Abstract
Bacillus subtilis endospores are exceptionally resistant cells encircled by two protective layers: a petidoglycan layer, termed the cortex, and the spore coat, a proteinaceous layer. The formation of both structures depends upon the proper assembly of a basement coat layer, which is composed of two proteins, SpoIVA and SpoVM. The present work examines the interactions of SpoIVA and SpoVM with coat proteins recruited to the spore surface during the early stages of coat assembly. We showed that the alanine racemase YncD associates with two morphogenetic proteins, SpoIVA and CotE. Mutant spores lacking the yncD gene were less resistant against wet heat and germinated to a greater extent than wild-type spores in the presence of micromolar concentrations of l-alanine. In seeking a link between the coat and cortex formation, we investigated the interactions between SpoVM and SpoIVA and the proteins essential for cortex synthesis and found that SpoVM interacts with a penicillin-binding protein, SpoVD, and we also demonstrated that SpoVM is crucial for the proper localization of SpoVD. This study shows that direct contacts between coat morphogenetic proteins with a complex of cortex-synthesizing proteins could be one of the tools by which bacteria couple cortex and coat formation.
Highlights
IntroductionMore than 80 coat proteins are arrayed in four morphologically distinct coat layers: a basement layer localized directly on the outer forespore membrane, an inner coat, an outer coat and a crust, the outermost layer of the spore [2]
SpoVM and SpoIVA and the proteins essential for cortex synthesis and found that SpoVM interacts with a penicillin-binding protein, SpoVD, and we demonstrated that SpoVM is crucial for the proper localization of SpoVD
Given the contact between YncD and SpoIVA, we considered whether the production of D-alanine, a peptidoglycan component, by YncD might be important for cortex synthesis
Summary
More than 80 coat proteins are arrayed in four morphologically distinct coat layers: a basement layer localized directly on the outer forespore membrane, an inner coat, an outer coat and a crust, the outermost layer of the spore [2]. A few coat proteins, the morphogenetic proteins, SpoIVA, SpoVM, SpoVID, SafA, CotE and CotZ, greatly influence coat assembly by controlling the localization of individual proteins on the spore surface and the proper assembly of the four coat layers [3]. SpoIVA and SpoVM form the basement layer of the coat on top of which the inner coat is built under the control of SafA, followed by the outer coat governed by CotE.
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