煤矿污染土壤降解苯并(a)芘微生物多样性及降解能力研究

以苯并(a)芘(50 mg/L)为唯一碳源,对新疆芦草沟煤矿开采区土壤微生物进行3代胁迫培养(每代60 d);采用PCR-DGGE方法了解不同污染程度土样中降解苯并(a)芘的微生物类群和多样性特点;利用高效液相色谱(HPLC)测定胁迫培养每代培养物混合菌群对苯并(a)芘的降解能力。PCR-DGGE结果显示:不同污染程度原始样品与苯并(a)芘胁迫培养第3代培养物的微生物香浓指数(H)、丰度(S)和均匀度(E)有所不同,其中重度污染培养物降解苯并(a)芘的微生物类群最丰富。对优势条带进行克隆,其主要归属于变形菌门(Proteobacteria)、拟杆菌门(Bacteroidetes)和放线菌门(Actinobacteria)。经HPLC检测发现重度污染样品中的群体微生物对苯并(a)芘的降解率明显高于轻度和中度污染样品,达到78.4%。研究表明新疆芦草沟煤矿开采区污染的土壤中可能蕴藏着降解苯并(a)芘的微生物资源。     

A Window to the Subsurface: Microbial Diversity in Hot Springs of a Sulfidic Cave (Kaklik,Turkey)

Caves are windows to the extreme habitats of deep subsurface, and provide answers of unknowns about the underground life. Furthermore, sulfidic caves are important analogues for the early Earth environments, since some environmental conditions are common, such as high sulfur concentration, high temperature and oxygen-poor conditions. Kaklik Cave (Denizli, Turkey) with its travertine formation, carbonate- and sulfur-rich thermal springs, exhibits a unique ecosystem as a sulfidic cave. This study represents the first molecular survey of the microbial community in the Kaklik Cave, Turkey using high-throughput 16S rRNA gene amplicon sequencing analysis. An average of 859–2,416 operational taxonomic units per sample were observed including 25 bacterial phyla and 3 archaeal phyla. The bacterial diversity profiles were generally dominated by Epsilonproteobacteria and Gammaproteobacteria. At the carbonate-rich hot spring, that formed travertine structure, 9.7% of sequence reads affiliated with Thiofaba spp. In contrast, 38.74% of the total sequence reads at the sulfidic hot spring samples associated with the genus Sulfurimonas and Sulfurovum. In the archaeal community composition, Thermoplasmata was the most abundant group in all sampling areas. The 454-pyrotag results provide leads about ammonia-, nitrite- and sulfur-oxidation as well as sulfur-reduction, carbon dioxide fixation, and nitrogen fixation.     

Microbial Diversity in Ngari,Hentak and Tungtap,Fermented Fish Products of North-East India

Ngari, hentak and tungtap are traditional fermented fish products of North-East India. Eighteen samples of ngari, hentak and tungtap were collected and were analysed for microbial load. Lactic acid bacteria, endospore-forming rods, yeasts and aerobic mesophilic counts ranged from 4.0 to 7.2, 3.3–4.6, <1–3.5 and 4.3–7.3 log c.f.u./g, respectively. Lactic acid bacteria were identified as Lactococcus lactis subsp. cremoris, Lactococcus plantarum, Enterococcus faecium, Lactobacillus fructosus, Lactobacillus amylophilus, Lactobacillus coryniformis subsp. torquens and Lactobacillus plantarum. Endospore-forming rods were identified as Bacillus subtilis and Bacillus pumilus, aerobic coccal strains were identified as Micrococcus. Yeasts were identified as species of Candida and Saccharomycopsis. Pathogenic contaminants were detected in all samples, however, none of the sample contained more than 10² c.f.u./g of Bacillus cereus, 10³ c.f.u./g of Staphylococcus aureus and enterobacteriaceae population, respectively. Enzymatic and antimicrobial activities of the isolates were tested. None of the strains produced biogenic amines in the method applied. Most strains of LAB had a high degree of hydrophobicity, indicating their ‘probiotic’ characters. This study has demonstrated the microbial diversity within the species of lactic acid bacteria, Bacillus and yeasts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Microbial Diversity in High Arsenic Groundwater in Hetao Basin of Inner Mongolia,China

