Invertebrates living in marine sediments and feeding on bacteria alter the biomass, metabolism, growth, and community structure of sedimentary microbes. This project will test and refine present models of bacterial associations within the gut of sediment deposit feeders. Bacteria ingested into the gut and exposed to lytic activity of gut enzymes, both in terms of space and time, will be examined in the two deposit feeders, Arenicola marina and Amphitrite johnsonii. Controlled experiments will be employed to clarify the influences of temperature, enzyme concentration, exposure time, and the interactions among these variables on the lysis of bacterial strains within the gut. Further experiments will determine to what degree quantity, as opposed to composition, of extra-cellular capsular layer dictates resistance to digestion. Also, lysis of bacterial strains devoid of capsular material will be compared to ascertain the importance of cell wall characteristics in bacterial lysis. The goals of these experiments are to determine how environmental parameters influence lysis of bacterial communities and to distinguish mechanisms for differential lysis, in order to make a priori predictions of natural patterns within the guts of deposit feeders. These predictions will then be tested in the field using epifluorescence microscopy coupled with the relevant measurements of environmental conditions and immunofluorescence microscopy to specifically track three bacterial isolates through the guts of the two model deposit feeders. This research will also determine whether deposit feeder digestion, both in terms of total biomass or selective removal, is an important determinant of bacterial biomass or community composition in bulk sediments.
