Autolytic enzymes and cell division of Escherichia coli

Autolysis of Neisseria gonorrhoeae

Autolysis of Neisseria gonorrhoeae was studied under different conditions. It was found that low pH and temperature, as well as the presence of divalent cations, spermine, sucrose, and polyvinylpyrrolidone, stabilized nongrowing gonococci. Ethylenediaminetetraacetic acid alone promoted lysis, whereas lysozyme had only a limited additive effect. The autolytic behavior of gonococci appears to be connected with their prolonged cell division process. The relative dependence on the outer membrane and the peptidoglycan layer for the mechanical stability of gonococci is discussed.

The effect of substitution of diaminopimelic acid by 4-hydroxy-diaminopimelic acid on the synthesis and degradation of murein in Escherichia coli 173-25

Defects in the formation of the septum and gradually autolysis of cells occur when the dap-dependent mutant of Escherichia coli is grown in a medium with 4-hydroxy-diaminopimelic acid. When the culture grown in the presence of the labelled analogue is supplemented with the non-radioactive diaminopimelic acid a portion of the TCA-soluble radioactivity is released from the cells during 20 min after the addition of diaminopimelic acid. During this time interval the elongated forms formed in the presence of the analogue divide, however, only on the condition that the above forms are not irreversibly damaged. The increased concentration of the analogue in the medium substantially suppresses the irregularities in the development of the septum as well as the degradation of analogue containing cell wall. However, the growth rate in the presence of the analogue is always slightly lower than that in the presence of diaminopimelic acid. The cell wall pulse-labelled with diaminopimelic acid or its analogue for a time interval shorter than 1/4 of the generation time exhibits the same or only slightly higher rate of diaminopimelic acid is probably utilized less effectively for the synthesis of murein than diaminopimelic acid. However, its incorporation into the wall does not result in pronounced damage of the cell.

On the mode of action of 5-diazouracil on bacterial cell division

Cell division by strains of Escherichia coli and Salmonella typhimurium is inhibited by 5-diazouracil (5-DU). Division recovers in the presence of the inhibitor after a period which is temperature-dependent. Recovery is probably due to breakdown of 5-DU and the rate of this breakdown is apparently increased at alkaline pH. Growth with 5-DU caused only a slight reduction in the rate of murein synthesis and no alteration in the properties or composition of membranes of S. typhimurium. The agent caused chaining in Streptococcus fecalis and inhibition of the penicillin-induced lysis of S. typhimurium. These effects may have been due to direct inhibition of lysin activity but an indirect effect seems more likely. The most marked effect of 5-DU on S. typhimurium was to cause a transient inhibition of DNA synthesis. Since 5-DU did not stop uncoupled cell division (i.e. division occurring independently of DNA replication) and since lon- strains were more sensitive to 5-DU than lon+ strains, it was concluded that 5-DU acts on cell division via an inhibitory effect on DNA replication.

Novel type of murein transglycosylase in Escherichia coli

The purification and properties of a novel type of murein transglycosylase from Escherichia coli are described. The purified enzyme appears as a single band on sodium dodecyl sulfate-polyacrylamide gels and has an apparent molecular weight of approximately 65,000 as estimated by gel filtration and gel electrophoresis. It degrades pure murein sacculi from E. coli almost completely into low-molecular-weight products. The two prominent muropeptide fragments in the digest are the disaccharide-tripeptide N-acetylglucosamine-N-acetylmuramic acid-L-alanine-D-iso-glutamic acid-meso-diaminopimelic acid and the corresponding disaccharide-tetrapeptide N-acetylglucosamine-N-acetylmuramic acid-L-alanine-D-iso-glutamic acid-meso-diaminopimelic acid-D-alanine. The unique feature of these compounds is that the disaccharide has no reducing end group and that the muramic acid residue possesses an internal 1 leads to 6 anhydro linkage. The new lytic enzyme is designated as a murein: murein transglycosylase. Its possible role in the rearrangement of murein during cell growth and division is discussed.

