Location and composition of spore mucopeptide in Bacillus species

Contrasting evolutionary patterns of spore coat proteins in two Bacillus species groups are linked to a difference in cellular structure

BACKGROUND

The Bacillus subtilis-group and the Bacillus cereus-group are two well-studied groups of species in the genus Bacillus. Bacteria in this genus can produce a highly resistant cell type, the spore, which is encased in a complex protective protein shell called the coat. Spores in the B. cereus-group contain an additional outer layer, the exosporium, which encircles the coat. The coat in B. subtilis spores possesses inner and outer layers. The aim of this study is to investigate whether differences in the spore structures influenced the divergence of the coat protein genes during the evolution of these two Bacillus species groups.

RESULTS

We designed and implemented a computational framework to compare the evolutionary histories of coat proteins. We curated a list of B. subtilis coat proteins and identified their orthologs in 11 Bacillus species based on phylogenetic congruence. Phylogenetic profiles of these coat proteins show that they can be divided into conserved and labile ones. Coat proteins comprising the B. subtilis inner coat are significantly more conserved than those comprising the outer coat. We then performed genome-wide comparisons of the nonsynonymous/synonymous substitution rate ratio, dN/dS, and found contrasting patterns: Coat proteins have significantly higher dN/dS in the B. subtilis-group genomes, but not in the B. cereus-group genomes. We further corroborated this contrast by examining changes of dN/dS within gene trees, and found that some coat protein gene trees have significantly different dN/dS between the B subtilis-clade and the B. cereus-clade.

CONCLUSIONS

Coat proteins in the B. subtilis- and B. cereus-group species are under contrasting selective pressures. We speculate that the absence of the exosporium in the B. subtilis spore coat effectively lifted a structural constraint that has led to relaxed negative selection pressure on the outer coat.

History of science – spores

Bacterial endospores were first studied 130 years ago by Cohn in 1876 and independently by Koch in the same year. Although spore dormancy and resistance have been much studied since then, questions still remain concerning the basic mechanisms and the kinetics of heat inactivation in particular. Likewise, the extreme dormancy and longevity of spores was recognized early on and later greatly extended but still evade complete understanding. Evidence has accumulated for the involvement of specific spore components such as calcium, dipicolinic acid, small acid soluble proteins in the core and peptidoglycan in the cortex. Involvement of physical factors too, such as the relative dehydration of the core, maybe in a high-viscosity state or even in a glassy state, has added to appreciation of the multicomponent nature of dormancy and resistance. Spore-former morphology formed the basis for early classification systems of sporeformers from about 1880 and consolidated in the mid-1900s, well prior to the use of modern genetic procedures. With respect to sporulation, groundbreaking sequence studies in the 1950s provided the basis for later elucidation of the genetic control widely relevant to many cell differentiation mechanisms. With respect to the breaking of dormancy (activation and germination), the elucidation of mechanisms began in the 1940s following the observations of Hills at Porton who identified specific amino acid and riboside 'germinants', and laid the basis for the later genetic analyses, the identification of germinant receptor genes and the elucidation of key germination reactions. The nonexponential nature of germination kinetics has thwarted the development of practical Tyndallization-like processing. So inactivation by heat remains the premier method of spore control, the basis of a huge worldwide industry, and still relying on the basic kinetics of inactivation of Clostridium botulinum spores, and the reasoning regarding safety first evolved by Bigelow et al. in 1920 and Esty and Meyer in 1922. 'Newer' processes such as treatment with ionizing radiation (first proposed in 1905) and high hydrostatic pressure (first proposed in 1899) may be introduced if consumer resistance and some remaining technical barriers could be overcome.

