Analysis of action of L-alanine analogues in spore germination

Catabolism of germinant amino acids is required to prevent premature spore germination in Bacillus subtilis

Spores of Bacillus subtilis germinate in response to specific germinant molecules that are recognized by receptors in the spore envelope. Germinants signal to the dormant spore that the environment can support vegetative growth, so many germinants, such as alanine and valine, are also essential metabolites. As such, they are also required to build the spore. Here we show that these germinants cause premature germination if they are still present at the latter stages of spore formation and beyond, but that B. subtilis metabolism is configured to prevent this: alanine and valine are catabolized and cleared from wild-type cultures even when alternative carbon and nitrogen sources are present. Alanine and valine accumulate in the spent media of mutants that are unable to catabolize these amino acids, and premature germination is pervasive. Premature germination does not occur if the germinant receptor that responds to alanine and valine is eliminated, or if wild-type strains that are able to catabolize and clear alanine and valine are also present in coculture. Our findings demonstrate that spore-forming bacteria must fine-tune the concentration of any metabolite that can also function as a germinant to a level that is high enough to allow for spore development to proceed, but not so high as to promote premature germination. These results indicate that germinant selection and metabolism are tightly linked, and suggest that germinant receptors evolve in tandem with the catabolic priorities of the spore-forming bacterium.

IMPORTANCE

Many bacterial species produce dormant cells called endospores, which are not killed by antibiotics or common disinfection practices. Endospores pose critical challenges in the food industry, where endospore contaminations cause food spoilage, and in hospitals, where infections by pathogenic endospore formers threaten the life of millions every year. Endospores lose their resistance properties and can be killed easily when they germinate and exit dormancy. We have discovered that the enzymes that break down the amino acids alanine and valine are critical for the production of stable endospores. If these enzymes are absent, endospores germinate as they are formed or shortly thereafter in response to alanine, which can initiate the germination of many different species' endospores, or to valine. By blocking the activity of alanine dehydrogenase, the enzyme that breaks down alanine and is not present in mammals, it may be possible to inactivate endospores by triggering premature and unproductive germination.

Bacterial spore germination receptors are nutrient-gated ion channels

Bacterial spores resist antibiotics and sterilization and can remain metabolically inactive for decades, but they can rapidly germinate and resume growth in response to nutrients. Broadly conserved receptors embedded in the spore membrane detect nutrients, but how spores transduce these signals remains unclear. Here, we found that these receptors form oligomeric membrane channels. Mutations predicted to widen the channel initiated germination in the absence of nutrients, whereas those that narrow it prevented ion release and germination in response to nutrients. Expressing receptors with widened channels during vegetative growth caused loss of membrane potential and cell death, whereas the addition of germinants to cells expressing wild-type receptors triggered membrane depolarization. Therefore, germinant receptors act as nutrient-gated ion channels such that ion release initiates exit from dormancy.

An Alanine Aminotransferase Is Required for Biofilm-Specific Resistance of Aspergillus fumigatus to Echinocandin Treatment

Alanine metabolism has been suggested as an adaptation strategy to oxygen limitation in organisms ranging from plants to mammals. Within the pulmonary infection microenvironment, Aspergillus fumigatus forms biofilms with steep oxygen gradients defined by regions of oxygen limitation. An alanine aminotransferase, AlaA, was observed to function in alanine catabolism and is required for several aspects of A. fumigatus biofilm physiology. Loss of alaA, or its catalytic activity, results in decreased adherence of biofilms through a defect in the maturation of the extracellular matrix polysaccharide galactosaminogalactan (GAG). Additionally, exposure of cell wall polysaccharides is also impacted by loss of alaA, and loss of AlaA catalytic activity confers increased biofilm susceptibility to echinocandin treatment, which is correlated with enhanced fungicidal activity. The increase in echinocandin susceptibility is specific to biofilms, and chemical inhibition of alaA by the alanine aminotransferase inhibitor β-chloro-l-alanine is sufficient to sensitize A. fumigatus biofilms to echinocandin treatment. Finally, loss of alaA increases susceptibility of A. fumigatus to in vivo echinocandin treatment in a murine model of invasive pulmonary aspergillosis. Our results provide insight into the interplay of metabolism, biofilm formation, and antifungal drug resistance in A. fumigatus and describe a mechanism of increasing susceptibility of A. fumigatus biofilms to the echinocandin class of antifungal drugs. IMPORTANCE Aspergillus fumigatus is a ubiquitous filamentous fungus that causes an array of diseases depending on the immune status of an individual, collectively termed aspergillosis. Antifungal therapy for invasive pulmonary aspergillosis (IPA) or chronic pulmonary aspergillosis (CPA) is limited and too often ineffective. This is in part due to A. fumigatus biofilm formation within the infection environment and the resulting emergent properties, particularly increased antifungal resistance. Thus, insights into biofilm formation and mechanisms driving increased antifungal drug resistance are critical for improving existing therapeutic strategies and development of novel antifungals. In this work, we describe an unexpected observation where alanine metabolism, via the alanine aminotransferase AlaA, is required for several aspects of A. fumigatus biofilm physiology, including resistance of A. fumigatus biofilms to the echinocandin class of antifungal drugs. Importantly, we observed that chemical inhibition of alanine aminotransferases is sufficient to increase echinocandin susceptibility and that loss of alaA increases susceptibility to echinocandin treatment in a murine model of IPA. AlaA is the first gene discovered in A. fumigatus that confers resistance to an antifungal drug specifically in a biofilm context.

