Protein synthesis and breakdown in the mother-cell and forespore compartments during spore morphogenesis in Bacillus megaterium

Proteomic analysis of Ketogulonicigenium vulgare under glutathione reveals high demand for thiamin transport and antioxidant protection

Ketogulonicigenium vulgare, though grows poorly when mono-cultured, has been widely used in the industrial production of the precursor of vitamin C with the coculture of Bacillus megaterium. Various efforts have been made to clarify the synergic pattern of this artificial microbial community and to improve the growth and production ability of K. vulgare, but there is still no sound explanation. In previous research, we found that the addition of reduced glutathione into K. vulgare monoculture could significantly improve its growth and productivity. By performing SEM and TEM, we observed that after adding GSH into K. vulgare monoculture, cells became about 4–6 folds elongated, and formed intracytoplasmic membranes (ICM). To explore the molecular mechanism and provide insights into the investigation of the synergic pattern of the co-culture system, we conducted a comparative iTRAQ-2-D-LC-MS/MS-based proteomic analysis of K. vulgare grown under reduced glutathione. Principal component analysis of proteomic data showed that after the addition of glutathione, proteins for thiamin/thiamin pyrophosphate (TPP) transport, glutathione transport and the maintenance of membrane integrity, together with several membrane-bound dehydrogenases had significant up-regulation. Besides, several proteins participating in the pentose phosphate pathway and tricarboxylic acid cycle were also up-regulated. Additionally, proteins combating intracellular reactive oxygen species were also up-regulated, which similarly occurred in K. vulgare when the co-cultured B. megaterium cells lysed from our former research results. This study reveals the demand for transmembrane transport of substrates, especially thiamin, and the demand for antioxidant protection of K. vulgare.

Integrated proteomic and metabolomic analysis of an artificial microbial community for two-step production of vitamin C

An artificial microbial community consisted of Ketogulonicigenium vulgare and Bacillus megaterium has been used in industry to produce 2-keto-gulonic acid (2-KGA), the precursor of vitamin C. During the mix culture fermentation process, sporulation and cell lysis of B. megaterium can be observed. In order to investigate how these phenomena correlate with 2-KGA production, and to explore how two species interact with each other during the fermentation process, an integrated time-series proteomic and metabolomic analysis was applied to the system. The study quantitatively identified approximate 100 metabolites and 258 proteins. Principal Component Analysis of all the metabolites identified showed that glutamic acid, 5-oxo-proline, L-sorbose, 2-KGA, 2, 6-dipicolinic acid and tyrosine were potential biomarkers to distinguish the different time-series samples. Interestingly, most of these metabolites were closely correlated with the sporulation process of B. megaterium. Together with several sporulation-relevant proteins identified, the results pointed to the possibility that Bacillus sporulation process might be important part of the microbial interaction. After sporulation, cell lysis of B. megaterium was observed in the co-culture system. The proteomic results showed that proteins combating against intracellular reactive oxygen stress (ROS), and proteins involved in pentose phosphate pathway, L-sorbose pathway, tricarboxylic acid cycle and amino acids metabolism were up-regulated when the cell lysis of B. megaterium occurred. The cell lysis might supply purine substrates needed for K. vulgare growth. These discoveries showed B. megaterium provided key elements necessary for K. vulgare to grow better and produce more 2-KGA. The study represents the first attempt to decipher 2-KGA-producing microbial communities using quantitative systems biology analysis.

A mathematical model for examining growth and sporulation processes of Bacillus subtilis

A mathematical model for the growth process of the bacterium Bacillus subtilis is described. The model is a highly structured one. The driving motivation for development of the model and explicit accounting of major interactions of metabolic networks in the model is related to our eventual goal that the model will be used in the analysis of complex biological patterns. Bacillus subtilis was chosen in our study due to the interesting sporulation process that these cells undergo in response to adverse environmental conditions including nutrient limitation. Sporulation process in B. subtilis represents a primordial prototype of cellular differentiation in higher cellular systems. Thus a model for the B. subtilis growth process should prove extremely useful for understanding questions of developmental biology. The model is capable of simulating the transition between the exponential and stationary phase of growth in a batch culture. Since during the transition period the growth process and the metabolism become decoupled and many transient processes are taking place, such predictions are a severe test for the validity of any model. A strategy to examine the leading hypothesis on B. subtills sporulation implementing GTP as a component which signals sporulation initiation is described.

