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 Pseudomonadaceae 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), Pseudomonadaceae were one of the two predominating families, along with Micrococcaceae (enrichment culture C) and Dietziaceae (enrichment culture D). The proportion of dsrA and apsA 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 rhlB 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 rhlB gene was not found.

尽管现有诸多关于油田生态系统的研究成果，但针对多数原油、油田及生产井的微生物群落结构与功能特征，相关数据仍存在显著缺口。俄罗斯鞑靼斯坦共和国境内的罗马什金（Romashkino）特大型油田，便是这类研究不足的典型油田之一。本研究针对该油田生产井采集的4份不同油水比样品开展厌氧富集培养实验，解析其中的原核生物群落组成，并定量检测编码硫酸盐还原与鼠李糖脂（rhamnolipid）合成的功能基因丰度。富集培养在厌氧条件下进行，以硫酸盐、硝酸盐作为电子受体，乙酸盐作为电子供体。在富集培养物A与富集培养物B中，假单胞菌科（Pseudomonadaceae）为绝对优势菌群，相对丰度分别达99%与93%。在基于中等含水率原油初始样品培养得到的富集培养物C，以及基于极高含水率原油初始样品培养得到的富集培养物D中，假单胞菌科与另一科细菌共同构成优势菌群：培养物C的另一优势科为微球菌科（Micrococcaceae），培养物D则为迪茨氏菌科（Dietziaceae）。编码硫酸盐还原功能的dsrA与apsA基因拷贝数占16S rRNA基因总拷贝数的比例极低，区间为0.003%（富集培养物A、B）至0.027%（富集培养物D）。编码鼠李糖脂合成的rhlB基因拷贝数占16S rRNA基因总拷贝数的比例，在样品A中为1.10%，样品B中为0.06%；而在富集培养物C与D中未检测到rhlB基因。