Mechanisms and Applications of Bacterial Sporulation and Germination in the Intestine

Recent studies have suggested a major role for endospore forming bacteria within the gut microbiota, not only as pathogens but also as commensal and beneficial members contributing to gut homeostasis. In this review the sporulation processes, spore properties, and germination processes will be explained within the scope of the human gut. Within the gut, spore-forming bacteria are known to interact with the host’s immune system, both in vegetative cell and spore form. Together with the resistant nature of the spore, these characteristics offer potential for spores’ use as delivery vehicles for therapeutics. In the last part of the review, the therapeutic potential of spores as probiotics, vaccine vehicles, and drug delivery systems will be discussed.

Dormant spores sense amino acids through the B subunits of their germination receptors

Bacteria from the orders Bacillales and Clostridiales differentiate into stress-resistant spores that can remain dormant for years, yet rapidly germinate upon nutrient sensing. How spores monitor nutrients is poorly understood but in most cases requires putative membrane receptors. The prototypical receptor from Bacillus subtilis consists of three proteins (GerAA, GerAB, GerAC) required for germination in response to L-alanine. GerAB belongs to the Amino Acid-Polyamine-Organocation superfamily of transporters. Using evolutionary co-variation analysis, we provide evidence that GerAB adopts a structure similar to an L-alanine transporter from this superfamily. We show that mutations in gerAB predicted to disrupt the ligand-binding pocket impair germination, while mutations predicted to function in L-alanine recognition enable spores to respond to L-leucine or L-serine. Finally, substitutions of bulkier residues at these positions cause constitutive germination. These data suggest that GerAB is the L-alanine sensor and that B subunits in this broadly conserved family function in nutrient detection.

Alanine, a Novel Growth Substrate for the Acetogenic Bacterium Acetobacterium woodii

Acetogenic bacteria are an ecophysiologically important group of strictly anaerobic bacteria that grow lithotrophically on H2 plus CO2 or on CO or heterotrophically on different substrates such as sugars, alcohols, aldehydes, or acids. Amino acids are rarely used. Here, we describe that the model acetogen Acetobacterium woodii can use alanine as the sole carbon and energy source, which is in contrast to the description of the type strain. The alanine degradation genes have been identified and characterized. A key to alanine degradation is an alanine dehydrogenase which has been characterized biochemically. The resulting pyruvate is further degraded to acetate by the known pathways involving the Wood-Ljungdahl pathway. Our studies culminate in a metabolic and bioenergetic scheme for alanine-dependent acetogenesis in A. woodiiIMPORTANCE Peptides and amino acids are widespread in nature, but there are only a few reports that demonstrated use of amino acids as carbon and energy sources by acetogenic bacteria, a central and important group in the anaerobic food web. Our finding that A. woodii can perform alanine oxidation coupled to reduction of carbon dioxide not only increases the number of substrates that can be used by this model acetogen but also raises the possibility that other acetogens may also be able to use alanine. Indeed, the alanine genes are also present in at least two more acetogens, for which growth on alanine has not been reported so far. Alanine may be a promising substrate for industrial fermentations, since acid formation goes along with the production of a base (NH3) and pH regulation is a minor issue.

Spore Germination

Despite being resistant to a variety of environmental insults, the bacterial endospore can sense the presence of small molecules and respond by germinating, losing the specialized structures of the dormant spore, and resuming active metabolism, before outgrowing into vegetative cells. Our current level of understanding of the spore germination process in bacilli and clostridia is reviewed, with particular emphasis on the germinant receptors characterized in Bacillus subtilis, Bacillus cereus, and Bacillus anthracis. The recent evidence for a local clustering of receptors in a "germinosome" would begin to explain how signals from different receptors could be integrated. The SpoVA proteins, involved in the uptake of Ca2+-dipicolinic acid into the forespore during sporulation, are also responsible for its release during germination. Lytic enzymes SleB and CwlJ, found in bacilli and some clostridia, hydrolyze the spore cortex: other clostridia use SleC for this purpose. With genome sequencing has come the appreciation that there is considerable diversity in the setting for the germination machinery between bacilli and clostridia.

