Cell wall composition in bacterial and L forms of Proteus vulgaris

MORPHOLOGICAL CHANGES IN GRAM-NEGATIVE BACILLI EXPOSED TO CEPHALOTHIN

Chang, Te-Wen (Tufts University School of Medicine, Boston, Mass.), and Louis Weinstein. Morphological changes in gram-negative bacilli exposed to cephalothin. J. Bacteriol. 88:1790-1797. 1964.-Exposure of gram-negative bacteria to cephalothin (7-[thiophene-2-acetamido]-cephalosporanic acid) revealed the formation of long filaments and large bodies, which were capable of reverting to normal cells when removed from contact with the drug. The degree of morphological change was found to be related to the concentration of antibiotic in which the organisms were suspended. The large bodies were altered by contact with solutions of varying osmolarity. Different species showed variation in the ability to develop large bodies. A relationship between antibiotic sensitivity and the capacity to resist morphological alteration was observed. Though most sensitive gram-negative bacilli were strikingly changed by exposure to cephalothin, naturally resistant ones were unaffected. Organisms made drug-resistant in vitro underwent changes in cellular form which were qualitatively the same but less intense than those which developed in parent strains originally sensitive to cephalothin.

In vitro synthesis of peptidoglycan by spheroplasts of Proteus mirabilis grown in the presence of penicillin

Spheroplasts of the unstable L-form of Proteus mirabilis with fragile, shape defective cell walls grown in medium containing 120 mg/l penicillin G and then killed and permeabilized by ether treatment, were capable of in vitro synthesis of peptidoglycan from the precursors UDP-GlcNAc and UDP-MurNAc-L-Ala-D-Glu(ms-A2pm-D-Ala-D-Ala). The in vitro peptidoglycan was extensively peptide-crosslinked, indicating a continuing function of peptidoglycan transpeptidase in the spheroplasts. The seven penicillin-binding proteins (PBPs) of P. mirabilis with their functions as multiple peptidoglycan transpeptidases were shown to be saturated in the spheroplasts and thereby functionally inactivated by the penicillin of the growth medium to a very different degree. Complete or almost complete saturation occurred with the PBPs 1A, 1B, and 3, for which functions as indispensable transpeptidases in Escherichia coli have been postulated. In contrast, PBPs 5 and 6 were not saturated in the L-form spheroplasts. Transpeptidase function has been described previously in PBP 5 of P. mirabilis. The working hypothesis is proposed that synthesis of the functionally defective peptidoglycan of L-form spheroplasts in the presence of penicillin takes place with transpeptidase function of PBP 5.

Differentiation of mycoplasmatales from bacterial protoplast L-forms by assay for penicillin binding proteins

Membrane proteins with the specific ability for binding penicillin with high affinity (penicillin binding proteins) were found to be present in two strains of the cell wall-less protoplast L-form of P. Mirabilis and were absent from different species of Mycoplasma and from Acholeplasma laidlawii. Thus, the assay for penicillin binding proteins appeared to be suitable for the differentiation of the cell wall-less procaryotes. The absence of penicillin binding proteins from the mycoplasmatales further confirmed the unrelatedness of this group to the bacteria.

Membranes of the protoplast L-form of Proteus mirabilis

Isolated membranes of the cell wall-less stable protoplast L-form of Proteus mirabilis were characterized by density gradient centrifugation and by assay for their major chemical constituents, proteins, phospholipids and lipopolysacchartide, and for some specific marker enzymes of the cytoplasmic membrane. In most of the analyzed properties the L-form protoplast membrane resembled the bacterial cytoplasmic membrane, with some notable modifications. Considerable amounts of lipopolysaccharide, normally an exclusive constituent of the outer membrane, were found. Furthermore, the L-form membranes contained the functions of the reduced nicotinamide adenine dinucleotide oxidase system, of D-lactate dehydrogenase (EC 1.1.1.28) and of succinate dehydrogenase (EC 1.3.99.1) at specific activities comparable to, or in some cases considerably higher than, those present in cytoplasmic membranes of the bacterial form. Of two peptidoglycan DD-carboxypeptidase/transpeptidases (EC 3.4.17.8 and EC 2.3.2.10). which are normally present in the cytoplasmic membrane of the bacterial form of P. mirabilis, the membrane of the protoplast L-form contained only one. Electron microscopy of thin sectioned L-form protoplasts showed extensive heterogeneity of membraneous structures. In addition to the single membraneous integument, internal membrane-bounded vesicles and multiple stacks of membranes were present, as the result of unbalanced growth and membrane synthesis in the L-form state.

Localization of enterobacterial common antigen: Proteus mirabilis and its various L-forms

An investigation of Proteus mirabilis wild-type strains and their various derived L-forms shows that the enterobacterial common antigen (ECA) is localized in the outer membrane of the cell envelope of these strains. In strains where the outer membrane is lacking (stable protoplast L-forms) or where its amount is reduced (spheroplast UL19) no ECA or only reduced amounts of it are detected by serological tests or by ferritin-labeling techniques.