The composition and structure of bacterial spores

The composition of the insoluble "integuments" and soluble "contents" fractions of spores of four Bacillus species of widely differing heat resistance were compared. Electron microscopy of thin sections was also used to determine and compare the morphological structures in the integument preparations. The soluble fractions of the thermophiles, B. coagulans and B. stearothermophilus, had a higher content of hexose and dipicolinic acid. The hexose content of both fractions of the four species was related to heat resistance. Integument fractions consisted chiefly of protein together with variable amounts of the mucopeptide constituents, alpha, epsilon-diaminopimelic acid (DAP) and hexosamine. In the thermophiles the DAP and hexosamine were found chiefly in the insoluble integuments fractions, while in B. cereus and B. subtilis most of this material was soluble. Integument preparations, containing mainly protein with little mucopeptide, consisted chiefly of outer and inner spore coats, while preparations having more mucopeptide contained also residual cortical material and a cortical membrane (possibly the germ cell wall). The results suggest that spore integuments consist of mainly proteinaceous outer and inner coats together with variable amounts of residual cortex and cortical membrane which contain the mucopeptide material.

Protoplast dehydration correlated with heat resistance of bacterial spores

Water content of the protoplast in situ within the fully hydrated dormant bacterial spore was quantified by use of a spore in which the complex of coat and outer (pericortex) membrane was genetically defective or chemically removed, as evidenced by susceptibility of the cortex to lysozyme and by permeability of the periprotoplast integument to glucose. Water content was determined by equilibrium permeability measurement with 3H-labeled water (confirmed by gravimetric measurement) for the entire spore, with 14C-labeled glucose for the integument outside the inner (pericytoplasm) membrane, and by the difference for the protoplast. The method was applied to lysozyme-sensitive spores of Bacillus stearothermophilus, B. subtilis, B. cereus, B. thuringiensis, and B. megaterium (four types). Comparable lysozyme-resistant spores, in which the outer membrane functioned as the primary permeability barrier to glucose, were employed as controls. Heat resistances were expressed as D100 values. Protoplast water content of the lysozyme-sensitive spore types correlated with heat resistance exponentially in two distinct clusters, with the four B. megaterium types in one alignment, and with the four other species types in another. Protoplast water contents of the B. megaterium spore types were sufficiently low (26 to 29%, based on wet protoplast weight) to account almost entirely for their lesser heat resistance. Corresponding values of the other species types were similar or higher (30 to 55%), indicating that these spores depended on factors additional to protoplast dehydration for their much greater heat resistance.

Autolysis of Thermoactinomyces vulgaris spores lacking carbon dioxide during germination

Ultrathin sections of early germinating endospores of Thermoactinomyces vulgaris were studied by electron microscope. Only spores aerated with an air-CO2 mixture (5% CO2) grow out, while spores aerated with air (0.03% CO2) lyse by the 25th min of inoculation. The lysis is due to progressive, unlimited degradation of the spore integuments and a lack of cell wall formation around the spore protoplast. The requirement of CO2 for outgrowth could not be replaced by oxaloacetate. CO2 seems to be needed to energize the dormant cytoplasmic membrane of the spore to render it capable of initiating active transport processes and of synthesizing the germ cell wall.

Bacterial spore heat resistance correlated with water content, wet density, and protoplast/sporoplast volume ratio

Five types of dormant Bacillus spores, between and within species, were selected representing a 600-fold range in moist-heat resistance determined as a D100 value. The wet and dry density and the solids and water content of the entire spore and isolated integument of each type were determined directly from gram masses of material, with correction for interstitial water. The ratio between the volume occupied by the protoplast (the structures bounded by the inner pericytoplasm membrane) and the volume occupied by the sporoplast (the structures bounded by the outer pericortex membrane) was calculated from measurements made on electron micrographs of medially thin-sectioned spores. Among the various spore types, an exponential increase in the heat resistance correlated directly with the wet density and inversely with the water content and with the protoplast/sporoplast volume ratio. Altogether with results supported a hypothesis that the extent of heat resistance is based in whole or in part on the extent of dehydration and diminution of the protoplast in the dormant spore, without implications about physiological mechanisms for attaining this state.

