First report of PST-producing Microseira wollei from China reveals its novel toxin profile.

Microseira wollei, a globally distributed freshwater bloom-forming benthic cyanobacterium, is known for its production of cyanotoxins and taste and odor (T&O). While CYN (Cylindrospermopsin)-producing populations of M. wollei are confined to Australia, PST (Paralytic shellfish toxins)-producing populations have been exclusively documented in North America. In this study, four benthic cyanobacterial strains, isolated from West Lake in China, were identified as M. wollei based on morphological and phylogenetic analyses. Detection of sxtA gene and UPLC-MS/MS analysis conclusively confirmed the PST-producing capability of M. wollei CHAB5998. In the phylogenetic tree of 16S rDNA, M. wollei strains formed a monophyletic group with two subclades. Notably, non-PST-producing Chinese strains clustered with Australian strains in Clade II, while all other strains, including PST-producing ones, clustered in Clade I. Additionally, CHAB5998 contains ten PST variants, of which STX, NEO, GTX2, GTX3, GTX5 and C1 were identified for the first time in M. wollei. Sequence analysis of PST biosynthetic gene cluster (sxt) genes indicated potential base variations, gene rearrangements, insertions, and deletions in the strain CHAB5998. Also, sxt gene has a longer evolutionary history in M. wollei than that in cyanobacteria from Nostocales. Multiple recombination breakpoints detected in sxt genes and the inconsistency in the topology of the phylogenetic trees between sxt and 16S rDNA suggested that multiple horizontal gene transfers (HGT) have occurred. Overall, the present study marks the first documented occurrence of PST-producing M. wollei outside of North America and identifies it as the first toxic freshwater benthic cyanobacterium in China. This revelation implies that benthic cyanobacteria may pose a higher environmental risk in China than previously acknowledged.

Defense against Paramecium predation via long filament morphology favors the survival of Raphidiopsis raciborskii populations.

Raphidiopsis blooms are notorious for cyanotoxin formation and strong invasiveness, threatening the stability of aquatic ecosystems and human health. The protozoa Paramecium can potentially serve as an organism for controlling Raphidiopsis blooms owing to its grazing effect. However, the grazing ability of Paramecium is largely determined by the size of the prey, and the population of Raphidiopsis consists of filaments of varying lengths and sizes. The selective grazing behavior of Paramecium toward short-length or small-sized filaments in the Raphidiopsis population, as opposed to long filaments, remains unclear. Therefore, in this study, we co-cultured the predator Paramecium sp. with different initial abundances and the prey Raphidiopsis raciborskii to explore this knowledge gap. Our results suggested that: (1) the population of R. raciborskii declined under the selective grazing effect of Paramecium sp. on short filaments, whereas R. raciborskii with long filaments survived; (2) the growth of Paramecium sp. feeding on the same abundance of R. raciborskii was reduced at higher initial abundances, whereas its carrying capacity exhibited an opposite trend; (3) under ingestion by Paramecium sp., the morphology of R. raciborskii developed in the direction of becoming larger, and higher initial abundances of Paramecium sp. intensified this process; (4) increasing initial abundance of Paramecium sp. aggravated the decline of R. raciborskii photosynthetic activity. Therefore, the grazing effect of Paramecium sp. on R. raciborskii mainly affects filaments of short length or small size. Collectively, these results clarify the inter-species interaction between the protozoa Paramecium and filamentous cyanobacteria Raphidiopsis, including population dynamics and morphological and physiological changes in the predator and prey. Such insights into the interactions between Paramecium and R. raciborskii may have implications for the biological control of blooms caused by filamentous cyanobacteria.

Comparative toxicology of algal cell extracts and pure cyanotoxins: insights into toxic effects and mechanisms of harmful cyanobacteria Raphidiopsis raciborskii.