Potentiating Effect of Mandelate and Lactate on Chemically Induced Germination in Members of Bacillus cereus Sensu Lato

Endospores of the genus Bacillus can be triggered to germinate by a limited number of chemicals. Mandelate had powerful additive effects on the levels and rates of germination produced in non-heat-shocked spores of Bacillus anthracis strain Sterne, Bacillus cereus, and Bacillus thuringiensis when combined with l-alanine and inosine. Mandelate had no germinant effect on its own but was active with these germinants in a dose-dependent manner at concentrations higher than 0.5 mM. The maximum rate and extent of germination were produced in B. anthracis by 100 mM l-alanine with 10 mM inosine; this was equaled by just 25% of these germinants when supplemented with 10 mM mandelate. Half the maximal germination rate was produced by 40% of the optimum germinant concentrations or 15% of them when supplemented with 0.8 mM mandelate. Germination rates in B. thuringiensis were highest around neutrality, but the potentiating effect of mandelate was maintained over a wider pH range than was germination with l-alanine and inosine alone. For all species, lactate also promoted germination in the presence of l-alanine and inosine; this was further increased by mandelate. Ammonium ions also enhanced l-alanine- and inosine-induced germination but only when mandelate was present. In spite of the structural similarities, mandelate did not compete with phenylalanine as a germinant. Mandelate appeared to bind to spores while enhancing germination. There was no effect when mandelate was used in conjunction with nonnutrient germinants. No effect was produced with spores of Bacillus subtilis, Clostridium sporogenes, or C. difficileIMPORTANCE The number of chemicals that can induce germination in the species related to Bacillus cereus has been defined for many years, and they conform to specific chemical types. Although not a germinant itself, mandelate has a structure that is different from these germination-active compounds, and its addition to this list represents a significant discovery in the fundamental biology of spore germination. This novel activity may also have important applied relevance given the impact of spores of B. cereus in foodborne disease and B. anthracis as a threat agent. The destruction of spores of B. anthracis, for example, particularly over large outdoor areas, poses significant scientific and logistical problems. The addition of mandelate and lactate to the established mixtures of l-alanine and inosine would decrease the amount of the established germinants required and increase the speed and level of germination achieved. The large-scale application of "germinate to decontaminate" strategy may thus become more practicable.

Inhibitory effect of indole analogs against Paenibacillus larvae, the causal agent of American foulbrood disease

Paenibacillus larvae, a Gram-positive bacterium, causes American foulbrood (AFB) in honey bee larvae (Apis mellifera Linnaeus [Hymenoptera: Apidae]). P. larvae spores exit dormancy in the gut of bee larvae, the germinated cells proliferate, and ultimately bacteremia kills the host. Hence, spore germination is a required step for establishing AFB disease. We previously found that P. larvae spores germinate in response to l-tyrosine plus uric acid in vitro. Additionally, we determined that indole and phenol blocked spore germination. In this work, we evaluated the antagonistic effect of 35 indole and phenol analogs and identified strong inhibitors of P. larvae spore germination in vitro. We further tested the most promising candidate, 5-chloroindole, and found that it significantly reduced bacterial proliferation. Finally, feeding artificial worker jelly containing anti-germination compounds to AFB-exposed larvae significantly decreased AFB infection in laboratory-reared honey bee larvae. Together, these results suggest that inhibitors of P. larvae spore germination could provide another method to control AFB.

The Cooperative and Interdependent Roles of GerA, GerK, and Ynd in Germination of Bacillus licheniformis Spores

When nutrients are scarce, Bacillus species form metabolically dormant and extremely resistant spores that enable survival over long periods of time under conditions not permitting growth. The presence of specific nutrients triggers spore germination through interaction with germinant receptors located in the spore's inner membrane. Bacillus licheniformis is a biotechnologically important species, but it is also associated with food spoilage and food-borne disease. The B. licheniformis ATCC 14580/DSM13 genome exhibits three gerA family operons (gerA, gerK, and ynd) encoding germinant receptors. We show that spores of B. licheniformis germinate efficiently in response to a range of different single l-amino acid germinants, in addition to a weak germination response seen with d-glucose. Mutational analyses revealed that the GerA and Ynd germination receptors function cooperatively in triggering an efficient germination response with single l-amino acid germinants, whereas the GerK germination receptor is essential for germination with d-glucose. Mutant spores expressing only GerA and GerK or only Ynd and GerK show reduced or severely impaired germination responses, respectively, with single l-amino acid germinants. Neither GerA nor Ynd could function alone in stimulating spore germination. Together, these results functionally characterize the germination receptor operons present in B. licheniformis We demonstrate the overlapping germinant recognition patterns of the GerA and Ynd germination receptors and the cooperative functionalities between GerA, Ynd, and GerK in inducing germination.

