Effects of salinity and light on organic carbon and nitrogen uptake in a hypersaline microbial mat

Abstract

Utilization of dissolved organic matter (DOM) is thought to be the purview of heterotrophic microorganisms, but photoautotrophs can take up dissolved organic nitrogen (DON) and dissolved organic carbon (DOC). This study investigated DOC and DON uptake in a laminated cyanobacterial mat community from hypersaline Salt Pond (San Salvador, Bahamas). The total community uptake of (3)H-labeled substrates was measured in the light and in the dark and under conditions of high and low salinity. Salinity was the primary control of DOM uptake, with increased uptake occurring under low-salinity, 'freshened' conditions. DOC uptake was also enhanced in the light as compared with the dark and in samples incubated with the photosystem II inhibitor 3(3,4-dichlorophenyl)-1, 1-dimethylurea, suggesting a positive association between photosynthetic activity and DOC uptake. Microautoradiography revealed that some DOM uptake was attributed to cyanobacteria. Cyanobacteria DOM uptake was negatively correlated with that of smaller filamentous microorganisms, and DOM uptake by individual coccoid cells was negatively correlated with uptake by colonial coccoids. These patterns of activity suggest that Salt Pond microorganisms are engaged in resource partitioning, and DOM utilization may provide a metabolic boost to both heterotrophs and photoautrophs during periods of lowered salinity.

Comparative Characterization of the Microbial Diversities of an Artificial Microbialite Model and a Natural Stromatolite

“…Despite this limitation, the prevalence of diazotrophic Rhizobiales and Rhodobacteriales in the artificial microbialites is consistent with previous analyses of nitrogen fixation in Bahamian stromatolites (53) and in Hamelin Pool of Shark Bay, Australia (42). Previous research has shown that noncyanobacterial nitrogen fixation may be important in mats whose cyanobacterial population tends to contain mostly nonheterocystous cyanobacteria (37,46,60,61), such as cyanobacteria with the sequences recovered in the Highborne Cay stromatolites.…”

Millimeter-scale patterns of phylogenetic and trait diversity in a salt marsh microbial mat

“…Competition theory presents an alternative mechanism to explain the increase in diversity with mat depth. We speculate that the pool of nutrients available for assimilation (primarily N and P ) may be limiting to heterotrophs in the oxic layer due to the large biomass of primary producers such as heterocystous Cyanobacteria and diatoms (Herbert and Welsh, 1994; Camacho and de Wit, 2003; Jonkers et al, 2003; Yannarell and Paerl, 2007). If competition for limiting nutrients, rather than competition for sources of C and energy, are resulting in competitive exclusion then we might expect competitive exclusion should not be as dominant a force deeper in the mat, allowing more taxa to coexist (Hutchinson, 1961).…”

Comparative microbial diversity analyses of modern marine thrombolitic mats by barcoded pyrosequencing

“…Previous studies have shown that light availability can have a strong impact on the composition of cyanobacterial communities (Havens et al ., 1998). As photosynthetic mat communities experience increases in light availability previous studies have shown there is an increase in uptake of dissolved organic carbon (Yannarell and Paerl, 2007). The rate of uptake is influenced by the type and composition of the cyanobacterial communities (e.g.…”

“…The rate of uptake is influenced by the type and composition of the cyanobacterial communities (e.g. filamentous, colony coccoid or solitary coccoid; Yannarell and Paerl, 2007). The transition to the coccoid rich communities of the beige (enriched in colony‐forming Pleurocapsales ) or the pink (enriched in solitary Chroococcales ) mats may reflect seasonal differences in uptake or differences in the substrate‐utilization patterns of the two distinct mat types.…”