Ongoing research on cyanotoxins, driven by the socioeconomic impact of harmful algal blooms, emphasizes the critical necessity of elucidating the toxicological profiles of algal cell extracts and pure toxins. This study comprehensively compares Raphidiopsis raciborskii dissolved extract (RDE) and cylindrospermopsin (CYN) based on Daphnia magna assays. Both RDE and CYN target vital organs and disrupt reproduction, development, and digestion, thereby causing acute and chronic toxicity. Disturbances in locomotion, reduced behavioral activity, and weakened swimming capability in D. magna have also been reported for both RDE and CYN, indicating the insufficiency of conventional toxicity evaluation parameters for distinguishing between the toxic effects of algal extracts and pure cyanotoxins. Additionally, chemical profiling revealed the presence of highly active tryptophan-, humic acid-, and fulvic acid-like fluorescence compounds in the RDE, along with the active constituents of CYN, within a 15-day period, demonstrating the chemical complexity and dynamics of the RDE. Transcriptomics was used to further elucidate the distinct molecular mechanisms of RDE and CYN. They act diversely in terms of cytotoxicity, involving oxidative stress and response, protein content, and energy metabolism, and demonstrate distinct modes of action in neurofunctions. In essence, this study underscores the distinct toxicity mechanisms of RDE and CYN and emphasizes the necessity for context- and objective-specific toxicity assessments, advocating nuanced approaches to evaluate the ecological and health implications of cyanotoxins, thereby contributing to the precision of environmental risk assessments.

Okeanomitos corallinicola gen. and sp. nov. (Nostocales, Cyanobacteria), a new toxic marine heterocyte-forming Cyanobacterium from a coral reef.

Cyanobacterial mats supplanting coral and spreading coral diseases in tropical reefs, intensified by environmental shifts caused by human-induced pressures, nutrient enrichment, and global climate change, pose grave risks to the survival of coral ecosystems. In this study, we characterized Okeanomitos corallinicola gen. and sp. nov., a newly discovered toxic marine heterocyte-forming cyanobacterium isolated from a coral reef ecosystem of the South China Sea. Phylogenetic analysis, based on the 16S rRNA gene and the secondary structure of the 16S-23S rRNA intergenic region, placed this species in a clade distinct from closely related genera, that is, Sphaerospermopsis stricto sensu, Raphidiopsis, and Amphiheterocytum. The O. corallinicola is a marine benthic species lacking gas vesicles, distinguishing it from other members of the Aphanizomenonaceae family. The genome of O. corallinicola is large and exhibits diverse functional capabilities, potentially contributing to the resilience and adaptability of coral reef ecosystems. In vitro assays revealed that O. corallinicola demonstrates notable cytotoxic activity against various cancer cell lines, suggesting its potential as a source of novel anticancer compounds. Furthermore, the identification of residual saxitoxin biosynthesis function in the genome of O. corallinicola, a marine cyanobacteria, supports the theory that saxitoxin genes in cyanobacteria and dinoflagellates may have been horizontally transferred between them or may have originated from a shared ancestor. Overall, the identification and characterization of O. corallinicola provides valuable contributions to cyanobacterial taxonomy, offering novel perspectives on complex interactions within coral reef ecosystems.

Gansulinema gen. nov. and Komarkovaeasiopsis gen. nov.: Novel Oculatellacean genera (Cyanobacteria) isolated from desert soils and hot spring.

To increase the understanding of simple thin filamentous cyanobacteria in harsh environmental areas, we previously isolated and identified four strains (XN101, XN102, GS121, NX122) from desert soils and hot spring in China. As a result, two new Oculatellacean genera of these four strains, Gansulinema gen. nov. and Komarkovaeasiopsis gen. nov., are described based on a polyphasic approach. The ultrastructure of these strains showed a similar arrangement of peripheral thylakoids with three to four parallel layers, indicating that they belonged to the orders Nodosilineales, Oculatellales, or Leptolyngbyales. In the 16S rRNA gene phylogeny, two sequences of the Gansulinema strains and the two sequences of the Komarkovaeasiopsis strains formed two independent and robust clusters, within the order Oculatellales. The 16S rRNA gene sequences of strains of Komarkovaeasiopsis and Gansulinema showed low identity to each other (≤93.2%) and to other sequences of the Oculatellacean genera (≤94.5% and ≤93.3%, respectively). Furthermore, the 16S-23S internal transcribed spacer rRNA region secondary structures of strains of Komarkovaeasiopsis and Gansulinema were not consistent with all existing descriptions of Oculatellacean taxa. These data suggest that cyanobacterial communities are rich sources of new taxa in under-exploited areas, such as desert soils and hot spring in China.

