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

ABSTRACT: Recently developed techniques for isolating forespores from bacilli at all stages of spore morphogenesis have been exploited to investigate the contribution of each of the two compartments of the sporulating cell to the overall pattern of protein synthesis and degradation during sporulation in Bacillus megaterium. These studies have shown: (1) that protein synthesis continues in both compartments throughout spore morphogenesis; (2) that the degradation of proteins made at all times during vegetative growth and sporulation is confined to the mother-cell compartment; (3) that proteins synthesized in the mother-cell compartment during sporulation are subsequently degraded more rapidly than proteins synthesized during vegetative growth. This rate of degradation increases the later the proteins are synthesized in the sporulation sequence. Mature spores were disrupted, and the percentage of the total protein in soluble and particulate fractions was determined. Pulse-labelling experiments were performed to investigate the extent to which the proteins of these two fractions are newly synthesized during sporulation. These data were used to calculate the extent of capture of vegetative cell protein at the time of formation of the forespore septum. The value obtained is consistent with evidence from electron micrographs and supports a model for the origin of spore protein in which there is no protein turnover in the developing forespore.

SUBMITTER: Eaton MW

PROVIDER: S-EPMC1168500 | biostudies-other | 1974 Nov

REPOSITORIES: biostudies-other

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Project description:The exosporium of Bacillus megaterium QM B1551 spores is morphologically distinct from exosporia observed for the spores of many other species. Previous work has demonstrated that unidentified genes carried on one of the large indigenous plasmids are required for the assembly of the Bacillus megaterium exosporium. Here, we provide evidence that pBM600-encoded orthologues of the Bacillus subtilis CotW and CotX proteins, which form the crust layer in spores of that species, are structural components of the Bacillus megaterium QM B1551 spore exosporium. The introduction of plasmid-borne cotW and orthologous cotX genes to the PV361 strain, which lacks all indigenous plasmids and produces spores that are devoid of an exosporium, results in the development of spores with a rudimentary exosporium-type structure. Additionally, purified recombinant CotW protein is shown to assemble at the air-water interface to form thin sheets of material, which is consistent with the idea that this protein may form a basal layer in the Bacillus megaterium QM B1551 exosporium.IMPORTANCE When starved of nutrients, some bacterial species develop metabolically dormant spores that can persist in a viable state in the environment for several years. The outermost layers of spores are of particular interest since (i) these represent the primary site for interaction with the environment and (ii) the protein constituents may have biotechnological applications. The outermost layer, or exosporium, in Bacillus megaterium QM B1551 spores is of interest, as it is morphologically distinct from the exosporia of spores of the pathogenic Bacillus cereus family. In this work, we provide evidence that structurally important protein constituents of the Bacillus megaterium exosporium are different from those in the Bacillus cereus family. We also show that one of these proteins, when purified, can assemble to form sheets of exosporium-like material. This is significant, as it indicates that spore-forming bacteria employ different proteins and mechanisms of assembly to construct their external layers.

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

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