Distribution of denitrification and nitrogen fixation genes inHyphomicrobiumspp. and other budding bacteria

Abstract

Genomic DNA of Hyphomicrobium spp., Hirschia baltica ATCC 49814T, Hyphomonas oceanitis ATCC 33897T, and Pedomicrobium ferrugineum S-1290Twas investigated with gene probes specific for nitrate reductase (narG), cytochrome cd1containing nitrite reductase (nirS), Cu-containing nitrite reductase (nirK), nitrous oxide reductase (nosZ), ammonia monooxygenase (amoA), and nitrogenase reductase (nifH) by Southern or dot blot hybridization. The presence of denitrification genes could be demonstrated for Hyphomicrobium denitrificans 1869T, Hyphomicrobium aestuarii IFAM NQ-521GrT, Hyphomicrobium zavarzinii IFAM ZV-580, Hyphomicrobium zavarzinii subsp. chengduense, in the Hyphomicrobium DNA-DNA hybridization groups 3, 12, 13, 18, 26a1, 26a2, 26c, 26d, 26e, 26f, 26g2, and 29, and in three isolates from a denitrifying sand filter in a municipal wastewater treatment plant. The Cu-containing nitrite reductase appeared to be more frequent than the cytochrome cd1containing nitrite reductase in hyphomicrobia. Resulting positive DNA-DNA hybridization signals correlated with physiological activity measurements of intact cells in all cases determined. The nifH-like gene fragment was found in Hyphomicrobium aestuarii, Hyphomicrobium zavarzinii, Hyphomicrobium zavarzinii subsp. chengduense, Hyphomicrobium facilis and eight additional DNA-DNA hybridization groups. Ammonia monooxygenase was not genetically detected in any of the strains investigated. The results significantly extended the previous findings that genetically different hyphomicrobia of a sewage treatment plant and its adjacent receiving lake could occupy different ecological niches. Denitrification genes or the nifH-like gene fragment were not found in the other budding bacteria investigated.Key words: Hyphomicrobium, denitrification, nitrification, nitrogen fixation, activated sludge, biofilm.