The dominant microbial components of fluids from wells in pristine and water-injected, high-temperature, Western Siberian oil fields, were analyzed by PCR-DGGE. Particular emphasis was placed on sulphatereducing organisms, due to their ecological and industrial importance. Bacterial phylotypes obtained from the non-water-injected Stolbovoye oil field were more diverse than those from the Samotlor field, which is subject to secondary oil recovery by reinjection of recycled production water. The majority of phylotypes from both sites were related to Firmicutes. The low similarity to their closest relatives indicates unique bacterial communities in deep underground production waters and crude oil. Archaeal phylotypes detected only in the Samotlor samples were represented by Methanosarcinales and
Methanobacteriales.Downloaded by [FU Berlin]