Analysis of fruE, a novel developmental gene of Myxococcus xanthus

Myxococcus xanthus is a gram-negative soil bacterium that undergoes multicellular development upon nutrient starvation. In the present study, a TnV insertion developmental mutation, Omega773, of M. xanthus was analyzed. The TnV Omega773 insertion was found to be located within a novel developmental gene, fruE. The FruE protein is composed of 140 amino acid residues and bears an N-terminal signal peptide. The amino acid sequence of FruE shared no significant similarity with any other known protein in the databases. The fruE mutant displayed a development-delayed phenotype. The formation of tightly aggregated mounds in the fruE mutant was slower than that in the wild-type strain. The initiation of spore production in the fruE mutant was delayed by 12 h in comparison to the wild-type strain, and the process of spore formation was more asynchronous than that of the wild-type strain. The transcription initiation sites of the fruE gene were located 81 bp (P1) and 57 bp (P2) upstream of the fruE initiation codon. Although both promoters were active during vegetative growth and development, the P1 promoter was more active during development and the P2 promoter was more active during vegetative growth. The expression of the fruE gene increased to a peak at 6 h poststarvation and then decreased. The decrease in fruE expression was not observed in the D and E signal mutants.