Effects of overexpression of Pkn2, a transmembrane protein serine/threonine kinase, on development of Myxococcus xanthus

Pkn2 is a putative transmembrane protein serine/threonine kinase required for normal development of Myxococcus xanthus. The effect of Pkn2 overexpression on development of M. xanthus was examined by expressing pkn2 under the control of a kanamycin promoter. Pkn2 was clearly detected by Western blot (immunoblot) analysis in the overexpression strain (the PKm/pkn2 strain) but could not be detected in the wild-type strain. Overexpressed Pkn2 was located almost exclusively in the membrane fraction, suggesting that Pkn2 is a transmembrane receptor-type protein Ser/Thr kinase. The PKm/pkn2 strain formed fruiting bodies more slowly than the wild-type strain, in contrast to a Pkn2 deletion strain, the Δpkn2 strain, which developed faster than the wild-type strain. However, spore production was reduced in both the PKm/pkn2 and Δpkn2 strains. These data suggest that Pkn2 functions as a negative regulator for fruiting-body formation and that the proper level of Pkn2 is necessary for maximum myxospore yield.