Combining single-cell RNA sequencing with spatial transcriptome analysis reveals dynamic molecular maps of cambium differentiation in the primary and secondary growth of trees.

Primary and secondary growth of the tree stem are responsible for corresponding increases in trunk height and diameter. However, our molecular understanding of the biological processes that underlie these two types of growth is incomplete. In this study, we used single-cell RNA sequencing and spatial transcriptome sequencing to reveal the transcriptional landscapes of primary and secondary growth tissues in the Populus stem. Comparison between the cell atlas and differentiation trajectory of primary and secondary growth revealed different regulatory networks involved in cell differentiation from cambium to xylem precursors and phloem precursors. These regulatory networks may be controlled by auxin accumulation and distribution. Analysis of cell differentiation trajectories suggested that vessel and fiber development followed a sequential pattern of progressive transcriptional regulation. This research provides new insights into the processes of cell identity and differentiation that occur throughout primary and secondary growth of tree stems, increasing our understanding of the cellular differentiation dynamics that occur during stem growth in trees.

Effect and mechanism of perfluorooctanoic acid (PFOA) on anaerobic digestion sludge dewaterability.

Perfluorooctanoic acid (PFOA) as nonbiodegradable organic pollutant, its presence and risks in wastewater treatment system has aroused wide concern. This study investigated the effect and underlying mechanism of PFOA on anaerobic digestion sludge (ADS) dewaterability. Long-term exposure experiments were set up to investigate the effect with various concentration of PFOA dosed. Experimental results suggested that the existence of high concentration PFOA (over 1000 µg/L) could deteriorate ADS dewaterability. The long-term exposure to 100,000 µg/L PFOA of ADS increased specific resistance filtration (SRF) by 81.57%. It was found that PFOA promoted the release of extracellular polymeric substances (EPS), which was strongly associated with sludge dewaterability. The fluorescence analysis revealed that the high PFOA concentration could significantly improve the percentage of protein-like substances and soluble microbial by-product-like content, and then further deteriorated the dewaterability. The FTIR results showed that long-term exposure of PFOA caused loose protein structure in sludge EPS, which led to loose sludge floc structure. The loose sludge floc structure aggravated the deterioration of sludge dewaterability. The solids-water distribution coefficient (Kd) decreased with the increase of initial PFOA concentration. Moreover, PFOA significantly affected microbial community structure. Metabolic function prediction results showed significant decrease of fermentation function exposed to PFOA. This study revealed that the PFOA with high concentration could deteriorated sludge dewaterability, which should be highly concerned.

Aridity modulates biogeographic distribution and community assembly of cyanobacterial morphotypes in drylands.

The patterns of biogeographic distribution and assembly processes of microbiota are of vital importance for understanding ecological adaptation and functioning maintenance. However, the role of morphological characteristics in microbial assembly is still poorly ascertained. Here, by integrating high-throughput sequencing and robust extrapolation of traits, we investigated taxonomic and phylogenetic turnovers of various cyanobacterial morphotypes in biocrusts to evaluate the contributions of deterministic and stochastic processes across a large scale of drylands in northwestern China. The results showed that the non-heterocystous filamentous category dominated biocrusts in the arid ecosystem and exhibited strong tolerance against environmental fluctuations. Despite the significant distance-decay relationship of ß-diversity detected in all categories, both species composition and phylogenetic turnover rates of coccoid cyanobacteria were higher than non-heterocystous filamentous and heterocystous morphotypes. Moreover, the assembly of cyanobacteria was driven by different ecological processes that the entire community and non-heterocystous filamentous morphotype were governed by deterministic processes, while stochasticity prevailed in heterocystous and coccoid cyanobacteria. Nonetheless, aridity can modulate the balance between determinism and stochasticity and prompt a shifting threshold among morphotypes. Our findings provide a unique perspective to understanding the critical role of microbial morphology in community assembly and facilitate the prediction of biodiversity loss under climate change.

Discovery of a High-Efficient Algicidal Bacterium against Microcystis aeruginosa Based on Examinations toward Culture Strains and Natural Bloom Samples.

