Quantification of cell specific uptake activity of microbial products by uncultured Chloroflexi by microautoradiography combined with fluorescence in situ hybridization

We, for the first time, quantitatively determined cell specific uptake activities of microbial products (bacterial cell detritus and extracellular polymeric substances, EPS) by the member of uncultured Chloroflexi by using a microautoradiography combined with fluorescence in situ hybridization (MAR-FISH) technique. For this MAR-FISH analysis, we prepared [C-14]-labeled microbial products from biomass sludge obtained and bacterial strains (Pseudomonas sp. and Acinetobacter sp.) isolated from our pilot-scale membrane bioreactor (MBR) as tracer substrates, which probably represent the more realistic food source in the MBR. The quantitative MAR-FISH analyses clearly showed that most of the uncultured Chloroflexi could indeed uptake the bacterial detritus of the two isolated strains with rates of 1.7-3.5 x 10(-17) g-C mu m(-2)-surface area h(-1) (corresponding to 1.2-1.7 mg-C-bacterial detritus L-1 h(-1)) in the cultures, which were, however, about 2 orders of magnitude lower than the uptake rates of simple monosaccharides (mannose, arabinose, fucose, and galactose). Based on these results and their high abundance (more than 20% of total bacteria detected with EUB338-mixed probes), it could be estimated that the uncultured Chloroflexi contributes 38-51% of the total degradation of microbial products occurred in the MAR-FISH cultures.