Evidence that the PBP 5 synthesis repressor (psr) of Enterococcus hirae is also involved in the regulation of cell wall composition and other cell wall-related properties.
psr has been reported by M. Ligozzi, F. Pittaluga, and R. Fontana, (J. Bacteriol. 175:2046-2051, 1993) to be a genetic element located just upstream of the structural gene for the low-affinity penicillin-binding protein 5 (PBP 5) in the chromosome of Enterococcus hirae ATCC 9790 and to be involved in the repression of PBP 5 synthesis. By comparing properties of strains of E. hirae that contain a full-length, functional psr with those of strains that possess a truncated form of the gene, we have obtained data that indicate that psr is involved in the regulation of several additional surface-related properties. We observed that cells of strains that possessed a truncated psr were more sensitive to lysozyme-catalyzed protoplast formation, autolyzed more rapidly in 10 mM sodium phosphate (pH 6.8), and, in contrast to strains that possess a functional psr, retained these characteristics after the cultures entered the stationary growth phase. Cellular lytic properties did not correlate with differences in the cellular contents of muramidase-1 or muramidase-2, with the levels of PBP 5 produced, or with the penicillin susceptibilities of the strains. However, a strong correlation was observed with the amounts of rhamnose present in the cell walls of the various strains. All of the strains examined that possessed a truncated form of psr also possessed approximately one-half of the rhamnose content present in the walls of strains that possessed a functional psr. These data suggest that psr is also involved in the regulation of the synthesis of, or covalent linkage to the cell wall peptidoglycan of, a rhamnose-rich polysaccharide. These differences in cell wall composition could be responsible for the observed phenotypic differences. However, the multiple effects of psr suggest that it is part of a global regulatory system that, perhaps independently, affects several cell surface-related properties.
Massidda
O
O
Department of Microbiology and Immunology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
Kariyama
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R
Daneo-Moore
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L
Shockman
G D
GD
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001433:Bacteriolysis; D002021:Buffers; D002473:Cell Wall / Q000737:chemistry / Q000378:metabolism; D016983:Enterococcus / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D009113:Muramidase / Q000378:metabolism; D009154:Mutation; D009996:Osmotic Fragility; D010400:Penicillin G / Q000494:pharmacology; D010403:Penicillin Resistance; D010710:Phosphates; D011523:Protoplasts; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; D002021:Buffers; D010710:Phosphates; C080374:Psr protein, Enterococcus hirae; D012097:Repressor Proteins; D009113:Muramidase; D010400:Penicillin G