Abstract
Biodegradation may result in physicochemical changes in crude oil and natural gas properties, being responsible for the decrease of saturated hydrocarbons and yielding heavy oil with low economic value. Studies on the diversity of microbial catabolic genes in oil reservoirs are scarce and could help to predict the potential of a petroleum sample to be biodegraded. The aim of this study was to evaluate the diversity of genes involved in hydrocarbon degradation in Brazilian petroleum samples (biodegraded and non-biodegraded) through the construction and analysis of gene libraries (alkane monooxygenase – alk, dioxygenase – ARHDs and 6-oxocyclohex-1-ene-1-carbonyl-CoA hydrolase - bamA). The results showed a differential distribution of catabolic genes between the sites, being the biodegraded oil more diverse for the alk and bamA genes. Sequences were similar to the alkB genes from Geobacillus thermoleovorans and several species of Acinetobacter, to ARHD genes from Pseudomonas spp. and two species of Burkholderia, and to bamA genes from deltaproteobacteria. Interestingly, most of the catabolic sequences recovered from both petroleum reservoirs grouped together forming distinct clusters in the phylogenetic tree reconstruction and may correspond to potentially new genes, possibly harbored by yet uncultivated microorganisms. This is the first report on the detection of alk, ARHD and bamA genes in petroleum reservoir environments, demonstrating the genetic potential of such microbial communities to biodegrade the oil.
Highlights
Most of the world’s oil is biodegraded and while the effects of biodegradation on the molecular composition and physical properties of crude oil and natural gas are relatively well known empirically, the actual processes that occur during the biodegradation of oil in deep reservoirs remain unclear [1]
This study examined the diversity of the functional gene involved in the degradation of hydrocarbons, the alkane hydroxylase gene, a membrane-bound enzyme that catalyzes the terminal or sub terminal oxidation of n-alkanes (C5-C16) for primary or secondary alcohols, which is the initial step in the aerobic degradation of n-alkanes [7]
This study aimed at investigating the presence and diversity of catabolic genes involved in the hydrocarbon degradation process in biodegraded and non-biodegraded oil samples from petroleum reservoirs through the construction and analyses of alk, aromatic-ring-hydroxylating dioxygenases (ARHDs) and bamA gene libraries
Summary
Most of the world’s oil is biodegraded and while the effects of biodegradation on the molecular composition and physical properties of crude oil and natural gas are relatively well known empirically, the actual processes that occur during the biodegradation of oil in deep reservoirs (below some hundred meters) remain unclear [1]. The hydrocarbon content is transformed, with a consequent increase in oil density, sulfur content, acidity and viscosity. All these factors interfere with the extraction and refining operations, resulting in significant economic losses [2]. The mechanisms of oil degradation in petroleum reservoirs, as well as the microorganisms involved are still poorly understood. Oil is a complex mixture of hydrocarbons such as saturated, unsaturated, linear, monoaromatic and polycyclic hydrocarbons [3,4]. Each of these compounds is biodegraded through different routes of several steps. Many studies have already demonstrated the existence of large and diverse populations of microbes with different metabolic activities in petroleum systems [5,6]
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