Research is proposed to continue the study of the mechanisms whereby heterotrophic bacterioplankton utilize particulate organic matter (POM) and dissolved organic matter (DOM) in the sea. The PI is also studying the magnitude and patterns of organic matter flux into bacteria in both the epipelagic and the mesopelagic zones to determine how heterotrophic bacteria may influence the vertical transport of biogenic production in the sea. The research will focus on studying the mechanisms and rates of bacterial utilization of small detritus (1-50 um). The PI will use laboratory produced and well-characterized "model detritus" consisting of killed phytoplankton, microflagellates, and chroococoid cyanobacteria. He will study colonization growth rates of bacteria on POM and will examine enzymic mechanisms whereby bacteria hydrolyze POM into utilizable DOM; determine shifts in bacterial cell-size, growth rate, and modes of organic matter hydrolysis as a consequence of attachment to, or release from, POM. The PI asks whether a colonized particle becomes a point-source of DOM as well as of bacteria ("baby-machine"). A hypothesis will be tested that firm attachment to POM is a survival/dispersal strategy of bacteria; they survive the passage through metazoan gut and thrive in the fecal pellets. In field work using uniformly ?14C! labeled detritus, the PI will measure the turnover times of detritus of a broad size range, biochemical composition, and origins. The research proposed will contribute towards developing a mechanistic framework for bacteria-organic matter interactions in an ecosytem context. This knowledge should be of value in elucidating the role of bacterioplankton in organic matter fluxes in the oceans.