IMPORTANCE

To ensure safe food production and durable foods, there is an obvious need for more knowledge on spore-forming bacteria. It is the process of spore germination that ultimately leads to food spoilage and food poisoning. Bacillus licheniformis is a biotechnologically important species that is also associated with food spoilage and food-borne disease. Despite its importance, the mechanisms of spore germination are poorly characterized in this species. This study provides novel knowledge on germination of B. licheniformis spores. We characterize the germinant recognition profiles of the three germinant receptors present in B. licheniformis spores and demonstrate that the GerA germinant receptor cooperates with the Ynd and GerK germinant receptors to enable an effective germination response to l-amino acids. We also demonstrate that GerK is required for germination in response to the single germinant glucose. This study demonstrates the complex interactions between germinant receptors necessary for efficient germination of B. licheniformis spores.

Requirements for in vitro germination of Paenibacillus larvae spores

Paenibacillus larvae is the causative agent of American foulbrood (AFB), a disease affecting honey bee larvae. First- and second-instar larvae become infected when they ingest food contaminated with P. larvae spores. The spores then germinate into vegetative cells that proliferate in the midgut of the honey bee. Although AFB affects honey bees only in the larval stage, P. larvae spores can be distributed throughout the hive. Because spore germination is critical for AFB establishment, we analyzed the requirements for P. larvae spore germination in vitro. We found that P. larvae spores germinated only in response to l-tyrosine plus uric acid under physiologic pH and temperature conditions. This suggests that the simultaneous presence of these signals is necessary for spore germination in vivo. Furthermore, the germination profiles of environmentally derived spores were identical to those of spores from a biochemically typed strain. Because l-tyrosine and uric acid are the only required germinants in vitro, we screened amino acid and purine analogs for their ability to act as antagonists of P. larvae spore germination. Indole and phenol, the side chains of tyrosine and tryptophan, strongly inhibited P. larvae spore germination. Methylation of the N-1 (but not the C-3) position of indole eliminated its ability to inhibit germination. Identification of the activators and inhibitors of P. larvae spore germination provides a basis for developing new tools to control AFB.

Does proximity to neighbours affect germination of spores of non-proteolytic Clostridium botulinum?

It is recognised that inoculum size affects the rate and extent of bacterial spore germination. It has been proposed that this is due to spores interacting: molecules released from germinated spores trigger germination of dormant neighbours. This study investigated whether changes to the total number of spores in a system or proximity to other spores (local spore density) had a more significant effect on interaction between spores of non-proteolytic Clostridium botulinum strain Eklund 17B attached to defined areas of microscope slides. Both the number of spores attached to the slides and local spore density (number of spores per mm(2)) were varied by a factor of nine. Germination was observed microscopically at 15 °C for 8 h and the probability of, and time to, germination calculated from image analysis measurements. Statistical analysis revealed that the effect of total spore number on the probability of germination within 8 h was more significant than that of proximity to neighbours (local spore density); its influence on germination probability was approximately four-times greater. Total spore number had an even more significant affect on time to germination; it had a nine-fold greater influence than proximity to neighbours. The applied models provide a means to characterise, quantitatively, the effect of the total spore number on spore germination relative to the effect of proximity to neighbouring spores.

Effect of amino acid substitutions in the GerAA protein on the function of the alanine-responsive germinant receptor of Bacillus subtilis spores

Spores of Bacillus subtilis require the GerAA, GerAB, and GerAC receptor proteins for L-alanine-induced germination. Mutations in gerAA, both random and site directed, result in phenotypes that identify amino acid residues important for receptor function in broad terms. They highlight the functional importance of two regions in the central, integral membrane domain of GerAA. A P324S substitution in the first residue of a conserved PFPP motif results in a 10-fold increase in a spore's sensitivity to alanine; a P326S change results in the release of phase-dark spores, in which the receptor may be in an "activated" or "quasigerminated" state. Substitutions in residues 398 to 400, in a short loop between the last two likely membrane-spanning helices of this central domain, all affect the germination response, with the G398S substitution causing a temperature-sensitive defect. In others, there are wider effects on the receptor: if alanine is substituted for conserved residue N146, H304, or E330, a severe defect in L-alanine germination results. This correlates with the absence of GerAC, suggesting that the assembly or stability of the entire receptor complex has been compromised by the defect in GerAA. In contrast, severely germination-defective mutants such as E129K, L373F, S400F, and M409N mutants retain GerAC at normal levels, suggesting more local and specific effects on the function of GerAA itself. Further interpretation will depend on progress in structural analysis of the receptor proteins.

