9805946 Holden Bacteria in the terrestrial unsaturated zone exist in biofilms: attached to surfaces and encapsulated in a hydrated matrix of microbially-produced exopolymeric substances (EPS). The EPS matrix represents a mass transfer region, separating bacteria from one another and from the external pore environment. Mass transfer of carbon substrates through EPS may determine local rates of carbon turnover, but little is known about EPS in unsaturated environments and its effects on local substrate availability. If we are to understand the controls on organic matter and pollutant decomposition in unsaturated systems as a function of climatic or other environmental variations, we must first understand the controls on substrate availability at the scale of microbial biofilms. This research will: 1) determine the production and role of a bioemulsifying protein in unsaturated biofilms where the controls on protein production in culture are known; 2) determine the role of biofilm mass transfer region and its control on the rate of weakly soluble substrate metabolism; 3) determine the influence of water potential on emulsifier production, EPS mass transfer characteristics, and bacterial metabolism of weakly soluble substrates; and 4) develop and test a bacterial biosensor of weakly soluble substrates for use in lab and field studies. This POWRE-supported research will provide fundamental knowledge of the bacterial micro-environment in unsaturated systems, by studying mechanisms that operate at particularly challenging, but extremely important spatial scales of resolution.
