MICROBIOLOGY OF A NITRITE-OXIDIZING BIOREACTOR

The microbiology of the biomass from a nitrite-oxidizing sequencing ba tch reactor (NOSBR) fed with an inorganic salts solution and nitrite a s the sole energy source that had been operating for 6 months was inve stigated by microscopy, by culture-dependent methods, and by molecular biological methods, and the seed sludge that was used to inoculate th e NOSBR was investigated by molecular biological methods, The NOSBR sl udge comprised a complex and diverse microbial community containing gr am-negative and gram-positive rods, cocci, and filaments. By culture-d ependent methods (i.e., micromanipulation and sample dilution and spre ad plate inoculation), 16 heterotrophs (6 gram positive and 10 gram ne gative) were identified in the NOSBR sludge (RC), but no autotrophs we re isolated. 16S ribosomal DNA clone libraries of the two microbial co mmunities revealed that the seed sludge (GC) comprised a complex micro bial community dominated by Proteobacteria (29% beta subclass; 18% gam ma subclass) and high G+C gram-positive bacteria (10%). Three clones ( 4%) were closely related to the autotrophic nitrite-oxidizer Nitrospir a moscoviensis, The NOSBR sludge was overwhelmingly dominated by bacte ria closely related to N. moscoviensis (89%). Two clone sequences were similar to those of the genus Nitrobacter, Near-complete insert seque nces of eight RC and one GC N. moscoviensis clone were determined and phylogenetically analyzed. This is the first report of the presence of bacteria from the Nitrospira phylum in wastewater treatment systems, and it is hypothesized that these bacteria are the unknown nitrite oxi dizers in these processes.