STRUCTURAL AND FUNCTIONAL DYNAMICS OF SULFATE-REDUCING POPULATIONS INBACTERIAL BIOFILMS

We describe the combined application of microsensors and molecular tec hniques to investigate the development of sulfate reduction and of sul fate-reducing bacterial populations in an aerobic bacterial biofilm. M icrosensor measurements for oxygen showed that anaerobic zones develop ed in the biofilm within 1 week and that oxygen was depleted in the to p 200 to 400 mu m during all stages of biofilm development. Sulfate re duction was first detected after 6 weeks of growth, although :favorabl e conditions for growth of sulfate-reducing bacteria (SRB) were presen t from the first week. In situ hybridization with a 16S rRNA probe for SRB revealed that sulfate reducers were present id high numbers (appr oximately 10(8) SRB/ml) in all stages of development, both in the oxic and anoxic zones of the biofilm. Denaturing gradient gel electrophore sis (DGGE) showed that the genetic diversity of the microbial communit y increased during the development of the biofilm. Hybridization analy sis of the DGGE profiles with taxon-specific oligonucleotide probes sh owed that Desulfobulbus and Desulfovibrio were the main sulfate-reduci ng bacteria in all biofilm samples as well as in the bulk activated sl udge. However, different Desulfobulbus and Desulfovibrio species were found in the 6th and 8th weeks of incubation, respectively, coinciding with the development of sulfate reduction. Our data indicate that not all SRB detected by molecular analysis were sulfidogenically active i n the biofilm.