The microbial diversity and community structure in twenty-one groundwater samples from high arsenic shallow aquifers of Hetao Basin, Inner Mongolia, China was investigated with an integrated approach including polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) and 16S rRNA gene phylogenetic analyses. A total of 25 bacterial and 32 archaeal DGGE bands were exercised for sequencing. Phylogenetic analyses showed that the bacterial DGGE bands were dominated by Proteobacteria, and the archaeal bands were dominated by Thaumarchaeota and Euryarchaeota. Based on arsenic concentrations, three samples (corresponding to low, medium, and high level of arsenic, respectively) were selected for construction of 16S rRNA gene clone libraries. A total of 912 (468 and 444 for bacteria and archaea, respectively) 16S rRNA gene clone sequences were obtained and subjected to phylogenetic analyses. The results showed that bacterial communities of these samples were dominated by Acinetobacter, Pseudomonas, Massilia, Dietzia, Planococcus, Brevundimonas, Aquabacterium and Geobacter, and archaeal communities by Nitrosophaera, Thermoprotei and Methanosaeta. The relative abundance of major groups varied as a function of changes in groundwater geochemistry. Acinetobacter, Brevundimonas, Geobacter, Thermoprotei and Methanosaeta dominated in high arsenic samples with high concentrations of methane and Fe(II), and low concentrations of SO^2? ₄ and NO^? ₃, while Pseudomonas and Nitrosophaera were abundant in low arsenic groundwater. These results imply that microbes play an important role in arsenic mobilization in the shallow aquifers of Hetao Basin, Inner Mongolia.     

磷脂脂肪酸法分析鹤山针叶林和荷木林的土壤微生物多样性

用磷脂脂肪酸法(PLFA)分析广东鹤山两种人工林——针叶林和荷木林不同土层(0~20 cm、20~40 cm、40~60 cm)的土壤微生物群落结构。结果表明,两种人工林的磷脂脂肪酸总量(PLFAs总量)、细菌特征脂肪酸(细菌PLFAs)、真菌特征脂肪酸(真菌PLFAs),以及革兰氏阳性菌和革兰氏阴性菌特征脂肪酸的含量都是0~20 cm土层最高;荷木林的PLFAs总量高于针叶林,但这种差异随土壤深度增加而递减, 且与土壤有机碳、全氮含量呈正相关。在相同土层,细菌PLFAs含量均显著高于真菌PLFAs含量。主成分分析表明,土壤微生物多样性及其丰富度受林型和土层综合作用的影响;单一的PLFAs中,i13:0、a13:0、17:0、cy17:0和16:0等脂肪酸对第一主成分的贡献较大;i16:0、cy19:0、18:1ω9c、i15:0、18:2ω6c和a17:0等脂肪酸对第二主成分贡献较大。     

Microbial diversity in the tick Argas japonicus (Acari: Argasidae) with a focus on Rickettsia pathogens

The soft tick Argas japonicus mainly infests birds and can cause human dermatitis; however, no pathogen has been identified from this tick species in China. In the present study, the microbiota in A. japonicus collected from an epidemic community was explored, and some putative Rickettsia pathogens were further characterized. The results obtained indicated that bacteria in A. japonicus were mainly ascribed to the phyla Proteobacteria, Firmicutes and Actinobacteria. At the genus level, the male A. japonicus harboured more diverse bacteria than the females and nymphs. The bacteria Alcaligenes, Pseudomonas, Rickettsia and Staphylococcus were common in nymphs and adults. The abundance of bacteria belonging to the Rickettsia genus in females and males was 7.27% and 10.42%, respectively. Furthermore, the 16S rRNA gene of Rickettsia was amplified and sequenced, and phylogenetic analysis revealed that 13 sequences were clustered with the spotted fever group rickettsiae (Rickettsia heilongjiangensis and Rickettsia japonica) and three were clustered with Rickettsia limoniae, which suggested that the characterized Rickettsia in A. japonicus were novel putative pathogens and also that the residents were at considerable risk for infection by tick‐borne pathogens.     

