Effects of hydroxylamine on microbial community structure and function of autotrophic nitrifying biofilms determined by in situ hybridization and the use of microelectrodes

摘要

Effects of hydroxylamine (NH_2OH), an intermediate of NH_4~+ oxidation, on microbial community structure and function of two autotrophic nitrifying biofilms fed with and without NH_2OH were analyzed by a 16S rRNA approach and the use of microelectrodes. In the NH_2OH-added biofilm, partial oxidation of NH_4~+ to NO_2~- was observed, whereas complete oxidation of NH_4~+ to NO_3~- was achieved in the control biofilm. In situ hybridization results revealed that no nitrite-oxidizing bacteria (NOB) hybridized with any specific probes were detected in the NH_2OH-added biofilm. Thus, the addition of low concentrations of NH_2OH (250 μM) completely inhibited the growth of NOB. Phylogenetic analysis of 16S rDNA indicated that the ammonia-oxidizing bacteria (AOB) detected in both biofilms were closely related to Nitrosomonas europaea, and that the clone sequences from both biofilm libraries have more than 99% similarity to each other. However, in situ hybridization results revealed that the addition of NH_2OH changed the form of growth pattern of the dominant Nitrosomonas spp. from dense clusters mode to single scattered cells mode. Microelectrode measurements revealed that the average NH_4~+ consumption rate calculated in the NH_2OH-added biofilm was two times higher than that in the control biofilm. This clearly demonstrated that the oxidation of NH_4~+ was stimulated by NH_2OH addition.