Identification of an outer membrane protein of Escherichia coli, with a role in the coordination of deoxyribonucleic acid replication and cell elongation

Protein G of molecular weight 15,000 is the fourth commonest protein in the outer membrane of Escherichia coli B/r. From experiments described here on the relationship of protein G production to cell elongation and septation, the hypothesis is proposed that protein G is a structural protein of cell elongation. Furthermore, a surplus of protein G is produced when deoxyribonucleic acid synthesis is arrested and septation is thereby prevented. Thus protein G may be an important coordination protein in E. coli for integration of deoxyribonucleic acid synthesis, cell envelope elongation, and septation. Inhibition of normal cell elongation in a rod configuration in E. coli B/r by the novel amidinopenicillanic acid FL1060 was accompanied by changes in the rate of appearance of protein G and several other outer membrane proteins. The rate of appearance of protein G decreased some 70% within 60 min, in parallel with termination of rounds of normal cell elongation. Filament-inducing concentrations of nalidixic acid increased dramatically the rate of appearance of protein G. After 30 min a plateau level some 250% higher than the control value was reached. Similar kinetics were observed in parallel with filament formation induced by incubation of a dnaB mutant of E. coli at the nonpermissive temperature. No change in the rate of appearance of protein G was observed during cephalexin- or benzylpenicillin-induced filament formation, indicating that increased protein G production was not a secondary consequence of filamentation. Cells treated with FL1060 lost their ability to be induced for protein G formation, with nalidixic acid, in parallel with their loss of ability to initiate rounds of normal cell elongation. A pulse-chase experiment demonstrated that the protein G appearing in the outer membrane as a consequence of inhibition of deoxyribonucleic acid synthesis was the result of de novo synthesis rather than of interconversion from previously synthesized protein species. A preliminary characterization of protein G revealed several similarities with the well-characterized lipoprotein of the outer membrane of E. coli. A comparison of the incorporation of several 14C-labeled amino acids into protein G and the lipoprotein revealed substantial differences, however, perhaps ruling out a simple relationship between these two proteins.

Study of cell wall growth in Bacillus megaterium by high-resolution autoradiography

Growth of the cell wall of Bacillus megaterium was studied by pulse-labeling the cell wall of a DAP- Lys- mutant for a very short time with tritium-labeled diaminopimelic acid. The distribution of radioactivity along the cell wall was examined by high-resolution autoradiography on isolated cell walls and thin sections of bacteria. The results indicate that cell wall elongation occurs by diffuse intercalation of newly synthesized murein into the expanding cell wall during exponential growth, as well as during germination, and that the only zone of highly localized diaminopimelic acid incorporation is found at the cross wall during its synthesis. This zone contains about 30% of the radioactivity incorporated into the cell wall. Analysis of autoradiographs of thin sections of bacteria shows that the total radioactivity incorporated per bacterium doubles during the life cycle. This doubling occurs in the cylindrical part of the cell wall but not in the polar caps. This seems to indicate that elongation of the bacterium is not constant during the life cycle but increases with the length of the cell.

Distinct penicillin binding proteins involved in the division, elongation, and shape of Escherichia coli K12

The varied effects of beta-lactam antibiotics on cell division, cell elongation, and cell shape in E. coli are shown to be due to the presence of three essential penicillin binding proteins with distinct roles in these three processes. (A) Cell shape: beta-Lactams that specifically result in the production of ovoid cells bind to penicillin binding protein 2 (molecular weight 66,000). A mutant has been isolated that fails to bind beta-lactams to protein 2, and that grows as round cells. (B) Cell division: beta-Lactams that specifically inhibit cell division bind preferentially to penicillin binding protein 3 (molecular weight 60,000). A temperature-sensitive cell division mutant has been shown to have a thermolabile protein 3. (C) Cell elongation: One beta-lactam that preferentially inhibits cell elongation and causes cell lysis binds preferentially to binding protein 1 (molecular weight 91,000). Evidence is presented that penicillin bulge formation is due to the inhibition of proteins 2 and 3 in the absence of inhibition of protein 1.

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.

On the control of septation in Escherichia coli

Mutants of E. coli defective in cell septation (ftsA to ftsG, conditional thermosensitive mutants isolated by Ricard and Hirota) were studied with respect to their membrane protein composition, murein hydrolase activities and rates of synthesis of murein and phospholipids. Three classes of mutants have been distinguished: 1) those affected in both murein and phospholipid synthesis; 2) those affected in either murein or phospholipid synthesis and 3) those affected in neither of these parameters. Overall murein hydrolase activities, after activation, is of the same order in all the mutants screened. In addition to soluble products of murein splitting, we have found insoluble products that appear to be in dynamic equilibrium with the murein of the sacculus. Endogenous levels of cyclic adenosine 3',5'-monophosphate measured after blocking septation showed no variation. This suggests that the cyclic nucleotide is not involved in the metabolic control of septation.

