances on forest biodiversity: an ecological synthesis.

Disturbances alter biodiversity via their specific characteristics, including severity and extent in the landscape, which act at different temporal and spatial scales. Biodiversity response to disturbance also depends on the community characteristics and habitat requirements of species. Untangling the mechanistic interplay of these factors has guided disturbance ecology for decades, generating mixed scientific evidence of biodiversity responses to disturbance. Understanding the impact of natural disturbances on biodiversity is increasingly important due to human-induced changes in natural disturbance regimes. In many areas, major natural forest disturbances, such as wildfires, windstorms, and insect outbreaks, are becoming more frequent, intense, severe, and widespread due to climate change and land-use change. Conversely, the suppression of natural disturbances threatens disturbance-dependent biota. Using a meta-analytic approach, we analysed a global data set (with most sampling concentrated in temperate and boreal secondary forests) of species assemblages of 26 taxonomic groups, including plants, animals, and fungi collected from forests affected by wildfires, windstorms, and insect outbreaks. The overall effect of natural disturbances on α-diversity did not differ significantly from zero, but some taxonomic groups responded positively to disturbance, while others tended to respond negatively. Disturbance was beneficial for taxonomic groups preferring conditions associated with open canopies (e.g. hymenopterans and hoverflies), whereas ground-dwelling groups and/or groups typically associated with shady conditions (e.g. epigeic lichens and mycorrhizal fungi) were more likely to be negatively impacted by disturbance. Across all taxonomic groups, the highest α-diversity in disturbed forest patches occurred under moderate disturbance severity, i.e. with approximately 55% of trees killed by disturbance. We further extended our meta-analysis by applying a unified diversity concept based on Hill numbers to estimate α-diversity changes in different taxonomic groups across a gradient of disturbance severity measured at the stand scale and incorporating other disturbance features. We found that disturbance severity negatively affected diversity for Hill number q = 0 but not for q = 1 and q = 2, indicating that diversity-disturbance relationships are shaped by species relative abundances. Our synthesis of α-diversity was extended by a synthesis of disturbance-induced change in species assemblages, and revealed that disturbance changes the ß-diversity of multiple taxonomic groups, including some groups that were not affected at the α-diversity level (birds and woody plants). Finally, we used mixed rarefaction/extrapolation to estimate biodiversity change as a function of the proportion of forests that were disturbed, i.e. the disturbance extent measured at the landscape scale. The comparison of intact and naturally disturbed forests revealed that both types of forests provide habitat for unique species assemblages, whereas species diversity in the mixture of disturbed and undisturbed forests peaked at intermediate values of disturbance extent in the simulated landscape. Hence, the relationship between α-diversity and disturbance severity in disturbed forest stands was strikingly similar to the relationship between species richness and disturbance extent in a landscape consisting of both disturbed and undisturbed forest habitats. This result suggests that both moderate disturbance severity and moderate disturbance extent support the highest levels of biodiversity in contemporary forest landscapes.

Characterization of putative circular plasmids in sponge-associated bacterial communities using a selective multiply-primed rolling circle amplification.

Plasmid transfers among bacterial populations can directly influence the ecological adaptation of these populations and their interactions with host species and environment. In this study, we developed a selective multiply-primed rolling circle amplification (smRCA) approach to enrich and characterize circular plasmid DNA from sponge microbial symbionts via high-throughput sequencing (HTS). DNA (plasmid and total community DNA) obtained from sponge (Cinachyrella sp.) samples and a bacterial symbiont (Vibrio sp. CyArs1) isolated from the same sponge species (carrying unknown plasmids) were used to develop and validate our methodology. The smRCA was performed during 16 hr with 141 plasmid-specific primers covering all known circular plasmid groups. The amplified products were purified and subjected to a reamplification with random hexamer primers (2 hr) and then sequenced using Illumina MiSeq. The developed method resulted in the successful amplification and characterization of the sponge plasmidome and allowed us to detect plasmids associated with the bacterial symbiont Vibrio sp. CyArs1 in the sponge host. In addition to this, a large number of small (<2 kbp) and cryptic plasmids were also amplified in sponge samples. Functional analysis identified proteins involved in the control of plasmid partitioning, maintenance and replication. However, most plasmids contained unknown genes, which could potentially serve as a resource of unknown genetic information and novel replication systems. Overall, our results indicate that the smRCA-HTS approach developed here was able to selectively enrich and characterize plasmids from bacterial isolates and sponge host microbial communities, including plasmids larger than 20 kbp.

Author Correction: Aquaponics using a fish farm effluent shifts bacterial communities profile in halophytes rhizosphere and endosphere.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Aquaponics using a fish farm effluent shifts bacterial communities profile in halophytes rhizosphere and endosphere.

The intensification of marine aquaculture raises multiple sustainability issues, namely the handling of nutrient-rich effluents that can adversely impact ecosystems. As integrated multi-trophic aquaculture (IMTA) gains momentum, the use of halophyte plants to phytoremediate aquaculture effluents has received growing attention, particularly in aquaponics. It is, therefore, important to obtain a more in-depth knowledge of the microbial communities present in the root systems of these plants, both in their natural environment (sediment) and in aquaponics, in order to understand their nutrient removal potential. The present study used denaturing gradient gel electrophoresis (DGGE) and barcoded pyrosequencing to assess the bacterial community present in the endosphere and rhizosphere of three halophyte plants: Halimione portulacoides, Salicornia ramosissima and Sarcocornia perennis. Species-specific effects were recorded in the profile and diversity of the bacterial communities present in halophyte roots, with significant differences also recorded for the same halophyte species grown in contrasting environments (sediment vs. aquaponics). In aquaponics the most abundant groups belonged to the orders Rhodocyclales, Campylobacterales, Rhodobacterales and Desulfobacterales, while in the natural environment (sediment) the most abundant groups belonged to the orders Rhizobiales, Sphingomonadales and Alteromonadales. An overall enrichment in bacterial taxa involved in nutrient cycling was recorded in the roots of halophytes grown in aquaponics (such as Denitromonas, Mesorhizobium, Colwellia, Dokdonella and Arcobacter), thereby highlighting their potential to reduce the nutrient loads from aquaculture effluents.