Exoenzyme Dynamics of Surface Ocean Microbial Communities in Response to Oil Exposure

Abstract

Oil spills, while one of the most infamous manmade ecological disasters, remain relatively poorly understood, in particular the responses of microbial communities to the diverse suite of components in raw oil and chemical dispersants are just beginning to be elucidated. The 2010 Deepwater Horizon oil spill was historic in not only its volume and ecological damage, but also in the extent to which its progress and effects were monitored, particularly with respect to the microbial community. Analysis of exoenzymes can provide insight into how oil-degrading bacteria, as well as the bacterial community as a whole, respond to the changing chemical conditions experienced over the course of an oil spill. Using a multiscale approach with both mesocosms and three oil-degrading environmental isolates in culture, surface ocean microbes in oiled conditions were shown to be highly active with respect to ẞ-glucosidase, leucine aminopeptidase, and alkaline phosphatase. The activities measured in the mesocosms are some of the highest reported for environmental systems in the literature. Additionally, both coastal and open ocean microbial communities in mesocosms and all three isolates in bottle experiments demonstrated the ability to significantly modify their alkaline phosphatase and ß-glucosidase kinetics over just a few days in culture. Exposure to oil tended to change the patterns in enzyme activity over the course of each experiment. In the mesocosm experiments, differences in enzyme activity between the offshore community and the coastal community were greater than the differences between the control and oil treatments, indicating source microbial community composition has a greater impact than exposure to oil for enzyme activity. Supporting this hypothesis, there was as much variability in activity for alkaline phosphatase and leucine aminopeptidase between the three oil-degrading strains, as between the two mesocosm experiments. In general, the mesocosms had higher Vmax and lower Km values for each enzyme than any of the strains, though for alkaline phosphatase and leucine aminopeptidase the strains showed as much diversity in terms of kinetic values as the mesocosms.