Marine Bacteria Chemotaxis to Crude Oil Components with Opposing Effects

Abstract

Marine microorganisms were critical to hydrocarbon removal from the Gulf of Mexico oil spill. Chemotaxis, a process attracting motile bacteria toward higher hydrocarbon concentrations, can increase biodegradation efficiency. However, crude oil also contains heavy metal ions that repel bacteria. Will bacteria migrate toward hydrocarbons or away from heavy metals? We exposed a marine isolate Halomonas sp. to decane and copper ions in a microfluidic device that maintained a constant concentration gradient across a channel. Bacterial distributions were used to quantify parameters in a mathematical model capturing bacteria motility and chemotaxis. This multi-scale model was adapted from the signal transduction mechanism of E. coli. For Halomonas sp., we used independent receptors for sensing attractant or repellent and chemotaxis parameter values were assessed. Predictions based on the multi-scale model correctly estimated the net attraction or repulsion responses of bacteria to the stimuli mixture. In some cases, the model yielded a stronger repulsion than what was observed experimentally, but still captured the general trends of bacteria distribution. Understanding how marine bacteria integrate information from multiple inputs to yield net migration toward or away from oil will improve predictions of hydrocarbon degradation rates.

Repulsion from slow-diffusing nutrients improves chemotaxis towards moving sources

“…When faced with two opposing attractant gradients microbes must choose between the two, with outcomes potentially dependent on previous environmental exposure and resulting receptor expression [21][22][23] . In the presence of parallel attractant and repellant gradients, microbes must make a similar choice between net attraction or repulsion [24][25][26][27][28][29] , with chemotaxis to an intermediate distance from the source or a 'bet-hedging' split into attracted and repelled subpopulations also being possible outcomes 25 . In some cases, a microbe will only respond to one chemoeffector if another is present 18 .…”