Germination properties of a spore coat-defective mutant of Bacillus subtilis

The presence of the gerE36 mutation in strains of Bacillus subtilis 168 resulted in poor germination of their spores in a range of germinants, as measured by the fall in absorbance of spore suspensions. Although resistant to heat and organic solvents, spores were sensitive to lysozyme; electron microscopy revealed that their coat structure was incomplete. These spores responded to germinants by losing heat resistance and changing from phase bright to phase gray. The release of dipicolinic acid and the fall in absorbance of spore suspensions reached only 75 and 50% of wild-type levels, respectively, but followed the same time course as the loss of heat resistance. Although the germination response was incomplete, the concentration of L-alanine required to elicit it was the same for the mutant as for the wild type. The properties of mutant spores suggest that an intact spore coat is not required for the initial interaction between germinant and spore, but that the coat layers may contain molecules important in later stages of germination. In transduction with phage SPP1, the gerE36 mutation mapped between citF and ilvB and was 90% cotransduced with citF2. The gerE mutation identifies the location of a gene important for the progress of late stages of spore formation.

Bacillus megaterium sporal peptidoglycan synthesis studied by high-resolution autoradiography

Cells of a Dap- Lys- mutant strain of Bacillus megaterium were pulse labeled with [3H]diaminopimelic acid at different times of growth and sporulation. They were processed for radioactivity measurements and high-resolution autoradiography either just after the pulse or after a chase in a nonradioactive medium until refractile forespores started to appear at time (t)4,5. In the pulse-labeled cells, autoradiographs and radioactivity measurements showed that the radioactivity incorporated during a pulse decreased abruptly after t0 and stayed at a low level until t5, although the forespore wall and cortex were formed between t4 and t5. In the pulse-chased bacteria, the acid-insoluble radioactivity, as well as the number of silver grains on autoradiographs, increased during the chase in cells labeled at t1 to t2, whereas it decreased in those labeled before t0. Furthermore, analysis of silver grain distribution showed that, in stage IV bacteria, grains were distributed at the outside of the forespore, mostly on the sporangium cell wall, when pulse-labeling occurred before or at t0; they were located along the cortex and in the forespore cytoplasm when labeling was made at t1 or t2. These facts show that [3H]diaminopimelic acid necessary for spore envelope synthesis was incorporated before their morphological appearance. Free or small diaminopimelic acid precursors entered the sporangium between t1 and t2. The appearance of silver grains in the forespore cytoplasm suggests that the forespore is implicated in sporal peptidoglycan synthesis.

Delayed germination of Bacillus cereus T spores after treatment with trichloroacetic acid and their reactivation by heating

Treatment of Bacillus cereus T spores with trichloroacetic acid delayed their germination. The extent of retardation depended on the concentration of trichloroacetic acid, and the temperature, pH and duration of treatment. The effect was completely reversed by subsequent heating, and this restoration of germination also depended on the temperature and duration of heat treatment. Fourteen compounds were examined for their ability to suppress germination of spores. The halogenated fatty acids tested, such as trifluoro-, tribromo-, and dichloroacetic acid, caused suppression of germination, whereas other compounds, i.e., free fatty acids and amino acids, did not. It is concluded that the charge distribution of fatty acid molecules is important for their effect in suppressing germination of spores.

Effect of trichloroacetic acid treatment on certain properties of spores of Bacillus cereus T

Spores of Bacillus cereus T treated with trichloroacetic acid (6.1--61.2 mM) were compared with untreated spores, and as the concentration of the chemical increased, the following alterations in spore properties were found: (1) the extent of germination decreased irrespective of the germination medium used; (2) the spores became sensitive to sodium hydroxide (1 N) and hydrochloric acid (0.27 N), but not to lysozyme (200 micrograms/ml); (3) loss of dipicolinate increased on subsequent heating; and (4) the spores became more sensitive to heat. However, trichloroacetic acid-treated spores were still viable and there was no significant change in spore components. The mechanism of action of trichloroacetic acid is discussed.

Distribution of peptidoglycan synthetase activities between sporangia and forespores in sporulating cells of Bacillus sphaericus

Sporulating cells of Bacillus sphaericus 9602 containing fully engulfed forespores at different stages of maturity were broken by ultrasonic disruption, followed by grinding with alumina. In this way soluble enzymes derived mainly from the sporangial or from the forespore cytoplasms were obtained. Diaminopimelate ligase activity is required exclusively for cortical peptidoglycan synthesis, is absent during vegetative growth, and is synthesized during forespore maturation. It is found exclusively in the sporangial cytoplasm. L-lysine ligase is required for vegetative cell wall peptidoglycan synthesis but not for cortex synthesis. It is found in both fractions, but it has a fourfold higher specific activity in the forespore cytoplasm. Other enzymes that are required for synthesis of the nucleotide-pentapeptide precursors of both cortical and vegetative cell wall peptidoglycans are found in similar specific activities in both compartments. Mature spores, free of any residual sporangial material, have specific activities of all of these enzymes and of L-lysine ligase similar to those in forespores and in vegetative cells and are devoid of diaminopimelate ligase activity. Thus, the differential expression of at least one gene required for spore cortex synthesis in B. sphaericus occurs exclusively in the sporangial cytoplasm.

