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Abstract: The intact polar lipid (IPL) composition of a microbial mat growing in a sulfidic Icelandic hot spring at 55°C was investigated. The composition was dominated by the glycolipids monoglycosyldiacylglycerol (MGDG), diglycosyldiacylglycerol (DGDG), sulfoquinovosyldiacylglycerol (SQDG) and the glycerophospholipid phosphatidylglycerol (PG). We also detected a series of heterocyst glycolipids (HGs) with an elongated aglycone moiety via comparison with those found in other microbial mats. Based on the mass spectra, we identified the components as 1-(O-hexose)-3,27,29-triacontanetriol (C30 HG triol) and 1-(O-hexose)-3,29,31-dotriacontanetriol (C32 HG triol). The principal mat builders were the thermophilic heterocystous cyanobacterium Mastigocladus laminosus (Stigonematales) and green nonsulfur-like bacteria (GNSLB) closely related to Chloroflexus aurantiacus. Since HGs are characteristic lipids for heterocystous cyanobacteria, M. laminosus is the likely source of the long chain HGs. IPL analysis of cultivated M. laminosus confirmed that this heterocystous cyanobacterium synthesized the C32 HG triol and a related isomer. Culture experiments at different growth temperatures showed no change in the overall HG composition but revealed that the relative proportion of the different C32 HG triol isomers varied, possibly as a physiological response to maintaining sub-μM O2 concentration within the heterocyst. Combined with previous studies, our results suggests that the C32 HG triol might be of chemotaxonomic value for identifying heterocystous cyanobacteria of the order Stigonematales in hot spring and other microbial mats. [Copyright &y& Elsevier]

Abstract: The creation of a mathematical simulation model of photosynthetic microbial mats is important to our understanding of key biogeochemical cycles that may have altered the atmospheres and lithospheres of early Earth. A model is presented here as a tool to integrate empirical results from research on hypersaline mats from Baja California Sur (BCS), Mexico into a computational system that can be used to simulate biospheric inputs of trace gases to the atmosphere. The first version of our model, presented here, calculates fluxes and cycling of O2, sulfide, and dissolved inorganic carbon (DIC) via abiotic components and via four major microbial guilds: cyanobacteria (CYA), sulfate reducing bacteria (SRB), purple sulfur bacteria (PSB) and colorless sulfur bacteria (CSB). We used generalized Monod-type equations that incorporate substrate and energy limits upon maximum rates of metabolic processes such as photosynthesis and sulfate reduction. We ran a simulation using temperature and irradiance inputs from data collected from a microbial mat in Guerrero Negro in BCS (Mexico). Model O2, sulfide, and DIC concentration profiles and fluxes compared well with data collected in the field mats. There were some model-predicted features of biogeochemical cycling not observed in our actual measurements. For instance, large influxes and effluxes of DIC across the MBGC mat boundary may reveal previously unrecognized, but real, in situ limits on rates of biogeochemical processes. Some of the short-term variation in field-collected mat O2 was not predicted by MBGC. This suggests a need both for more model sensitivity to small environmental fluctuations for the incorporation of a photorespiration function into the model. [Copyright &y& Elsevier]

The extension of ecological tolerance limits may be an important mechanism by which microorganisms adapt to novel environments, but it may come at the evolutionary cost of reduced performance under ancestral conditions. We combined a comparative physiological approach with phylogenetic analyses to study the evolution of thermotolerance in hot spring cyanobacteria of the genus Synechococcus. Among the twenty laboratory clones of Synechococcus isolated from collections made along an Oregon hot spring thermal gradient, four different 16S ribosomal RNA gene sequences were identified. Phylogenies constructed using these sequence data indicated that the clones were polyphyletic but also that three of the four sequence groups formed a clade. Differences in thermotolerance were observed for clones with different 16S rRNA gene sequences, and comparison of these physiological differences within a phylogenetic framework provided evidence that more thermotolerant lineages of Synechococcus evolved from less thermotolerant ancestors. The extension of the thermal limit in these bacteria was correlated with a reduction in thermal niche breadth, which may have implications for the geographic distributions of these organisms. This study illustrates the utility of using phylogenetic comparative methods to investigate how evolutionary processes have shaped historical patterns of ecological diversification in microorganisms. [ABSTRACT FROM AUTHOR]