Bacterial Diversity in the Metal-Rich Terrestrial Deep Subsurface Sediments of Krishna Godavari Basin,India

Abstract

Krishna Godavari (KG) basin, located in the eastern continental margin of India, is a geological region well known for the abundance of economically important minerals. However, less is known about the microbial ecology of its subsurface sediments. The present study is the first report on the comprehensive culture-independent census of bacterial communities of deep subsurface of KG basin and their relationship with the geochemical environment. Elemental and mineralogical characterization of the sediments highlighted the presence of carbon and nitrogen deprived conditions along with the abundance of metalliferous minerals, especially rich in valuable elements like zirconium, vanadium, cesium, and rare earth elements. Diversity analysis based on Illumina MiSeq high-throughput sequencing platform revealed the predominance of Firmicutes (44.24%), Proteobacteria (34.17%), Bacteroidetes (15.18%), and Actinobacteria (3.81%) in the deep subsurface of this basin. ‘Abundant’ and ‘rare’ sub-communities analysis indicated that a large number of phyla like Acidobacteria, Armatimonadetes, Chloroflexi, and Deinococcus-Thermus were exclusively present as a rare community. Statistical analyses demonstrated that geochemical parameters, especially depth, pH, and metal content, showed significant influence on the microbial community structure. The present study should help future investigations for microbial mediated sustainable utilization of mineral-rich sediments of the region.     

Spatial covariance between ecosystem services and biodiversity pattern at a national scale (France)

We present at a national-scale estimates of spatial covariance between areas important for ecosystem services (ES) and biodiversity, at a fixed spatial scale in France. We calculated different diversity and community metrics for common bird communities: taxonomic diversity (TD), functional diversity (FD), community specialization index (CSI), trophic index (TI), phylogenetic diversity (PD) and community evolutionary distinctiveness (CED). The ES multifunctionality (ES_MF) was measured using a combination of ES evenness and overall ES estimator. Spatially explicit tests were used to compare the spatial patterns of ES and diversity metrics. Mixed models were used for comparisons.We found low spatial congruence between ES and both diversity and community metrics in France. However, we detected even opposite associations between ES and each biodiversity component. Crop production was negatively associated with CED, it was positively correlated with CSI. No positive associations were found between ES_MF and any diversity metric, independently of farming systems. The only significant association was negative: lower values of CED were associated with hotspots of ES_MF. We found also a negative effect of crop production on bird CED. The conservation implication is remarkable, because conservation policies focusing solely on the economic value of ES will fail to protect overall biodiversity.     

Microbial Diversity at a Hot,Shallow-Sea Hydrothermal Vent in the Southern Tyrrhenian Sea (Italy)

Microbial community thriving at shallow hydrothermal vent named Black Point, close to the Island of Panarea in the Southern Tyrrhenian Sea (Italy), was studied by microscopic, cultural and molecular methods. New strains of Bacillus and Geobacillus were isolated. Members of sulphur-oxidizing bacteria, belonging to the genera Halothiobacillus and Thiomicrospira were demonstrated by both culture-dependent and -independent methods. Genetic diversity of Bacteria was higher than that of Archaea. Bacterial 16S rRNA gene sequences from Black Point showed low levels of similarity with other yet deposited sequences, suggesting that new bacterial phylotypes are present in this site. Dominant populations of Bacteria belonged to uncultured members of Proteobacteria (mainly of the class Gammaproteobacteria), Firmicutes and Acidobacteriaceae. Primary production appeared to be supported by chemosynthetic and photosynthetic bacteria affiliated with members of Gammaproteobacteria. Most of the archaeal sequences matched those of yet-uncultivated Archaea, thus their role at this vent is not well understood.     