Compartmentalization of gene expression during Bacillus subtilis spore formation

Gene expression in members of the family Bacillaceae becomes compartmentalized after the distinctive, asymmetrically located sporulation division. It involves complete compartmentalization of the activities of sporulation-specific sigma factors, sigma(F) in the prespore and then sigma(E) in the mother cell, and then later, following engulfment, sigma(G) in the prespore and then sigma(K) in the mother cell. The coupling of the activation of sigma(F) to septation and sigma(G) to engulfment is clear; the mechanisms are not. The sigma factors provide the bare framework of compartment-specific gene expression. Within each sigma regulon are several temporal classes of genes, and for key regulators, timing is critical. There are also complex intercompartmental regulatory signals. The determinants for sigma(F) regulation are assembled before septation, but activation follows septation. Reversal of the anti-sigma(F) activity of SpoIIAB is critical. Only the origin-proximal 30% of a chromosome is present in the prespore when first formed; it takes approximately 15 min for the rest to be transferred. This transient genetic asymmetry is important for prespore-specific sigma(F) activation. Activation of sigma(E) requires sigma(F) activity and occurs by cleavage of a prosequence. It must occur rapidly to prevent the formation of a second septum. sigma(G) is formed only in the prespore. SpoIIAB can block sigma(G) activity, but SpoIIAB control does not explain why sigma(G) is activated only after engulfment. There is mother cell-specific excision of an insertion element in sigK and sigma(E)-directed transcription of sigK, which encodes pro-sigma(K). Activation requires removal of the prosequence following a sigma(G)-directed signal from the prespore.

Analysis by fluorescence microscopy of the development of compartment-specific gene expression during sporulation of Bacillus subtilis

The use of a fluorogenic substrate, 5-octanoylaminofluorescein-di-beta-D-galactopyranoside, for beta-galactosidase has made it possible to visualize enzyme activity in individual cells of sporulating populations of Bacillus subtilis by fluorescence microscopy. lacZ fusions to different sporulation-associated genes have been used to investigate the cell compartmentalization of gene expression during sporulation. A strain with a lacZ fusion to sspA, a gene which is transcribed by E-sigma G at a late stage of sporulation, displayed predominantly compartment-specific fluorescence. Expression of the early-expressed spoIIA locus, which includes the structural gene for sigma F, was seen not to be compartmentalized. Populations of strains with lacZ fusions to gpr and dacF, genes which are transcribed by E-sigma F at intermediate stages of sporulation, included some organisms showing uncompartmentalized fluorescence and others showing compartment-specific fluorescence; the proportion showing compartment-specific fluorescence increased in samples taken later in sporulation. Several possible explanations of the results obtained with gpr and dacF are considered. A plausible interpretation is that sigma F activity is initially not compartmentalized and becomes compartmentalized as sporulation progresses. The progression to compartmentalization does not require the activities of the sporulation-specific factor sigma E or sigma G but may require some product of sigma F activity.

Single amino acid changes in the Bacillus thuringiensis var. israelensis delta-endotoxin affect the toxicity and expression of the protein

Site-directed mutagenesis has been used to change individual amino acids of the larvicidal 27,000 Mr delta-endotoxin of Bacillus thuringiensis var. israelensis. Basic and acidic residues have been systematically replaced by alanine, and the resulting mutant polypeptides analysed for cytolytic and larvicidal activity, and binding to phosphatidyl choline liposomes. Replacement of residues at positions 154, 163, 164, 213 and 225 results in proteins which accumulate as inclusions in recombinant Bacillus subtilis cells similar to the wild-type, but have considerably reduced in-vitro and in-vivo toxicity. One mutant (Glu45 to Ala45) results in a protein that has reduced activity in vitro, but retains wild-type larvicidal toxicity. In addition, seven other mutations of charged residues result in proteins which form small or no inclusions in recombinant cells, despite being produced at levels similar to the wild-type in six out of seven cases. In most instances, the toxicity of these aberrantly expressed proteins is considerably less than the wild-type, although one (Lys124 to Ala124) results in a polypeptide with approximately threefold increased activity in vitro. A secondary structural model is proposed to explain these observations.

Protein turnover and proteolysis during sporulation of Bacillus subtilis

A two-dimensional electrophoretic method was used to show that protein degradation occurs immediately after the end of exponential growth but that its occurrence is masked in the usual assay methods for a 2-h period and that degradation is apparently nonselective with respect to protein molar mass or charge. The results suggest that considerable reutilization of internal amino acids may occur during sporulation regardless of the size of the external chase. Finally, the levels of intracellular proteinase activities present even at the end of exponential phase growth, as measured in vitro, are sufficient to account for the maximum rates of protein degradation observed in vivo.

