Spatial and temporal variations in chitinolytic gene expression and bacterial biomass production during chitin degradation

Growth of the chitin-degrading marine bacterium S91 on solid surfaces under oligotrophic conditions was accompanied by the displacement of a large fra ction of the surface-derived bacterial production into the flowing bulk aqu eous phase, irrespective of the value of the surface as a nutrient source, Over a 200-h period of surface colonization, 97 and 75% of the bacterial bi omass generated on biodegradable chitin and a nonnutritional silicon surfac e, respectively, detached to become part of the free-living population in t he bulk aqueous phase. Specific surface-associated growth rates that includ ed the cells that subsequently detached from the substrata varied depending on the nutritional value of the substratum and during the period of surfac e colonization. Specific grow-th fates of 3.79 and 2.83 day(-1) were obtain ed when cells first began to proliferate on a pure chitin film and a silico n surface, respectively. Later, when cell densities on the surface and deta ched cells as CFU in the bulk aqueous phase achieved a quasi-steady state, specific growth rates decreased to 1.08 and 0.79 day(-1) on the chitin and silicon surfaces, respectively, Virtually all of the cells that detached fr om either the chitin or the silicon surfaces and the majority of tells asso ciated with the chitin surface over the 200-h period of surface colonizatio n displayed no detectable expression of the chitin-degrading genes chiA and chiB. Cells displaying high levels of chiA-chiB expression were detected o nly on the chitin surface and then only clustered in discrete areas of the surface. Surface-associated, differential gene expression and displacement of bacterial production from surfaces represent adaptations at the populati on level that promote efficient utilization of limited resources and disper sal of progeny to maximize access to new sources of energy and maintenance of the population.