Characterization of Bacillus anthracis germinant receptors in vitro

Bacillus anthracis begins its infectious cycle as a metabolically dormant cell type, the endospore. Upon entry into a host, endospores rapidly differentiate into vegetative bacilli through the process of germination, thus initiating anthrax. Elucidation of the signals that trigger germination and the receptors that recognize them is critical to understanding the pathogenesis of B. anthracis. Individual mutants deficient in each of the seven putative germinant receptor-encoding loci were constructed via temperature-dependent, plasmid insertion mutagenesis and used to correlate these receptors with known germinant molecules. These analyses showed that the GerK and GerL receptors are jointly required for the alanine germination pathway and also are individually required for recognition of either proline and methionine (GerK) or serine and valine (GerL) as cogerminants in combination with inosine. The germinant specificity of GerS was refined from a previous study in a nonisogenic background since it was required only for germination in response to aromatic amino acid cogerminants. The gerA and gerY loci were found to be dispensable for recognition of all known germinant molecules. In addition, we show that the promoter of each putative germinant receptor operon, except that of the gerA locus, is active during sporulation. A current model of B. anthracis endospore germination is presented.

Isolation and characterization of mutations in Bacillus subtilis that allow spore germination in the novel germinant D-alanine

Bacillus subtilis spores break their metabolic dormancy through a process called germination. Spore germination is triggered by specific molecules called germinants, which are thought to act by binding to and stimulating spore receptors. Three homologous operons, gerA, gerB, and gerK, were previously proposed to encode germinant receptors because inactivating mutations in those genes confer a germinant-specific defect in germination. To more definitely identify genes that encode germinant receptors, we isolated mutants whose spores germinated in the novel germinant D-alanine, because such mutants would likely contain gain-of-function mutations in genes that encoded preexisting germinant receptors. Three independent mutants were isolated, and in each case the mutant phenotype was shown to result from a single dominant mutation in the gerB operon. Two of the mutations altered the gerBA gene, whereas the third affected the gerBB gene. These results suggest that gerBA and gerBB encode components of the germinant receptor. Furthermore, genetic interactions between the wild-type gerB and the mutant gerBA and gerBB alleles suggested that the germinant receptor might be a complex containing GerBA, GerBB, and probably other proteins. Thus, we propose that the gerB operon encodes at least two components of a multicomponent germinant receptor.

Calcium dipicolinic acid-induced germination of Bacillus cereus spores

Keynan, A. (University of Wisconsin, Madison) and H. O. Halvorson. Calcium dipicolinic acid-induced germination of Bacillus cereus spores. J. Bacteriol. 83:100-105. 1962.-The germination of spores of Bacillus cereus strain T can be initiated by calcium dipicolinic acid. The kinetics of germination are characterized by a long lag period followed by a rapid loss of refractility. The lag period displays the temperature dependence of a metabolic reaction, whereas the rate of germination is relatively independent of temperature. Germination induced by calcium dipicolinic acid is insensitive to l-alanine analogues, is sensitive to metabolic poisons, and proceeds without a detectable activation stage. It was concluded that calcium dipicolinic acid-induced germination has a metabolic basis and differs, at least in its initial phases, from l-alanine-induced germination.

Nitrogenous compounds in germination and postgerminative development of Bacillus megaterium spores

Levinson, Hillel S. (Quartermaster Research and Engineering Center, Natick, Mass.) and Mildred T. Hyatt. Nitrogenous compounds in germination and postgerminative development of Bacillus megaterium spores. J. Bacteriol. 83:1224-1230. 1962.-Of the 48 inorganic and organic nitrogenous compounds tested, only l-alanine, glucosamine, and N-acetylglucosamine promote germination of unheated spores of Bacillus megaterium. Heated spores also germinate in nitrate, nitrite, l-cysteine, dl-isoleucine, l-leucine, dl-methionine, dl-norleucine, l-proline and l-valine.A source of nitrogen is required for postgerminative development, but nitrogenous compounds which effect germination do not necessarily support postgerminative development. Nitrogenous compounds which support postgerminative development include (NH(4))(2)SO(4), nitrates, d-alanine, l-alanine, l-arginine, l-asparagine, l-aspartic and l-glutamic acids, glutamine, l-proline, adenine, adenosine, and guanosine. Oxygen consumption rates during postgerminative development are different with different nitrogen sources, and these rates, in general, reflect the extent of postgerminative development. Utilization of amino and ammonium nitrogen during postgerminative development was followed, and the concentration requirements were determined (ca 10 mm for at least one cell division of 5 x 10(8) spores). Inhibitor studies on postgerminative development are included.

The effects of D-amino acids on Alcaligenes fecalis

D-Amino acids have been found to induce protoplast-like forms (crescents) in Alcaligenes fecalis strain LB. This induction is similar in most respects to that by penicillin with the exception of the effects produced in tryptone. D-Amino acids appear to act synergistically with penicillin. The amino acid composition of cell walls of D-amino acid and penicillin-induced crescents as well as of normal cells has been examined by column chromatography. The main difference between normal and crescent cell walls consists of a reduction in the amount of the basic peptide unit of the phenol-insoluble fraction. These results are discussed in relation to the induction of protoplast-like forms.