Precursor processing during the maturation of a spore-coat protein in Bacillus megaterium KM

A protein of apparent mol.wt. 35000 that is extractable from the purified coat fraction of Bacillus megaterium KM spores is synthesized during sporulation as a precursor protein from which a 12-13 amino acid peptide is removed. Cleavage of this small peptide is delayed until 60-90 min after precursor synthesis and is concomitant with the morphological appearance of stage VI. The addition of chloramphenicol, subsequent to precursor synthesis, prevents the appearance of this late processing event. Two-dimensional non-equilibrium pH-gradient gel electrophoresis of the integument extract of forespores isolated at stage V from sporangia pulse-labelled with L-[35S]methionine 1 h before isolation, revealed both unprocessed and processed components. Similar analysis of total protein from the corresponding mother cells revealed only the unprocessed component in relatively small amounts, suggesting that, although the protein may be synthesized in the mother-cell compartment, processing may be restricted to the forespore. Peptide analysis by limited proteolysis was used to examine the relationship between the 35000- and a 17500-mol.wt. coat protein. The possible implications of limited proteolytic processing to maturation of the spore coat are discussed.

Protein synthesis in the isolated forespores from sporulating cells of Bacillus subtilis

Developing forespores were isolated from Bacillus subtilis at different stages of sporulation and protein synthesis in the forespore compartment was examined. Pulse-labeling experiments indicated that [14C]phenylalanine was continuously incorporated into the sporangium throughout sporulation, and at t5 (early stage V of sporulation) 58% of the radioactivity was located in the forespore compartment. Significantly high incorporation of [14C]phenylalanine was observed when the isolated forespores at t5 were incubated with the corresponding mother-cell cytoplasmic fraction or an amino acid mixture. About 73% of the radioactivity incorporated into the isolated forespore at t5 was found in the cytoplasmic fraction and 26% in the membranous fraction. Analysis by sodium dodecyl sulfate-gel electrophoresis showed that the 14C-labeled cytoplasmic protein had a molecular weight of about 20,000, and that a protein having the same molecular weight was present in the t5 forespore as a slight protein band and also in the mature spore as a clear protein band. Gel electrophoresis also revealed that the 14C-labeled membranous-soluble protein (prepared by solubilization with detergents) had broad peaks with molecular weights of about 74,000, 33,000, 20,000, and 12,000.

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.

Turnover of proteins in asporogenic Bacillus megaterium. Evidence for a gradual decrease of the turnover rate

The rate of protein turnover in asporogenic Bacillus megaterium decreases continuously during incubation in a sporulation medium. The capability of equilibration of external amino acids with amino acids in the metabolic pool of non-growing cells was retained for at least 5 h. Leucine, while repressing the synthesis of the exocellular protease, does not significantly influence the course of protein degradation in vivo. Transfer of non-growing cells after 4 h to a fresh sporulation medium does not influence the rate of protein degradation. The gradual decrease of the rate of protein turnover in non-growing cells of the asporogenic variant is thus not an artifact caused by a decreased uptake of amino acids by cells or by conditions under which the protein turnover is determined.

Multiple acid proteinases in the cellular slime mould Dictyostelium discoideum

Proteinase activity in the cellular slime mould Dictyostelium discoideum has been analyzed by electrophoresis on polyacrylamide gels containing denatured hemoglobin. At least eight bands due to acid proteinases have been defined using extracts of myxamoebae, four bands A-D which move faster than the fifth and major band E, a minor band E' which moves just behind E and two slow bands G and H. Fruiting body formation was accompanied by the appearance of one new proteinase band F. The proteinases were present in extracts of both axenically-grown and bacterially-grown cells. Differences between the pH dependence and stability of the individual proteinases were detected. Inhibitor studies suggested that the faster proteinases A-D may be cathepsin B-like, whilst the slower enzymes E, E' and F do not fit readily into any known group of proteinases since they were sensitive to HgCl2 but not to other inhibitors of cathepsin B and not to inhibitors of cathepsin D-like proteinases under standard conditions. None of the proteinases was apparently formed during or after preparation of extracts and the proteinases could be re-run on polyacrylamide gels to give only the band expected from the first run. The bands are believed to reflect multiple proteinase activities within the cell.

