The structural organization of four microbial communities was analysed by a novel computer program, COMSTAT, which comprises ten features for quantifying three-dimensional biofilm image stacks. Monospecies biofilms of each of the four bacteria, Pseudomonas putida, P. aureofaciens, P. fluorescens and P. aeruginosa, tagged with the green fluorescent protein (GFP) were grown in flow chambers with a defined minimal medium as substrate. Analysis by the COMSTAT program of four variables describing biofilm structure -mean thickness, roughness, substratum coverage and surface to volume ratioshowed that the four Pseudomonas strains represent different modes of biofilm growth. P. putida had a unique developmental pattern starting with single cells on the substratum growing into micro-colonies, which were eventually succeeded by long filaments and elongated cell clusters. P. aeruginosa colonized the entire substratum, and formed flat, uniform biofilms. P. aureofaciens resembled P. aeruginosa, but had a stronger tendency to form micro-colonies. Finally, the biofilm structures of P. fluorescens had a phenotype intermediate between those of P. putida and P. aureofaciens. Analysis of biofilms of P. aureofaciens growing on 003 mM, 01 mM or 05 mM citrate minimal media showed that mean biofilm thickness increased with increasing citrate concentration. Moreover, biofilm roughness increased with lower citrate concentrations, whereas surface to volume ratio increased with higher citrate concentrations.

Chitin, an insoluble polymer of GlcNAc, is an abundant source of carbon, nitrogen, and energy for marine microorganisms. Microarray expression profiling and mutational studies of Vibrio cholerae growing on a natural chitin surface, or with the soluble chitin oligosaccharides (GlcNAc) 2-6, GlcNAc, or the glucosamine dimer (GlcN) 2 identified three sets of differentially regulated genes. We show that (i) ChiS, a sensor histidine kinase, regulates expression of the (GlcNAc) 2-6 gene set, including a (GlcNAc)2 catabolic operon, two extracellular chitinases, a chitoporin, and a PilA-containing type IV pilus, designated ChiRP (chitin-regulated pilus) that confers a significant growth advantage to V. cholerae on a chitin surface; (ii) GlcNAc causes the coordinate expression of genes involved with chitin chemotaxis and adherence and with the transport and assimilation of GlcNAc; (iii) (GlcN) 2 induces genes required for the transport and catabolism of nonacetylated chitin residues; and (iv) the constitutively expressed MSHA pilus facilitates adhesion to the chitin surface independent of surface chemistry. Collectively, these results provide a global portrait of a complex, multistage V. cholerae program for the efficient utilization of chitin.T he agent of Asiatic cholera, Vibrio cholerae O1, causes a dehydrating diarrheal illness and sometimes death. However, outside the human host, V. cholerae is a normal member of natural aquatic environments such as lakes, rivers, estuaries, and the ocean, which serve as the principal reservoir for this organism in nature (1). How it survives in habitats of this kind and the mechanisms by which it periodically emerges as a human pathogen are compelling questions in the ecology of infectious diseases (2). Observational studies in Bangladesh epidemiologically link seasonal phytoplankton and zooplankton blooms with cholera outbreaks. Studies of this epidemiological association identified V. cholerae attached to plankton in the environment, an observation that was confirmed by microcosm coinfection experiments. The interaction of V. cholerae with zooplankton is particularly intriguing because copepods, a subclass of crustacean zooplankton, have been incriminated in the transmission of this agent from aquatic reservoirs to susceptible human hosts (3).Chitin, composed of ␤1,4-linked GlcNAc residues, is the most abundant polysaccharide in nature after cellulose. In the aquatic biosphere alone, Ͼ10 11 metric tons of chitin are produced annually. This vast amount of insoluble, carbon-containing material is recycled mainly by chitinolytic bacteria, including members of the family Vibrionaceae. Chitin is found throughout all kingdoms and is the main component of the cell walls of fungi and of the exoskeletons of crustaceans. Copepods are estimated to produce billions of tons of chitin each year (4).Many Vibrio species that live in aquatic environments are capable of using chitin as the sole carbon source. Studies of the nonpathogenic marine organism Vibrio furnissii have shown that chitin utili...

No abstract