Phospholipid and lipopolysaccharide in Proteus mirabilis and its stable protoplast L-form. Difference in content and fatty acid composition

Cells of the stable protoplast L-form of Proteus mirabilis contain 1.5 to 2 times more extractable lipid, mostly phospholipid, per dry weight than cells of the bacterial form. Under identical conditions of cultivation the qualitative and quantitiative composition of the phospholipid is very similar in both cell forms. The range of mole percentages of individual phospholipid species is 78-80 for phosphatidylethanolamine, 10-13 for phosphatidylglycerol, 3.9-5.5 for diphosphatidylglycerol and 1.0-2.1 for lysophospholipid. However, all phospholipid species in the L-form differ from those of the bacterial form by a lower content of long-chain fatty acids and a higher content of short-chain fatty acids. Growth of the L-form in the presence of growth-stimulating horse serum results in a change of phospholipid composition accompanied by the uptake of phospholipid and fatty acids from the serum into L-form phospholipid. L-form protoplasts synthesize the same two types of lipopolysaccharide, I and II, that were previously identified in the bacterial form of Proteus mirabilis. However, only small amounts of the more hydrophilic lipopolysaccharide II are present in the L-form. Lipopolysaccharides from both cell forms have virtually identical polysaccharide compositions but differ strikingly in the relative content of fatty acids in their lipid-A moieties. Molar ratios of tetradecanoic acid, hexadeconoic acid and 3-hydroxytetradecanoic acid are 5:1:6 in the bacterial form and 5:0:1:6 in the L-form grown in serum-free medium. The observated differences between the bacterial form and the protoplast L-form are interpreted as results of the adaptation of the L-form to life in the state lacking an envelope by formation of a physically more stable but still sufficiently fluid protoplast membrane. A rapid method based on fatty acid analysis for the simultaneous quantitative determination of phospholipid and lipopolysaccharide content of whole cells is reported.

D-alanyl-D-alanine carboxypeptidase in the bacterial form and L-form of Proteus mirabilis

Membranes of the bacterial form and the stable and unstable L-forms of Proteus mirabilis contain LD and DD-carboxypeptidase. The DD-carboxypeptidase is inhibited non-competitively by penicillin G. The enzyme of the bacterial form is highly penicillin-sensitive (Ki - 4 X 10(-9) M penicillin G). Inhibition is only partly reversible by treatment with penicillinase or by dialysis against buffer. In contrast, the DD-carboxypeptidase of the unstable L-form, grown in the presence of penicillin, is 175-fold less penicillin-sensitive (Ki = 7 X 10(7) M penicillin G). Inhibition is completely reversed by penicillinase or dialysis. After inhibition by penicillin and subsequent reactivation the penicillin sensitivity of the bacterial DD-carboxtpeptidase is similar to the sensitivity of the enzyme of the unstable L-form. The hypothesis is proposed that P. mirabilis contains two DD-carboxypeptidases of different penicillin sensitivity and with different mechanisms of penicillin binding. Peptidoglycan synthesis in the cell walls of the unstable L-form is probably carried out with the help of only one DD-carboxypeptidase, viz. the completely reactivatable enzyme with the lower penicillin sensitivity.

The chemical composition of the membranes of protoplasts and L-forms of Staphylococcus aureus

Membrane fractions were prepared from Staphylococcus aureus H and 100 after dissolution of the cell walls by a lytic enzyme from Streptomyces griseus. Membranes were also prepared from the L-forms derived from the same strains. The membranes were analysed for protein, lipid, carbohydrate and RNA contents, and the fatty acid composition of the lipids was determined. A branched-chain saturated C(15) acid was the major component in all samples, and the correspondence between L-forms and parent bacteria was fairly close. The lipids were separated into non-polar-lipid, glycolipid and phospholipid fractions; the L-forms contained a little more neutral lipid and much more glycolipid than the parent bacteria. In all membranes the glycolipid, which accounted for all the carbohydrate present, was a diglucosyl diglyceride. The major phospholipids of the protoplast membranes were phosphatidylglycerol and some lipoamino acids (lysine and a little alanine). On the other hand, diphosphatidylglycerol was the chief phospholipid found in L-form membranes.

DEMONSTRATION OF LYSOGENY IN STABLE L FORMS OF PROTEUS MIRABILIS

Taubeneck, Udo (Institut für Mikrobiologie und Experimentelle Therapie, Jena, Germany). Demonstration of lysogeny in stable L forms of Proteus mirabilis . J. Bacteriol. 86: 1265–1269. 1963.—Stable L forms of eight different lysogenic Proteus mirabilis strains have proved to be lysogenic. In an additional strain, phage production was induced upon transfer into the stable L form. This demonstrates that the stable L forms, like their parent bacillary types, are capable of forming mature phage. Their phage resistance is not due to an inability to form mature phage but to a loss of phage receptors. In some instances, the transition into the stable L form is associated with altered phage production, usually with increased phage production, in comparison with the parental bacillary type.