Cyanide-resistant electron transport in sporulating Bacillus megaterium KM

The NADH oxidase activity of stage V mother-cell membranes, isolated from sporulating Bacillus megaterium KM, shows a greater inhibition by cyanide and displays this response at lower concentrations of cyanide than the stage V forespore inner membrane. Comparison of the effects of various respiratory inhibitors reveals that the difference in cyanide sensitivity between these membranes is located on the oxidase side of the 2-heptyl-4-hydroxyquinoline N-oxide-sensitive step. Both membranes contain cytochromes a+a3, b-562, b-555, c and d, with three potential oxidases: cytochromes a+a3, o and d. Cyanide difference spectra suggest that cytochromes b-562 and d may be the components involved in the cyanide-resistant electron transport pathway. Membrane ascorbate-N,N,N',N'-tetramethylphenylenediamine and ascorbate 2,6-dichlorophenolindophenol oxidase activities are highly sensitive to cyanide. Evidence is presented for terminal branching of the respiratory chain with branches differing in cyanide sensitivity. The cyanide sensitivity of the NADH oxidase of membranes prepared from various stages of sporulation is compared. Morphogenesis of the mother-cell plasma membrane to a cyanide-sensitive form during stages II and III of sporulation is postulated.

Synthesis of deoxyribonucleic acid, ribonucleic acid, and protein during sporulation of Clostridium perfringens

The kinetics of deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and protein synthesis as well as protein breakdown during sporulation by Clostridium perfringens were determined. Maximum levels of DNA and net RNA synthesis occurred 3 and 2 h, respectively, after inoculation of sporulation medium. The rate of RNA synthesis decreased as sporulation progressed. Deoxyadenosine increased uptake of [14C]uracil and [14C]thymine but depressed the level of sporulation and the formation of heat-resistant spores when added at concentrations above 100 mug/ml. Unlike Bacillus species, net protein synthesis, which was sensitive to chloramphenicol inhibition, continued during sporulation. The rate of protein breakdown during vegetative growth was 1%/h. During sporulation this rate increased to 4.7%/h. When added to sporulation medium at 0 time chloramphenicol reduced protein breakdown to 1%/h. If added at 3 h the rate decreased to 2.1%/h. The role of proteases in this process is discussed.

Biochemical evidence for the reversed polarity of the outer membrane of the bacterial forespore

Measurement of certain membrane-bound enzymic activities was used to study the orientation of the outer membrane of the double-membraned forespore of Bacillus megaterium KM. 2. Adenosine triphosphatase, NADH dehydrogenase and L-malate intact protoplasts, but were readily detected in intact stage II or IV forespores, consistent with reversed polarity of the outer forespore membrane relative to the mother-cell plasma membrane. 3. Measurement of NADH oxidase activity revealed that intact stage III forespores had the same high affinity for NADH as protoplast membrane preparations and protoplast lystates, consistent with ready access of NADH to oxidation sites on the outer forespores membrane. 4. Forespores and protoplasts showed osmometric behaviour in solutions of non-permanent solutes consistent with the presence of an intact permeability barrier in these structures.

Morphogenesis of the membrane-bound electron-transport system in sporulating Bacillus megaterium KM

The properties of electron transport systems present in soluble and particulate fractions of spores of Bacillus megaterium KM?HAVE BEEN COMPARED WIth those of similar fractions prepared from exponential-phase vegetative cells of this organism. The timing and localization of modifications of the electron transport system occurring during sporulation have been investigated by using a system for separating forespores from mother cells at all stages during development [8]. Spore membranes contained cytochromes a + a3, and o at lower concentrations than in vegetative membranes, and in addition cytochrome c, which was not found in exponential-phase vegetative membranes. An NADH oxidase activity of similar specific activity was found in both spore and vegetative membranes but DL-glycerol 3-phosphate and L-malate oxidase activities were found only in vegetative membranes. A soluble NADH oxidase of low specific activity was found in spores and vegetative cells which probably involves a flavoprotein reaction with oxygen because the activity was stimulated by FAD or FMN and difference spectra of concentrated soluble fractions showed spectra typical of a flavoprotein. Particulate NADH oxidase was sensitive to all classical inhibitors of electron transport tested whereas soluble NADH oxidase was insensitive to many of these inhibitors. Cytochrome c was formed between stage I and II of sporulation and this coincided with a five-fold increase in NADH-cytochrome c reductase activity. Forespore membranes had lower contents of cytochromes than sporangial cell membranes but similar levels of NADH and L-malate oxidases; DL-glycerol 3-phosphate oxidase activity could not be detected in either membranes by stage III of sporulation. This characterization of spore electron transport systems provides a basis for suggestions concerning initial metabolic events during spore germination and the effect of a number of germination inhibitors.