An electron microscopic study of antagonism between cephalexin and erythromycin in Staphylococcus aureus

This study concerns investigations at the cellular level of antagonism between cephalexin (CEX) and erythromycin (EM) with the aid of electron microscopes and a liquid scintillation counter. Exposure of Staphylococcus aureus 209-P to CEX and EM in combination was found to result in a marked antagonism between the two antibiotics in their effects on the growth of the organism. Observations under a scanning electron microscope revealed lysed cells in the presence of CEX alone but almost no lysis in the presence of a combination of CEX and EM. Observations under a transmission electron microscope, on the other hand, disclosed that nearly all of the cells exposed to 20 mug/ml of CEX were transformed into protoplasts with their morphological changes being most marked after 4 hr of exposure. When 1 mug/ml of EM was allowed to act alone, this exposure resulted in thickening of the cell walls. The combined use of CEX and EM, however, resulted in neither thickening of the cell walls as in the presence of EM alone nor in the formation of protoplasts as in the presence of CEX alone but merely produced the swelling of separating walls. Cellular uptake of 14C-L-lysine and N-acetylglucosamine-1-14C into the cell wall fraction and the protein fraction was affected by CEX and EM, respectively, when used alone or in combination.

Mode of growth and division of Salmonella typhimurium

A temperature-sensitive strain (HD 20) of Salmonella typhimurium is described. At restrictive temperature this strain shows an envelope alteration and a defect in division associated with an increase in cell diameter. On a shift to 42 degrees C there is residual division for ca. 30 min and then no further increase in cell number. In minimal medium (MM) at 42 degrees C cell diameter remains unchanged for about one mass doubling and then increases. From measurements of cell elongation, it is concluded that such increases in diameter occur because cell volume increases exponentially at 42 degrees C but increases in the rate of elongation occur for only a short period and then elongation rate becomes constant. This conclusion is supported by the observation that HD 20 cells show no increase in diameter at 42 degrees C when cultured in media supplemented with sucrose and Mg++; normal increases in elongation rate occur in such media. A model which fits the experimental data has been constructed. This model has two main features namely (1) the elongation of individual cells is linear with the rate of elongation doubling close to division and (2) such doublings in elongation rate are linked to division such that division cannot occur if elongation rate has not doubled shortly before. In the mutant it is proposed that only a few doublings in elongation rate occur at 42 degrees C and these are responsible for the residual division. The model fits the data for cultures shifted to 42 degrees C in MM or in yeast extract casamino acids MM (YE Cas MM) and for cultures shifted to 42 degrees C and shifted up from MM to YE Cas MM. The observations on these medium shifted cultures suggest that the activity of growth zones responsible for elongation is medium dependent.

Interaction of penicillin with the bacterial cell: penicillin-binding proteins and penicillin-sensitive enzymes

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Electron microscope study of septum formation in Escherichia coli strains B and B-r during synchronous growth

The formation of cell wall septa was monitored in Escherichia coli B and B/r during synchronous growth in glucose media at 37 C by means of electron microscopy. The visible events of septation comprised the following sequence, starting at about 30 min of incubation: (a) bleb formation of the outer membrane; (b) invagination of mucopeptide and cytoplasmic membrane (with associated mesosomes); the outer membrane is excluded from the septum; (c) formation of a cross-wall; (d) ingrowth of the outer membrane during cell separation. The septum is composed of a fold of cytoplasmic membrane plus mucopeptide, and the latter is a double structure, composed of two opposed lamellae separated by an electron-transparent gap. Experiments with chloramphenicol and nalidixic acid suggested that division could occur in the presence of these inhibitors once a round of deoxyribonucleic acid replication is completed. The initial stages of septation, as estimated by the potential of the cells to produce bulges in the presence of ampicillin, may involve the modification of mucopeptide by hydrolases at the end of the C period. Assembly of the septum may occur during the first half of the D period by means of precursors synthesized during the preceding C period.