Harmful cyanobacterial blooms occur worldwide and pose a great threat to aquatic ecosystems and public health. The application of algicidal bacteria represents an eco-friendly strategy for controlling harmful cyanobacterial blooms; thus, searching for a high efficiency of algicidal bacteria has been becoming an important and continuous task in science. Herein, we identified a bacterial strain coded Streptomyces sp. HY with a highly algicidal activity, and investigated its algicidal efficiency and mechanism against Microcystis aeruginosa. The strain HY displayed high algicidal activity toward Microcystis aeruginosa cells, with a removal rate of 93.04% within 2 days via indirect attack. Streptomyces sp. HY also showed the ability to lyse several genera of cyanobacterial strains, including Dolichospermum, Pseudanabaena, Anabaena, and Synechocystis, whereas it showed a minor impact on the green alga Scenedesmus obliquus, demonstrating its selectivity specially for targeting cyanobacteria. Its algicidal mechanism involved damages to the photosynthesis system, morphological injury of algal cells, oxidative stress, and dysfunction of the DNA repair system. Furthermore, HY treatment reduced the expression levels of genes (mcyB and mcyD) related to microcystin biosynthesis and decreased the total content of microcystin-leucine-arginine by 79.18%. Collectively, these findings suggested that the algicidal bacteria HY is a promising candidate for harmful cyanobacterial bloom control.

Dual characteristics of Bellamya aeruginosa encountering Microcystis aeruginosa: Algal control and toxin depuration.

The benthic gastropods Bellamya aeruginosa (B. aeruginosa) is ubiquitous in freshwater in China and neighboring countries with great edible value. It has been recognized as a potential manipulator to control harmful algal blooms due to its filtration on algal cells. In this study, the control effect of B. aeruginosa on toxic and non-toxic Microcystis aeruginosa (M. aeruginosa), and the accumulation and depuration of microcystins (MCs) in the snail were systematically explored. Results indicated that although toxic M. aeruginosa could protect itself via producing MCs, the introduction of B. aeruginosa could still effectively inhibit the algae with cell density below 1 × 106 cells/mL. Hepatopancreas was the primary target of MCs in all tissues of B. aeruginosa, presenting a maximum of 3089.60 ng/g DW when exposed to toxic M. aeruginosa of 1.0 × 107 cells/mL. The enrichment of MCs in other tissues following the order of digestive tract > gonad > mantle > muscle. Interestingly, snail could again excrete previously enriched MCs when transferred to non-toxic M. aeruginosa, giving rise to over 80% reduction of MCs in the body. After depuration, the estimated daily intake (EDI) of free MCs in intact individuals and the edible parts of B. aeruginosa were both lower than the tolerable daily intake (TDI). These results implicated that B. aeruginosa could control low density of M. aeruginosa in spring. Particularly, the snail could be perfectly safe to consume by purifying for a while after using as manipulator.

Recent Advances in the Ecology of Bloom-Forming Raphidiopsis (Cylindrospermopsis) raciborskii: Expansion in China, Intraspecific Heterogeneity and Critical Factors for Invasion.

Water blooms caused by the invasive cyanobacterium Raphidiopsis raciborskii occur in many reservoirs in the tropical and subtropical regions of China. In recent decades, this species has spread rapidly to temperate regions. Phenotypic plasticity and climate warming are thought to promote the worldwide dispersion of R. raciborskii. However, investigations into the genetic and phenotypic diversities of this species have revealed significant intraspecific heterogeneity. In particular, competition between R. raciborskii and Microcystis aeruginosa was highly strain dependent. Although the concept of an ecotype was proposed to explain the heterogeneity of R. raciborskii strains with different geographic origins, microevolution is more reasonable for understanding the coexistence of different phenotypes and genotypes in the same environment. It has been suggested that intraspecific heterogeneity derived from microevolution is a strong driving force for the expansion of R. raciborskii. Additionally, temperature, nutrient fluctuations, and grazer disturbance are critical environmental factors that affect the population establishment of R. raciborskii in new environments. The present review provides new insights into the ecological mechanisms underlying the invasion of R. raciborskii in Chinese freshwater ecosystems.

Chlorophyll f production in two new subaerial cyanobacteria of the family Oculatellaceae.

