Turnover of the cell wall peptidoglycan of Lactobacillus acidophilus. The presence of a fraction immune to turnover.

Exponentially growing cultures of Lactobacillus acidophilus strain 60AM Gasser were previously shown to lose about one-third of their cell wall peptidoglycan per generation via turnover (Boothby, D., Daneo-Moore, L., Higgins, M. L., Coyette, J., and Shockman, G. D. (1973) J. Biol. Chem. 248, 2161-2169). We now show that 20 to 30% of the [3H]lysine initially present in insoluble peptidoglycan fractions was retained after 4 or more generations of continued exponential growth of cultures in the absence of label. Treatment of peptidoglycan fractions, before and after 6 or 8 generations of chase with lysozyme (EC 3.2.1.17), released soluble products containing [3H]lysine which had electrophoretic mobilities identical with the disaccharide-peptide derivatives obtained from the wall peptidoglycan of this species. Because protein is known to contaminate peptidoglycan residues, the double labeled technique was used to show that one-half or less of the label lysine present after 6 or 8 generations of chase could be attributed to protein contamination. This then left a minimum fraction of 10 to 20% of the peptidoglycan that was immune to turnover. The absence of turnover of peptidoglycan labeled during short pulses has now been quantitated to show that pulses shorter than 12% of a generation (6 to 7 min) did not turn over. This turnover-immune fraction is in reasonably good agreement with the immune fraction of 10 to 20% observed after long periods of chase of extensively labeled peptidoglycan.