Hydrocarbon degradation by halophilic bacteria

Abstract

Halophilic microorganisms are a viable option for the bioremediation of oil spills in saline regions worldwide. Halophiles can be found among all three branches in the tree of life, including bacteria. A mixed culture capable of degrading BTEX (a 1:1:1:1 mixture of benzene, toluene, ethylbenzene, and xylene) under conditions of high salinity (2.5 M NaCl) was enriched from a crude oil-contaminated sediment from Kuwait. The enrichment's metagenome revealed that the culture was dominated by organisms belonging to the genus Arhodomonas (>99% abundance). Functional analysis revealed the presence of numerous genes that code for aromatic ring hydroxylating and ring cleaving enzymes, and most of the downstream genes needed for complete mineralization dearomatized intermediates. A pure culture of bacteria that degrades BTEX at high salinity was isolated from produced water collected from the Wilcox oil production facility in Payne County, OK. Amplification of 16S rRNA-gene of the isolate showed >99% sequence similarity to Modicisalibacter tunisiensis, a species previously isolated from fracking water in Tunisia. The genome of strain Wilcox was sequenced and its biodegradation potential of petroleum compounds was assessed in silico. Laboratory-scale microcosms containing produced water amended BTEX as representative hydrocarbons were set up to test the bioremediation capacity of both Kuwait enrichment and Modicisalibacter sp. strain Wilcox. Results showed that both cultures efficiently degrade BTEX and other hydrocarbons at high salinity. Strain Wilcox appears to have the capacity to degrade ethylbenzene as the sole carbon source under nitrate-respiring conditions. These observations are supported by the presence of nitrate reductase encoding genes in the genome.