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Filamentous anoxygenic phototrophs (FAPs) are abundant members of microbial mat communities inhabiting neutral and alkaline geothermal springs. Natural populations of FAPs related to Chloroflexus spp. and Roseiflexus spp. have been well characterized in Mushroom Spring, where they occur with unicellular cyanobacteria related to Synechococcus spp. strains A and B′. Metatranscriptomic sequencing was applied to the microbial community to determine how FAPs regulate their gene expression in response to fluctuating environmental conditions and resource availability over a diel period. Transcripts for genes involved in the biosynthesis of bacteriochlorophylls (BChls) and photosynthetic reaction centers were much more abundant at night. Both Roseiflexus spp. and Chloroflexus spp. expressed key genes involved in the 3-hydroxypropionate (3-OHP) carbon dioxide fixation bi-cycle during the day, when these FAPs have been thought to perform primarily photoheterotrophic and/or aerobic chemoorganotrophic metabolism. The expression of genes for the synthesis and degradation of storage polymers, including glycogen, polyhydroxyalkanoates and wax esters, suggests that FAPs produce and utilize these compounds at different times during the diel cycle. We summarize these results in a proposed conceptual model for temporal changes in central carbon metabolism and energy production of FAPs living in a natural environment. The model proposes that, at night, Chloroflexus spp. and Roseiflexus spp. synthesize BChl, components of the photosynthetic apparatus, polyhydroxyalkanoates and wax esters in concert with fermentation of glycogen. It further proposes that, in daytime, polyhydroxyalkanoates and wax esters are degraded and used as carbon and electron reserves to support photomixotrophy via the 3-OHP bi-cycle. [ABSTRACT FROM AUTHOR]

Many eukaryotic communities exhibit predictable seasonality in species composition, but such phenological patterns are not well-documented in bacterial communities. This study quantified seasonal variation in the community composition of bacterioplankton in a high-elevation lake in the Sierra Nevada of California over a 3-year period of 2004–2006. Bacterioplankton exhibited consistent phenological patterns, with distinct, interannually recurring community types characteristic of the spring snowmelt, ice-off and fall-overturn periods in the lake. Thermal stratification was associated with the emergence of specific communities each summer and increased community heterogeneity throughout the water column. Two key environmental variables modulated by regional meteorologic variation, lake residence time and thermal stability, predicted the timing of occurrence of community types each year with 75% accuracy, and each corresponded with different aspects of variation in community composition (orthogonal ordination axes). Seasonal variation in dissolved organic matter source was characterized fluorometrically in 2005 and was highly correlated with overall variation in bacterial community structure (rMantel=0.75, P<0.001) and with the relative contributions of specific phylotypes within the Cyanobacteria, Actinobacteria and β-Proteobacteria. The seasonal dynamics of bacterial clades (tracked through coupling of randomized clone sequence libraries to restriction fragment length polymorphism fingerprints) matched previous results from alpine lakes and were variously related to solute inputs, thermal stability and temperature. Taken together, these results describe a phenology of high-elevation bacterioplankton communities linked to climate-driven physical and chemical lake characteristics already known to regulate eukaryotic plankton community structure.The ISME Journal (2009) 3, 13–30; doi:10.1038/ismej.2008.81; published online 11 September 2008 [ABSTRACT FROM AUTHOR]