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1.
FEMS Microbiol Ecol ; 96(2)2020 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-31905236

RESUMO

Ecological communities are regulated by the flow of energy through environments. Energy flow is typically limited by access to photosynthetically active radiation (PAR) and oxygen concentration (O2). The microbial mats growing on the bottom of Lake Fryxell, Antarctica, have well-defined environmental gradients in PAR and (O2). We analyzed the metagenomes of layers from these microbial mats to test the extent to which access to oxygen and light controls community structure. We found variation in the diversity and relative abundances of Archaea, Bacteria and Eukaryotes across three (O2) and PAR conditions: high (O2) and maximum PAR, variable (O2) with lower maximum PAR, and low (O2) and maximum PAR. We found distinct communities structured by the optimization of energy use on a millimeter-scale across these conditions. In mat layers where (O2) was saturated, PAR structured the community. In contrast, (O2) positively correlated with diversity and affected the distribution of dominant populations across the three habitats, suggesting that meter-scale diversity is structured by energy availability. Microbial communities changed across covarying gradients of PAR and (O2). The comprehensive metagenomic analysis suggests that the benthic microbial communities in Lake Fryxell are structured by energy flow across both meter- and millimeter-scales.

2.
PLoS One ; 14(12): e0225551, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31790456

RESUMO

The community structure and assemblages of marine benthic organisms were investigated in coastal areas near the Jang Bogo Antarctic Research Station in Terra Nova Bay during the 2012-2018 summer seasons. We also examined the recovery pattern of marine benthic organisms following disturbance due to the construction of the Jang Bogo Station. A total of 26 taxa were identified in the study area during the experimental period. Species number and diversity indices (richness, evenness, and diversity) were relatively low compared to data previously reported from Terra Nova Bay. Sphaerotylus antarcticus, Clavularia frankliniana, Hydractinia sp., Iridaea cordata, Fragilariopsis spp., Alcyonium antarcticum, and Metalaeospira pixelli were the dominant species in this area. Of these, the diatom Fragilariopsis spp. were the most abundant species, indicating their key role in maintaining the marine benthic community and controlling biogeochemical cycling. During the construction of the Jang Bogo Station, sediment coverage increased and diatoms declined due to the release of sediment into the coastal area. In February 2014, one month after the disturbance due to cyclone, the diatom coverage increased dramatically and thereby species number, richness index, and diversity index steadily rose from 2015 to 2018. However, non-metric multidimensional scaling ordination analysis of species similarities among sampling times showed that community structure had not completely recovered by 2018. Thus, long-term monitoring is required to elucidate the post-disturbance settlement mechanisms of marine benthic organisms at the study area in Terra Nova Bay.

3.
Chemosphere ; 236: 124404, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31545201

RESUMO

Tetrodotoxin (TTX) is a potent neurotoxin responsible for countless human intoxications and deaths around the world. The distribution of TTX and its analogues is diverse and the toxin has been detected in organisms from both marine and terrestrial environments. Increasing detections seafood species, such as bivalves and gastropods, has drawn attention to the toxin, reinvigorating scientific interest and regulatory concerns. There have been reports of TTX in 21 species of bivalves and edible gastropods from ten countries since the 1980's. While TTX is structurally dissimilar to saxitoxin (STX), another neurotoxin detected in seafood, it has similar sodium channel blocking action and potency and both neurotoxins have been shown to have additive toxicities. The global regulatory level for the STX group toxins applied to shellfish is 800 µg/kg. The presence of TTX in shellfish is only regulated in one country; The Netherlands, with a regulatory level of 44 µg/kg. Due to the recent interest surrounding TTX in bivalves, the European Food Safety Authority established a panel to assess the risk and regulation of TTX in bivalves, and their final opinion was that a concentration below 44 µg of TTX per kg of shellfish would not result in adverse human effects. In this article, we review current knowledge on worldwide TTX levels in edible gastropods and bivalves over the last four decades, the different methods of detection used, and the current regulatory status. We suggest research needs that will assist with knowledge gaps and ultimately allow development of robust monitoring and management protocols.


