A recent study, published in the Proceedings of the National Academy of Sciences, shows that mating preference of fruit flies (the ones you see swarming near a piece of rotten fruit) is dependent on their diet because it changes the composition of bacteria that live in their gut (gut microbiota). This intriguing study stems from previous experiments in which fruit flies bred under different environmental conditions preferentially mated with other fruit flies from the environment in which they have been reared.

Gil Sharon and his colleagues at Tel Aviv University in Israel and University of Maine in the United States decided to experiment with food sources and see if they induce preferential mating in fruit flies. They reared one population of fruit flies on a diet of cornmeal, molasses and yeast for 37 generations and another population on starch for the same amount of time. After eleven generations, the flies showed preferential mating when the populations were mixed in equal proportions. Of the 38 recorded matings observed 29 were homogamic (i.e. “starch males” and “starch females” or “CMY males” and “CMY females”).

However, this trend was abolished if the fruit flies were fed antibiotics before the two populations were mixed. Of the 38 recorded matings in this experiment only 18 were homogamic whilst the other 20 were heterogamic. Antibiotics are chemicals that target bacteria, and this experiment suggests that the bacteria living in the gut of the fruit fly might have some role to play in who they chose as a mate.

After fingerprinting the gut microbiota, the authors noticed that eating starch led to enrichment of a particular type of bacteria in the “starch flies”. This increase in number corresponded to a change in cutaneous hydrocarbons (CH) secreted by the “starch flies”. CH are components of sex pheromones (sex pheromones are chemicals that animals secrete to convey their species and type and attract similar mates) in fruit flies and play an important role in mate selection. Hence, an altered composition of CH would mean that the “starch flies” would smell very different compared to the “CMY flies”. How the “starch flies” respond to their own altered sex pheromones is a question that is yet unaddressed….

The role of commensal gut bacteria in influencing behavioral patterns is an intriguing aspect of evolution. Think about it when you walk into a bar….

Sadly, we don’t have any answers yet. And let’s face it – there is no right answer. What we do have are cues from the environment itself. Scientists from the Lawrence Berkeley National Laboratory, University of Oklahoma, Pacific University, and The Lawrence Livermore National Laboratory have taken the proverbial stethoscope and are listening intently to the heartbeat of the deep underwater plume near the wellhead…and they have good news for us. In a recent paper, published in the journal Science, these scientists report some of their latest findings on the microscopic life that is abuzz in the hydrocarbon plume near the wellhead where the oil spill occurred.

Why is an oil spill an environmental hazard in the first place? Crude oil, as you may know, is a cocktail of high molecular weight aromatic hydrocarbons such as isopropyl benzene, n-propylbenzene, and naphthalene. These hydrocarbons are extremely persistent in the environment, which means that most organisms cannot use them as a substrate for growth or energy, nor do they get degraded by physical or chemical processes. Add to that, the fact that some of these chemicals are highly toxic and a few of them carcinogenic. So when oil spills occur, especially in such large quantities in such a small amount of time, it leads to a sudden loss of flora and fauna and a major imbalance in the prevalent ecosystem. These large opaque clumps of crude oil emanating from the Earth’s interior can be reduced to tiny droplets that can disperse in the water column by adding chemicals known as dispersants. If the sudden insurgence of crude oil in the marine ecosystem wasn’t hard to deal with, the organisms in the deep sea near the hydrocarbon plume in the Gulf had to also deal with the added toxicity of Corexit 9500 – the dispersant that was added in copious quantities soon after the spill.

Did anyone survive this massive onslaught? Surprisingly, yes! The authors of this study took samples from the deep sea up to 10 kms( 6.2 miles) away from the wellhead and saw that around the depth where the oil spill occurred there was a slight reduction in the amount of oxygen. This reduction in oxygen levels, usually indicative of respiration by living beings, was the first clue that led them to think that life is prospering in these toxic waters. They knew, from previous studies, that these living beings had to be microorganisms especially bacteria. With an a priori hypothesis that bacteria are living in this hydrocarbon plume, the authors went on to measure the density of bacteria in the water column in the Gulf and their hypothesis was proved right — the cell density was especially high just at the depth where the oil spill occurred. With these exciting preliminary results, the authors decided to take water samples near the plume and peer at them under the microscope and there was living proof – their paper has a few pictures of big, fat bacteria happily chomping down the hydrocarbons.

Where did these bacteria come from? How can they survive? Further analysis showed that there is a wide diversity of bacteria in the deep sea waters of the Gulf. Samples that the authors extracted from parts of the deep sea that were not affected by the oil spill showed up to 951 different bacterial taxa. Only 16 of them were found in the hydrocarbon plume. Did these 16 taxa just get lucky? No way, luck rarely works in the natural environment. These 16 taxa of bacteria, not surprisingly, have representatives, that have previously been reported to eat up hydrocarbons especially at low temperatures (as observed in the deep sea). How did these 16 taxa get to the plume? They didn’t happen to get there by luck either, they were already present in the deep sea water before the oil spill but were not as abundant because they were competing with many other taxa for food and resources. When there was a sudden insurgence of oil into their ecosystem, whilst most other bacteria perished, they survived because they could eat up the oil. Their numbers increased rapidly. Selecting for certain taxa that can degrade persistent compounds in the natural environment is termed by environmental engineers as ‘enrichment’. The authors analyzed the phospholipid fatty acids – components of the bacterial cell membrane, used as a signature for identifying different taxa – of bacteria in the plume to further deduce that there were two distinct groups of a taxa known as Oceanospiralles. Oceanospiralles have been found in hydrocarbon-enriched environments commonly and some of them are also known to be psychrophiles (cold-loving). Oceanospiralles are capable of surviving an oil spill because they contain genes for hydrocarbon utilization, such as the phdCI gene that is needed for naphthalene degradation.

These results show that the microbial community in the deep sea hydrocarbon plume in the Gulf of Mexico has already undergone a rapid adaptive shift. Selection has led to the formation of a new-fangled community that is not as diverse but highly specialized to degrade the oil. Apart from marveling at the rapid, dynamic response of the microscopic super heroes we must realize that these results imply that there is an intrinsic potential for bioremediation (removal of contaminants by microbes plants etc.) of oil contamination in the Gulf. We must devise our clean-up plans keeping them in mind.

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