A GENE INVOLVED IN BOTH PROTEIN SECRETION DURING GROWTH AND STARVATION-INDUCED DEVELOPMENT ENCODES A SUBUNIT OF THE NADH-UBIQUINONE OXIDOREDUCTASE IN MYXOCOCCUS-XANTHUS

The secretion of numerous proteins during vegetative growth of Myxococ cus xanthus, and the multicellular development cycle induced upon star vation of these bacteria, are partially interrelated in so far as muta nts impaired in extracellular protein production are unable to undergo development. We have cloned and sequenced a gene in which a Tn5 inser tion leads to a decrease in the production of most, if not all, extrac ellular proteins, and prevents development and sporulation. The deduce d protein is homologous to the putative ubiquinone-binding subunit of bacterial and mitochondrial NADH:ubiquinone oxidoreductases (complex I ). This is the first example of the presence of this complex in a bact erium from subclass delta of the proteobacteria. This gene is expresse d during growth and during early development. As its disruption by Tn5 does not impair growth of the mutant strain, we assume the presence o f a second alternative NADH oxidoreductase, and suggest that the pheno typic alterations caused by the mutation are due to a decrease in the proton-motive force.