Cell wall metabolism in Bacillus subtilis subsp. niger: effects of changes in phosphate supply to the culture

A dispensable role for forespore-specific gene expression in engulfment of the forespore during sporulation of Bacillus subtilis

During the stage of engulfment in the Bacillus subtilis spore formation pathway, the larger mother cell engulfs the smaller forespore. We have tested the role of forespore-specific gene expression in engulfment using two separate approaches. First, using an assay that unambiguously detects sporangia that have completed engulfment, we found that a mutant lacking the only forespore-expressed engulfment protein identified thus far, SpoIIQ, is able to efficiently complete engulfment under certain sporulation conditions. However, we have found that the mutant is defective, under all conditions, in the expression of the late-forespore-specific transcription factor sigma(G); thus, SpoIIQ is essential for spore production. Second, to determine if engulfment could proceed in the absence of forespore-specific gene expression, we made use of a strain in which activation of the mother cell-specific sigma factor sigma(E) was uncoupled from forespore-specific gene expression. Remarkably, engulfment occurred in the complete absence of sigma(F)-directed gene expression under the same conditions permissive for engulfment in the absence of SpoIIQ. Our results demonstrate that forespore-specific gene expression is not essential for engulfment, suggesting that the machinery used to move the membranes around the forespore is within the mother cell.

The functions of autolysins in the growth and division of Bacillus subtilis

Some bacteria, such as streptococci, exhibit growth from discrete and well-defined zones. In Streptococcus faecalis, growth zones can be observed in the electron microscope, and the position of the zone can be used as a marker for cell cycle events. Growth of the cell surface of Bacillus subtilis appears to be by a much different mechanism from that of streptococci. Cell elongation takes place by the insertion at many sites in the cell cylinder of peptidoglycan components. The insertion occurs on the inner face of the wall, and upon cross linking, the new wall material becomes stress bearing and older wall is pushed to the surface. When old wall reaches the surface, it becomes susceptible to excision by autolysins, resulting in wall turnover; cell elongation, due to the stretching of the cross-linked peptidoglycan, therefore, accompanies turnover and does not require a specialized growth zone.

Biosynthetic capacity for type-specific antigen synthesis determines the virulence of serotype III strains of group B streptococci

The level of type-specific antigen (that covalently associated with the cell wall peptidoglycan and that released extracellularly) synthesized by virulent and avirulent strains of type III group B streptococci was quantitated and compared. Additionally, the effect of the physiological age of the cells and the influence of the exogenous phosphate ion concentration on the level of antigen synthesis by these organisms were also examined. Approximately 4% of the total antigen synthesized by the organism is noncovalently bound to the cell surface, and the difference in level of the noncovalently associated type-specific antigen between virulent and avirulent strains was negligible. In contrast, when the cell-associated covalently bound type antigens were evaluated, virulent strains were demonstrated to have two- to threefold higher levels than those of avirulent strains during the exponential and stationary phases of growth under various growth conditions. Furthermore, virulent strains that had high levels of cell-associated type antigen also secreted more extracellular type antigen than did avirulent strains. Thus, the data were consistent with the hypothesis that an overall production of type-specific antigen correlated with virulence in mice. However, the cell-associated type-specific antigen probably represented a better indicator for virulence potential since the addition of purified extracellular type-specific antigen to a mutant strain that lacks cell surface type antigen did not alter the 50% lethality value of the organism. To account for variation in the level of type-specific antigen produced by these strains, the kinetics of both the group- and type-specific antigens synthesis was investigated at the cell membrane level by utilizing an intact protoplast system.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation, chemical composition, and molecular size of extracellular type II and type Ia polysaccharides of group B streptococci

Polysaccharides carrying the type II- and type Ia-specific determinants of Lancefield group B streptococci were isolated and purified by anion-exchange chromatography and gel filtration from the supernatant culture medium after growth of strain 18RS21/67/1 (type II) and strain DS/1204/78 (type Ia), respectively. The average molecular weights of these polysaccharides were 97,000 (type II) and 94,000 (type Ia), as determined by reducing end group analyses. These molecular weights were in reasonably good agreement with molecular weights determined by gel filtration at high ionic strength on calibrated columns. The polysaccharides did not cross-react with antisera specific for the other type-specific determinants or with group B-specific antisera. Their content of galactose, glucose, glucosamine, and neuraminic acid (the last two calculated as N-acetyl derivatives) accounted for over 96% of their dry weight. The two polysaccharides differed from each other (and from type III polysaccharide) in their relative content of these monosaccharides. The molar ratios of galactose, glucose, and neuraminic acid to glucosamine were 3.3:2.3:1.35:1.0 for the type II polysaccharide and 2.0:0.8:1.4:1.0 for the type Ia polysaccharides. The results obtained indicate that these extracellular type II and Ia polysaccharides contain larger amounts of neuraminic acid than can be accounted for by previously proposed structures of their repeating units.

Cell wall turnover in growing and nongrowing cultures of Bacillus subtilis

Cell wall turnover was studied in cultures of Bacillus subtilis in which growth was inhibited by nutrient starvation or by the addition of antibiotics. Concomitantly, the synthesis of wall, as measured by the incorporation of radioactively labeled N-acetylglucosamine, was followed in some of these cultures. In potassium- or phosphate-starved cultures, growth stopped, but wall turnover continued at a rate slightly lower than that in the control cultures. Lysis of cells did not occur. In glucose-starved cultures, continued wall turnover caused lysis of cells, since wall synthesis apparently was inhibited. The same phenomenon was observed after growth arrest by the addition of wall synthesis inhibitors such as fosfomycin, cycloserine, penicillin G, and vancomycin. Growth arrest by the addition of chloramphenicol allowed the continuation of wall synthesis; therefore, the observed turnover generally did not cause cell lysis.

Cell wall metabolism in Bacillus subtilis subsp. niger: accumulation of wall polymers in the supernatant of chemostat cultures

Cell wall polymers were measured both in the cells and in the cell-free medium of samples from steady-state chemostat cultures of Bacillus subtilis, growing at various rates under magnesium or phosphate limitation. The presence of both peptidoglycan and anionic wall polymers in the culture supernatant showed the occurrence of wall turnover in these cultures. Variable proportions of the total peptidoglycan present in the culture samples were found outside the cells in duplicate cultures, indicating that the rate of peptidoglycan turnover is variable in B. subtilis. Besides peptidoglycan, anionic wall polymers were detected in the culture supernatant: teichoic acid in magnesium-limited cultures and teichuronic acid in phosphate-limited cultures. In several samples, the ratio between the peptidoglycan and the anionic polymer concentrations was significantly lower in the extracellular fluid than in the walls. This divergency was attributed to the occurrence of direct secretion of anionic polymers after their synthesis.