Assuntos
Bivalves/química , Contaminação de Alimentos/análise , Gastrópodes/química , Frutos do Mar/análise , Tetrodotoxina/análise , Animais , Contaminação de Alimentos/legislação & jurisprudência , Inocuidade dos Alimentos , Humanos , Países Baixos , Neurotoxinas/análise , Neurotoxinas/farmacocinética , Saxitoxina/análise , Tetrodotoxina/farmacocinética
4.
Toxins (Basel) ; 11(8)2019 Jul 24.
Artigo em Inglês | MEDLINE | ID: mdl-31344917

RESUMO

Understanding of colony specific properties of cyanobacteria in the natural environment has been challenging because sampling methods disaggregate colonies and there are often delays before they can be isolated and preserved. Microcystis is a ubiquitous cyanobacteria that forms large colonies in situ and often produces microcystins, a potent hepatotoxin. In the present study a new cryo-sampling technique was used to collect intact Microcystis colonies in situ by embedding them in a sheet of ice. Thirty-two of these Microcystis colonies were investigated with image analysis, liquid chromatography-mass spectrometry, quantitative polymerase chain reaction and high-throughput sequencing to assess their volume, microcystin quota and internal transcribed spacer (ITS) genotype diversity. Microcystin quotas were positively correlated to colony volume (R2 = 0.32; p = 0.004). Individual colonies had low Microcystis ITS genotype diversity and one ITS operational taxonomic unit predominated in all samples. This study demonstrates the utility of the cryo-sampling method to enhance the understanding of colony-specific properties of cyanobacteria with higher precision than previously possible.

5.
Geobiology ; 17(5): 551-563, 2019 09.
Artigo em Inglês | MEDLINE | ID: mdl-31325234

RESUMO

Bacteriohopanepolyols (BHPs) are pentacyclic triterpenoid lipids that contribute to the structural integrity and physiology of some bacteria. Because some BHPs originate from specific classes of bacteria, BHPs have potential as taxonomically and environmentally diagnostic biomarkers. For example, a stereoisomer of bacteriohopanetetrol (informally BHT II) has been associated with anaerobic ammonium oxidation (anammox) bacteria and suboxic to anoxic marine environments where anammox is active. As a result, the detection of BHT II in the sedimentary record and fluctuations in the relative abundance of BHT II may inform reconstructions of nitrogen cycling and ocean redox changes through the geological record. However, there are uncertainties concerning the sources of BHT II and whether or not BHT II is produced in abundance in non-marine environments, both of which are pertinent to interpretations of BHT II signatures in sediments. To address these questions, we investigate the BHP composition of benthic microbial mats from Lake Fryxell, Antarctica. Lake Fryxell is a perennially ice-covered lake with a sharp oxycline in a density-stabilized water column. We describe the diversity and abundance of BHPs in benthic microbial mats across a transect from oxic to anoxic conditions. Generally, BHP abundances and diversity vary with the morphologies of microbial mats, which were previously shown to reflect local environmental conditions, such as irradiance and oxygen and sulfide concentrations. BHT II was identified in mats that exist within oxic to anoxic portions of the lake. However, anammox bacteria have yet to be identified in Lake Fryxell. We examine our results in the context of BHPs as biomarkers in modern and ancient environments.


Assuntos
Bactérias/metabolismo , Sedimentos Geológicos/análise , Lipídeos/análise , Triterpenos Pentacíclicos/análise , Regiões Antárticas , Bactérias/química , Fenômenos Fisiológicos Bacterianos , Lagos/química , Polímeros/análise
6.
Geobiology ; 17(3): 308-319, 2019 05.
Artigo em Inglês | MEDLINE | ID: mdl-30707499

