Mutant analysis reveals a specific requirement for protein P30 in Mycoplasma pnenmoniae gliding motility

The cell-wall-less prokaryote Mycoplasma pneumoniae, long considered among the smallest and simplest cells capable of self-replication, has a distinct cellular polarity characterized by the presence of a differentiated terminal organelle which functions in adherence to human respiratory epithelium, gliding motility, and cell division. Characterization of hemadsorption (HA)-negative mutants has resulted in identification of several terminal organelle proteins, including P30, the loss of which results in developmental defects and decreased adherence to host cells, but their impact on M. pneumoniae gliding has not been investigated. Here we examined the contribution of P30 to gliding motility on the basis of satellite growth and cell gliding velocity and frequency. M. pneumoniae HA mutant II-3 lacking P30 was nonmotile, but HA mutant II-7 producing a truncated P30 was motile, albeit at a velocity 50-fold less than that of the wild type. HA-positive revertant II-3R producing an altered P30 was unexpectedly not fully wild type with respect to gliding. Complementation of mutant II-3 with recombinant wild-type and mutant alleles confirmed the correlation between gliding defect and loss or alteration in P30. Surprisingly, fusion of yellow fluorescent protein to the C terminus of P30 had little impact on cell gliding velocity and significantly enhanced HA. Finally, while quantitative examination of HA revealed clear distinctions among these mutant strains, gliding defects did not correlate strictly with the HA phenotype, and all strains attached to glass at wild-type levels. Taken together, these findings suggest a role for P30 in gliding motility that is distinct from its requirement in adherence.