Diel Variations in Carbon Metabolism by Green Nonsulfur-Like Bacteria in Alkaline Siliceous Hot Spring Microbial Mats from Yellowstone National Park

Abstract

Green nonsulfur-like bacteria (GNSLB) in hot spring microbial mats are thought to be mainly photoheterotrophic, using cyanobacterial metabolites as carbon sources. However, the stable carbon isotopic composition of typical Chloroflexus and Roseiflexus lipids suggests photoautotrophic metabolism of GNSLB. One possible explanation for this apparent discrepancy might be that GNSLB fix inorganic carbon only during certain times of the day. In order to study temporal variability in carbon metabolism by GNSLB 14 C]bicarbonate labeling indicated that during the morning, incorporation of label was light dependent and that both cyanobacteria and GNSLB were involved in bicarbonate uptake.13 C-labeling experiments indicated that during the morning, GNSLB incorporated labeled bicarbonate at least to the same degree as cyanobacteria. The incorporation of [ 13 C]bicarbonate into specific lipids could be stimulated by the addition of sulfide or hydrogen, which both were present in the morning photic zone. The results suggest that GNSLB have the potential for photoautotrophic metabolism during low-light periods. In high-light periods, inorganic carbon was incorporated primarily into Cyanobacteria-specific lipids. The results of a pulse-labeling experiment were consistent with overnight transfer of label to GNSLB, which could be interrupted by the addition of unlabeled acetate and glycolate. In addition, we observed direct incorporation of [ 13 C]acetate into GNSLB lipids in the morning. This suggests that GNSLB also have a potential for photoheterotrophy in situ.

Cultivation and Genomic, Nutritional, and Lipid Biomarker Characterization of Roseiflexus Strains Closely Related to Predominant In Situ Populations Inhabiting Yellowstone Hot Spring Microbial Mats

“…This pathway, which is known to be used by Chloroflexus spp., results in isotopically heavier organic carbon than that fixed in the Calvin cycle (21,22,40,43). This photoautotrophic biochemistry of FAPs in the mat was confirmed in labeling experiments using 13 C-labeled bicarbonate, which suggested that the 13 C label was incorporated into FAP biomarkers and FAP biomass (46,47). However, Roseiflexus spp., not Chloroflexus spp., are the dominant mat FAPs, and R. castenholzii has not been shown to grow photoautotrophically (20).…”

“…Although a recent pyrosequencing study argued against this producer-consumer relationship (33), we have observed evidence that 13 CO 2 fixed by Synechococcus spp. into polyglucose is transferred to FAPs via assimilation of [ 13 C]acetate derived from cyanobacterial fermentation (46). Compound-specific stable carbon isotope studies of FAP biomarkers also suggested that FAPs may be photoautotrophic (42,45).…”

“…); they also contain newly described anoxygenic phototrophic bacteria (8) and many organisms involved in mat decomposition (49). We have studied the composition and structure of the mat community using both nucleic acid and lipid biomarker approaches (50), as well as the functional contributions of and interactions among community members (34,46,47).…”

Structure and function of natural sulphide-oxidizing microbial mats under dynamic input of light and chemical energy

“…The activity of such phototrophs is, however, expected to be affected by the local oxygen concentration. For example, filamentous anoxygenic phototrophs (also known as green non-sulphur bacteria) can switch from sulphide-driven anoxygenic P to photoorganoheterotrophy or aerobic respiration when oxygen and cyanobacterial excudates are available in the light ( Van der Meer et al, 2005;Polerecky et al, 2007). Additionally, anaerobic anoxygenic phototrophs, such as green and purple sulphur bacteria, are expected to be poisoned by high oxygen concentrations (Van Gemerden and Mas, 1995).…”

Reconstruction of bacteriochlorophyll biosynthesis pathways in the filamentous anoxygenic phototrophic bacterium Oscillochloris trichoides DG-6 and evolution of anoxygenic phototrophs of the order Chloroflexales

“…Autotrophic CO 2 assimilation by the representatives of family Oscillochloridaceae is performed through the reductive pentose phosphate cycle (Berg et al, 2005;Ivanovsky et al, 1999;Turova et al, 2006). FAPs belonging to the family Roseiflexaceae are photo-organotrophs, and they do not grow photolithotrophically as pure cultures (Hanada et al, 2002), but it has been suggested that Roseiflexus is capable of growing photo-autotrophically in hot spring microbial mats (van der Meer et al, 2005(van der Meer et al, , 2010.…”