Transcriptional control of peptidoglycan precursor synthesis during sporulation in Bacillus sphaericus

Synthesis of enzymes functional in the synthesis of nucleotide precursors of peptidoglycan ceases upon initiation of sporulation in Bacillus sphaericus. During sporulation, two periods of synthesis of these enzymes occur. The first starts at spore septum formation and is conincident with forespore engulfment; it involves the synthesis of those enzymes required for making the precursor of vegetative-type peptidoglycan, including L-lysyl ligase but no mesodiaminopimelyl ligase. The second period occurs shortly before the appearance of cortex. It involves the synthesis of diaminopimelyl ligase and the other enzymes needed for making the precursor of cortical peptidoglycan, but not lysyl ligase. Both events are a consequence of derepression at the level of transcription. Neither period of synthesis occurs in asporogenous mutants whose morphological block is at the point of spore septum formation.

Heat resistance of bacterial endospores and concept of an expanded osmoregulatory cortex

The extreme resistance of bacterial endospores to heat may result from dehydration of the central protoplast brought about and maintained by osmotic activity of expanded electronegative peptidoglycan polymer, and positively charged counterions associated with it, in the surrounding cortex. The cortex may thus act as a specialised osmoregulatory organelle. Changes in the environment which would be expected reversibly to affect osmotic properties alter the heat resistance of spores.

Use of ultraviolet radiation to locate dipicolinic acid in Bacillus cereus spores

A novel method is described that allows a direct determination of the location of a portion of the dipicolinic acid (DPA) in spores. Ultraviolet (UV) irradiation is shown to cause cross-linkage of DPA to spore proteins which have the characteristics of membrane proteins. We suggest that DPA resides in the inner forespore membrane (IFSM) and spore cytoplasm (i.e., the spore protoplast). Only that portion of the DPA in the vicinity of the IFSM appeared to form UV-induced DPA-protein adducts.

Germination of heat- and alkali-altered spores of Clostridium perfringens type A by lysozyme and an initiation protein

The normal system functioning in the utilization of metabolizable germinants by both heat-sensitive and heat-resistant spores of Clostridium perfringens was inactivated by heat or by treatment of the spores with alkali to remove a soluble coat protein layer. Altered spores were incapable of germination (less than 1%) and outgrowth (less than 0.0005%) in complex media without the addition of either lysozyme or an initiation protein produced by C. perfringens. The addition of either of these agents permitted, in the case of alkali-treated spores, both 90 to 95% germination and outgrowth, as measured by colony formation. In the case of heat-damaged spores, only 50% germination and 2% outgrowth resulted from addition of the initiation protein, whereas lysozyme permitted 85% germination and 8% outgrowth. Alteration of the spores by heat or alkali apparently inactivated the normal lytic system responsible for cortical degradation during germination. Kinetics of production of the initiation protein and conditions affecting both its activity and that of lysozyme on altered spores are described.

Spore refractility in variants of Bacillus cereus treated with actinomycin D

Refractility as indicated by light microscopy, electron microscopy of thin sections, and freeze fracture etching was increased and maintained in a cortexless mutant, A(-)1, of Bacillus cereus var. alesti by the addition during sporulation stage 4 of actinomycin D, which prevents the terminal lysis of spore core associated with sporulation in this organism. (45)Calcium uptake levels and dipicolinic acid (DPA) content were similarly maintained. The location of these components appears to be in the spore protoplast. In the parent A(-), treated with actinomycin D during stage 4, spore particles with similar morphology to the mutant, that is without a cortex and with the characteristics of refractility, were obtained. A major difference in sensitivity to actinomycin D between the processes of (45)Ca uptake and DPA synthesis was observed. Some heat resistance in A(-) made cortexless by actinomycin D could be observed. These studies indicate that the role of the cortex is not to produce the dehydrated refractile spore state but to maintain it.

