Distribution of sulfate-reducing bacteria in a stratified Fjord (Mariager Fjord, Denmark) as evaluated by most-probable-number counts and denaturing gradient gel electrophoresis of PCR-amplified ribosomal DNA fragments

The sulfate-reducing bacterial populations of a stratified marine water column, Mariager Fjord, Denmark, were investigated by molecular and culture-dependent approaches in parallel. Denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA and DNA encoding rRNA (rDNA) isolated from the water column indicated specific bacterial populations in different water column layers and revealed a highly differentiated pattern of rRNA- and rDNA-derived PCR amplificates, probably reflecting active and resting bacterial populations. Hybridization of DGGE patterns with rRNA probes indicated the increased presence and activity (by at least 1 order of magnitude) of sulfate-reducing bacteria within and below the chemocline. Parallel to this molecular approach, an approach involving most-probable-number (MPN) counts was used, and it found a similar distribution of cultivable sulfate-reducing bacteria in the water column of Mariager Fjord, Approximately 25 cells and 250 cells per ml above and below the chemocline, respectively, were found. Desulfovibrio-and Desulfobulbus-relateA strains occurred in the oxic zone. DGGE bands from MPN cultures were sequenced and compared with those obtained from nucleic acids extracted from water column samples. The MPN isolates were phylogenetically affiliated with sulfate-reducing delta subdivision proteobacteria (members of the genera Desulfovibrio, Desulfobulbus, and Desulfobacter), whereas the molecular isolates constituted an independent lineage of the delta subdivision proteobacteria. DGGE of PCR-amplified nucleic acids with general eubacterial PCR primers conceptually revealed the general bacterial population, whereas the use of culture media allowed cultivable sulfate-reducing bacteria to be selected. A parallel study of Mariager Fjord biogeochemistry, bacterial activity, and bacterial counts complementing this investigation has been presented elsewhere (N. B. Ramsing, H. Fossing, T. G. Ferdelman, F. Andersen, and B. Thamdrup, Appl. Environ. Microbiol. 62:1391-1404, 1996)

Sulfate-reducing bacteria and their activities in cyanobacterial mats of Solar Lake (Sinai, Egypt)

The sulfate-reducing bacteria within the surface layer of the hypersaline cyanobacterial mat of Solar Lake (Sinai, Egypt) were investigated with combined microbiological, molecular, and biogeochemical approaches. The diurnally oxic surface layer contained between 106 and 107 cultivable sulfate-reducing bacteria ml-1 and showed sulfate reduction rates between 1,000 and 2,200 nmol ml-1 day-1, both in the same range as and sometimes higher than those in anaerobic deeper mat layers. In the oxic surface layer and in the mat layers below, filamentous sulfate-reducing Desulfonema bacteria were found in variable densities of 104 to 106 cells ml-1. A Desulfonema-related, diurnally migrating bacterium was detected with PCR and denaturing gradient gel electrophoresis within and below the oxic surface layer. Facultative aerobic respiration, filamentous morphology, motility, diurnal migration, and aggregate formation were the most conspicuous adaptations of Solar Lake sulfate-reducing bacteria to the mat matrix and to diurnal oxygen stress. A comparison of sulfate reduction rates within the mat and previously published photosynthesiS rates showed that CO2 from sulfate reduction in the upper 5 mm accounted for 7 to 8% of the total photosynthetic CO2 demand of the mat

Oxygen dynamics at the base of a biofilm studied with planar optodes

The O-2 dynamics at the base of biofilms was studied using planar optodes. Biofilms were grown directly on the optodes and the 2-dimensional distribution of O-2 at the base of biofilms was resolved at a spatial resolution of 30 x 30 mu m, using a CCD camera. The average O-2 Saturation at the base decreased and the heterogeneity increased as biofilms developed. In mature biofilms heterogeneous O-2 distributions were caused by clusters of high biomass which had low O-2 saturations surrounded by O-2-rich voids and channels. The O-2 distribution at the base of biofilms was highly dependent on the free flow velocity above the biofilm, e.g. in a 400 mu m thick biofilm the average O-2 saturation increased from 0 to 23.1% air saturation as the free flow velocity increased from 6.2 to 35.1 cm s(-1). Addition of glucose to a concentration of 2 mM in the water phase at maximum flow velocity caused the O-2 consumption rate to increase and the base of the biofilm to go anoxic. The insertion of an O-2 microelectrode into a biofilm caused the O-2 saturation at the base of the biofilm to increase by approximately 25 mu M. This effect, presumably caused by hydrodynamic disturbances, typically extended several mm away from the position of the microsensor tip. The presented data show for the first time the true distribution of O-2 at the basis of heterogeneous biofilms and demonstrate the great potential of planar optodes for the study of solute dynamics within biofilms at a very high spatial and temporal resolution