Monitoring diel variations of physiological status and bacterial diversity in an estuarine microbial mat: an integrated biomarker analysis.

Microbial mats are highly productive microbial systems and a source of not-yet characterized microorganisms and metabolic strategies. In this article, we introduced a lipid biomarker/microbial isolation approach to detect short-term variations of microbial diversity, physiological and redox status, and also characterize lipid biomarkers from specific microbial groups that can be further monitored. Phospholipid fractions (PLFA) were examined for plasmalogens, indicative of certain anaerobes. The glycolipid fraction was processed for polyhydroxyalkanoates (PHA) and the neutral lipid fraction was used to evaluate respiratory quinone content. Data demonstrate an increase in the metabolic stress, unbalanced growth, proportion of anaerobic bacteria and respiratory rate after the maximal photosynthetic activity. Higher accumulation of polyhydroxyalkanoates at the same sampling point also suggested a situation of carbon storage by heterotrophs closely related to photosynthetic microorganisms. Besides, the characterization of lipid biomarkers (plasmalogens, sphingolipids) from specific microbial groups provided clues about the dynamics and diversity of less-characterized mat members. In this case, lipid analyses were complemented by the isolation and characterization of anaerobic spore formers and sulfate reducers to obtain insight into their affiliation and lipid composition. The results revealed that temporal shifts in lipid biomarkers are indicative of an intense change in the physiology, redox condition, and community composition along the diel cycle, and support the hypothesis that interactions between heterotrophs and primary producers play an important role in the carbon flow in microbial mats.

Analysis of diurnal and vertical microbial diversity of a hypersaline microbial mat.

Microbial mats are prokaryotic communities that provide model systems to analyze microbial diversity and ecophysiological interactions. Community diversity of microbial mat samples was assessed at 8:00 a.m. and 3:00 p.m. in a combined analysis consisting of 16S rRNA-denaturing gradient gel electrophoresis (DGGE) and phospholipid fatty acid (PLFA) profiles. The divergence index determined from PLFA and DGGE data showed that depth-related differences have a greater influence on diversity than temporal variations. Shannon and Simpson indices yielded similar values in all samples, which suggested the stable maintenance of a structurally diverse microbial community. The increased diversity observed at 3:00 p.m. between 2.5 and 4 mm can be explained mainly by diversification of anaerobic microorganisms, especially sulfate-reducing bacteria. In the afternoon sampling, the diversity index reflected a higher diversity between 4 and 5.5 mm depth, which suggested an increase in the diversity of strict anaerobes and fermenters. The results are consistent with the conclusion that hypersaline microbial mats are characterized by high degree of diversity that shifts in response to the photobiological adaptations and metabolic status of the microbial community.

Combined phospholipid biomarker-16S rRNA gene denaturing gradient gel electrophoresis analysis of bacterial diversity and physiological status in an intertidal microbial mat.

A combined lipid biomarker-16S rRNA gene denaturing gradient gel electrophoresis analysis was used to monitor changes in the physiological status, biomass, and microbial composition of a microbial mat. In the morning hours, an increase in the biomass of layers containing a high density of phototrophs and a decrease in the growth rate in the deep layers were observed. The combined approach also revealed differences in major groups of microorganisms, including green nonsulfur, gram-positive, and heterotrophic bacteria.

Isolation and characterization of cyanobacteria from microbial mats of the Ebro Delta, Spain.

Isolation and identification of several strains of cyanobacteria from microbial mats of the Ebro Delta, Spain, are described. A series of tenfold dilutions was the first step of isolation. Self-isolation techniques, which use one or several physiological characteristics of a cyanobacterium, were applied in some cases to obtain enrichment cultures. Twelve filamentous strains were isolated and stored in axenic culture. As only a few cyanobacterial species can be frozen and revived without any cryoprotective agent, preservation of isolated strains was assayed with several cryoprotective solutions. Methanol and glycerol were not suitable as cryoprotective agents for most of the isolates. Dimethyl sulfoxide (DMSO) was apparently the best cryoprotector. A new method, which used a filter paper as a growing substratum that later could be directly stored at -80 degrees C, was successfully used. A morphological study of each strain under light and electron microscopy was made to classify them. All isolated strains belong to phylum BX, Class 1, subsection III of the Bergey's manual of systematic bacteriology, 2nd ed., vol. 1. Most genera are included in the LPP group as Lyngbya aestuarii and Microcoleus chthonoplastes.