The asgE locus is required for cell-cell signalling during Myxococcus xanthus development

In response to starvation, Myxococcus xanthus undergoes a multicellular dev elopmental process that produces a dome-shaped fruiting body structure fill ed with differentiated cells called myxospores. Two insertion mutants that block the final stages of fruiting body morphogenesis and reduce sporulatio n efficiency were isolated and characterized. DNA sequence analysis reveale d that the chromosomal insertions are located in open reading frames ORF2 a nd asgE, which are separated by 68 bp. The sporulation defect of cells carr ying the asgE insertion can be rescued phenotypically when co-developed wit h wild-type cells, whereas the sporulation efficiency of cells carrying the ORF2 insertion was not improved when mixed with wild-type cells. Thus, the asgE insertion mutant appears to belong to a class of developmental mutant s that are unable to produce cell-cell signals required for M. xanthus deve lopment, but they retain the ability to respond to them when they are provi ded by wild-type cells. Several lines of evidence indicate that asgE cells fail to produce normal levels of A-factor, a cell density signal. A-factor consists of a mixture of heat-stable amino acids and peptides, and at least two heat-labile extracellular proteases. The asgE mutant yielded about 10- fold less heat-labile A-factor and about twofold less heat-stable A-factor than wild-type cells, suggesting that the primary defect of asgE cells is i n the production or release of heat-labile A-factor.