Abstract
Gliding motility is critical for normal development of spore-filled fruiting bodies in the soil bacterium Myxococcus xanthus. Mutations in mgl block motility and development but one mgl allele can be suppressed by a mutation in masK, the last gene in an operon adjacent to the mgl operon. Deletion of the entire 5.5 kb masABK operon crippled gliding and fruiting body development and decreased sporulation. Expression of pilAGHI, which encodes type IV pili (TFP) components essential for social (S) gliding, several cryptic pil genes, and a LuxR family protein were reduced significantly in the Δmas mutant while expression of the myxalamide operon was increased significantly. Localization and two-hybrid analysis suggest that the three Mas proteins form a membrane complex. MasA-PhoA fusions confirmed that MasA is an integral cytoplasmic membrane protein with a ≈100 amino acid periplasmic domain. Results from yeast two-hybrid assays showed that MasA interacts with the lipoprotein MasB and MasK, a protein kinase and that MasB and MasK interact with one another. Additionally, yeast two-hybrid analysis revealed a physical interaction between two gene products of the mas operon, MasA and MasB, and PilA. Deletion of mas may be accompanied by compensatory mutations since complementation of the Δmas social gliding and developmental defects required addition of both pilA and masABK.
Highlights
The Gram-negative d-proteobacterium Myxococcus xanthus provides a model for social interaction and gliding motility
Other genes in the pil gene cluster such as pilS and pilT did not differ significantly in expression from the was electroporated into DK1622 (WT) levels, these genes are expressed under the control of different promoters as shown in Fig. 4B. pilS, shown in Fig. 4B as an orange arrow, encodes a sensor histidine kinase in a two component system (TCS) with its corresponding transcriptional activator response regulator pilR [5]. pilT (Fig. 4B, light blue arrow) encodes an ATP-binding cassette protein that is essential for retraction of pili in M. xanthus [11,12]
Neither pilS nor pilT was expressed in DmasABK at a significantly different level from that observed in the wild-type, which suggests that global regulation of the pil gene cluster is not responsible for the defect in social motility observed in the DmasABK strain. fibA expression in a DmasABK strain was found to be slightly decreased relative to the WT
Summary
The Gram-negative d-proteobacterium Myxococcus xanthus provides a model for social interaction and gliding motility. S-motility is similar to ‘‘twitching’’ motility in Neisseria and Pseudomonas, TFP in M. xanthus do not adhere to the substratum [4,5,6,7]. Rather, they adhere to extracellular components such as fibrils and exopolysaccharides on an adjacent cell, which stimulate retraction of the pili [8]. They adhere to extracellular components such as fibrils and exopolysaccharides on an adjacent cell, which stimulate retraction of the pili [8] When these signals are absent, cells are non-motile regardless of the integrity of the social motor, which indicates that signaling via cell surface material is inherently crucial to S-motility
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