Chlorophyll (Chl) f was recently identified in a few cyanobacteria as the fifth chlorophyll of oxygenic organisms. In this study, two Leptolyngbya-like strains of CCNU0012 and CCNU0013 were isolated from a dry ditch in Chongqing city and a brick wall in Mount Emei Scenic Area in China, respectively. These two strains were described as new species: Elainella chongqingensis sp. nov. (Oculatellaceae, Synechococcales) and Pegethrix sichuanica sp. nov. (Oculatellaceae, Synechococcales) by the polyphasic approach based on morphological features, phylogenetic analysis of 16S rRNA gene and secondary structure comparison of 16S-23S internal transcribed spacer domains. Both strains produced Chl a under white light (WL) but additionally induced Chl f synthesis under far-red light (FRL). Unexpectedly, the content of Chl f in P. sichuanica was nearly half that in most Chl f-producing cyanobacteria. Red-shifted phycobiliproteins were also induced in both strains under FRL conditions. Subsequently, additional absorption peak beyond 700 nm in the FRL spectral region appeared in these two strains. This is the first report of Chl f production induced by FRL in the family Oculatellaceae. This study not only extended the diversity of Chl f-producing cyanobacteria but also provided precious samples to elucidate the essential binding sites of Chl f within cyanobacterial photosystems.

Geographic pattern of phytoplankton community and their drivers in lakes of middle and lower reaches of Yangtze River floodplain, China.

Disentangling the relative contributions of deterministic and stochastic processes was critical to compressive understanding of underlying mechanism governing geographic pattern and assembly of phytoplankton community, while it was seldom performed in connected lakes under human pressure. Here, we investigated phytoplankton community pattern in relation to environmental and spatial factors over 81 lakes located in the middle and lower reaches of Yangtze River (MLYR) floodplain, where many lakes suffered from eutrophication and cyanobacterial blooms. A majority of MLYR lakes had higher phytoplankton abundance surpassing 107 cells/L and were dominated by common bloom-forming cyanobacterial genera, including Pseudanabaena, Microcystis, Merismopedia, Dolichospermum, Limnothrix, and Raphidiopsis. Phytoplankton community exhibited a striking geographical pattern both for taxonomic and functional compositions, while functional groups were less sensitive, and dissimilarity in communities displayed no significant increases with increasing geographical distance. Further, species richness explained much higher percentage of community variations than species turnover, indicating a reduced effect of environmental filtering of phytoplankton species with tolerance to similar environments in connected MLYR lakes. Both deterministic and stochastic processes governed assembly and biogeographic of phytoplankton community. Variation partition analysis showed that spatial factors exhibited greater influence on phytoplankton community compared to environmental variables. The stronger influence of spatial factors was further demonstrated by Mantel test and neutral community model. These findings indicate that deterministic and stochastic processes exhibited similar biogeographic patterns for phytoplankton community in MLYR lakes, but stochastic process was overwhelmingly dominated. Moreover, a large proportion of unexplained variation implies that complex interactions exist to shape assembly mechanism of phytoplankton community in MLYR lakes.

Methane production from peroxymonosulfate pretreated algae biomass: Insights into microbial mechanisms, microcystin detoxification and heavy metal partitioning behavior.

This study investigated the methane production potential of algal biomass by anerobic digestion with the addition of peroxymonosulfate (PMS), the removal of microcystin were analyzed and discussed. The microcystin concentration in the collected algal sludge was 1.20 µg/L in the liquid phase and 1393 µg/g in the algal sludge before anaerobic fermentation. The microcystin concentration decreased to 0.20-0.35 µg/L in the liquid phase and 4.16-11.51 µg/g in the sludge phase after 60 days of digestion. The initial PMS dose and residue microcystin concentration could be simulated with a logarithmic decay model (R2 > 0.87). Anaerobic digestion could recover energy from algal source in the form of methane gas, which was not affected in the presence of microcystin, and the microcystin removal rate was >99%. Digestion decreased the total contents of Cd and Zn in the liquid phase and increased the total contents of Cr and Pb in the liquid phase. The microbial community and function prediction results indicated that the PMS0.1 system had the highest methane production, which was attributed to the high abundance of Mechanosaeta (40.52%). This study provides insights into microbial mechanisms, microcystin detoxification and the heavy metal partitioning behavior of the algal biomass during methane production.

