ISOLATED FIBRILS RESCUE COHESION AND DEVELOPMENT IN THE DSP MUTANT OFMYXOCOCCUS-XANTHUS

Extracellular fibrils are involved in cell cohesion and cell developme nt in Myxococcus xanthus. One group of social motility mutants, Dsp, i s unable to produce extracellular fibrils; these mutants also lose the abilities to cohere and to develop. Extracellular fibrils isolated fr om vegetative wild-type cells and added to Dsp cells fully restored th e abilities of these cells to cohere and to undergo normal morphologic al development. The fibrils thus mimic the ability of intact, wild-typ e cells to carry out the same rescue. Optimal cohesion rescue by fibri ls required calcium and magnesium ions, did not require protein synthe sis, but was energy dependent, i.e., sodium azide and sodium cyanide b locked rescue. Cohesion rescue was also blocked by the diazo dye Congo red. Cohesion rescue is genus specific, i.e., isolated fibrils did no t cause the cohesion of Pseudomonas aeruginosa, Bacillus subtilis, Pro teus mirabilis, Escherichia coli, or the related myxobacterium Stigmat ella aurantiaca. Developmental rescue of Dsp by isolated fibrils inclu ded aggregation, fruiting body formation, and myxospore morphogenesis. Developmental gene expression in the Dsp mutant was only partially re scued by the isolated fibrils.