Starvation-Dependent Inhibition of the Hydrocarbon Degrader Marinobacter sp. TT1 by a Chemical Dispersant

Saskia Rughöft,Sara Kleindienst,Tony Gutierrez,Anjela L Vogel,Samantha B Joye

doi:10.3390/jmse8110925

Abstract

During marine oil spills, chemical dispersants are used routinely to disperse surface slicks, transferring the hydrocarbon constituents of oil into the aqueous phase. Nonetheless, a comprehensive understanding of how dispersants affect natural populations of hydrocarbon-degrading bacteria, particularly under environmentally relevant conditions, is lacking. We investigated the impacts of the dispersant Corexit EC9500A on the marine hydrocarbon degrader Marinobacter sp. TT1 when pre-adapted to either low n-hexadecane concentrations (starved culture) or high n-hexadecane concentrations (well-fed culture). The growth of previously starved cells was inhibited when exposed to the dispersant, as evidenced by 55% lower cell numbers and 30% lower n-hexadecane biodegradation efficiency compared to cells grown on n-hexadecane alone. Cultures that were well-fed did not exhibit dispersant-induced inhibition of growth or n-hexadecane degradation. In addition, fluorescence microscopy revealed amorphous cell aggregate structures when the starved culture was exposed to dispersants, suggesting that Corexit affected the biofilm formation behavior of starved cells. Our findings indicate that (previous) substrate limitation, resembling oligotrophic open ocean conditions, can impact the response and hydrocarbon-degrading activities of oil-degrading organisms when exposed to Corexit, and highlight the need for further work to better understand the implications of environmental stressors on oil biodegradation and microbial community dynamics.

Highlights

During major marine oil spills, chemical dispersants are applied routinely with the aim of breaking up surface slicks and dispersing the oil into the water column
The aim of this study was to investigate the impact of chemical dispersant exposure on the growth and n-hexadecane biodegradation activity of Marinobacter sp
With added Corexit, growth of these cells was 55% lower (2.22 × 108 vs. 4.95 × 108 cells mL−1; p = 0.0103; Figure 1A) and 30% less n-hexadecane was biodegraded (33.94 vs. 0.89 mg n-hexadecane L−1 remained, p = 0.0224; Figure 1C) after five days

Summary

Introduction

During major marine oil spills, chemical dispersants are applied routinely with the aim of breaking up surface slicks and dispersing the oil into the water column. Following the Deepwater Horizon blowout in the Gulf of Mexico on April 20th of 2010, seven million liters of dispersant (Corexit EC9500A and EC9527A) were applied in response to the discharge of an estimated 800 million liters of crude oil into the Gulf ecosystem [1,2]. The impacts of the oil spill on the Gulf’s ecosystem and the health of its human inhabitants are well documented [3,4]. A number of different explanations for these contradictory findings have been proposed, ranging from methodological issues (e.g., dispersant concentrations, types and weathering status of crude oil or HCs used) to microbiological and ecological considerations (e.g., species-/strain-specific dispersant responses and the relevance of the native microbial community composition) [7,11,13,14,15]

Objectives

Methods

Results

Conclusion