Requirement of deoxyribonucleic acid synthesis for microcycle sporulation in Bacillus megaterium

Characterization of a new sporulation factor in Bacillus subtilis

We report the existence and partial purification of sporulation factor, which stimulates sporulation of Bacillus subtilis at low cell density. Proline or arginine is required for stimulation under the conditions of our assay. Sporulation factor is a small heat-stable substance produced by the cells during exponential growth phase. It is required in small amounts and is resistant to various proteolytic agents. Several spo mutants were tested for the ability to produce functional sporulation factor. All of these mutants produce factor and do not sporulate in the presence of factor from wild-type cells. Sporulation factor is not involved in the induction of alpha-amylase synthesis at the initiation of sporulation.

Growth and morphogenesis in Streptomyces

In this report we propose a model of apical growth for streptomycetes. The apical tip is considered as a multilayered wall that expands by an inside-to-outside mechanism of growth. It is also assumed that each layer is made up of peptidoglycan blocks, each of them being the result of the biosynthetic activity of a wall-synthesizing unit or membrane-associated growth zone. According to our model, apical growth occurs as follows: as a consequence of the hydrostatic pressure and the cleavage of some bonds, the layers are pushed and forced to slide (one with respect to the other), migrating from the center of the tip (at the inside of the wall) towards a peripheral location (at the outside of the wall). The model also incorporates a mechanism by which apical growth can be regulated and coordinated with the replication of the chromosome.

Achievement of complete Bacillus subtilis microcycle sporulation by the addition of S-adenosylmethionine and phospholipids

In an attempt to find factors that may be responsible for the initiation of sporulation, a system in which the germination and outgrowth phases were separate was applied to Bacillus subtilis. Outgrowth of the germinated spores to only the primary singlet cells was followed in chemically defined medium. Addition of specific metabolites induced the primary singlet cells to sporulate via microcycle sporulation. Experiments are described that led to complete sporulation by the addition of diaminopimelic acid, S-adenosyl-L-methionine and phosphatidylethanolamine.

A model for asymmetric septum formation during sporulation in Bacillus subtilis

Many differentiation processes in both prokaryotes and eukaryotes begin with an asymmetric division, producing 'daughter' cells that differ in size and developmental fate. This is particularly obvious in the well-studied prokaryotic life cycles of Caulobacter and Bacillus. In no system, however, is the mechanism of asymmetric division understood. Here I propose a model for the mechanism of asymmetric division during sporulation in Bacillus subtilis. The model explains both the timing and asymmetric localization of spore-septum formation. It also explains the morphological phenotypes of various asporogenous (spo) mutants.

Chromosome replication in sporulating cells of Bacillus subtilis

A method of specifically labeling the chromosomal terminus of Bacillus subtilis is described. When sporulating cultures were pulse-labeled with [(3)H]thymidine and then treated with 6-(p-hydroxyphenylazo)uracil, a drug which inhibits deoxyribonucleic acid (DNA) synthesis rapidly and completely, the only labeled spores formed were those that had completed replication during the pulse period. DNA-mediated transformation was used to show that the DNA of spores formed in the presence of 6-(p-hydroxyphenylazo)uracil had the same ratio of origin to terminus markers as DNA from untreated spores. Furthermore, spores formed in the presence of 6-(p-hydroxyphenylazo)uracil had the same DNA content as untreated spores. These two observations indicated that spores formed in the presence of 6-(hydroxyphenylazo)uracil contained completed chromosomes. The rate of termination of chromosomes destined to be packaged into spores was determined by this method, using the Sterlini-Mandelstam replacement system and a single medium exhaustion system for inducing sporulation. With both systems the rate of termination reached a broad peak 2 h after the start of sporogenesis. This was measured from the time of resuspension by using the replacement system and from the point where exponential growth ceased in the exhaustion system. The amount of spore DNA synthesized in the Sterlini-Mandelstam sporulation-inducing medium was very close to one-half the amount of the DNA present in mature spores. This suggests that chromosomes destined to be packaged into spores were replicated from close to the origin and possibly initiated in the sporulation-inducing medium. A method was devised for estimating the time taken to complete replication of the chromosomes destined to be packaged into spores. This was probably no more than 50 min. Whereas starvation must have occurred almost simultaneously in most cells in the population, the chromosome replication that was essential for sporogenesis was distributed over a wide time span. Thus, in some cells, replication started within 10 min of the nutritional step-down, but the peak rate was not reached for 1 h; thereafter replication continued at a substantial rate.

Changes in sporulation potential during the growth cycle of Bacillus subtilis

The sporulation potential of Bacillus subtilis as a function of position in the cell cycle was determined by transferring cells from growth medium to sporulation medium at various times during growth. Growth was induced by incubating heat-activated spores in rich medium or by diluting stationary phase vegetative cultures with fresh growth medium. The results supported earlier observations that sporulation potential is cell cycle dependent. The rise in sporulation potential was studied by exposing cultures to the inhibitors of cell wall and protein synthesis, vancomycin and chloramphenicol. The delay in the appearance of the peak of sporulation potential caused by these inhibitors compared with the reported lack of effect of nalidixic acid, indicates that the appearance of sporulation potential requires synthesis of a macromolecular component other than deoxyribonucleic acid. The effect of nalidixic acid in preventing the decline of the sporulation potential was compared with the effect of high temperature on a mutant temperature sensitive for the initiation of DNA replication. It was found that prevention of chromosome completion with nalidixic acid maintained a high sporulation potential, whereas prevention of chromosome re-initiation in the temperature sensitive mutant did not affect the decline in sporulation potential as the cells enter stationary phase.

Induction of microcycle sporulation in Bacillus brevis spp. AG4 by amethopterin

Addition of amethopterin to medium before inoculation inhibited DNA synthesis and induced microcycle sporogenesis in Bacillus brevis spp. AG4. Synthesis of RNA and proteins occurred at a considerably reduced rate.

Genetic aspects of bacterial endospore formation

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Resporulation of outgrowing Bacillus subtilis spores

Germinated spores of Bacillus subtilis were incubated in outgrowth medium and tested periodically for capacity to sporulate when suspended in sporulation medium. Concurrent measurements were made of deoxyribonucleic acid (DNA) content and numbers of cell division septa and nucleoids. Sporulation potential is shown to reach a peak at about 110 min at which time the chromosomes are probably well into the second round of replication. Experiments with nalidixic acid show that sporulation potential can be generated in the outgrowth medium even when DNA synthesis is largely prevented. Further experiments show that nalidixic acid apparently does not prevent the formation of DNA initiation complexes, which can subsequently function after resuspension in the sporulation medium. The results support those previously obtained with a temperature-sensitive DNA mutant which indicated that sporulation could only be induced at a specific stage of chromosome replication, and then only if the cells are in a state of nutritional "step-down".

Encystment and germination in Azotobacter vinelandii

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