Composition of Prokaryotic Communities in Anaerobic Enrichment Cultures of Crude Oil from Romashkino Oilfield (Russia)

Despite the many papers published on oilfield ecosystems, there is a lack of data about microbial community structure and functioning in many crude oils or oilfields and wells. One of such poorly studied oilfields is supergiant Romashkino situated in Tatarstan (Russia). In the present study, prokaryotic community composition and abundance of functional genes encoding sulfate reduction and rhamnolipid production, was investigated in enrichment cultures of four samples from Romashkino oilfield production wells with different oil/water ratios. The enrichment was conducted under anaerobic conditions, sulfate and nitrate were used as electron acceptors, and acetate – as an electron donor. In enrichment culture A and enrichment culture B, bacteria of the <i>Pseudomonadaceae</i> family predominated with 99% and 93% relative abundance, respectively. In enrichment culture C (obtained on the basis of initial sample contained oil with medium water content) and D (obtained on the basis of initial sample contained oil with very high water content), <i>Pseudomonadaceae</i> were one of the two predominating families, along with <i>Micrococcaceae</i> (enrichment culture C) and <i>Dietziaceae</i> (enrichment culture D). The proportion of <i>dsrA</i> and <i>apsA</i> genes encoding sulfate reduction to 16S rRNA gene copy numbers was quite low and ranged between 0.003% (enrichment cultures A, B) and 0.027% (enrichment culture D). The proportion of <i>rhlB</i> gene encoding rhamnolipid production from the total 16S rRNA gene copy number was 1.10% in sample A and 0.06% in sample B. In enrichment cultures C and D the <i>rhlB</i> gene was not found.