RESUMO

Bacteriohopanepolyols (BHPs) are bacterial membrane lipids that may be used as biological or environmental biomarkers. Previous studies have described the diversity, distribution, and abundance of BHPs in a variety of modern environments. However, the regulation of BHP production in polar settings is not well understood. Benthic microbial mats from ice-covered lakes of the McMurdo Dry Valleys, Antarctica provide an opportunity to investigate the sources, physiological roles, and preservation of BHPs in high-latitude environments. Lake Vanda is one of the most stable lakes on Earth, with microbial communities occupying specific niches along environmental gradients. We describe the influence of mat morphology and local environmental conditions on the diversity and distribution of BHPs and their biological sources in benthic microbial mats from Lake Vanda. The abundance and diversity of C-2 methylated hopanoids (2-MeBHP) are of particular interest, given that their stable degradation products, 2-methylhopanes, are among the oldest and most prevalent taxonomically informative biomarkers preserved in sedimentary rocks. Furthermore, the interpretation of sedimentary 2-methylhopanes is of great interest to the geobiology community. We identify cyanobacteria as the sole source of 2-MeBHP in benthic microbial mats from Lake Vanda and assess the hypothesis that 2-MeBHP are regulated in response to a particular environmental variable, namely solar irradiance.


Assuntos
Cianobactérias/metabolismo , Lagos/química , Lipídeos de Membrana/análise , Regiões Antárticas , Cianobactérias/isolamento & purificação , Meio Ambiente , Camada de Gelo , Lagos/microbiologia
7.
Toxins (Basel) ; 10(7)2018 07 06.
Artigo em Inglês | MEDLINE | ID: mdl-29986427

RESUMO

Tetrodotoxin (TTX) is one of the most potent neurotoxins known. It was originally thought to only occur in puffer fish but has now been identified in twelve different classes of freshwater and marine organisms, including bivalves. Despite being one of the world’s most studied biotoxins, its origin remains uncertain. There is contradictory evidence regarding the source of TTX and its pathway through food webs. To date, the distribution of TTX has not been examined in bivalves. In the present study, 48 Paphies australis, a TTX-containing clam species endemic to New Zealand, were collected. Thirty clams were dissected, and organs and tissues pooled into five categories (siphons, digestive gland, adductor muscles, and the ‘rest’) and analyzed for TTX using liquid chromatography-mass spectrometry (LC-MS). The micro-distribution of TTX was visualized in the remaining 18 individuals using an immunohistological technique incorporating a TTX-specific monoclonal antibody. The LC-MS analysis revealed that siphons contained the highest concentrations of TTX (mean 403.8 µg/kg). Immunohistochemistry analysis showed TTX in the outer cells of the siphons, but also in the digestive system, foot, and gill tissue. Observing TTX in organs involved in feeding provides initial evidence to support the hypothesis of an exogenous source in P. australis.


Assuntos
Bivalves/química , Tetrodotoxina/análise , Poluentes Químicos da Água/análise , Animais , Bivalves/parasitologia , Cromatografia Líquida , Monitoramento Ambiental , Trato Gastrointestinal/química , Brânquias/química , Imuno-Histoquímica , Músculos/química , Nova Zelândia , Espectrometria de Massas em Tandem , Trematódeos/química
8.
Sci Total Environ ; 612: 71-80, 2018 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-28846906

RESUMO

Toxic benthic cyanobacterial proliferations, particularly of the genus Phormidium, are a major concern in many countries due to their increasing extent and severity. The aim of this study was to improve the current understanding of the dominant physicochemical variables associated with high Phormidium cover and toxin concentrations. Phormidium cover and anatoxin concentrations were assessed weekly for 30weeks in eight predominately cobble-bed rivers in the South Island of New Zealand. Phormidium cover was highly variable both spatially (among and within sites) and temporally. Generalized additive mixed models (GAMMs) identified site, month of the year, conductivity and nutrient concentrations over the accrual period as significant variables associated with Phormidium cover. Cover was greatest under low to intermediate accrual dissolved inorganic nitrogen (DIN) and dissolved reactive phosphorus (DRP) concentrations. Accrual nutrients had a strong, negative effect on cover at concentrations>0.2mgL-1 DIN and 0.014mgL-1 DRP. The effect of flow was generally consistent across rivers, with cover accruing with time since the last flushing flow. Total anatoxins were detected at all eight study sites, at concentrations ranging from 0.008 to 662.5mgkg-1 dried weight. GAMMs predicted higher total anatoxin concentrations between November and February and during periods of accrual DRP<0.02mgL-1. This study suggests that multiple physicochemical variables may influence Phormidium proliferations and also evidenced large site-to-site variability. This result highlights a challenge from a management perspective, as it suggests that mitigation options are likely to be site-specific.