Occurrence of Mycosporine-like Amino Acids (MAAs) from the Bloom-Forming Cyanobacteria Aphanizomenon Strains.

Mycosporine-like amino acids (MAAs) are widespread in various microbes and protect them against harsh environments. Here, four different Aphanizomenon species were isolated from severely eutrophic waterbodies, Lake Dianchi and the Guanqiao fishpond. Morphological characters and molecular phylogenetic analysis verified that the CHAB5919, 5921, and 5926 strains belonged to the Aphanizomenon flos-aquae clade while Guanqiao01 belonged to the Aphanizomenon gracile clade. Full wavelength scanning proved that there was obvious maximal absorption at 334 nm through purified methanol extraction, and these substances were further analyzed by HPLC and UPLC-MS-MS. The results showed that two kinds of MAAs were discovered in the cultured Aphanizomenon strains. One molecular weight was 333.28 and the other was 347.25, and the daughter fragment patterns were in accordance with the previously articles reported shinorine and porphyra-334 ion characters. The concentration of the MAAs was calibrated from semi-prepared MAAs standards from dry cells of Microcystis aeruginosa PCC7806 algal powder, and the purity of shinorine and porphyra-334 were 90.2% and 85.4%, respectively. The average concentrations of shinorine and porphyra-334 were 0.307−0.385 µg/mg and 0.111−0.136 µg/mg in Aphanizomenon flos-aquae species, respectively. And there was only one kind of MAAs (shinorine) in Aphanizomenon gracile species.,with a content of 0.003−0.049 µg/mg dry weight among all Aphanizomenon gracile strains. The shinorine concentration in Aphanizomenon flos-aquae was higher than that in Aphanizomenon gracile strains. The total MAAs production can be ranked as Aphanizomenon flos-aquae > Aphanizomenon gracile.

Kovacikia minuta sp. nov. (Leptolyngbyaceae, Cyanobacteria), a new freshwater chlorophyll f-producing cyanobacterium.

A few groups of cyanobacteria have been characterized as having far-red light photoacclimation (FaRLiP) that results from chlorophyll f (Chl f) production. In this study, using a polyphasic approach, we taxonomically transferred the Cf. Leptolyngbya sp. CCNUW1 isolated from a shaded freshwater pond, which produces Chl f under far-red light, to the genus Kovacikia and named this taxon Kovacikia minuta sp. nov. This strain was morphologically similar to Leptolyngbya-like strains. The thin filaments were purplish-brown under white light but became grass green under far-red light. The 31-gene phylogeny grouped K. minuta CCNU0001 into order Synechococcales and family Leptolyngbyaceae. Phylogenetic analysis based on 16S rRNA gene sequences further showed that K. minuta CCNU0001 was clustered into Kovacikia with similarities of 97.2-97.4% to the recently reported type species of Kovacikia muscicola HA7619-LM3. Additionally, the internal transcribed spacer region between 16S-23S rRNA genes had a unique sequence and secondary structure compared with other Kovacikia strains and phylogenetically related taxa. Draft genome sequences of K. minuta CCNU0001 (8,564,336 bp) were assembled into one circular chromosome and two circular plasmids. A FaRLiP 20-gene cluster comprised two operons with the unique organization. In sum, K. minuta was established as a new species, and it is the first species reported to produce Chl f and for which a draft genome was produced in genus Kovacikia. This study expanded our knowledge regarding the diversity of Chl f-producing cyanobacteria in far-red light-enriched environments and provides important foundational information for future investigations of FaRLiP evolution in cyanobacteria.

Cyanobacterial blooms in China: diversity, distribution, and cyanotoxins.

Cyanobacterial blooms, which refer to the massive growth of harmful cyanobacteria, have altered the global freshwater ecosystems during the past decades. China has the largest population in the world, and it is suffering from the harmful effect of water eutrophication and cyanobacterial blooms along with rapid development of the economy and society. Research on cyanobacterial blooms and cyanotoxins in China have been overwhelmingly enhanced and emphasized during the past decades. In the present review, the research on cyanobacterial blooms in China is generally introduced, including the history of cyanobacterial bloom studies, the diversity of the bloom-forming cyanobacteria species (BFCS), and cyanotoxin studies in China. Most studies have focused on Microcystis, its blooms, and microcystins. Newly emerging blooms with the dominance of non-Microcystis BFCS have been gradually expanding to wide regions in China. Understanding the basic features of these non-Microcystis BFCS and their blooms, including their diversity, occurrence, physio-ecology, and harmful metabolites, will provide direction on future studies of cyanobacterial blooms in China.

