Vertical migration of phototrophic bacterial populations in a hypersaline microbial mat from Salins-de-Giraud (Camargue, France)

Abstract

The spatio-temporal distribution of phototrophic communities of the hypersaline photosynthetic Camarguc microbial mat (Salins-de-Giraud, France) was investigated over a diel cycle by combining microscopic and molecular approaches. Microcoleus chthonoplastes and Halomicronema excentricum, the dominant cyanobacteria of this oxyphotrophic community, were observed with confocal laser scanning microscopy to determine their biomass profiles. Both bacteria have similar vertical distributions, varying from a homogenous distribution through the mat during the night, to a specific localization in the upper oxic zone of 1.5 mm during the day. Terminal restriction fragment length polymorphism of PCR-amplified pufM gene fragments revealed three groups of anoxyphototrophic populations, which varied according to the two opposite periods of the diel cycle under study. They were either specifically detected in only one period, or homogenously distributed through the mat in all periods, or located in specific zones of the mat depending on the period considered. Oxygen concentrations, pH and biomass of the major filamentous cyanobacteria were the determinative factors in the distribution of these anoxyphototrophs across the mat. Thus, vertical migration, cell-cell aggregate formation and metabolic switches were the most evident defence of the photosynthetic populations against the adverse effects of sulfide and oxygen fluxes during a diel cycle.

The Hydrogenase Chip: a tiling oligonucleotide DNA microarray technique for characterizing hydrogen-producing and -consuming microbes in microbial communities

“…The lowered DNA hybridization intensity at night is probably due to some aerobic microbes having migrated in the night from deeper layers into the upper layers toward atmospheric O 2 , thereby diluting the cyanobacteria in the uppermost layer of the mat, or due to downwards migration by the cyanobacteria themselves. Such diel migration has been previously described in similar mats (Bebout and Garcia-Pichel, 1995;Fourçans et al, 2006;Dillon et al, 2009). …”

Biogeochemical conditions determine virulence of black band disease in corals

“…The stratification in hypersaline mats is mainly driven by gliding filamentous members (cyanobacteria, Beggiatoa sp.) that are highly motile and exhibit active diurnal migration (Fourcans et al, 2006;Hinck et al, 2007;Dillon et al, 2009). The vertical orientation of functional groups within hypersaline mats results in the development of pronounced biogeochemical microgradients (e.g., O 2 , light, pH, sulphate and sulphide), reciprocally influenced by and influencing their environment.…”

Effects of Heavy Fuel Oil on the Bacterial Community Structure of a Pristine Microbial Mat

“…Microbial mats are complex microbial communities that exhibit extensive genetic and metabolic diversification, which confers a high capacity to adapt to hostile environments (15,16,44). The diverse microbial activities found in these mats suggest that they may have the capacity to degrade petroleum compounds and other pollutants (3).…”