Identity and potential functions of heterotrophic bacterial isolates from a continuous-upflow fixed-bed reactor for denitrification of drinking waterwith bacterial polyester as source of carbon and electron donor

A collection of 186 heterotrophic bacteria, isolated directly from a contin uous-upflow fixed-bed reactor for the denitrification of drinking water, in which poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) granules acted a s biofilm carrier, carbon source and electron donor, was studied with regar d to taxonomic affiliation and degradation and dentrification characteristi cs. Two granule samples were taken from a fully operating reactor for enume ration and isolation of heterotrophic bacteria. One sample was drawn from t he lower part of the reactor, near the oxic zone, and the other sample from the upper, anoxic part of the fixed bed. Dominant colonies were isolated a nd the cultures were identified using fatty acid analysis and 16S rDNA sequ encing. Their ability to degrade the polymer and 3-hydroxybutyrate and to d enitrify in pure culture was assessed. The results show that high numbers o f heterotrophic bacteria were present in the biofilms on the polymer granul es, with marked differences in taxonomic composition and potential function s between the lower and upper part of the fixed bed. The majority of the is olates were Gram negative bacteria, and most of them were able to reduce ni trate to nitrite or to denitrify, and to utilize 3-hydroxybutyrate as sole source of carbon. Only two groups, one identified as Acidovorax facilis and the other phylogenetically related to Brevundimonas intermedia, could comb ine denitrification and utilization of poly(3-hydroxybutyrate) (PHB), and w ere found only in the upper sample. The other groups occurred either in the lower or upper part, or in both samples. They were assigned to Brevundimon as, Pseudomonas, Agrobacterium, Achromobacter, or Phyllobacterium, or were phylogenetically related to Afipia or Stenotrophomonas.