Formation of protoplasts from resting spores

Coat-stripped spores suspended in hypertonic solutions and supplied with two essential cations can be converted into viable protoplasts by lysozyme digestion of both cortex and germ cell wall. Calcium ions are necessary to prevent membrane rupture, and magnesium ions are necessary for changes indicative of hydration of the core, particularily the nuclear mass. Since remnant spore coat covered such protoplasts of Bacillus subtilis and the germ cell wall of B. cereus spores is not lysozyme digestible, coatless spores of B. megaterium KM were more useful for these studies. Lysozyme digestion in cation-free environment produced a peculiar semi-refractile spore core free of a cortex but prone to rapid hydration and lytic changes on the addition of cations. Strontium could replace Ca(2+) but Mn(2+) could not replace Mg(2+) in these digestions. When added to the spores, dipicolinic acid and other chelates appeared to compete with the membrane for the calcium needed for stabilization during lysozyme conversion to protoplasts. It is argued that calcium could function to stabilize the inner membrane anionic groups over the anhydrous dipicolinic acid-containing core of resting spores.

Sporulation of a cortexless mutant of a variant of Bacillus cereus

A stage 4 sporulation mutant of a strain of Bacillus cereus var. alesti fails to synthesize a cortex although all other structural components appear normal. With terminal lysis the spore core as well as the sporangium is lysed. Both the uptake of (45)Ca and the synthesis of dipicolinic acid (DPA) are similar to these activities in the parent strain, but these components (DPA and Ca) are lost to the medium with the drastic lysis. The first stage of diaminopimelic acid incorporation, that into germ cell wall mucopeptide, is intact in the mutant; the second stage, that into cortical mucopeptide, is absent. These biochemical studies as well as phospholipid metabolism and freeze-etch analysis suggest the lesion lies in the outer forespore membrane.

Cell wall polymers of Bacillus sphaericus 9602. II. Synthesis of the first enzyme unique to cortex synthesis during sporulation

The cell wall peptidoglycan of vegetative cells of Bacillus sphaericus 9602 contains l-lysine and d-isoasparagine and is devoid of diaminopimelic acid (Dap), whereas the peptidoglycan of its spore cortex is devoid of l-lysine and d-isoasparagine and contains meso-Dap. These two structures have a common biosynthetic precursor, uridine-diphospho-N-acetylmuramyl-l- alanyl-d-glutamic acid, which accepts either l-lysine or meso-Dap, the latter reaction being the first unique to the synthesis of the spore cortex peptidoglycan. l-lysine-adding activity decays at the end of vegetative growth to a level which is maintained until Dap-adding activity appears, when it declines rapidly again. Dap-adding activity is not detectable in refractile spores, in vegetative cells, or in sporulating cells until about 4 hr after the end of vegetative growth, when it increases rapidly for about 1.5 hr in a process dependent on continued protein and ribonucleic acid (RNA) synthesis. This process apparently involves transcription and translation during this period of a "sporulation-specific" gene whose product is essential for and unique to sporulation. It is closely followed by the acquirement of refractility. Another sporulation-specific gene, that for dipicolinate synthase, is apparently transcribed and translated in an overlapping period commencing about 0.5 hr later, although dipicolinate does not accumulate rapidly until 1.5 hr later, when about 75% of the cells are already refractile. Inhibition of protein synthesis with chloramphenicol or of RNA synthesis with streptolydigin inhibited accumulation of these enzymes in sporulating cells; this inhibition could be reversed by washing out the antibiotics after 1.5 hr. Sporulation recommenced with an unaltered sequence of events but with poorer synchrony. There was no evidence for a messenger RNA for either enzyme of lifetime greater than a small fraction of the period of enzyme accumulation, although dilution with 10 volumes of fresh medium failed to prevent synthesis of Dap-adding enzyme in cells which had become terminally swollen, a process preceding enzyme synthesis by about 1.5 hr. The synthesis of this enzyme in B. sphaericus is apparently dependent on programmed transcription of the appropriate gene.

