Turnover of bacterial cell wall peptidoglycans.

The cell wall peptidoglycan of LactobaciZZus acido$hiZus strain 63 AM Gasser has been shown to turn over rapidly during balanced exponential growth and recovery from amino acid deprivation. In contrast, turnover of either pulselabeled or extensively labeled peptidoglycan of Streptococcus fuecalis ATCC 9790 was not detected by the same method and experimental conditions. In S. faecalis, peptidoglycan turnover could not be induced either by brief exposure of the cells to a low concentration of lysozyme or by growth in the presence of a low concentration of penicillin. The peptidoglycan turnover rate of rapidly growing cultures of L. acidophilus was equivalent to a loss of about one third of their peptidoglycan per generation. This was not due to cellular lysis since turnover of protein was below detectable levels. Comparably rapid peptidoglycan turnover rates per generation were observed in slowly growing cultures (30% lost per generation) and in a mutant which autolyzed at about one fifth the rate of the wild type (25% lost per generation). In cultures labeled for 6 or more generations, turnover was preceded by a lag equivalent to 0.8 to 2 generation times. Turnover of pulses of less than 0.2 generations was not observed for periods exceeding 2 generations. These last two results cannot be interpreted as indicating that newly made wall is immune to turnover since in both cases nonsynchronized cultures were used, and the short pulses would eventually age as the culture grew. The addition of chloramphenicol or deprivation of valine completely prevented peptidoglycan turnover. The absence of detectable peptidoglycan turnover in S. faecalis (and other species) suggests that turnover is not an essential feature of cell wall growth. On the other hand, in L. acidophilus, peptidoglycan turnover appears to be closely associated with that portion of wall synthesis related to wall (and surface) enlargement and not to the portion related to wall thickening.