Assuntos
Cianobactérias/crescimento & desenvolvimento , Toxinas Marinhas/análise , Nitrogênio/análise , Fósforo/análise , Rios , Nova Zelândia , Estações do Ano , Análise Espaço-Temporal , Movimentos da Água
9.
Front Microbiol ; 8: 1347, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28824553

RESUMO

In this study, we report the distribution of microbial taxa and their predicted metabolic functions observed in the top (U1), middle (U2), and inner (U3) decadal growth laminae of a unique large conical microbial mat from perennially ice-covered Lake Untersee of East Antarctica, using NextGen sequencing of the 16S rRNA gene and bioinformatics tools. The results showed that the U1 lamina was dominated by cyanobacteria, specifically Phormidium sp., Leptolyngbya sp., and Pseudanabaena sp. The U2 and U3 laminae had high abundances of Actinobacteria, Verrucomicrobia, Proteobacteria, and Bacteroidetes. Closely related taxa within each abundant bacterial taxon found in each lamina were further differentiated at the highest taxonomic resolution using the oligotyping method. PICRUSt analysis, which determines predicted KEGG functional categories from the gene contents and abundances among microbial communities, revealed a high number of sequences belonging to carbon fixation, energy metabolism, cyanophycin, chlorophyll, and photosynthesis proteins in the U1 lamina. The functional predictions of the microbial communities in U2 and U3 represented signal transduction, membrane transport, zinc transport and amino acid-, carbohydrate-, and arsenic- metabolisms. The Nearest Sequenced Taxon Index (NSTI) values processed through PICRUSt were 0.10, 0.13, and 0.11 for U1, U2, and U3 laminae, respectively. These values indicated a close correspondence with the reference microbial genome database, implying high confidence in the predicted metabolic functions of the microbial communities in each lamina. The distribution of microbial taxa observed in each lamina and their predicted metabolic functions provides additional insight into the complex microbial ecosystem at Lake Untersee, and lays the foundation for studies that will enhance our understanding of the mechanisms responsible for the formation of these unique mat structures and their evolutionary significance.

10.
Proc Biol Sci ; 284(1857)2017 Jun 28.
Artigo em Inglês | MEDLINE | ID: mdl-28637848

RESUMO

Evidence of climate-driven environmental change is increasing in Antarctica, and with it comes concern that this will propagate to impacts on biological communities. Recognition and prediction of change needs to incorporate the extent and timescales over which communities vary under extant conditions. However, few observations of Antarctic microbial communities, which dominate inland habitats, allow this. We therefore carried out the first molecular comparison of Cyanobacteria in historic herbarium microbial mats from freshwater ecosystems on Ross Island and the McMurdo Ice Shelf, collected by Captain R.F. Scott's 'Discovery' Expedition (1902-1903), with modern samples from those areas. Using 16S rRNA gene surveys, we found that modern and historic cyanobacteria assemblages showed some variation in community structure but were dominated by the same genotypes. Modern communities had a higher richness, including genotypes not found in historic samples, but they had the highest similarity to other cyanobacteria sequences from Antarctica. The results imply slow cyanobacterial 16S rRNA gene genotype turnover and considerable community stability within Antarctic microbial mats. We suggest that this relates to Antarctic freshwater 'organisms requiring a capacity to withstand diverse stresses, and that this could also provide a degree of resistance and resilience to future climatic-driven environmental change in Antarctica.