Growth, sporulation, and enzyme defects of glucosamine mutants of Bacillus subtilis

Two glucosamine (GCA)-requiring mutants have been isolated which grow on glucose minimal or nutrient sporulation medium only in the presence of either GCA or acetyl-GCA. They lack the l-glutamine-d-fructose-6-phosphate aminotransferase (EC 2.6.1.13), which is repressible by GCA and whose activity in the standard strain decreases after cessation of growth. But the mutants can grow on GCA as sole carbon and ammonia source, because GCA induces the synthesis of 2-amino-2-deoxy-d-glucose-6-phosphate ketol-isomerase (deaminating) (EC 5.3.1.10). With respect to sporulation, the GCA-requiring mutants are in a serious dilemma, as GCA represses the onset of massive sporulation and yet a small amount of GCA-6-phosphate derivatives is necessary to allow sporulation. When GCA is continuously provided in small quantities, sporelike particles are produced which contain little or no spore cortex but a normal spore coat. Apparently, GCA derivatives are needed especially for cortex formation. Many of the sporelike particles can produce colonies after octanol, but not after heat treatment. When they are purified by treatment with lysozyme and sodium dodecylsulfate, they do not show the decrease in optical density at 600 nm typical of germination nor do they produce offspring.

Structure of the peptidoglycan of bacterial spores: occurrence of the lactam of muramic acid

Six major oligosaccharides were released from the peptidoglycan of spores of Bacillus subtilis by lysozyme treatment. They were isolated and characterized as a disaccharide, tetrasaccharide, and hexasaccharide composed of equal amounts of muramic acid and glucosamine and containing two, three, and four acetyl groups, respectively. Three of the compounds were substituted by a single L-alanine residue, and the other three by a single tetrapeptide substituent on the acetylmuramic acid residue at the reducing end of each compound. The other muramic acid residue in the tetrasaccharides (and two of the three in the hexasaccharides) were shown to be present as muramic lactams, a sugar not previously found in nature and, hence, a unique spore constituent. Other features of the structure of spore peptidoglycan are discussed.

Comparative ultrastructure of selected aerobic spore-forming bacteria: a freeze-etching study

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Germination of single bacterial spores

Changes in refractility and optical density occurring in individual spores of Bacillus cereus T and B. megaterium QM B1551 during germination were investigated by use of a Zeiss microscope photometer. The curves revealed that the germination process in single spores had two distinct phases; an initial rapid phase was followed by a second slower phase. Under the experimental condition employed, the first phase of germination of B. cereus spores lasted for approximately 75 +/- 15 sec, whereas the second phase lasted for 3 to 4.5 min. In B. megaterium spores, the first phase was observed to last for approximately 2 min and the second phase for more than 7 min. The duration of the second phase was dependent on conditions employed for germination. The kinetics of the first phase were strikingly similar under all conditions of physiological germination. Time-lapse phase-contrast microscopy of germinating spores also revealed the biphasic nature of germination. It was postulated that the first phase represents changes induced by an initial partial hydration of the spore and release into the medium of dipicolinic acid, whereas the second phase reflects degradation of the cortex and hydration of the core.

Effect of lysozyme on resting spores of Bacillus megaterium

Resting spores of Bacillus megaterium ATCC 9885 were found to be markedly affected by lysozyme. Exposure to as little as 1.5 mug of lysozyme per ml caused the spores to lose refractility, the darkened spores to shed their coat structures, and the spore central bodies to lyse. The spores of seven other strains of B. megaterium and seven other Bacillus species were not similarly affected by lysozyme. Proteolytic enzymes such as pronase, trypsin, pepsin, and subtilisin did not induce the change. The action of lysozyme differed in certain important respects from that of common "physiological" germinants. Its action was considered to be direct via its enzymatic attack on exposed sites directly accessible in the resting spores of B. megaterium ATCC 9885.

