Global Mutational Analysis of NtrC-Like Activators in Myxococcus xanthus : Identifying Activator Mutants Defective for Motility and Fruiting Body Development

Abstract

ABSTRACT The multicellular developmental cycle of Myxococcus xanthus requires large-scale changes in gene transcription, and recent findings indicate that NtrC-like activators play a prominent role in regulating these changes. In this study, we made insertions in 28 uncharacterized ntrC -like activator ( nla ) genes and found that eight of these insertions cause developmental defects. Hence, these results are consistent with the idea that M. xanthus uses a series of different NtrC-like activators during fruiting body development. Four of the eight developmental mutants we identified have motility defects. The nla1 , nla19 , and nla23 mutants show S-motility defects, while the nla24 mutant shows defects in both S-motility and A-motility. During development, aggregation of the nla1 , nla19 , and nla23 mutants is delayed slightly and the nla24 mutant shows no signs of aggregation or sporulation. The nla4 , nla6 , nla18 , and nla28 mutants have no appreciable loss in motility, but they fail to aggregate and to sporulate normally. The nla18 mutant belongs to a special class of developmental mutants whose defects can be rescued when they are codeveloped with wild-type cells, suggesting that nla18 fails to produce a cell-cell signal required for development. The three remaining activator mutants, nla4 , nla6 , and nla28 , appear to have complex developmental phenotypes that include deficiencies in cell-cell developmental signals.