Septum formation in Escherichia coli: characterization of septal structure and the effects of antibiotics on cell division

Septa can be demonstrated in sections of Escherichia coli strains B and B/r after fixation with acrolein and glutaraldehyde. The septum consists of an ingrowth of the cytoplasmic membrane and the mucopeptide layer; the outer membrane is excluded from the septum until the cells begin to separate. Mesosomes have also been observed. The septum is highly labile and, except in the chain-forming strains, E. coli D22 env A and CRT 97, not easily preserved by standard procedures. The labile nature of the septum may be due to the presence of autolysin(s) located at the presumptive division site. Blocking division by addition of ampicillin (2 to 5 mug/ml) to cells of E. coli B/r produces a bulge at the middle of the cells; bulge formation is stopped by addition of chloramphenicol. Cephalosporins also induce bulge formation but may stop cell elongation as well as division. Bulge formation, due to the presumed action of an autolysin(s), may be an initial step in the septation sequence when the mucopeptide is modified to allow construction of the septum. In a nonseptate filament-forming strain, PAT 84, which ceases to divide at 42 C, bulge formation only occurs in the presence of ampicillin at the time of a shift-down at 30 C or at 42 C in the presence of NaCl (0.25 to 0.34 M). Experiments with chloramphenicol suggest that the filaments are fully compartmentalized but fail to divide owing to the inactivation, rather than loss of synthesis, of an autolysin at 42 C.

Control of cell division in bacteria

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Effect of Ca2+ on morphology and division of Yersinia pestis

Wild-type cells of Yersinia pestis are known to exhibit a nutritional requirement for physiological levels of Ca(2+) ( approximately 2.5 mM) at 37 but not 26 C. Upon shift of Ca(2+)-deficient cultures from 26 (permissive condition) to 37 C (restrictive condition), bacterial mass quadrupled as the organisms doubled in number and then became elongated to about twice their normal size. As shown in thin sections, the resulting static cells contained axial filaments which differed from the typical irregularly lobate nucleoids of normal yersiniae grown under the permissive condition. Following prolonged cultivation under the restrictive condition (12 h), the organisms generally exhibited apparent degenerative changes, including separation or infolding of the cell wall and cytoplasmic membrane, degeneration of deoxyribonucleic acid, and appearance of vacuoles within the cytoplasm. At this time, the cells were unable to reinitiate cell division at 37 C upon addition of Ca(2+) but divided in partial synchrony after return to 26 C. This observation indicated that, at 37 C, continuous exposure to Ca(2+) is necessary for yersiniae to maintain normal morphology and the ability to divide.

Penetration of Bdellovibrio bacteriovorus into host cells

Electron microscopy reveals that, in Bdellovibrio infection, after the formation of a passage pore in the host cell wall, the differentiated parasite penetration pole is associated with the host protoplast. This firm contact persists throughout the parasite penetration and after this process is completed. In penetrated hosts this contact is also apparent by phase microscopy. The association between the walls of the parasite and the host at the passage pore, on the other hand, is transient. Bdellovibrio do not penetrate hosts whose protoplast and cell walls are separated by plasmolysis, or in which the membrane-wall relationship is affected by low turgor pressure. It is concluded, therefore, that for penetration to occur it is essential that the host protoplast be within reach of the parasite, so that a firm contact can be established between them. A penetration mechanism is proposed that is effected by forces generated by fluxes of water and solutes due to structural changes in the infected host envelope. These forces cause a differential expansion of the host protoplast and cell wall and their separation from each other around the entry site, while the parasite remains firmly anchored to the host protoplast. Consequently, the parasite ends up enclosed in the expanded host periplasm. The actual entry, therefore, is a passive act of the parasite.

Review lecture on the growth and form of a bacterial cell

The size, shape and composition of cells in cultures of bacteria maintained in steady states of exponential growth depend on the cultural conditions employed. Important factors influencing these parameters are the growth rate of the culture and the transit time of replication forks from one end of a chromosome to the other. The considerable progress which has been made in the last ten years in elucidating the rules governing the form and composition of cells of Escherichia coli as a function of growth rate and transit time is outlined in the Review.

Mutant of Bacillus subtilis lacking exo-beta-N-acetylglucosaminidase activity

A procedure for the isolation of exo-beta-N-acetylglucosaminidase mutants, by using a plate assay method incorporating a fluorescent substrate, has been developed. A mutant lacking exo-beta-N-acetylglucosaminidase activity has been isolated and shown to grow, divide, autolyze, and sporulate as well as the parental strain.

