Factors influencing cell shape in the mutans group of streptococci

Abstract

Electron and light microscopic and growth studies of representatives of the diverse species of mutans streptococci revealed the cells to be either bacillary or coccoid in shape. Some strains changed from bacillary to coccoid if the HCO3-/K' ratio of the media was increased and from coccoid to bacillary if the ratio was decreased. Doubling times of rods and cocci were the same despite an HCO3/K+ ratio change between 0.008 and 2.84. For strain 10449S, no tested anions or cations substituted for HC03-or K+ to produce this effect, except for B4072. Strain 10449S grown at a high B4072-/K' ratio became ellipsoid, and this phenomenon was associated with slower doubling times. Up to three incomplete septa could be observed in one rod, but no more than one incomplete septum could be observed in either ellipsoid or spherical cells. Interseptal distances were greatest in rods, shorter in spheres, and shortest in ellipses. All of the above differences were statistically significant (P < 0.001).The mutans group of streptococci is indigenous to the oral cavity and is the major etiological agent of dental caries (6, 10). These bacteria were apparently named mutans because they were first found, by Clark (2), to be rods, and thus they were thought to be mutants of other streptococci. The bacillary shape of at least some of these cells was again recognized many years later (4).Our previous study (14) demonstrated that the shape of Streptococcus mutans NCTC 10449S can be changed from bacillary to coccoid, and vice versa, by adjusting the salt contents of a variety of complex and defined culture media in which it is grown. Within wide ranges, the shape of this cell is not dependent on the absolute concentrations of HC03-K+, Na+, or phosphate; on the ratio Na+/K+; or on the addition (or deletion) of iron, magnesium, or manganese salts to (or from) media. The change from rod to coccoid form is growth dependent and is blocked by protein synthesis inhibitors. Shape change is not dependent on the pH change of a fermenting culture; it occurs in pH-stat controlled incubations. Rather, the shape of this cell is clearly dictated by the ratio HCO3-/K' in the growth medium.When the ratio is low (0.008), as in the mnodified Jordan complex medium (JM; 9, 13), the cells are bacillary; when it is high (2.84), as in the defined FMC medium (15), the cells are coccoid (14).The present study was concerned with whether shapes of other strains among the mutans streptococcus group could be changed by manipulating this ratio, whether ions other than HCO3-and K+ could similarly affect cell shapes, whether change of shape was associated with change of growth rate, and whether differences in cellular ultrastructure occurred when the cells grew in diverse shapes.To test whether the phenomenon of changing shape in 10449S is general among the mutans group of streptococci, several strains (Table 1) representing its diverse species (3, 11) were grown anaerobically in JM (9, 13) and FMC (15) liquid media containing 0.5% glucose. Cells were examined by Gram stain...

Transformation Efficiency of EMS-induced Mutants of Streptococcus mutans of Altered Cell Shape

“…2Present address: Department ofMicrobiology and Immunology, College of Medicine, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73190 5To whom correspondence and reprint requests should be addressed Coykendall et al (1971) also recognized this shape variation, and our work (Tao et al, 1987(Tao et al, , 1988 revealed that the bicarbonate-to-potassium ratio in growth media regulates the expression of shape of Streptococcus mutans strains NCTC 10449S and GS5, independent of growth rate, pH, and other culture medium constituents. When the ratio of bicarbonate-to-potassium is low, as in modified Jordan (JM) medium (Tanzer et al, 1973), the cells are bacillary; when it is high, as in FMC defined medium (Terleckyj et al, 1975) or in JM adjusted to the same high bicarbonate to potassium ratio as in FMC, the cells grow as cocci.…”

The Elongation of Ovococci

“…Interestingly, Streptococcus mutans NCTC 10449S was shown to adopt a rod-like or an ellipsoid conformation depending on the salt composition of the medium. 24,25 Similarly, planktonic cells of L. lactis IL1403 underwent ovococcus to rod transition in a particular medium. Biofilms grown in this medium had elongated cells at their surface, while bacteria not directly exposed to the medium were only ovococci.…”

Ultrastructural Changes in Streptococcussobrinus Induced by Xylitol, NaF and ZnCl2

“…A high bicarbonate-to-K+ ra tio reportedly produces spherical cells, whereas a low bicarbonate-to-K* ratio results in bacillary cells. In terestingly, several incomplete septae corresponding to cell division sites were found in the bacillary forms of Streptococcus mutans 10449S [Tao et al, 1987[Tao et al, , 1988. In mitochondria, accumulation of P; is known to cause swelling [Klingenberg et al, 1974; D'arctangelo et al, 1987], It is tempting to speculate that a similar mechanism accounts for the presently ob served 'ballooning' or swelling of the bacteria grown in the presence of zinc ions.…”

“…Lack of ATP and the intracellular accumulation of P,, in turn, upset their chemiosmotic regulation. Recent publications indicate that morphological alterations in mutans streptococci may occur in response to the bicarbonate to potassium ratio in the growth medium [Tao et al, 1987[Tao et al, , 1988. A high bicarbonate-to-K+ ra tio reportedly produces spherical cells, whereas a low bicarbonate-to-K* ratio results in bacillary cells.…”

“…The ultrastructure of oral bacteria may be influ enced by growth conditions [Shockman et al, 1976;Tao et al, 1987Tao et al, , 1988. Moreover, it is well known that the growth and metabolism of oral bacteria, in vitro and in vivo, may be affected by a variety of agents used for prophylactic purposes.…”