Isolation and Characterization of Streptococcus mutans Mutants with Altered Cellular Morphology or Chain Length

Abstract

A nitrosoguanidine-induced mutant, designated UAB90, of Streptococcus mutans PS14 (serotype c) strain UAB62, was identified on the basis of its unique colony morphology and isolated on brain heart infusion agar. Other mutants displaying similar colony morphologies on brain heart infusion agar were isolated after ethyl methane sulfonate mutagenesis of UAB62 and S. miltans 6715 (serotype g) strains UAB61 and UAB66, and these were found to exhibit abnormalities in cell morphology, chain length, or both. All mutants were examined further for (i) adherence and aggregation after overnight growth in medium containing sucrose, (ii) growth and aggregation in brain heart infusion broth and medium containing glucose, (iii) aggregation of nongrowing cells in the presence of 2 mg of sucrose per ml or 200 Vig of dextran per ml, (iv) dextranase activity, and (v) ease of cell lysis. Mutants isolated included several with long chains of enlarged cocci, and two of these strains, UAB261 and UAB433, along with UAB90, were more susceptible to cell lysis than were their parents. UAB261, isolated from UAB62, maintained other parental characteristics, whereas UAB433, isolated from UAB66, lost its ability to aggregate in the presence of either sucrose or dextran. The "fragile" mutant UAB90 was particularly useful in the isolation of high-molecular-weight DNA for early gene cloning experiments by our laboratory. Two other cell morphology mutants, UAB272 from UAB66 and UAB289 from UAB61, did not lyse better than their parents, but both lacked measurable dextranase activity. A final mutant, UAB276 from UAB66, displayed only increased chain length without apparent cell morphology variations. Chains produced by this mutant were up to 10 times longer than those produced by UAB66. UAB276 lysed slightly less well than its parent but retained all other wildtype characteristics examined.

Chain formation and de‐chaining in Streptococcus sobrinus SL‐1

“…Similar results have been reported [or BaciUu.s .siihtilis, for which it has been shown that crude autolysin extracts prepared frotn the organism were capable of de-chaining exponentially growing cells (6). In genetic studies involving oral streptococci, it Was shown that chetnical tnutagenesis of specific eel] types resulted in the gi-owth of elongated chains almost 10 times longer than normal (16). U waŝ hypothesized that the observed increase in chain length could be caused by increased celJ-to-cell adhesion or the re-"loval of a fector that promotes dechaining.…”

“…In addition, heat-treated crude extracts demotistrated no de-chaining activity cotnpared with controls. Most studies that have evaluated factors that control or infiuence bacterial chain length have itnplicated a role for autolysitis in the process (5,6,16,18). Typically, tnany autolytic acfivities have been shown to be regulated by pH (11,18).…”

“…A number of studies have suggested that autolysins are active in the oral streptococci. It has been suggested that autolysins tnay assist in lysozyme-tnediated de-chaining of S. tnutans (10) and that they tnay be involved in reguladng the cell morphology and chain length of the organistn (16). Other investigators have also elicited a role for autolysins to explain the antibacterial actions of penicillin G and other antibiotics (12) and the activity of salivary hisddine-rich polypeptides against the mutans streptococci (14).…”

“…It has been reported, however. that the conditions that affect chain length can also change the acidurance (10), aggregadon (16) and resistance of phagocytosis (5) of specific organistns. The results presented in this study suggest that conditions cotntnon to dental plaque can effect chain length.…”

Streptococcus mutans isolated from a 4‐year‐old girl diagnosed with infective endocarditis

“…Our observation of the HM strain revealed that the chain structure of this bacterium is shorter than that of NCTC 10449. Some studies have predicted that the conditions that may affect cellular chain length may also affect adhesion (Murchison, Larrimore, Hull, & Curtiss, 1982) and aggregation (Murchison et al, 1982;Nakano, Fujita, Nishimura, Nomura, & Ooshima, 2005), both of which can contribute to virulence. Streptococcal cellular chain length and morphology are influenced by several factors.…”