Evidence relating cessation of respiration, cell envelope changes, and death in ultraviolet-irradiated Escherichia coli B-r cells

Ionic and nonionic detergents have little effect on respiring bacteria, but in cultures poisoned with KCN rapid solubilization of the cell membrane, as indicated by turbidity losses, takes place. Ultraviolet radiations cause Escherichia coli cells grown in minimal medium with glycerol as a carbon source to cease respiring and growing about 1 h after irradiation. We tested the effect of the nonionic detergent Triton X-100 on growth and cell membrane dissolution (both measured by turbidity changes), respiration, and viability of unirradiated and irradiated E. coli B/r cells. When the detergent was added to cells immediately after irradiation, a decrease in turbidity occurred only when respiration was about to cease; when it was added after cessation of respiration, the turbidity loss was immediate. In both cases the turbidity loss was about 60%, and disintegration of the cell walls did not take place. 5-Fluorouracil (FU) and thermal (42 C) treatments cause respiration of irradiated cells to be maintained and also cause viability increases. Irradiated cells treated with FU and detergent show no turbidity loss just prior to the time respiration normally ceases, but a loss does occur in irradiated cells incubated with detergent at 42 C. We conclude that FU maintains respiration for all of the cells, but that thermal treatment maintains respiration for only part of the cells. In all cases the detergent had only a negligible effect on the respiration and viability of unirradiated and irradiated cells. We conclude that Triton X-100 causes solubilization of cell membranes of only nonrespiring cells that are not destined to survive.

Freeze-etching of the cell envelope of an Acinetobacter species which carries a regular array of surface subunits

Freeze-etching was applied to preparations, with and without glycerol, of Acinetobacter sp. strain MJT/F5/199A, consisting of intact cells after normal growth or after incubation with chloramphenicol, spheroplasts, and isolated cell walls and outer membranes. Etched preparations show that a regular array of subunits forms the surface of normal cells. Near the zones of constriction in dividing cells, blebs and irregularities are seen, and some blebs, consisting of both surface subunits and outer membrane, are released from the cells. The cross-fractured cell envelope shows four layers which are related to the structures seen in section as follows: cw1, which is not visible in section, contains the surface subunits; cw2 consists of all or part of the outer membrane; cw3 includes the intermediate and dense, peptidoglycan-containing layers; within these cell wall layers is the plasma membrane. Internal fracture of the plasma membrane occurs under all conditions tested, but the fracture plane in the cell wall is only revealed in chloramphenicol-treated cells or normal cells freeze-fractured with glycerol present; the characteristic fracture faces are not seen in spheroplasts or isolated outer membranes. The concave fracture face cw2 consists of densely packed granules, while the convex face cw3 is fibrillar. The probable location of this fracture plane is discussed. After incubation with chloramphenicol, the outer surface of the cells is obscured by extracellular material, the dense peptidoglycan-containing layer is increased in thickness, and the cytoplasm contains rounded bodies bounded by one or more unit membranes.

Regulation of cell division in a temperature-sensitive division mutant of Escherichia coli

Escherichia coli fil ts forms multinucleate filaments when suspensions of about 10(7) organisms per ml are shifted from 37 to 43 C in rich medium. Occasional septation continues, chiefly at the poles, and immediately becomes more frequent when the filaments are returned to 37 C. The addition of chloramphenicol (200 mug/ml) at either temperature initially stimulates the formation of polar septa. When very dilute suspensions of the strain (<10(6) organisms per ml) are shifted to the restrictive temperature, the inhibition of septation is more complete and only seldom reversible. Conversely, cell division is little affected when suspensions of >10(8) organisms per ml, or microcolonies of several hundred organisms on agar, are incubated at 43 C; evidence is presented that this is a consequence of a slight reduction in the mutant's growth rate. In certain media, septation is blocked irreversibly by even brief exposure to 43 C, after which cell elongation without division proceeds at 37 C for some hours. Several findings, when considered together, suggest that the cytoplasmic membrane is normal at the restrictive temperature, and that the block in septation is caused by a defect in the cell wall: it is largely overcome by NaCl, but not by sucrose; in some circumstances the filaments become swollen and develop localized bulges in the wall, yet the membrane remains intact and retains its selective permeability; lastly, the strain is insensitive to deoxycholate at both temperatures. The mutation has been mapped between arg B and thr, at a locus which appears to be distinct from others known primarily to influence cell division.

