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Surface polysaccharide biosynthesis and function, and regulation by DmxA and c-di-GMP in Myxococcus xanthus
Bacteria possess surface polysaccharides that fulfill different functions, e.g. mediate host/pathogen interactions and protect cells from desiccatio stress, predation or immunological reactions. Myxococcus xanthus is a Gram-negative deltaproteobacterium with a complex and nutrient-dependent life cyc...
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| Format: | Dissertation |
| Sprache: | Englisch |
| Veröffentlicht: |
Philipps-Universität Marburg
2020
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| Online Zugang: | PDF-Volltext |
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| Zusammenfassung: | Bacteria possess surface polysaccharides that fulfill different functions, e.g. mediate host/pathogen interactions and protect cells from desiccatio stress, predation or immunological reactions. Myxococcus xanthus is a Gram-negative deltaproteobacterium with a complex and nutrient-dependent life cycle. In the presence of nutrients, cells grow, divide and form coordinately spreading colonies on a solid surface. Upon starvation, cells initiate a developmental program that culminates in the formation of spore-filled fruiting bodies. Both parts of the lifecycle involve extensive cell-cell interactions. So far, three different surface polysaccharides have been identified in M. xanthus: lipopolysaccharide (LPS), exopolysaccharide (EPS) and spore coat polysaccharide. However little is known about their biosynthetic machineries, regulation and composition.
To understand how these polysaccharides are synthesized in M. xanthus, we identified homologs of proteins involved in surface polysaccharide biosynthesis (i.e. proteins of Wzx/Wzy or ABCtransporter dependent pathways). Bioinformatics, genetic analyses, heterologous expression, and biochemical experiments, in combination with detection of LPS, EPS or spore coat polysaccharide biosynthesis, allowed us to elucidate the biosynthetic pathways for LPS Oantigen and EPS. Moreover, we identified the missing components of the spore coat
polysaccharide biosynthesis machinery. While synthesis of LPS O-antigen depends on an ABCtransporter-dependent pathway, synthesis of EPS and spore coat polysaccharide involves Wzx/Wzy-dependent pathways. Each individual pathway is dedicated to the biosynthesis of one polysaccharide. We also identified a polysaccharide biosynthesis locus of unknown function encoding homologs of a Wzx/Wzy-dependent pathway. Using selected mutants exclusively blocked in the synthesis of one of these sugars, we reevaluated the role of these surface glycans. We show that O-antigen is essential for development and gliding motility, but conditionally important for type IV pili (T4P)-dependent motility. By contrast, EPS is important for agglutination, T4P-dependent motility and T4P formation, and is conditionally important for development.
The nucleotide-based second messenger c-di-GMP has critical functions in M. xanthus. During growth, the diguanylate cyclase (DGC) DmxA is important for motility. We show that DGC activity of DmxA is important for motility and that DmxA is involved in regulation of the polarity of the two motility systems. Because DmxA-mVenus localizes to mid-cell and this localization depends on FtsZ, and DmxA does not contribute to the overall c-di-GMP pool, we suggest that DmxA function may be restricted to a local pool. |
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| Umfang: | 192 Seiten |
| DOI: | 10.17192/z2020.0474 |