Award: OCE-1322928

There is a growing appreciation that most organisms on earth host microbiomes, yet for most, we know almost nothing about the physiology of their microbes and how these microbes interact with their host and environment. In terms of numbers, host-associated microbes often rival or exceed the free-living microbes in their environment. In addition, since the host organism provides them with resources or optimal conditions, the rates of host-associated microbes may be especially high. Despite this, for most symbiotic taxa we have a limited knowledge of their symbiotic function, metabolic activity, and impact on their ecosystems. Symbioses between anaerobic protozoa and intracellular, methane-producing archaea have been found in many anoxic habitats, however the contribution of symbiont-produced CH4 is yet unconstrained in most of these ecosystems. Studies of methane production by these symbioses are few, and, outside of their methanogenic function, nothing is known about the physiological capacity of their symbionts. To develop our understanding of the details of these partnerships and to address their contribution to the CH4 cycle, genomic information was gathered for the symbionts of 6 methanogen-hosting ciliates. In addition, a series of physiological experiments was conducted that measured the production of methane during different points in one of these ciliate?s growth cycle, as well as when exposed to varying oxygen concentrations. Rates of methane production by the symbionts of this ciliate was found to be at least 6X greater than the per cell rate of methane production that has been reported for free-living methanogens. Ongoing analysis of the gene expression of this partnership during these experiments will further our understanding of the functioning and physiology of this association. Methanogenesis by the symbionts of protists may account for a significant fraction of the CH4 budget in these areas. Since rising temperatures are predicted to cause the expansion of oxygen-depleted habitats, better insight into CH4 cycling in these areas will become increasingly important to our understanding and modeling of global CH4 emissions. Broader Impacts: A high school student from the local community conducted a science fair project relating to this work, and presented her findings at local, regional, and state science fairs. In addition, an educational unit about marine microbiology was developed with a local non-profit marine education foundation. This unit will be used as part of the activity program for K-12 students from the southern New England area. Last Modified: 12/17/2016 Submitted by: Roxanne Beinart