This research story concerned the symbiotic relationship between V. fischeri and the host organism, and how V. fischeri adapts to the changing environment of the host. V. fischeri, being aerobic fermenters, can produce acid even in the presence of oxygen, and thus it was asked whether their aerobic acid production could be a symbiotic effect for bioluminescence with fish. However, it was soon discovered that fish was not a proper system to study this question, and the studies switched over to squid, for which V. fischeri resided in a dedicated organ in the squid. What was odd is that the squid expelled approximately 90% of the residing bacteria every morning, and that the bacteria then underwent a growth phase to reach maximal bioluminescence at night, and had a minimum of luminescence during the day (during their growth phase). This proved fascinating in that it led to the next question – what genes changed in expression level over this period of time, particularly with respect to the dynamic microenvironment of the squid organ. It was found utilizing microarray technology that in the mornings, the anaerobic respiration of glycerol – a pH neutral reaction, led to the fermentation of chitin at night, which acidified the solution. This pH difference was hypothesized to be correlated with a shift in metabolism. This was further corroborated by studying juvenile vs. adult squid hosts, in which it was found that chitin acted as a nutrient . Going back to the pH of the squid light organ, this was confirmed via “asking the bacteria” by checking for acid adaptation conditions with respect to survival. By excising bacteria and testing their resistance to various levels of acidity, it was found that the bacteria were indeed acid adapted following a night cycle, and only in the adult squid. Finally, the remaining question was how bacteria is able to undergo fermentation reactions even while in the presence of oxygen. This is relateable to how obligate aerobes nitrogenases, which are oxygen sensitive, can fix nitrogen even in the presence of oxygen, via the spatio-temporal regulation of nitrogenase expression.
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