Diversity of gymnamoebae (Rhizopoda, Gymnamoebia) in a rain-water pool

The diversity of species of gymnamoebae in a single sample from a rain-water pool in Bratislava (Slovakia) was investigated. To maximize the recovery of species, six enrichment cultivation media were used. A total of 12 taxa, representing five families and eight genera of Gymnamoebia, were recovered.     

Microbial diversity of a sulfide black smoker in main endeavour hydrothermal vent field,Juan de Fuca Ridge

Submarine hydrothermal vents are among the least-understood habitats on Earth but have been the intense focus of research in the past 30 years. An active hydrothermal sulfide chimney collected from the Dudley site in the Main Endeavour vent Field (MEF) of Juan de Fuca Ridge was investigated using mineralogical and molecular approaches. Mineral analysis indicated that the chimney was composed mainly of Fe-, Zn-and Cu-rich sulfides. According to phylogenetic analysis, within the Crenarchaeota, clones of the order Desulfurococcales predominated, comprising nearly 50% of archaeal clones. Euryarchaeota were composed mainly of clones belonging to Thermococcales and deep-sea hydrothermal vent Euryarchaeota (DHVE), each of which accounted for about 20% of all clones. Thermophilic or hyperthermophilic physiologies were common to the predominant archaeal groups. More than half of bacterial clones belonged to ɛ-Proteobacteria, which confirmed their prevalence in hydrothermal vent environments. Clones of Proteobacteria (γ-, δ-, β-), Cytophaga-Flavobacterium-Bacteroides (CFB) and Deinococcus-Thermus occurred as well. It was remarkable that methanogens and methanotrophs were not detected in our 16S rRNA gene library. Our results indicated that sulfur-related metabolism, which included sulfur-reducing activity carried out by thermophilic archaea and sulfur-oxidizing by mesophilic bacteria, was common and crucial to the vent ecosystem in Dudley hydrothermal site.     

丛枝菌根真菌对辣椒光合特性及根际微生物多样性和酶活性的影响

在育苗和栽培基质中添加具有生物活性的微生物群体是改善无土栽培有机基质性状和提高应用效果的重要途径。该试验通过在辣椒育苗和栽培基质中添加丛枝菌根真菌制剂恩益碧(NEB-F),研究了AMF对辣椒生长、果实产量、光合特性以及根际微生物多样性和酶活性的影响。结果显示:(1)基质添加AMF显著促进了辣椒植株生长,并明显提高了产量。(2)AMF处理显著提高了辣椒植株叶片的净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)、水分利用效率(WUE),而使胞间二氧化碳浓度(Ci)显著降低,同时对辣椒叶片最大光化学效率(Fv/Fm)的影响不大,而使实际光化学效率(ФPSⅡ)、光化学猝灭(qP)和表观光合电子传递效率(ETR)显著提高。(3)基质添加AMF显著增加基质中细菌、放线菌数量,而降低真菌数量,并明显提高了根际微生物多样性指数以及过氧化氢酶、碱性磷酸酶和尿酶活性;添加AMF基质中的细菌、真菌、放线菌数量均与其过氧化氢酶、脲酶、碱性磷酸酶之间呈显著或极显著正相关关系。研究表明,基质添加AMF不仅增大了辣椒叶片气孔导度,而且促进电子传递速率,提高CO2同化利用效率和净光合速率;同时促使辣椒根际微生物区系从低肥力的"真菌型"向高肥力的"细菌型"转化,提高根际微生物多样性和酶活性,有助于维持辣椒根际生态系统的稳定性与和谐性,从而促进辣椒幼苗生长,并提高产量。基质中添加AMF是提高有机基质应用效果的有效途径。     

