Unexpected population distribution in a microbial mat community: Sulfate-reducing bacteria localized to the highly oxic chemocline in contrast to a eukaryotic preference for anoxia

The distribution and abundance of sulfate-reducing bacteria (SRB) and eukar yotes within the upper 4 mm of a hypersaline cyanobacterial mat community w ere characterized at high resolution with group-specific hybridization prob es to quantify 16S rRNA extracted from 100-mu m depth intervals. This revea led a preferential localization of SRB within the region defined by the oxy gen chemocline. Among the different groups of SRB quantified, including mem bers of the provisional families "Desulfovibrionaceae" and "Desulfobacteria ceae," Desulfonema-like populations dominated and accounted for up to 30% o f total rRNA extracted from certain depth intervals of the chemocline. Thes e data suggest that recognized genera of SRB are not necessarily restricted by high levels of oxygen in this mat community and the possibility of sign ificant sulfur cycling within the chemocline. In marked contrast, eukaryoti c populations in this community demonstrated a preference for regions of an oxia.