Assuntos
Biodiversidade , Cianobactérias/classificação , Regiões Antárticas , Ecossistema , Filogenia , RNA Ribossômico 16S/genética
11.
J Phycol ; 53(3): 476-485, 2017 06.
Artigo em Inglês | MEDLINE | ID: mdl-28207158

RESUMO

Global declines of macroalgal beds in coastal waters have prompted a plethora of studies attempting to understand the drivers of change within dynamic nearshore ecosystems. Photosynthetic measurements are good tools for assessing the consequences of numerous stressors of macroalgae, but there is somewhat of a disconnection between studies that focus on organism-specific ecophysiological responses and those that address causes and consequences of shifts in macroalgal productivity. Our goal is to highlight the applications of two complementary tools for measuring photosynthesis-variable chlorophyll a fluorescence and photorespirometry-and provide guidance for the integration of physiology and ecology to understand the drivers of change in macroalgal communities. Photorespirometry can provide an integrated measure of whole-community metabolism, including an estimate of the physiological costs associated with stressors, while fluorescence-based techniques provide point measures of the efficiency of the photosynthetic apparatus within communities. Variable chlorophyll a fluorescence does not provide an estimate of carbon balance or integrated photosynthesis across either whole plants or whole communities but can be used to estimate the contribution of individual community components in the dynamic subcanopy environment to help us understand the mechanisms underlying observed responses. We highlight the importance of the highly dynamic light environment within macroalgal communities and call for better integration of physiological techniques in an ecological context to enhance our understanding of the responses of whole communities to local and global stressors.


Assuntos
Processos Autotróficos , Fluorometria , Fotossíntese , Alga Marinha/fisiologia , Clorofila/metabolismo , Clorofila A , Fluorescência
12.
Appl Environ Microbiol ; 82(2): 620-30, 2016 01 15.
Artigo em Inglês | MEDLINE | ID: mdl-26567300

RESUMO

Lake Fryxell is a perennially ice-covered lake in the McMurdo Dry Valleys, Antarctica, with a sharp oxycline in a water column that is density stabilized by a gradient in salt concentration. Dissolved oxygen falls from 20 mg liter(-1) to undetectable over one vertical meter from 8.9- to 9.9-m depth. We provide the first description of the benthic mat community that falls within this oxygen gradient on the sloping floor of the lake, using a combination of micro- and macroscopic morphological descriptions, pigment analysis, and 16S rRNA gene bacterial community analysis. Our work focused on three macroscopic mat morphologies that were associated with different parts of the oxygen gradient: (i) "cuspate pinnacles" in the upper hyperoxic zone, which displayed complex topography and were dominated by phycoerythrin-rich cyanobacteria attributable to the genus Leptolyngbya and a diverse but sparse assemblage of pennate diatoms; (ii) a less topographically complex "ridge-pit" mat located immediately above the oxic-anoxic transition containing Leptolyngbya and an increasing abundance of diatoms; and (iii) flat prostrate mats in the upper anoxic zone, dominated by a green cyanobacterium phylogenetically identified as Phormidium pseudopriestleyi and a single diatom, Diadesmis contenta. Zonation of bacteria was by lake depth and by depth into individual mats. Deeper mats had higher abundances of bacteriochlorophylls and anoxygenic phototrophs, including Chlorobi and Chloroflexi. This suggests that microbial communities form assemblages specific to niche-like locations. Mat morphologies, underpinned by cyanobacterial and diatom composition, are the result of local habitat conditions likely defined by irradiance and oxygen and sulfide concentrations.


Assuntos
Bactérias/isolamento & purificação , Camada de Gelo/microbiologia , Lagos/microbiologia , Oxigênio/análise , Regiões Antárticas , Bactérias/classificação , Bactérias/genética , Bactérias/metabolismo , Biodiversidade , Camada de Gelo/química , Lagos/análise , Dados de Sequência Molecular , Filogenia
13.
Harmful Algae ; 55: 282-294, 2016 05.
Artigo em Inglês | MEDLINE | ID: mdl-28073542

