Oil field bacteria were characterized by cloning and sequencing of PCR-amplified 16S rRNA genes. A variety of gram-negative, sulfate-reducing bacteria was detected (16 members of the family Desulfovibrionaceae and 8 members of the family Desulfobacteriaceae). In contrast, a much more limited number of anaerobic, fermentative, or acetogenic bacteria was found (one Clostridium sp., one Eubacterium sp., and one Synergistes sp.). Potential sulfide oxidizers and/or microaerophiles (Thiomicrospira, Arcobacter, Campylobacter, and Oceanospirillum spp.) were also detected. The first two were prominently amplified from uncultured production water DNA and represented 28 and 47% of all clones, respectively. Growth on media containing sulfide as the electron donor and nitrate as the electron acceptor and designed for the isolation of Thiomicrospira spp. gave only significant enrichment of the Campylobacter sp., which was shown to be present in different western Canadian oil fields. This newly discovered sulfide oxidizer may provide a vital link in the oil field sulfur cycle by reoxidizing sulfide formed by microbial sulfate or sulfur reduction.

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Numerous purified and characterized sulfate-reducing bacteria and bacterial communities isolated from oil-field production facilities were shown to convert dibenzothiophene (DBT) into biphenyl (BP). The maximum degree of conversion to biphenyl was 1.14 % and 0.39% for purified sulfatereducing bacteria and community bacteria, respectively.The purified sulfate-reducing bacteria and bacterial communities were identified by 16S rRNA ribotyping.

One hundred and nine returning adult salmon were radio‐tagged in the estuary of the Aberdeenshire Dee, Scotland between February and August 1985 to 1989 and the times when 62 fish entered the river were recorded. Elapsed times between tagging and river entry were significantly greater during periods of lower than average river flows in all months where there were sufficient data to allow statistical comparison. The degree of association between river entry and particular levels of river discharge rate varied seasonally. The proportion of days associated with river entry declined at the lower end of the range of flows available to tagged fish in the summer months. Absolute levels of river discharge played a significant role in modifying the response of salmon to changing flows. During periods of lower than average seasonal flow, river entry was closely associated with days when flow had increased since the previous day. During periods of higher than average flow, river entry was not significantly associated with such periods of increased flow. The results suggest that models which relate river entry by salmon to absolute discharge rates alone are unlikely to be generally reliable.

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