Enrichment of methanotrophic microorganisms from sludge of UASB reactor treating domestic sewage

ABSTRACT

In this study, methanotrophic microorganisms were enriched from sludge derived from a UASB reactor treating domestic sewage. The enrichment was performed in a sequencing batch reactor (RBS) with an autotrophic medium containing nitrite and nitrate. The nitrite and nitrate removal efficiencies were 68% and 53%, respectively, probably due to heterotrophic denitrification. Archaeal cells of the ANME-I and ANME-II groups were detected by PCR throughout the whole cultivation period. The microbial community composition of the biomass present in the inoculum and enriched in RBS after 100 days of operation was investigated and compared with the help of data obtained from pyrosequencing analyses. Pyrosequencing analysis demonstrated that the community enriched in the reactor had differing composition from the inoculum. The dominant phyla detected in the inoculum were Synergistestes , Firmicutes and Euryarchaeota while in the enriched biomass Planctomycetes, Verrucomicrobia, Chloroflexi and Proteobacteria predominated. The cultivation conditions applied decreased the abundance of Methanobacterium (from 8 to 1%) and selected for methanotrophic bacteria such as Methylocaldum , Methylocistis and Methylosinus . Sequences of Methylocaldum sp. accounted for 2.5% of the total reads. The presence and high predominance of Verrucomicrobia in the enriched biomass suggest that other unknown methanotrophic species related to this phylum might also have occurred in the reactor. The potential for anaerobic oxidation of methane was determined for both samples and revealed that the methanotrophic activity of the enriched biomass was almost three times greater than in the inoculum. Taken together these results indicated that the inoculum used and the cultivation conditions applied were adequate for the methanotrophic enrichment.

Keywords:
methanotrophic microorganisms; methanotrophic activity; sequencing batch reactor,; pyrosequencing; UASB reactor sludge.