L-Alanine dehydrogenase: a mechanism controlling the specificity of amino acid-induced germination of Bacillus cereus spores

O'Connor, R. J. (University of Wisconsin, Madison), and Harlyn O. Halvorson. L-Alanine dehydrogenase: A mechanism controlling the specificity of amino acid-induced germination of Bacillus cereus spores. J. Bacteriol. 82:706-713. 1961.-A study has been undertaken of the properties and specificity of germination of spores of Bacillus cereus strain T. In the absence of additional carbon sources, only l-alanine, l-alpha-NH(2)-n-butyric acid, and l-cysteine were effective germinating agents. The physical properties of germination, induced by l-alanine and l-alpha-NH(2)-n-butyric acid following extended heat shock, were in close agreement with those of l-alanine dehydrogenase. The specificity of the germination system, as well as amino acid deamination in vivo, support the view that l-alanine dehydrogenase activity is essential for germination and that the enzyme serves as the initial binding site for l-alanine in heat-shocked spores.

The effect of temperature on the germination of single spores of Clostridium botulinum 62A

Phase-contrast microscopy coupled with image analysis has been used to study the germination of single spores of Clostridium botulinum and to investigate the variation of germination lag of individual spores in a population (biovariability). The experiment was repeated at five different temperatures between 20 degrees C and 37 degrees C to look at the effect of temperature on the biovaribility of the spore germination. Data analysis shows that the germination lag distribution is skewed, with a tail, and that its shape is affected by the temperature. The origin of this biovariability is not exactly known, but could be due to a distribution of characteristics (e.g. permeabilities) or molecules (e.g. lytic enzymes) in the spore population. The method developed in this study will help us to describe and better understand the kinetics of spore germination and how this is influence by different environmental factors such as temperature and other factors that influence germination.

KINETICS OF SPORE GERMINATION

McCormick, Neil G. (University of Virginia, Charlottesville). Kinetics of spore germination. J. Bacteriol. 89:1180-1185. 1965.-An empirically derived equation was developed which accurately describes the time-course of the decrease in optical density during spore germination. A method is described for calculating the final value, the inflection point, and the maximal velocity from knowledge of three experimental values and the initial value at time-zero. A number of germination curves were analyzed by application of the equation, and the effects of various environmental conditions on the parameters of the equation (k, c, and alpha) are noted. The constant c was found to be dependent upon the temperature and perhaps upon the degree of heat activation and the l-alanine concentration. The constants k and alpha appear to be more basic functions of the initial state of the spore suspension. Variation of the concentration of spores changes only the initial optical density, but does not change any of the three constants.

KINETICS OF GERMINATION OF BACILLUS SPORES

Vary, J. C. (University of Wisconsin, Madison), and H. O. Halvorson. Kinetics or germination of Bacillus spores. J. Bacteriol. 89:1340-1347. 1965.-The kinetics of germination of Bacillus cereus strain T spores was accurately described by McCormick. To study the mechanism of germination, it is necessary to correlate the characteristic changes in a population of germinating spores with the behavior of the individual spores in the same population. Two microscopic events are apparent during germination: microlag, the time interval between the addition of l-alanine to heat-activated spores and the beginning of loss in refractility, and microgermination time, the time for the actual change in refractility to occur. The frequency distributions of both events are skewed, and appear to be independent. The effects of l-alanine concentration, heat activation, and temperature of germination on three parameters, microlag, microgermination, and per cent germination, were microscopically studied. The data are discussed in relation to the mechanism of germination, and a correlation between microlag and microgermination times with the constants of McCormick's equation has been suggested.

EFFECT OF SUGARS AND OTHER CARBON COMPOUNDS ON GERMINATION AND POSTGERMINATIVE DEVELOPMENT OF BACILLUS MEGATERIUM SPORES

Hyatt, Mildred T. (Pioneering Research Division. U.S. Army Natick Laboratories, Natick, Mass.), and Hillel S. Levinson. Effect of sugars and other carbon compounds on germination and postgerminative development of Bacillus megaterium spores. J. Bacteriol. 88:1403-1415. 1964.-A total of 77 carbon-containing compounds were tested for their ability to support germination and postgerminative development of Bacillus megaterium spores. The only effective germination agents were certain of the hexose sugars and their derivatives. With unheated spores, only d-glucose, d-mannose, 2-deoxy-d-glucose, d-glucosamine, and N-acetyl-d-glucosamine (all at 25 mm) supported appreciable germination (ca. 25%). Heat-shock at 60 C for 10 min increased germination and decreased the concentration of sugar required for germination, so that these compounds, at 2.5 mm, supported 40 to 60% germination. Higher concentrations (25 mm) of other compounds, d-fructose, l-sorbose, d-allose, d-altrose, 2-hydroxyethyl-d-glucose, and beta-methyl-d-glucoside, were required for appreciable germination of heated spores. Glucose or mannose contamination accounted for the germination apparently induced by certain other sugars. Ionic contamination did not appear to contribute to the germination induced by d-glucose, d-fructose, 2-deoxy-d-glucose, or l-sorbose. There was no clear-cut evidence for a multiplicity of metabolic pathways in the triggering of B. megaterium spore germination by various sugars. Postgerminative development of germinated spores was supported by a wider variety of carbon compounds, including some pentoses and hexoses, many oligosaccharides, sugar derivatives, some alcohols, and some of the tricarboxylic acid cycle intermediates. Compounds effective for germination were not necessarily utilizable for growth, and vice versa. Oxygen consumption rates reflected the progress and extent of postgerminative development on the various carbon compounds. Utilization of glucose during postgerminative development was followed, and the concentration requirements were determined.