Membrane synthesis in synchronous cultures of Bacillus subtilis 168

Synthesis of bacterial membranes has been investigated in Bacillus subtilis by examining incorporation of amino acids and glycerol into the protein and lipid of membranes of synchronous cultures. A simple reproducible fractionation scheme divides cellular proteins into three classes (i) truly cytoplasmic, (ii) loosely membrane bound, released by chelating agents, and (iii) tightly membrane bound. These comprise approximately 75, 10, and 15%, respectively, of cellular proteins in this organism. Incorporation of radioactivity into these fractions, using steady-state and pulse labeling has been followed during the cell cycle. Cytoplasmic proteins and the loosely membrane-bound proteins are labeled at an exponential rate throughout the cell cycle. The membrane fraction is labeled discontinuously in the cell cycle, with periods of rapid synthesis over the latter part of the cycle and a period with no net synthesis during the early part of the cycle. Pulse labeling indicates that synthesis of membrane occurs at a linear rate that doubles at a fixed time in each cycle, which coincides with the period of zero net synthesis. Rates of membrane synthesis measured by pulse labeling during the period of rapid membrane synthesis are significantly less than indicated by steady-state labeling. These discrepancies are consistent with the hypothesis that during the cell cycle certain proteins are added to the membrane from the cytoplasm and that during the period of zero net synthesis there is an efflux of proteins from the membrane. Evidence in favor of this has been presented. The activity of succinic dehydrogenase (a representative of class c) varies in a step-wise manner with periods of rapid increase, approximately coincident with bursts of membrane protein synthesis, alternating with periods without any increase in activity. The activities of malate dehydrogenase (class a) and reduced nicotinamide adenine dinucleotide dehydrogenase (class b) increased throughout the cell cycle. Phospholipid synthesis is continuous throughout the cell cycle.

Process of cellular division in Escherichia coli: physiological study on thermosensitive mutants defective in cell division

Thermosensitive fts mutants of Escherichia coli belonging to seven previously identified genetic classes (ftsA to ftsG) were studied from a physiological standpoint. These mutants immediately stopped dividing and formed multinucleated filaments when the temperature was shifted to 41 C. Macromolecular syntheses (deoxyribonucleic acid), ribonucleic acid, cell mass, and murein) continued exponentially for at least 40 to 120 min. The number of surviving bacteria remained constant during the time of incubation, and this number began to decrease exponentially, as the rate of cell mass increase leveled off from the initial rate. The recovery of cell division at 30 C in these filamentous cells was studied after 60 min of incubation at 41 C. The existence of three types of mutants was shown. The ftsA and ftsE mutants resumed cell division without new protein synthesis; ftsD mutants resumed cell division only if new protein synthesis occured, while ftsB, C, F and G mutants did not resume cell division at all. No alteration in the cell envelope was detected by the method used here, although the ftsA, B, D, F and G mutations, in contrast with ftsC and E, caused an increased resistance to penicillin G. It was also shown that the recA mutation did not suppress the effect of the fts mutations and that none of the lysogenic fts mutants induced prophage multiplication while forming filaments. The effects of osmotic pressure and salts which rescue the mutant phenotype is described.

Temperature-sensitive divisionless mutant of Bacillus subtilis defective in the initiation of septation

A temperature-sensitive divisionless mutant of Bacillus subtilis 168, tms-12, is shown to be defective in an early step in septum formation at the restrictive temperature. The nature of this defect has been studied by comparing the growth and composition of mutant and wild-type (tms-12(+)) cells at the restrictive (48 C) and permissive (34 C) temperatures. At 48 C, tms-12 cells grow as nonseptate, multinucleate filaments. Filamentation does not appear to be a result of alterations in properties of the cell wall, since the ratio of mucopeptide to teichoic acid, the autolytic activity, and the ability of the walls to protect cells against osmotic shock are comparable in tms-12 filaments and tms-12(+) bacilli grown at 48 C. Synthesis of deoxyribonucleic acid and the segregation of nucleoids also proceed normally during filamentation. The synthesis of membrane, however, is delayed during filamentation of tms-12. No gross alterations were observed in the protein or lipid composition of membranes isolated from mutant filaments. Septum formation resumes when filaments are returned to 34 C and appears to be associated with an increased synthesis of membrane. The occurrence of septa was monitored both by microscopic observation of cross walls and by assays of the number of viable protoplasts released from bacillary filaments upon removal of the cell wall. Septation recovery can be blocked by inhibitors of ribonucleic acid and protein synthesis added during, but not after, the first 7 min of recovery at 34 C. By contrast, inhibition of deoxyribonucleic synthesis does not block recovery.