Calcium carbonate mineralization: involvement of extracellular polymeric materials isolated from calcifying bacteria.
ABSTRACT This study highlights the role of specific outer bacterial structures, such as the glycocalix, in calcium carbonate crystallization in vitro. We describe the formation of calcite crystals by extracellular polymeric materials, such as exopolysaccharides (EPS) and capsular polysaccharides (CPS) isolated from Bacillus firmus and Nocardia calcarea. Organic matrices were isolated from calcifying bacteria grown on synthetic medium--in the presence or absence of calcium ions--and their effect on calcite precipitation was assessed. Scanning electron microscopy observations and energy dispersive X-ray spectrometry analysis showed that CPS and EPS fractions were involved in calcium carbonate precipitation, not only serving as nucleation sites but also through a direct role in crystal formation. The utilization of different synthetic media, with and without addition of calcium ions, influenced the biofilm production and protein profile of extracellular polymeric materials. Proteins of CPS fractions with a molecular mass between 25 and 70 kDa were overexpressed when calcium ions were present in the medium. This higher level of protein synthesis could be related to the active process of bioprecipitation.
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ABSTRACT: Cytoplasmic free-Ca2+ levels in Escherichia coli were measured by use of the fluorescent Ca(2+)-indicator dye fura-2. Chemotactically wild-type E. coli regulated cytoplasmic free Ca2+ at approximately 100 nM when no stimuli were encountered, but changes in bacterial behavior correlated with changes in cytoplasmic free-Ca2+ concentration. For chemotactically wild-type E. coli, addition of a repellent resulted in cells tumbling and a transient increase in cytoplasmic free-Ca2+ levels. Conversely, addition of an attractant to wild-type cells caused running and produced a transient decrease in cytoplasmic free-Ca2+ levels. Studies with mutant strains showed that the chemoreceptors were required for the observed changes in cytoplasmic free-Ca2+ levels in response to chemical stimuli.Proceedings of the National Academy of Sciences 12/1995; 92(23):10777-81. · 9.74 Impact Factor
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ABSTRACT: In Streptococcus pneumoniae, Ca2+ induces a stress response which is regulated by a proteic activator known as competence factor (CF). This stress response is expressed as the induction of competence for DNA uptake and genetic transformation in exponentially growing cultures and by autolysis in late exponential phase. DNA transport during competence can be described as a homeostatic response that prevents autolysis of the cultures. Electrogenic and cooperative calcium transport with a Hill number (nH) of 2 appears to mediate this Ca2+ response. Mutant strains altered in their kinetics for Ca2+ transport, with nHs of 1 and 4, were isolated and characterized in order to address the role of the kinetics of Ca2+ transport in the Ca2+ response. The reduced cooperativity of Ca2+ uptake in mutant strain Cp2200 was associated with an absolute requirement for added CF to develop competence and with resistance to autolysis. The enhanced cooperativity of Ca2+ uptake in mutant strain Cp3300 was associated with facilitated competence and hypersensitivity to autolysis. Moreover, the mutation carried by strain Cp3300 increases the CF response of previously described competence-defective mutants. The pleiotropic mutants Cp2200 and Cp3300 allowed us to demonstrate that cooperativity of transport determines the Ca2+ response in S. pneumoniae.Journal of Bacteriology 05/1994; 176(7):1992-6. · 3.19 Impact Factor
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ABSTRACT: Pseudomonas aeruginosa synthesizes an exopolysaccharide called alginate in response to environmental conditions. Alginate serves to protect the bacteria from adversity in its surroundings and also enhances adhesion to solid surfaces. Transcription of the alginate biosynthetic genes is induced upon attachment to the substratum and this leads to increased alginate production. As a result, biofilms develop which are advantageous to the survival and growth of the bacteria. In certain circumstances, P. aeruginosa produces an alginate lyase enzyme which cleaves the polymer into short oligosaccharides. This negates the anchoring properties of the alginate and results in increased detachment of the bacteria away from the surface, allowing them to spread and colonize new sites. Thus, both alginate biosynthetic and degradative enzymes are important for the development, maintenance and spread of P. aeruginosa biofilms.Journal of Industrial Microbiology 10/1995; 15(3):162-8.