Multiple modes of inhibition of spore germination and outgrowth by reduced pH and sorbate

Germination and outgrowth of three strains of Clostridium botulinum in PYEG medium were measured by phase contrast microscopy. Reduction in pH from 7 to 5.5 completely inhibited germination of strain 12885A, reduced the extent of germination of strain 62A and had no effect on the extent of germination of strain 53B. At pH 5.5, 225 mg/l of undissociated sorbic acid had no effect on the germination of strain 53B, while at pH 6.5, 225 mg/l of undissociated sorbic acid completely inhibited germination of strains 62A and 12885A. Outgrowth of germinated spores of strains 62A and 53B was not inhibited at pH 5.5, but the addition of sorbate (225 mg/l undissociated sorbic acid) completely inhibited outgrowth. Sorbate inhibited germination of Cl. botulinum and Bacillus cereus spores triggered to germinate by amino acids. Inhibition occurred after germinant binding, as measured by commitment to germinate.

Germination-initiation and inhibitory activities of L- and D-alanine analogues for Bacillus subtilis spores. Modification of methyl group of L- and D-alanine

The ability of 33 compounds of L-alanine analogues over a wide range of concentrations to initiate germination of Bacillus subtilis spores was determined, and the inhibitory activity against L-alanine-initiated germination was determined for the above compounds and 22 of their D- and DL-isomers. Nineteen L-isomers were able to initiate the germination. The maximum germination rate and the apparent binding affinity of the germinant were obtained from concentration-germination response curves. Not only D-isomers but also L-isomers of many alanine analogues showed inhibitory action on L-alanine-initiated germination. The apparent binding affinity of an inhibitor was calculated by Schild's method. D-Alanine, D-serine, glycine, D-2-amino-n-butyric acid, D-cysteine, D-norvaline, and D-threonine were competitive inhibitors for the L-alanine action. Analysis of the relation between the structure of the side chain of L- and D-alanine analogues and their apparent affinity suggested that there are separate binding portions, which differ in size and electrostatic nature, for germination and for inhibition on the receptor. Certain L-alanine analogues had a dualistic property of initiating germination at low concentrations and inhibitory activity at higher concentrations, i.e., autoinhibition. The autoinhibitory phenomenon might be explained by the above postulation of the presence of separate binding portions for germination and for inhibition.

Effect of alanine-containing dipeptides on germination of Bacillus thiaminolyticus spores

Stereoisomeric alanylalanine (Ala-Ala) derivatives were examined for their effects on germination of Bacillus thiaminolyticus spores. L-Ala-L-Ala and L-Ala-glycine were effective in inducing germination, and their activities were completely inhibited by D-Ala. L-Ala-D-Ala and glycine-D-Ala competitively prevented L-Ala-induced germination. Sarcosine- or beta-Ala-containing L-alanyldipeptides and eight kinds of alanyltripeptides did not show any detectable effect on germinability or any inhibitory effect. No detectable amounts of Ala were found in germination exudates when alanylpeptides were incubated with spores. The ability of these peptides to induce or inhibit germination depends on their steric conformation and a certain distance between the primary amino group and the free carboxyl groups. Involvement of L-Ala dehydrogenase in the initiation of germination is unlikely because L-Ala-L-Ala was not a substrate and L-Ala-D-Ala was not an effective inhibitor of enzyme activity.

Germination of unactivated spores of Bacillus cereus T. Effect of preincubation with L-alanine or inosine on the subsequent germination

Heat-activated spores of Bacillus cereus T germinate rapidly in the presence of L-alanine alone or inosine alone. In contrast, unactivated spores can not germinate in the presence of either germinant alone but rapidly in the presence of both germinants. The highest level of cooperative action of L-alanine and inosine on the germination was observed when they were present in a ratio 1:1. Preincubations of unactivated spores with L-alanine or inosine had opposite effects on the subsequent germination in the presence of both germinants: preincubation with L-alanine stimulated the initiation of subsequent germination, while preincubation with inosine inhibited it. These results suggest that germination of unactivated spores initiated by L-alanine and inosine includes two steps, the first initiated by L-alanine and the second prompted by inosine. The effect of preincubation of unactivated spores with L-alanine was not diminished by washings. The pH dependence of the preincubation of unactivated spores was not so marked as that of the subsequent germination in the presence of inosine.