RESUMO

There has been a marked increase in the distribution, intensity and frequency of proliferations of some species of the benthic mat-forming, toxin-producing genus Phormidium in rivers globally over the last decade. This review summarises current knowledge on their taxonomy, distribution, toxin content, environmental drivers of proliferations, and monitoring and management strategies in New Zealand. Although toxic Phormidium proliferation occurs in rivers worldwide little is known about these factors in most countries. Proliferations, defined as >20% cover of a riverbed, have been identified in 103 rivers across New Zealand. Morphological and molecular data indicate the main species responsible is Phormidium autumnale. In New Zealand Phormidium produces anatoxins (anatoxin-a, homoanatoxin-a, dihydroanatoxin-a, and dihydrohomoanatoxin-a) and these were detected in 67% of 771 samples from 40 rivers. The highest concentration measured was 712mgkg-1 dried weight (Oreti River, Southland), with considerable spatial and temporal variability in anatoxin concentrations between and within rivers. A synthesis of field based studies suggests that Phormidium proliferations are most likely when there is some enrichment of dissolved inorganic nitrogen but when water-column dissolved reactive phosphorus is less than 0.01mgL-1. Once established Phormidium-dominated mats trap sediment and internal mat biogeochemistry can mobilise sediment-bound phosphorus, which is then available for growth. Removal of Phormidium-dominated mats is primarily due to shear stress and substrate disturbance, although there is also evidence for autogenic detachment. A combination of factors including; changes to riparian margins, increased nitrate and fine sediment loads, and alterations in flow regimes are likely to have contributed to the rise in Phormidium proliferations.


Assuntos
Toxinas Bacterianas , Cianobactérias/classificação , Cianobactérias/fisiologia , Cianobactérias/química , Nova Zelândia , Dinâmica Populacional , Prevalência , Rios/microbiologia
14.
FEMS Microbiol Ecol ; 91(12)2015 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-26572547

RESUMO

Closed cryoconite holes (CCHs) are small aquatic ecosystems enclosed in glacier surface ice, and they collectively contribute substantial aquatic habitat to inland Antarctica. We examined the morphology, geochemistry and bacterial diversity of 57 CCHs, spread over seven sites, located on five glaciers, covering a range of latitudes, elevations and distance from open seawater. Isotopes confirmed glacial ice as the initial water source, with water chemistry evolving through freeze concentration and photosynthetic processes to have conductivities ranging from <0.005 to >4 mS cm(-1) and pH from <5 to >11. Nitrate concentrations were more elevated in inland, higher altitude sites. Bacterial communities were characterized by Automated Ribosomal Intergenic Spacer Analysis and high-throughput sequencing. The dominant phyla were Cyanobacteria, Bacteroides, Proteobacteria and Actinobacteria. CCH bacterial communities predominantly grouped by geographic location, suggesting initial wind-borne inocula from local and regional sources play a role in structuring assemblages. However, multivariate multiple regression analysis indicated that internal CCH conditions also influenced community structure, particularly the ion content and pH of the liquid water. This highlights the importance of founder bacterial populations, isolation and water chemistry in the evolution of CCH bacterial communities.


Assuntos
Bactérias/classificação , Camada de Gelo/microbiologia , Água do Mar/química , Água do Mar/microbiologia , Microbiologia da Água , Actinobacteria/classificação , Actinobacteria/isolamento & purificação , Regiões Antárticas , Bactérias/isolamento & purificação , Bacteroides/classificação , Bacteroides/isolamento & purificação , Biodiversidade , Cianobactérias/classificação , Cianobactérias/isolamento & purificação , Ecossistema , Geografia , Proteobactérias/classificação , Proteobactérias/isolamento & purificação
15.
PLoS One ; 10(10): e0141063, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-26479491

RESUMO

Proliferations of the benthic mat-forming cyanobacteria Phormidium have been reported in rivers worldwide. Phormidium commonly produces natural toxins which pose a health risk to animal and humans. Recent field studies in New Zealand identified that sites with Phormidium proliferations consistently have low concentrations of water column dissolved reactive phosphorus (DRP). Unlike other river periphyton, Phormidium mats are thick and cohesive, with water and fine sediment trapped in a mucilaginous matrix. We hypothesized that daytime photosynthetic activity would elevate pH inside the mats, and/or night time respiration would reduce dissolved oxygen. Either condition could be sufficient to facilitate desorption of phosphates from sediment incorporated within mats, thus allowing Phormidium to utilize it for growth. Using microelectrodes, optodes and pulse amplitude modulation fluorometry we demonstrated that photosynthetic activity results in elevated pH (>9) during daytime, and that night-time respiration causes oxygen depletion (<4 mg L-1) within mats. Water trapped within the mucilaginous Phormidium mat matrix had on average 320-fold higher DRP concentrations than bulk river water and this, together with elevated concentrations of elements, including iron, suggest phosphorus release from entrapped sediment. Sequential extraction of phosphorus from trapped sediment was used to investigate the role of sediment at sites on the Mangatainoka River (New Zealand) with and without Phormidium proliferations. Deposition of fine sediment (<63 µm) was significantly higher at the site with the most extensive proliferations and concentrations of biological available phosphorus were two- to four- fold higher. Collectively these results provide evidence that fine sediment can provide a source of phosphorus to support Phormidium growth and proliferation.


