Spatial and Temporal Variations in Chitinolytic Gene Expression and Bacterial Biomass Production during Chitin Degradation

Abstract

Growth of the chitin-degrading marine bacterium S91 on solid surfaces under oligotrophic conditions was accompanied by the displacement of a large fraction of the surface-derived bacterial production into the flowing bulk aqueous 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 biomass generated on biodegradable chitin and a nonnutritional silicon surface, respectively, detached to become part of the free-living population in the bulk aqueous phase. Specific surface-associated growth rates that included the cells that subsequently detached from the substrata varied depending on the nutritional value of the substratum and during the period of surface colonization. Specific growth rates of 3.79 and 2.83 day ؊1 were obtained when cells first began to proliferate on a pure chitin film and a silicon surface, respectively. Later, when cell densities on the surface and detached 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 from either the chitin or the silicon surfaces and the majority of cells associated with the chitin surface over the 200-h period of surface colonization displayed no detectable expression of the chitin-degrading genes chiA and chiB. Cells displaying high levels of chiA-chiB expression were detected only 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 population level that promote efficient utilization of limited resources and dispersal of progeny to maximize access to new sources of energy and maintenance of the population.In the marine environment, hydrolysis of particulate organic matter (POM) to low-molecular-weight dissolved organic matter (DOM) is mediated primarily by ectohydrolytic enzymes produced by particle-associated bacteria (25). While some of the DOM derived from POM hydrolysis is respired as CO 2 , a portion is used for new bacterial production (BP) (53). It has also been hypothesized that a significant portion of the DOM derived from enzymatic attack of POM by POM-associated bacteria supports maintenance and reproduction of free-living bacteria in the pelagic marine environment (3, 9). In fact, POM-associated bacteria are thought to provide more DOM for production of the free-living bacterial populations than for production of POM-associated populations (4, 20, 45, 51). However, detachment of POM-derived cells could lead to overestimation of dissolved organic carbon-derived, free-living BP. Jacobsen and Azam (23) reported that bacteria associated with copepod fecal pellets were displaced into the surrounding water during fecal pellet degradation. While these researchers recognized the potential importance of detachment as a process that contributes to free-livin...

Microbial dynamics on diatom aggregates in Øresund, Denmark

“…Baty et al (2001) as well as Kiørboe et al (2002) found high detachment rates for aggregate-associated bacteria. This is in good agreement with the hypothesis that aggregates act as 'baby machines' (Azam 1998), continuously releasing bacteria into the surrounding water.…”

Biofilm Dispersal: Mechanisms, Clinical Implications, and Potential Therapeutic Uses

“…Another example of this dispersal mechanism may be found in the marine bacteria Pseudoaltermonas sp. strain S91 and Vibrio furnissii (Yu et al, 1991;Baty et al, 2000). These bacteria form biofilms on solid chitin surfaces in marine environments, and also produce chitinase, which degrades the chitin for use as a food source.…”

“…These bacteria form biofilms on solid chitin surfaces in marine environments, and also produce chitinase, which degrades the chitin for use as a food source. Chitin degradation results in detachment of the attached biofilm cells from artificially prepared chitin surfaces and from natural squid chitin surfaces in vitro (Baty et al, 2000).…”

Changes in the spectrum and rates of extracellular enzyme activities in seawater following aggregate formation

“…Physical attachment of microorganisms onto aggregates may also trigger or enhance the production of specific enzymes (Baty et al, 2000). A laboratory study with pure cultures of bacteria isolated from marine snow showed a 20-fold increase in enzyme activity within 2 h of particle attachment .…”