METHYLATION OF FRZCD DEFINES A DISCRETE STEP IN THE DEVELOPMENTAL PROGRAM OF MYXOCOCCUS-XANTHUS

Myxococcus xanthus is a gram-negative soil bacterium which undergoes f ruiting body formation during starvation. The frz signal transduction system has been found to play, an important role in this process. FrzC D, a methyl-accepting taxis protein homologue, shows modulated methyla tion during cellular aggregation, which is thought to be part of an ad aptation response to an aggregation signal. In this study, we assayed FrzCD methylation in many known and newly isolated mutants defective i n fruiting body formation to determine a possible relationship between the methylation response and fruiting morphology. The results of our analysis indicated that the developmental mutants could be divided int o two groups based on their ability to show normal FrzCD methylation d uring development. Many mutants blocked early in development, i.e., no naggregating or abnormally aggregating mutants, showed poor FrzCD meth ylation. The well-characterized asg, bsg, csg, and esg mutants were fo und to be of this type. The defects in FrzCD methylation of these sign aling mutants could be partially rescued by extracellular complementat ion with wild-type cells or addition of chemicals which restore their fruiting body formation. Mutants blocked in late development, i.e., tr anslucent mounds, showed normal FrzCD methylation. Surprisingly, some mutants blocked in early development also exhibited! a normal level of FrzCD methylation. The characterized mutants in this group were found to be defective in social motility. This indicates that FrzCD methyla tion defines a discrete step in the development of M. xanthus and that social motility mutants are not blocked in these early developmental steps.