Microbial Community Structure at Different Fermentation Stages of Kutajarista, a Herbal Formulation

Kutajarista is an Ayurvedic fermented herbal formulation prescribed for gastrointestinal disorders. This herbal formulation undergoes a gradual fermentative process and takes around 2 months for production. In this study, microbial composition at initial stages of fermentation of Kutajarista was assessed by culture independent 16S rRNA gene clone library approach. Physicochemical changes were also compared at these stages of fermentation. High performance liquid chromatography–mass spectrometry analysis showed that Gallic acid, Ellagic acid, and its derivatives were the major chemical constituents recovered in this process. At 0 day of fermentation, Lactobacillus sp., Acinetobacter sp., Alcaligenes sp., and Methylobacterium sp. were recovered, but were not detected at 8 day of fermentation. Initially, microbial diversity increased after 8 days of fermentation with 11 operational taxonomic units (OTUs), which further decreased to 3 OTUs at 30 day of fermentation. Aeromonas sp., Pseudomonas sp., and Klebsiella sp. dominated till 30 day of fermentation. Predominance of γ- Proteobacteria and presence of gallolyl derivatives at the saturation stage of fermentation implies tannin degrading potential of these microbes. This is the first study to highlight the microbial role in an Ayurvedic herbal product fermentation.     

Effects of Copper,Nickel, and Sulfate from the Smelters at Sudbury,Ontario (Canada) on Microbial Communities in Lakes

Analysis of water and sediments from deep and shallow environments in lakes located 6–154 km east or southeast of the smelters at Sudbury, Ontario (Canada) revealed variable, interactive effects of copper, nickel, and sulfate from smelter fallout on lacustrine microfloras. Metal species in sediments were differentiated by sequential extractions, and the nature, abundances, and activities of microbial populations were represented by chlorophyll-a in water and by CO₂ production, fatty acids, phospholipids, dehydrogenase, alkaline phosphatase, and spectral properties of humic matter in sediments. Smelter fallout declined logarithmically with distance from the smelters, and its effects on microfloras depended on the type of microorganism or microbial process and on environmental factors and the abundances of metal species and detoxifying agents. Extractable copper and nickel had toxic effects, which were not attributable solely to the exchangeable fractions, but in certain cases nickel counteracted copper toxicity. Sedimentary sulfide as a whole or sulfide produced by bacterial sulfate reduction, or low oxidation–reduction potential regardless of sulfide concentration, ameliorated metal toxicity by making the metals less bioavailable; and toxicity showed a “quantum jump” when detoxifying agents fell below certain critical concentrations, implying the existence of threshold levels of bioavailable metals above which toxicity increased abruptly. In some cases metal toxicity was lowest in the lakes closest to the smelters (because sulfate concentrations were highest) as well as in the lakes furthest away, and was highest at intermediate distances. The results also suggest that nickel pollution led to ecological succession whereby nickel-tolerant microbial populations replaced nickel-sensitive ones.     

Characterization of Microbial Mats from a Siliciclastic Tidal Flat (Bahía Blanca Estuary,Argentina)

