EFFECT OF NITRATE INJECTION ON THE MICROBIAL COMMUNITY IN AN OIL-FIELD AS MONITORED BY REVERSE SAMPLE GENOME PROBING

The reverse sample genome probe (RSGP) method, developed for monitorin g the microbial community in oil fields with a moderate subsurface tem perature, has been improved by (i) isolation of a variety of heterotro phic bacteria and inclusion of their genomes on the oil field master f ilter and (ii) use of phosphorimaging technology for the rapid quantit ation of hybridization signals. The new master filter contains the gen omes of 30 sulfate-reducing, 1 sulfide-oxidizing, and 16 heterotrophic bacteria, Most have been identified by partial 16S rRNA sequencing, U se of improved RSGP in monitoring the effect of nitrate injection in a n oil field indicated that the sulfide-oxidizing, nitrate-reducing iso late CVO (a Campylobacter sp,) becomes the dominant community componen t immediately after injection, No significant enhancement of other com munity members, including the sulfate-reducing bacteria, was observed, The elevated level of CVO decayed at most sampling sites within 30 da ys after nitrate injection was terminated. Chemical analyses indicated a corresponding decrease and subsequent increase in sulfide concentra tions, Thus, transient injection of a higher potential electron accept or into an anaerobic subsurface system can have desirable effects (i.e ., reduction of sulfide levels) without a permanent adverse influence on the resident microbial community.