Genome Evolution of Filamentous Cyanobacterium Nostoc Species: From Facultative Symbiosis to Free Living.

In contrast to obligate bacteria, facultative symbiotic bacteria are mainly characterized by genome enlargement. However, the underlying relationship of this feature with adaptations to various habitats remains unclear. In this study, we used the global genome data of Nostoc strains, including 10 novel genomes sequenced in this study and 26 genomes available from public databases, and analyzed their evolutionary history. The evolutionary boundary of the real clade of Nostoc species was identified and was found to be consistent with the results of polyphasic taxonomy. The initial ancestral species of Nostoc was demonstrated to be consistent with a facultative symbiotic population. Further analyses revealed that Nostoc strains tended to shift from facultative symbiosis to a free-living one, along with an increase in genome sizes during the dispersal of each exterior branch. Intracellular symbiosis was proved to be essentially related to Nostoc evolution, and the adaptation of its members to free-living environments was coupled with a large preference for gene acquisition involved in gene repair and recombination. These findings provided unique evidence of genomic mechanisms by which homologous microbes adapt to distinct life manners and external environments.

Inhibitory effects of Prorocentrum donghaiense allelochemicals on Sargassum fusiformis zygotes probed by JIP-test based on fast chlorophyll fluorescence kinetics.

The macro- and microalgae have been found to inhibit the growth and photosynthesis of one another due to allelopathic interactions between them. Sargassum fusiformis is a common and commercially cultivated seaweed in coastal waters of the East China Sea (ECS) and usually encounters dense harmful algal blooms (HABs) formed by dinoflagellates during their sexual reproduction period. In the present study, the effects of Prorocentrum donghaiense lipophilic extracted allelochemicals on the growth and photosynthesis of S. fusiformis zygotes were probed by fast chlorophyll fluorescence rise kinetics and chlorophyll a transient analysis (JIP-test). It was found that exposure to the allelochemicals led to decreased chlorophyll a content and photosynthetic rates of the zygotes in comparison to the ones in the control. In addition, using the JIP-test, it was found that the inhibitory effects of allelochemicals on photosynthesis of the zygotes were mainly exerted on the electron transport within PSII. The decrease of photosynthetic parameters such as VJ, Mo, ϕPo, ϕo, ϕEo, PI, PTR, PET in the zygotes exposed to the allelochemicals all revealed that the obstruction of electron transport, and the dominant decrease in PET, both implied that inhibition on the dark reaction contributed to the highest photosynthetic reduction. In addition, some reaction centers (RCs) in the zygotes exposed to the allelocamicals were inactivated, which led to higher dissipation of excitation energy, as demonstrated by the significant enhancement of the photosynthetic parameter DIo/RC. All the results indicated that the lipophilic extracts contained the allelochemicals of P. donghaiense which could inhibit the growth and photosynthesis of S. fusiformis zygotes by damaging the electron acceptors and inactivating RCs, and finally block the electron transport.

Phylogenetic insights into chroococcus-like taxa (Chroococcales, Cyanobacteria), describing Cryptochroococcus tibeticus gen. nov. sp. nov. and Limnococcus fonticola sp. nov. from Qinghai-Tibet plateau.

Several coccoid cyanobacterial strains, morphologically similar to typical characteristics of Chroococcus, from the Qinghai-Tibet Plateau were isolated and characterized using a polyphasic approach including morphological and molecular information. Morphological characteristics, the phylogeny based on 16S rRNA gene, and 16S-23S internal transcribed spacer secondary structures support establishing a novel Chroococcus-like genus, Cryptochroococcus gen. nov., as well as Limnococcus fonticola sp. nov. Limnococcus is phylogenetically included in Chroococcaceae and has irregularly arranged thylakoids. Therefore, it should no longer be a member of Merismopediaceae (Synechococcales). The phylogeny based on the 16S rRNA gene revealed that Chroococcus-associated genera were monophyletic.