Properties of Bacillus megaterium temperature-sensitive germination mutants

Bacillus megaterium mutants JV-9 and JV-10 are temperature sensitive for initiation of spore germination. At 46 C, they did not lose heat resistance, dipicolinic acid, or absorbance, indicating that the temperature-sensitive blocks are very early in the sequence of initiation reactions. Strain JV-9 was temperature sensitive for initiation by glucose alone, and strain JV-10 was temperature sensitive for initiation by glucose, L-leucine, L-proline, KBr, or calcium dipicolinate. The kinetics of initiation were followed after two kinds of temperature change (shift-up and shift-down) experiments. Mutant spores incubated for different times at 46 C and then shifted down to 30 C showed no significant differences in the rates of absorbance decrease, i.e., no stimulation or inhibition. Conversely, when mutant spores were incubated for different times at 30 C, a fraction of the population initiated germination, and after shift-up to 46 C an additional fraction continued initiation while a third fraction stopped. This latter fraction did initiate germination when the temperature was lowered to 30 C. The kinetics of initiation after shift-up and shift-down in temperature suggest that the early events in initiation reagents, whereas the other four initiated sensitivity for all of the above initiation reagents, whereas the other four initiated very poorly. It was suggested that the lesion in strain JV-10 may result in the formation of one temperature-sensitive protein. Revertants of strain JV-9 could not be isolated.

Macromolecular syntheses during germination and outgrowth of Bacillus subtilis spores

Alanine and glucose used jointly are known to be necessary and sufficient for spore germination in Bacillus subtilis 168. By testing them separately, we have verified that alanine provokes optimal phase-darkening of the spores but inhibits macromolecular syntheses, while glucose is specifically needed for initiating those syntheses. By using them in succession we obtained evidence suggesting that: (i) sporal modifications which lead to phase-darkening must occur before macromolecular synthesis can start; (ii) the amino acid pool, on which the early protein synthesis is solely dependent, expands during incubation in alanine which allows degradative but prevents synthetic activities; and (iii) progression of degradations in alanine not promptly followed by syntheses in glucose produce a metabolic imbalance in the germinating spore. A sharp transition in the origin of building blocks was shown by using a tryptophan-defective mutant. At first the synthesis of proteins depended on pre-existing amino acids from turnover of sporal material since it occurred in the absence of any exogenous amino acid and its rate remained unaltered by supplying either all amino acids except tryptophan or tryptophan alone. Eventually, protein synthesis became dependent strictly on exogenous tryptophan and strongly on the supply of several other amino acids, not required later during vegetative growth. Clearly, by the start of outgrowth, all building blocks must be provided either by endogenous de novo synthesis or by exogenous supply.

-aminobutyric acid as a required germinant for mutant spores of Bacillus megaterium

Germinated spores of Bacillus megaterium QM B1551 were irradiated with ultraviolet light, and spore-forming survivors were screened for germination requirements. Spore strains which failed to germinate in a variety of defined solutions germinative for spores of the parent strain were obtained. Mutant spores germinated readily in solutions containing yeast extract or one of numerous complex preparations. gamma-Aminobutyric acid, obtained from yeast extract by column chromatography, was shown to be required for germination by the mutant spores. gamma-Aminobutyric acid and l-alanine at final concentrations of 1 mm each, in solutions of KI (40 mm), equaled the potency of yeast extract (1 mg/ml) in the germination of the mutant spores. One of several other amino acids could be substituted, though less effectively, for l-alanine. alpha-Aminobutyric acid, beta-aminobutyric acid, beta-alanine, and 5-aminovaleric acid were ineffective substitutes for gamma-aminobutyric acid in mutant spore germination.

Germination requirements of Bacillus macerans spores

2-Phenylacetamide is an effective germinant for spores of five strains of Bacillus macerans, particularly in the presence of fructose. Benzyl penicillin, the phenyl acetamide derivative of penicillin, and phenylacetic acid are also good germinants. l-Asparagine is an excellent germinant for four strains. alpha-Amino-butyric acid is moderately effective. Pyridoxine, pyridoxal, adenine, and 2,6-diaminopurine are potent germinants for NCA strain 7X1 only. d-Glucose is a powerful germinant for strain B-70 only. d-Fructose and d-ribose strongly potentiate germination induced by other germinants (except l-asparagine) but have only weak activity by themselves. Niacinamide and nicotinamide-adenine dinucleotide, inactive by themselves, are active in the presence of fructose or ribose. Effects of pH, ion concentration, and temperature are described.