Fundamental features of microbial cellulose utilization are examined at successively higher levels of aggregation encompassing the structure and composition of cellulosic biomass, taxonomic diversity, cellulase enzyme systems, molecular biology of cellulase enzymes, physiology of cellulolytic microorganisms, ecological aspects of cellulase-degrading communities, and rate-limiting factors in nature. The methodological basis for studying microbial cellulose utilization is considered relative to quantification of cells and enzymes in the presence of solid substrates as well as apparatus and analysis for cellulose-grown continuous cultures. Quantitative description of cellulose hydrolysis is addressed with respect to adsorption of cellulase enzymes, rates of enzymatic hydrolysis, bioenergetics of microbial cellulose utilization, kinetics of microbial cellulose utilization, and contrasting features compared to soluble substrate kinetics. A biological perspective on processing cellulosic biomass is presented, including features of pretreated substrates and alternative process configurations. Organism development is considered for "consolidated bioprocessing" (CBP), in which the production of cellulolytic enzymes, hydrolysis of biomass, and fermentation of resulting sugars to desired products occur in one step. Two organism development strategies for CBP are examined: (i) improve product yield and tolerance in microorganisms able to utilize cellulose, or (ii) express a heterologous system for cellulose hydrolysis and utilization in microorganisms that exhibit high product yield and tolerance. A concluding discussion identifies unresolved issues pertaining to microbial cellulose utilization, suggests approaches by which such issues might be resolved, and contrasts a microbially oriented cellulose hydrolysis paradigm to the more conventional enzymatically oriented paradigm in both fundamental and applied contexts.

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Microbial cellulose utilization: fundamentals and biotechnology.

Biology, immunology, and cariogenicity of Streptococcus mutans

Bacterial gene transfer by natural genetic transformation in the environment.

Background: From an ecological viewpoint, the oral cavity, in fact the oro-pharynx, is an ‘open growth system’. It undergoes an uninterrupted introduction and removal of both microorganisms and nutrients. In order to survive within the oro-pharyngeal area, bacteria need to adhere either to the soft or hard tissues in order to resist shear forces. The fast turn-over of the oral lining epithelia (shedding 3 ×/day) is an efficient defence mechanism as it prevents the accumulation of large masses of microorganisms. Teeth, dentures, or endosseous implants, however, providing non-shedding surfaces, allow the formation of thick biofilms. In general, the established biofilm maintains an equilibrium with the host. An uncontrolled accumulation and/or metabolism of bacteria on the hard surfaces forms, however, the primary cause of dental caries, gingivitis, periodontitis, peri-implantitis, and stomatitis.

Objectives: This systematic review aimed to evaluate critically the impact of surface characteristics (free energy, roughness, chemistry) on the de novo biofilm formation, especially in the supragingival and to a lesser extent in the subgingival areas.

Methods: An electronic Medline search (from 1966 until July 2005) was conducted applying the following search items: ‘biofilm formation and dental/oral implants/surface characteristics’, ‘surface characteristics and implants’, ‘biofilm formation and oral’, ‘plaque/biofilm and roughness’, ‘plaque/biofilm and surface free energy’, and ‘plaque formation and implants’. Only clinical studies within the oro-pharyngeal area were included.

Results: From a series of split-mouth studies, it could be concluded that both an increase in surface roughness above the Ra threshold of 0.2 μm and/or of the surface-free energy facilitates biofilm formation on restorative materials. When both surface characteristics interact with each other, surface roughness was found to be predominant. The biofilm formation is also influenced by the type (chemical composition) of biomaterial or the type of coating. Direct comparisons in biofilm formation on different transmucosal implant surfaces are scars.

Conclusions: Extrapolation of data from studies on different restorative materials seems to indicate that transmucosal implant surfaces with a higher surface roughness/surface free energy facilitate biofilm formation.

Effect of material characteristics and/or surface topography on biofilm development

An efficient method for genetic transformation of lactococci by electroporation is presented. Highly competent lactococci for electrotransformation were obtained by growing cells in media containing high concentrations of glycine and 0.5 M sucrose as the osmotic stabilizers. These cells could be stored at -85 degrees C without loss of competence. With Lactococcus lactis subsp. cremoris BC101, a transformation frequency of 5.7 x 10 transformants per mug of pIL253 DNA was obtained, which represents 5% of the surviving cells. All the lactococcal strains tested could be transformed by the present method.

High-Frequency Transformation, by Electroporation, of Lactococcus lactis subsp. cremoris Grown with Glycine in Osmotically Stabilized Media.

A gentle method for the lysis of oral streptococci.

https://www.cell.com/trends/biotechnology/pdf/0167-7799(88)90025-X.pdf

Transformation of bacteria by electroporation

Strategies for the development of bacterial transformation systems

Nucleotide sequence of the β-d-phosphogalactoside galactohydrolase gene of Lactobacillus casei: comparison to analogous pbg genes of other Gram-positive organisms

An extracellular cyclic nucleotide phosphodiesterase was isolated from either growing cultures or aggregating amoebas of Dictyostelium discoideum. The enzyme is released in a form with a low Michaelis constant (15 micromolar) and spontaneously undergoes a slow conversion to a less active form with a high Michaelis constant (2 mnillimolar). Inactivation was prevented or reversed by use of Cleland's reagent, dithiothreitol. The two enzyme forms may be part of a mechanism for control of concentration of cyclic adenosine monophosphate.

https://science.sciencemag.org/content/sci/175/4025/1016.full.pdf

Bruce M. Chassy

Papers

A gentle method for the lysis of oral streptococci.

Transformation of bacteria by electroporation

Strategies for the development of bacterial transformation systems

Nucleotide sequence of the β-d-phosphogalactoside galactohydrolase gene of Lactobacillus casei: comparison to analogous pbg genes of other Gram-positive organisms

Cyclic nucleotide phosphodiesterase in Dictyostelium discoideum: interconversion of two enzyme forms.