Abstract
As prokaryotic models for multicellular development, Stigmatella aurantiaca and Myxococcus xanthus share many similarities in terms of social behaviors, such as gliding motility. Our current understanding of myxobacterial grouped-cell motilities comes mainly from the research on M. xanthus, which shows that filamentous type IV pili (TFP), composed of type IV pilin (also called PilA protein) subunits, are the key apparatus for social motility (S-motility). However, little is known about the pilin protein in S . aurantiaca . We cloned and sequenced four genes (pilA Sa1~4) from S . aurantiaca DSM17044 that are homologous to pilA Mx (pilA gene in M. xanthus DK1622). The homology and similarities among PilASa proteins and other myxobacterial homologues were systematically analyzed. To determine their potential biological functions, the four pilA Sa genes were expressed in M. xanthus DK10410 (ΔpilA Mx), which did not restore S-motility on soft agar or EPS production to host cells. After further analysis of the motile behaviors in a methylcellulose solution, the M. xanthus strains were categorized into three types. YL6101, carrying pilA Sa1, and YL6104, carrying pilA Sa4, produced stable but unretractable surface pili; YL6102, carrying pilA Sa2, produced stable surface pili and exhibited reduced TFP-dependent motility in methylcellulose; YL6103, carrying pilA Sa3, produced unstable surface pili. Based on these findings, we propose that pilA Sa2 might be responsible for the type IV pilin production involved in group motility in S . aurantiaca DSM17044. After examining the developmental processes, it was suggested that the expression of PilASa4 protein might have positive effects on the fruiting body formation of M. xanthus DK10410 cells. Moreover, the formation of fruiting body in M. xanthus cells with stable exogenous TFPSa were compensated by mixing them with S . aurantiaca DSM17044 cells. Our results shed some light on the features and functions of type IV pilin homologues in S . aurantiaca .
Highlights
Myxobacteria belong to a branch of intriguing prokaryotes recognized for their complex social behaviors [1]
Our current understanding of myxobacterial social cell behaviors comes mainly from research on M. xanthus, which shows that social motility (S-motility) plays a fundamental role in these processes [4,5]
Energy-dependent cohesion and motility are suggested to be related phenomena in S. aurantiaca [21,22], which is consistent with the finding in M. xanthus that extracellular polysaccharides (EPS) is involved in both cohesion and S-motility [9,23]
Summary
Myxobacteria belong to a branch of intriguing prokaryotes recognized for their complex social behaviors [1]. Our current understanding of myxobacterial social cell behaviors comes mainly from research on M. xanthus, which shows that social motility (S-motility) plays a fundamental role in these processes [4,5]. During S-motility, TFP function by extending at one of the cell poles, attaching to the solid surfaces of the substratum or another cell, and retracting to pull the cell forward [10,11,12,13,14]. To achieve the cycles of extension and retraction, pilin proteins are assembled into polar filaments mediated by the ATPase PilB, and the extracellular TFP are disassembled into single subunits with the assistance of the ATPase PilT [13,15]. In addition to being the key apparatus for S-motility, TFP play divergent roles in other physiological aspects of M. xanthus. The TFP apparatus has been proposed to be involved in plasmid natural transformation in M. xanthus [18]
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