Assuntos
Cianobactérias/efeitos dos fármacos , Cianobactérias/crescimento & desenvolvimento , Sedimentos Geológicos/química , Fósforo/farmacologia , Rios/química , Rios/microbiologia , Disponibilidade Biológica , Cianobactérias/metabolismo , Concentração de Íons de Hidrogênio , Oxigênio/química , Fósforo/análise , Fotossíntese/efeitos dos fármacos , Fatores de Tempo , Água/química
16.
Front Microbiol ; 6: 1035, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-26500612

RESUMO

The Atacama Desert of northern Chile is one of the driest regions on Earth, with areas that exclude plants and where soils have extremely low microbial biomass. However, in the driest parts of the desert there are microorganisms that colonize the interior of halite nodules in fossil continental evaporites, where they are sustained by condensation of atmospheric water triggered by the salt substrate. Using a combination of in situ observations of variable chlorophyll fluorescence and controlled laboratory experiments, we show that this endolithic community is capable of carbon fixation both through oxygenic photosynthesis and potentially ammonia oxidation. We also present evidence that photosynthetic activity is finely tuned to moisture availability and solar insolation and can be sustained for days, and perhaps longer, after a wetting event. This is the first demonstration of in situ active metabolism in the hyperarid core of the Atacama Desert, and it provides the basis for proposing a self-contained, endolithic community that relies exclusively on non-rainfall sources of water. Our results contribute to an increasing body of evidence that even in hyperarid environments active metabolism, adaptation, and growth can occur in highly specialized microhabitats.

17.
PLoS One ; 9(12): e114146, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-25438045

RESUMO

Phototrophs underpin most ecosystem processes, but to do this they need sufficient light. This critical resource, however, is compromised along many marine shores by increased loads of sediments and nutrients from degraded inland habitats. Increased attenuation of total irradiance within coastal water columns due to turbidity is known to reduce species' depth limits and affect the taxonomic structure and architecture of algal-dominated assemblages, but virtually no attention has been paid to the potential for changes in spectral quality of light energy to impact production dynamics. Pioneering studies over 70 years ago showed how different pigmentation of red, green and brown algae affected absorption spectra, action spectra, and photosynthetic efficiency across the PAR (photosynthetically active radiation) spectrum. Little of this, however, has found its way into ecological syntheses of the impacts of optically active contaminants on coastal macroalgal communities. Here we test the ability of macroalgal assemblages composed of multiple functional groups (including representatives from the chlorophyta, rhodophyta and phaeophyta) to use the total light resource, including different light wavelengths and examine the effects of suspended sediments on the penetration and spectral quality of light in coastal waters. We show that assemblages composed of multiple functional groups are better able to use light throughout the PAR spectrum. Macroalgal assemblages with four sub-canopy species were between 50-75% more productive than assemblages with only one or two sub-canopy species. Furthermore, attenuation of the PAR spectrum showed both a loss of quanta and a shift in spectral distribution with depth across coastal waters of different clarity, with consequences to productivity dynamics of diverse layered assemblages. The processes of light complementarity may help provide a mechanistic understanding of how altered turbidity affects macroalgal assemblages in coastal waters, which are increasingly threatened by diminishing light quantity and altered spectral distributions through sedimentation and eutrophication.