Biofilms and microbial mats cover the tidal flats of the central zone of the Bahía Blanca estuary (Argentina), creating extensive layers. The objective of this study was to characterize the microphytobenthic communities in these biofilms and mats from sediment cores taken in March, June, September and December 2010. Microorganisms were identified and enumerated by microscopy, and their biomass (chlorophyll a, biovolume) quantified at two different stations in the lower supratidal zone, located ～210 m apart from each other (namely S1 and S2). Additionally, the colloidal carbohydrates produced by these microbial communities were quantified, together with physical parameters such as temperature, granulometry, moisture and organic matter content of the sediment layers that comprise a typical epibenthic mat. On the other hand, changes in biomass and colloidal carbohydrate content were studied through a half-tidal cycle (7 h). There were significant seasonal differences in microphytobenthic biovolume (P < 0.001) with a considerably lower biomass in summer, but no significant differences in microalgal biovolume between stations (P = 0.454). Cyanobacterial biomass (largely composed of the filamentous Microcoleus chthonoplastes) was dominant on all dates at both stations, followed by pennate diatoms. Chlorophyll a and colloidal carbohydrate contents in sediment presented a similar pattern to that of microalgal biovolume; with a 5-fold variation in chlorophyll a for S1 between consecutive sampling events on September and December. There were significant differences between sampling dates in colloidal carbohydrates (P < 0.001) with the lowest values recorded during fall and winter; conversely there were no significant differences between stations (P = 0.324). Silt was the dominant sediment fraction at S1 while sand dominated throughout the uppermost 20 mm at S2. Chlorophyll a contents did not show significant differences throughout a half-tidal cycle, likely the product of vertical migration along the section sampled. Conversely, the content of colloidal carbohydrates varied 5-fold, showing a significant (P < 0.001) and steady increase with time of exposure to air and pointing to the rapid metabolic rates of the community. In conclusion, the microphytobenthic community of the Bahía Blanca estuary presented marked seasonality in its biological parameters and overall physiognomy, also showing elevated metabolic rates when subject to tidal fluctuations.     

Fine-scale urbanization affects Odonata species diversity in ponds of a megacity (Paris,France)

Current developments in urban ecology include very few studies focused on pond ecosystems, though ponds are recognized as biodiversity hotspots. Using Odonata as an indicator model, we explored changes in species composition in ponds localized along an urban gradient of a megacity (Paris, France). We then assessed the relative importance of local- and landscape-scale variables in shaping Odonata α-diversity patterns using a model-averaging approach. Analyses were performed for adult (A) and adult plus exuviae (AE) census data. At 26 ponds, we recorded 657 adults and 815 exuviae belonging to 17 Odonata species. The results showed that the Odonata species assemblage composition was not determined by pond localization along the urban gradient. Similarly, pond characteristics were found to be similar among urban, suburban and periurban ponds. The analyses of AE census data revealed that fine-scale urbanization (i.e., increased density of buildings surrounding ponds) negatively affects Odonata α-diversity. In contrast, pond localization along the urban gradient weakly explained the α-diversity patterns. Several local-scale variables, such as the coverage of submerged macrophytes, were found to be significant drivers of Odonata α-diversity. Together, these results show that the degree of urbanization around ponds must be considered instead of pond localization along the urban gradient when assessing the potential impacts of urbanization on Odonata species diversity. This work also indicates the importance of exuviae sampling in understanding the response of Odonata to urbanization.     

Geological summary of the Busidima Formation (Plio-Pleistocene) at the Hadar paleoanthropological site, Afar Depression, Ethiopia

The Hadar paleoanthropological site in Ethiopia preserves a record of hominin evolution spanning from approximately 3.45 Ma to 0.8 Ma. An angular unconformity just above the ca. 2.95 Ma BKT-2 complex divides the sediments into the Hadar Formation (ca. 3.8-2.9 Ma) and the Busidima Formation (ca. 2.7-0.15 Ma). The unconformity is likely a response to a major tectonic reorganization in the Afar Depression, and activation of the As Duma fault near the Ethiopian Escarpment (west of Hadar) created a half-graben in which the Busidima Formation was deposited. The pattern and character of sedimentation in the region changed dramatically above the unconformity, as cut-and-fill channel conglomerates and silt-dominated paleosols that comprise the Busidima Formation stand in sharp contrast to the underlying deposits of the Hadar Formation. Conglomerate deposition has been related to both the perennial, axial paleo-Awash and ephemeral, escarpment-draining tributaries. Overbank silts have yielded fossils attributed to early Homo and Oldowan stone tools. Numerous tuffaceous deposits exist within the Busidima Formation, but they are often spatially limited, fine-grained, and reworked. Recent work on the tephrostratigraphic framework of the Busidima Formation at Hadar has identified at least 12 distinct vitric tephras and established the first geochemical-based correlations between Hadar and the neighboring project areas of Gona and Dikika. Compared to Gona and Dikika, where Busidima Formation sediments are exposed over large areas, the highly discontinuous sediments at Hadar comprise less than 40 m in composite section and are exposed over an area of <20 km², providing only snapshots into the 2.7-0.15 Ma window. The stratigraphic record at Hadar confirms the complex depositional history of the Busidima Formation, and also provides important details on regional stratigraphic correlations and the pattern of deposition and erosion in the lower Awash Valley reflective of its tectonic history.     

