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J. Bacteriol. doi:10.1128/JB.01846-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Identification of Major Sporulation Proteins of Myxococcus xanthus Using a Proteomic Approach

School of Molecular Biosciences, Washington State University, Pullman, Washington, 99164; Department of Biology, Syracuse University, Syracuse, New York, 13244; and Proteomics Resource Facility, Integrated Biotechnology Laboratories, University of Georgia, 458 Animal and Dairy Sciences Bldg, 425 River Road, Athens, Georgia, 30602

^* To whom correspondence should be addressed. Email: johndahl{at}wsu.edu.

	Abstract

Myxococcus xanthus is a soil-dwelling, Gram-negative bacterium that during nutrient deprivation is capable of undergoing morphogenesis from a vegetative rod into a spherical, stress-resistant spore inside domed-shaped, multicellular fruiting bodies. To identify proteins required for building stress-resistant M. xanthus spores, we compared the proteome of liquid-grown vegetative cells with the proteome of mature fruiting body spores. Two proteins, protein S and protein S1, were differentially expressed in spores, as has been previously reported. In addition, we identified three previously uncharacterized proteins that are differentially expressed in spores and show no homology to known proteins. The genes for these three novel major spore proteins (mspA, mspB, and mspC) were inactivated by insertion mutagenesis, and the resulting mutant strains were characterized for development. All three mutants were capable of aggregating, but for two of the strains the resulting fruiting bodies remained as flattened mounds of cells. The most pronounced structural defect of spores produced by all three mutants was an altered cortex layer. We found that mspA and mspB mutant spores were more sensitive specifically to heat and sodium dodecyl sulfate than wild-type spores, while mspC mutant spores were more sensitive to all stress treatments tested. Hence, the products of mspA, mspB, and mspC play significant roles in morphogenesis of M. xanthus spores and in the ability of spores to survive environmental stress.