PilA localization affects extracellular polysaccharide production and fruiting body formation in Myxococcus xanthus

Abstract

SummaryMyxococcus xanthus is a Gram-negative bacterium capable of complex developmental processes involving vegetative swarming and fruiting body formation. Social (S-) gliding motility, one of the two motility systems used by M. xanthus, requires at least two cell surface structures: type IV pili (TFP) and extracellular polysaccharides (EPS). Extended TFP that are composed of thousands of copies of PilA retract upon binding to EPS and thereby pull the cell forward. TFP also act as external sensor to regulate EPS production. In this study, we generated a random PilA mutant library and identified one derivative, SW1066, which completely failed to undergo developmental processes. Detailed characterization revealed that SW1066 produced very little EPS but wild-type amounts of PilA. These mutated PilA subunits, however, are unable to assemble into functional TFP despite their ability to localize to the membrane. By preventing the mutated PilA of SW1066 to translocate from the cytoplasm to the membrane, fruiting body formation and EPS production were restored to the levels observed in mutant strains lacking PilA. This apparent connection between PilA membrane accumulation and reduction in surface EPS implies that specific cellular PilA localization are required to maintain the EPS level necessary to sustain normal S-motility in M. xanthus.

Two Isoforms of Geobacter sulfurreducens PilA Have Distinct Roles in Pilus Biogenesis, Cytochrome Localization, Extracellular Electron Transfer, and Biofilm Formation

“…This finding was attributed to rapid cleavage of the preprotein by the peptidase PilD at the inner membrane (62), where both isoforms were cleaved after the glycine at position Ϫ1 (3, 16), resulting in the same mature protein. Similar observations have been reported for type IV PilA of Myxococcus xanthus (73), where rapid cleavage by PilD prevented the detection of uncleaved PilA in wild-type strains on Western blots. The slower migration of the prepilin protein was detected only when the cleavage site was mutated.…”

Myxococcus xanthus Developmental Cell Fate Production: Heterogeneous Accumulation of Developmental Regulatory Proteins and Reexamination of the Role of MazF in Developmental Lysis

“…Since biogenesis of the pilus requires PilC (65,66), it is tempting to speculate that the concomitant accumulation of PilA and reduction of PilC could trap PilA either in the inner membrane pool or as pili at the cell surface. PilA trapped in the inner membrane reduces EPS production and prevents fruiting body formation (67). Since the sedimented cell fraction displays significantly more EPS ( Fig.…”

Type IV Pilin Proteins: Versatile Molecular Modules

“…Interestingly, when pilR or pilS was inactivated, levels of the assembly system components were similar to those in the wild type, suggesting that even though there was no PilA expression in either of those mutants, the cells were unable to sense its absence and respond accordingly. In M. xanthus, pilB mutations that caused the accumulation of pilins in the inner membrane led to the downregulation of EPS synthesis, a phenotype that could be relieved partially by inactivating pilA in the pilB background (425). In contrast, mutations that led to the accumulation of PilA in the cytoplasm (signal sequence mutations) did not repress EPS synthesis.…”