Characterization of functional bacterial groups in a hypersaline microbial mat community (Salins-de-Giraud, Camargue, France)

A photosynthetic microbial mat was investigated in a large pond of a Mediterranean saltern (Salins-de-Giraud, Camargue, France) having water salinity from 70 per thousand to 150 per thousand (w/v). Analysis of characteristic biomarkers (e.g., major microbial fatty acids, hydrocarbons, alcohols and alkenones) revealed that cyanobacteria were the major component of the pond, in addition to diatoms and other algae. Functional bacterial groups involved in the sulfur cycle could be correlated to these biomarkers, i.e. sulfate-reducing, sulfur-oxidizing and anoxygenic phototrophic bacteria. In the first 0.5 mm of the mat, a high rate of photosynthesis showed the activity of oxygenic phototrophs in the surface layer. Ten different cyanobacterial populations were detected with confocal laser scanning microscopy: six filamentous species, with Microcoleus chthonoplastes and Halomicronema excentricum as dominant (73% of total counts); and four unicellular types affiliated to Microcystis, Chroococcus, Gloeocapsa, and Synechocystis (27% of total counts). Denaturing gradient gel electrophoresis of PCR-amplified 16S rRNA gene fragments confirmed the presence of Microcoleus, Oscillatoria, and Leptolyngbya strains (Halomicronema was not detected here) and revealed additional presence of Phormidium, Pleurocapsa and Calotrix types. Spectral scalar irradiance measurements did not reveal a particular zonation of cyanobacteria, purple or green bacteria in the first millimeter of the mat. Terminal-restriction fragment length polymorphism analysis of PCR-amplified 16S rRNA gene fragments of bacteria depicted the community composition and a fine-scale depth-distribution of at least five different populations of anoxygenic phototrophs and at least three types of sulfate-reducing bacteria along the microgradients of oxygen and light inside the microbial mat.     

Regulation of photosynthesis and oxygen consumption in a hypersaline cyanobacterial mat (Camargue, France) by irradiance, temperature and salinity

Short-term effects of irradiance (0-1560 micromol photons m(-2) s(-1)), temperature (10-25 degrees C), and salinity (40-160) on oxygenic photosynthesis and oxygen consumption in a hypersaline mat (Salin-de-Giraud, France) were investigated with microsensors under controlled laboratory conditions. Dark O(2) consumption rates were mainly regulated by the mass transfer limitations imposed by the diffusive boundary layer. Areal rates of net photosynthesis increased with irradiance and saturated at irradiances >400 micromol photons m(-2) s(-1). At low irradiances, oxygen consumption increased more strongly with temperature than photosynthesis, whereas the opposite was observed at saturating irradiances. Net photosynthesis vs. irradiance curves were almost unaffected by decreasing salinity (100 to 40), whereas increasing salinities (100 to 160) led to a decrease of net photosynthesis at each irradiance. Dark O(2) consumption rates, maximal gross and net photosynthesis at light saturation were relatively constant over a broad salinity range (60-100) and decreased at salinities above the in situ salinity of 100. Within the range of natural variation, temperature was more important than salinity in regulating photosynthesis and oxygen consumption. At higher salinities the inhibitory impact of salinity on these processes and therefore the importance of salinity as a regulating environmental parameter increased, indicating that in more hypersaline systems, salinity has a stronger limiting effect on microbial activity.