David L. Gutnick

Bio: David L. Gutnick is an academic researcher from Tel Aviv University. The author has contributed to research in topics: Acinetobacter calcoaceticus & Escherichia coli. The author has an hindex of 40, co-authored 94 publications receiving 7171 citations. Previous affiliations of David L. Gutnick include Laboratory of Molecular Biology & National Institutes of Health.

A role for exopolysaccharides in the protection of microorganisms from desiccation.

Abstract: Mucoid strains of Escherichia coli, Acinetobacter calcoaceticus, and Erwinia stewartii were significantly more resistant to desiccation than corresponding isogenic nonmucoid mutants (survival rates of up to 35% in mucoid strains and between 0.7 and 5% in nonmucoid variants), even in colonies containing both cell types. Desiccation was found to bring about an induction of beta-galactosidase in Lon strains of E. coli K-12 carrying transcriptional lac fusions in the capsule biosynthetic (cps) regulon. This induction was dependent on the transcriptional activators RcsA and RcsB. Induction was lower in cells carrying mutations in the membrane sensor protein RcsC.

Emulsifier of Arthrobacter RAG-1: isolation and emulsifying properties.

Abstract: The oil-degrading Arthrobacter sp. RAG-1 produced an extracellular nondialyzable emulsifying agent when grown on hexadecane, ethanol, or acetate medium. The emulsifier was prepared by two procedures: (i) heptane extraction of the cell-free culture medium and (ii) precipitation with ammonium sulfate. A convenient assay was developed for measurement of emulsifier concentrations between 3 and 75 micrograms/ml. The rate of emulsion fromation was proportional to both hydrocarbon and emulsifier concentrations. Above pH 6, activity was dependent upon divalent cations; half-maximum activity was obtained in the presence of 1.5 mM Mg2+. With a ratio of gas oil to emulsifier of 50, stable emulsions were formed with average droplet sizes of less than 1 micron. Emulsifier production was parallel to growth on either hydrocarbon or nonhydrocarbon substrates during the exponential phase; however, production continued after growth ceased.

Compounds Which Serve as the Sole Source of Carbon or Nitrogen for Salmonella typhimurium LT-2

Abstract: About 600 compounds were screened as possible carbon or nitrogen sources for Salmonella typhimurium LT-2. About 100 utilizable compounds were found.

RcsA, an unstable positive regulator of capsular polysaccharide synthesis.

Abstract: RcsA is an unstable positive regulator required for the synthesis of colanic acid capsular polysaccharide in Escherichia coli Degradation of the RcsA protein in vivo depends on the ATP-dependent Lon protease DNA sequence analysis of the rcsA gene reveals a single open reading frame for a 23,500-Da highly basic protein (pI = 99), consistent with the observed size of the purified subunit of RcsA The DNA and protein sequences are highly homologous to the rcsA gene and protein from Klebsiella pneumoniae and other species The carboxy-terminal region of RcsA contains a possible helix-turn-helix DNA-binding motif that resembles sequences found at the carboxy terminus of RcsB, another positive regulator of capsule synthesis, and in several other transcriptional regulators including members of the LuxR family rcsA62, a mutation in rcsA that leads to increased capsule synthesis, encodes a protein designated RcsA*, which differs from wild-type RcsA only in the replacement of Met-145 by valine The RcsA* protein is subject to Lon-dependent degradation The stability of wild-type RcsA in vivo is increased by multicopy RcsB Conversely, RcsA is degraded more rapidly in rcsB mutant hosts than in wild-type hosts These results suggest that RcsA and RcsB interact in vivo and are consistent with genetic experiments that indicate an interaction between RcsA and RcsB Based on these experiments, we propose a model for capsule regulation in which RcsA interacts directly with RcsB to promote transcription of the genes for capsule synthesis

Microbial Biofilms: from Ecology to Molecular Genetics

Abstract: Biofilms are complex communities of microorganisms attached to surfaces or associated with interfaces. Despite the focus of modern microbiology research on pure culture, planktonic (free-swimming) bacteria, it is now widely recognized that most bacteria found in natural, clinical, and industrial settings persist in association with surfaces. Furthermore, these microbial communities are often composed of multiple species that interact with each other and their environment. The determination of biofilm architecture, particularly the spatial arrangement of microcolonies (clusters of cells) relative to one another, has profound implications for the function of these complex communities. Numerous new experimental approaches and methodologies have been developed in order to explore metabolic interactions, phylogenetic groupings, and competition among members of the biofilm. To complement this broad view of biofilm ecology, individual organisms have been studied using molecular genetics in order to identify the genes required for biofilm development and to dissect the regulatory pathways that control the plankton-to-biofilm transition. These molecular genetic studies have led to the emergence of the concept of biofilm formation as a novel system for the study of bacterial development. The recent explosion in the field of biofilm research has led to exciting progress in the development of new technologies for studying these communities, advanced our understanding of the ecological significance of surface-attached bacteria, and provided new insights into the molecular genetic basis of biofilm development.

Microbial production of surfactants and their commercial potential.

Abstract: Many microorganisms, especially bacteria, produce biosurfactants when grown on water-immiscible substrates. Biosurfactants are more effective, selective, environmentally friendly, and stable than many synthetic surfactants. Most common biosurfactants are glycolipids in which carbohydrates are attached to a long-chain aliphatic acid, while others, like lipopeptides, lipoproteins, and heteropolysaccharides, are more complex. Rapid and reliable methods for screening and selection of biosurfactant-producing microorganisms and evaluation of their activity have been developed. Genes involved in rhamnolipid synthesis (rhlAB) and regulation (rhlI and rhlR) in Pseudomonas aeruginosa are characterized, and expression of rhlAB in heterologous hosts is discussed. Genes for surfactin production (sfp, srfA, and comA) in Bacillus spp. are also characterized. Fermentative production of biosurfactants depends primarily on the microbial strain, source of carbon and nitrogen, pH, temperature, and concentration of oxygen and metal ions. Addition of water-immiscible substrates to media and nitrogen and iron limitations in the media result in an overproduction of some biosurfactants. Other important advances are the use of water-soluble substrates and agroindustrial wastes for production, development of continuous recovery processes, and production through biotransformation. Commercialization of biosurfactants in the cosmetic, food, health care, pulp- and paper-processing, coal, ceramic, and metal industries has been proposed. However, the most promising applications are cleaning of oil-contaminated tankers, oil spill management, transportation of heavy crude oil, enhanced oil recovery, recovery of crude oil from sludge, and bioremediation of sites contaminated with hydrocarbons, heavy metals, and other pollutants. Perspectives for future research and applications are also discussed.

The biofilm matrix

Abstract: The extracellular matrix is a complex and extremely important component of all biofilms, providing architectural structure and mechanical stability to the attached population. The matrix is composed of cells, water and secreted/released extracellular macromolecules. In addition, a range of enzymic and regulatory activities can be found within the matrix. Together, these different components and activities are likely to interact and in so doing create a series of local environments within the matrix which co-exist as a functional consortium. The matrix architecture is also subject to a number of extrinsic factors, including fluctuations in nutrient and gaseous levels and fluid shear. Together, these intrinsic and extrinsic factors combine to produce a dynamic, heterogeneous microenvironment for the attached and enveloped cells.