Ratio of teichoic acid and peptidoglycan in cell walls of Bacillus subtilis following spire germination and during vegetative growth

Cell walls were isolated from cells of Bacillus subtilis strain Marburg during synchronous outgrowth of spores, during the two synchronous cell divisions which followed, and at various times during exponential and early stationary growth. The amounts of teichoic acid and peptidoglycan components were determined in each cell wall preparation. The peptidoglycan is composed of hexosamine, alanine, diaminopimelic acid, and glutamic acid. The ratio of these was relatively constant in the cell walls at each stage of growth. The teichoic acid is composed of glycerol, phosphate, glucose, and ester-linked alanine. With the exception of glucose and ester-linked alanine, the ratios of these components were relatively constant throughout the growth cycle. There was a slight increase in the glucose content of the teichoic acid as the cells aged. There was no correlation between the amount of ester-linked alanine and the stage of growth. The ratio of teichoic acid (based upon phosphate content) to peptidoglycan (based upon diaminopimelic acid content) remained at nearly a constant level throughout the growth cycle. The conclusion is presented that these two cell wall polymers are coordinately synthesized during spore outgrowth and throughout the vegetative growth cycle.

Correlation between spore structure and spore properties in Bacillus megaterium

The spores of six strains of Bacillus megaterium were divided into two distinct groups on the basis of germination. Three of the strains germinated in a mixture of l-alanine and inosine (AL type spores), and three strains germinated in a mixture of glucose and potassium nitrate (GN type spores); recriprocal germination in the respective solutions did not occur. The AL spores and the GN spores were morphologically distinct. Other differences between the two spore groups included germination inhibition characteristics, dipicolinic acid content, hexosamine content, phosphorus and magnesium content, spore coat features, ion exchange properties, and heat resistance. A correlation appears to exist between spore morphology and certain other spore properties in strains of B. megaterium.

Variation in the fine structure of a marine achromobacter and a marine pseudomonad grown under selected nutritional and temperature regimes

Certain features of the fine structure of a marine achromobacter and a marine pseudomonad were dependent upon the conditions of growth. Cells of achromobacter grown at 10 C in a low peptone-seawater (SW) medium displayed the characteristic morphology of the achromobacter: a regularly undulant outer element of the cell wall and a planar inner element, tightly packed ribonucleoprotein (RNP) particles in the cytoplasm, deoxyribonucleic acid (DNA) disposed in a lobate manner, and dense inclusion bodies. Few mesosomes, however, were seen. Cells of achromobacter grown at 10 C in a high peptone-SW medium had larger and more highly organized mesosomes. At 22 C, in a low peptone-SW medium, no mesosomes were seen, but the inclusions were more frequently seen and were larger in the achromobacter cells. At 22 C, in a high peptone-SW medium, these cells revealed the greatest variation in cellular morphology. They contained both small and large mesosomes, or no mesosomes, and both small and large inclusions, or no inclusions. Pseudomonad cells at 10 C in a low peptone-SW medium revealed a typical gram-negative morphology: double-layered, irregularly undulant cell wall; more nearly planar cytoplasmic membrane; densely stained, lightly packed RNP particles; finely fibrillar, axially disposed DNA; simple mesosomes. At 10 C, in a high peptone-SW medium, pseudomonad cells revealed associated strands of material and intracytoplasmic ringlike structures. At 22 C, in a low peptone-SW medium, pseudomonad cells had a more undulant cell-wall and a more nearly planar cytoplasmic membrane. At 22 C, in a high peptone-SW medium, these cells revealed prominent blebs of the cell wall.

Glycopeptide synthesis during sporulation of Bacillus megaterium

The present study was initiated to determine the amount of glycopeptide synthesized during sporulation of Bacillus megaterium. The glycopeptide fraction was isolated quantitatively from vegetative cells, sporulated cells, and free spores, and then assayed for amino sugars. The yields of glycopeptide hexosamine (GPH) in these preparations were compared on the basis of number of cells. During the early stationary phase of cultural growth, cells continued to synthesize cell wall material even though they did not divide or increase in size significantly. In the sporulation medium GPH synthesis was synchronized with the development of the endospore within the bacilli. During this period GPH formation occurred at an increased rate. Synthesis terminated as free spores were liberated from their sporangia. The total amount of GPH synthesized in the sporulating bacilli could be accounted for in the cleaned, free spores.