Oil Hydrocarbon Degradation by Caspian Sea Microbial Communities.

John I Miller,Jiang Liu,Nargiz Garajayeva,Scott Olesen,Julian Fortney,Faig S Askerov,Dominique Joyner,Nagissa Mahmoudi,Terry C Hazen,Adolfo Fernandez,Stephen Techtmann,Eric Alm,Piero Gardinali

doi:10.3389/fmicb.2019.00995

Abstract

The Caspian Sea, which is the largest landlocked body of water on the planet, receives substantial annual hydrocarbon input from anthropogenic sources (e.g., industry, agriculture, oil exploration, and extraction) and natural sources (e.g., mud volcanoes and oil seeps). The Caspian Sea also receives substantial amounts of runoff from agricultural and municipal sources, containing nutrients that have caused eutrophication and subsequent hypoxia in the deep, cold waters. The effect of decreasing oxygen saturation and cold temperatures on oil hydrocarbon biodegradation by a microbial community is not well characterized. The purpose of this study was to investigate the effect of oxic and anoxic conditions on oil hydrocarbon biodegradation at cold temperatures by microbial communities derived from the Caspian Sea. Water samples were collected from the Caspian Sea for study in experimental microcosms. Major taxonomic orders observed in the ambient water samples included Flavobacteriales, Actinomycetales, and Oceanospirillales. Microcosms were inoculated with microbial communities from the deepest waters and amended with oil hydrocarbons for 17 days. Hydrocarbon degradation and shifts in microbial community structure were measured. Surprisingly, oil hydrocarbon biodegradation under anoxic conditions exceeded that under oxic conditions; this was particularly evident in the degradation of aromatic hydrocarbons. Important microbial taxa associated with the anoxic microcosms included known oil degraders such as Oceanospirillaceae. This study provides knowledge about the ambient community structure of the Caspian Sea, which serves as an important reference point for future studies. Furthermore, this may be the first report in which anaerobic biodegradation of oil hydrocarbons exceeds aerobic biodegradation.

Highlights

The Caspian Sea is the largest enclosed body of water on earth, with a volume of 78,000 km3 and a surface area of 3.8 × 105 km2 (Dumont, 1998; Tuzhilkin et al, 2005) and has been landlocked for five million years
Petroleum hydrocarbon inputs are estimated to be between 70 and 90 tons per year (Chicherina et al, 2004), with total petroleum hydrocarbon concentrations ranging from 0.12 mg/L in the shallow water to
The purpose of this study was to characterize the in situ community structure, and to investigate the ability of that community to degrade oil hydrocarbon under oxic or anoxic conditions

Summary

Introduction

The Caspian Sea is the largest enclosed body of water on earth, with a volume of 78,000 km and a surface area of 3.8 × 105 km (Dumont, 1998; Tuzhilkin et al, 2005) and has been landlocked for five million years. Freshwater input from rivers is nutrient-rich, deriving from industrial and agricultural runoff, and contributes substantial pollution to the Caspian Sea, and this has increased in recent years (Zonn, 2005). This causes eutrophication, resulting in hypoxia in the deep-waters (Diaz, 2001). The highest petroleum hydrocarbon concentrations have been reported in the southern basin and in surface waters and sediments, but are “almost undetectable” in the water column below 500 m (Korshenko and Gul, 2005).

Objectives

Methods

Results

Conclusion