Assuntos
Clorófitas/fisiologia , Feófitas/fisiologia , Rodófitas/fisiologia , Alga Marinha/fisiologia , Ecossistema , Luz , Fotossíntese
18.
Environ Microbiol Rep ; 5(4): 583-7, 2013 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-23864573

RESUMO

Endolithic cyanobacteria are found in halite nodules in the hyperarid core of the Atacama Desert. Using Pulse Amplitude Modulated Fluorometry, we show here that photosynthetic systems of these cyanobacteria become active when the relative humidity rises above 70% and the salt becomes wet by way of deliquescence. This is the first evidence of active metabolism in the hyperarid core of the Atacama, and supports the view of a microbial community sustained by deliquescence. Our results expand the water activity envelope of life on Earth.


Assuntos
Cianobactérias/fisiologia , Fotossíntese , Sais/metabolismo , Microbiologia do Solo , Cianobactérias/crescimento & desenvolvimento , Cianobactérias/metabolismo , Clima Desértico , Fluorometria
19.
Biology (Basel) ; 2(1): 151-76, 2013 Jan 25.
Artigo em Inglês | MEDLINE | ID: mdl-24832656

RESUMO

Lake Vanda is a perennially ice-covered, closed-basin lake in the McMurdo Dry Valleys, Antarctica. Laminated photosynthetic microbial mats cover the floor of the lake from below the ice cover to >40 m depth. In recent decades, the water level of Lake Vanda has been rising, creating a "natural experiment" on development of mat communities on newly flooded substrates and the response of deeper mats to declining irradiance. Mats in recently flooded depths accumulate one lamina (~0.3 mm) per year and accrue ~0.18 µg chlorophyll-a cm-2 y-1. As they increase in thickness, vertical zonation becomes evident, with the upper 2-4 laminae forming an orange-brown zone, rich in myxoxanthophyll and dominated by intertwined Leptolyngbya trichomes. Below this, up to six phycobilin-rich green/pink-pigmented laminae form a subsurface zone, inhabited by Leptolyngbya, Oscillatoria and Phormidium morphotypes. Laminae continued to increase in thickness for several years after burial, and PAM fluorometry indicated photosynthetic potential in all pigmented laminae. At depths that have been submerged for >40 years, mats showed similar internal zonation and formed complex pinnacle structures that were only beginning to appear in shallower mats. Chlorophyll-a did not change over time and these mats appear to represent resource-limited "climax" communities. Acclimation of microbial mats to changing environmental conditions is a slow process, and our data show how legacy effects of past change persist into the modern community structure.

20.
Photosynth Res ; 112(2): 103-15, 2012 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-22544283

RESUMO

We undertook a series of measurements of photophysiological parameters of sea ice algae over 12 days of early spring growth in a West Greenland Fjord, by variable chlorophyll fluorescence imaging. Imaging of the ice-water interface showed the development of ice algae in 0.3-0.4 mm wide brine channels between laminar ice crystals in the lower 4-6 mm of the ice, with a several-fold spatial variation in inferred biomass on cm scales. The maximum quantum yield of photosynthesis, F(v) /F(m), was initially low (~0.1), though this increased rapidly to ~0.5 by day 6. Day 6 also saw the onset of biomass increase, the cessation of ice growth and the time at which brine had reached <50 psu and >-2 °C. We interpret this as indicating that the establishment of stable brine channels at close to ambient salinity was required to trigger photosynthetically active populations. Maximum relative electron transport rate (rETR(max)), saturation irradiance (E(k)) and photosynthetic efficiency (α) had also stabilised by day 6 at 5-6 relative units, ~30 µmol photons m⁻² s⁻¹ and 0.4-0.5 µmol photons m⁻²s⁻¹, respectively. E(k) was consistent with under-ice irradiance, which peaked at a similar value, confirming that daytime irradiance was adequate to facilitate photosynthetic activity throughout the study period. Photosynthetic parameters showed no substantial differences with depth within the ice, nor variation between cores or brine channels suggesting that during this early phase of ice algal growth cells were unaffected by gradients of environmental conditions within the ice. Variable chlorophyll fluorescence imaging offers a tool to determine how this situation may change over time and as brine channels and algal populations evolve.


Assuntos
Clorofila/metabolismo , Gelo , Microalgas/metabolismo , Fotobiologia , Água do Mar , Biomassa , Groenlândia , Microscopia Eletrônica
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