Conditional requirement of SglT for type IV pili function and S-motility in Myxococcus xanthus

Abstract

Myxobacteria exhibit complex social behaviors such as predation, outer membrane exchange and fruiting body formation. These behaviors depend on coordinated movements of cells on solid surfaces that involve social (S) motility. S-motility is powered by extension-retraction cycles of type 4 pili (Tfp) and exopolysaccharides (EPS) that provide a matrix for group cellular movement. Here, we characterized a new class of S-motility mutants in Myxococcus xanthus . These mutants have a distinctive phenotype: they lack S-motility even though they produce pili and EPS and the phenotype is temperature-sensitive. The point mutations were mapped to a single locus, MXAN_3284, named sglT. Similar to pilT mutants, sglT mutants are hyperpiliated and, strikingly, the temperature-sensitive phenotype is caused by null mutations. Our results indicate that SglT plays a critical role in Tfp function associated with pilus retraction and that the block in pili retraction is caused by a Tfp assembly defect in the absence of SglT at high-temperature growth.

Conditional and Synthetic Type IV Pili-Dependent Motility Phenotypes in Myxococcus xanthus

“…Right, molecular weight markers. (C) Phase contrast and fluorescence microscopy images shows SglT-GFP ( Troselj et al, 2020 ) uniformly localized in cytoplasm, while GFP-SglS forms puncta in the cytosol (white triangles), which are dynamic (see Supplementary Video 5 ). Scale bar, 5 μm.…”

“…Here we describe a new S-motility protein, named SglS, which exhibits similar mutant phenotypes as pilT mutants, but are conditional. We additionally show that when a sglT null mutation ( Troselj et al, 2020 ), which has similar phenotypes as sglS mutants, are combined, the resulting double mutant exhibits an enhanced synthetic S-motility phenotype, suggesting these proteins function in redundant pathways, possibly related to Tfp retraction.…”

“…Since SglS and SglT have similar phenotypes as PilT mutants, that is they all produce EPS, are hyperpiliated and non-motile ( Wu et al, 1997 ; Black et al, 2006 ; Treuner-Lange et al, 2020 ; Troselj et al, 2020 ), suggests that SglS and SglT might facilitate PilT function in the retraction of pili at non-permissive temperatures. Alternatively, since a pilT null mutant in M. xanthus still exhibits residual retraction of Tfp ( Clausen et al, 2009 ), other factors, including SglS-SglT, could be involved in a redundant or parallel pathway to PilT for pili retraction.…”

“…Transformants were confirmed by phenotypic analysis, western blotting and microscopy. The Δ sglS-sglT ::Km double mutant was created by homologous recombination of a sglT insertion KO plasmid [pVT24, ( Troselj et al, 2020 )] into a Δ sglS strain by selecting Km r .…”

“…One example of this phenotype are pilT mutants, which are defective in motor function for pili retraction ( Clausen et al, 2009 ). Another example are sglT (MXAN_3284) mutants, which we recently described ( Troselj et al, 2020 ). These type of mutants offer insights into Tfp function and the control of pili retraction.…”