Cyst Formation by Rhodospirillum centenum

Rhodospirllum centenum exhibits a very complex life cycle involving swim cell to swarm cell differentiation and the formation of desiccation resistant cysts. Cysts are metabolically dormant cells that are highly resistant to desiccation. Induction of the cyst phase of the R. centenum life cycle readily occurs when the cells are starved for nutrients (Berleman and Bauer 2004).

We have published detailed analysis of the cyst developmental phase of the R. centenum life cycle (Berleman and Bauer 2004). We have also determined growth conditions that will synchronously initiate cyst development by shifting cells from rich medium to butyrate minimal medium (Berleman and Bauer 2004). This has allowed us to define the timing of microscopically observable intermediate stages of cyst development. Fig. 2 shows different stages in cyst development (Berleman and Bauer 2004).

We have also isolated a number of mutants that arrest at various stages of this developmental pathway as well as numerous hypercyst mutant that are de-repressed for cyst formation (Fig. 3, and Berleman et al., 2004). These mutants are mapped to defined locations of the  sequenced R. centenum genome. The results of these genetic studies have allowed us to identify numerous regulatory proteins that are involved in controlling cyst formation in this species. This includes that identification of a novel chemotaxis-like signal transduction cascade that is responsible for controlling cyst development (Berleman, J., & C. E. Bauer 2005).  We have also established that cyclic GMP is an important signaling molecule involved in cyst formation (Marden et al., 2011)

Recently, we have published detailed biochemical and site directed mutational analysis of the Che-like signal transduction cascade to determine the flow of phosphates among various regulatory components (Fig 4; He et al. 2013). In addition, we are undertaking RNASeq and CHIP Seq analysis to defining global changes in gene expression that occur as these cells transition from vegetative to cyst phases of the life cycle. We can synchronously induce cyst formation so it is a relatively easy task of isolating mRNA at various time points (Fig. 2) for use in analysis of global changes in gene expression. Comparative analysis of the alteration of global gene expression in wild type and in mutant strains are defining the involvement of individual regulators in controlling this developmental pathway. The long-term goal is to use a combination of classic genetics, biochemistry and systems biology approaches to understand the cyst developmental pathway in this species.

Finally, the formation of desiccation resistant cysts occur in many Gram-negative species including Azospirillum brasilense, Azospirillum lipoferum, R. centenum in the a-proteobacteria group; Methylocystis parvus , Azotobacter chroococcum and Azotobacter vinelandii in the g-proteobacteria and Bdellovibrio sp in the d-proteobacteria. Myxospores synthesized by Myxobacteria are also very similar in appearance, and in desiccation resistance properties, to that of cysts described in the species listed above. Thus, the results obtained from the characterization of cyst formation in R. centenum have far-ranging implications for many species of bacteria.

References :

He, K., J. M. Marden, E. M. Quardokus & C. E. Bauer. 2013. Phosphate flow between hybrid histidine kinases CheA3 and CheS3 controls Rhodospirillum centenum cyst formation. PLOS Genetics, DOI: 10.1371/journal.pgen.1004002 (This work was highlighted by Nature Reviews Microbiology)

Marden, J.N., J.E. Berleman, & C.E. Bauer. 2011. Cyclic GMP controls Rhodospirillum centenum cyst development.  Mol. Micro. 79:600-615 (Commentary of this study in Mol. Micro 79:562-565).

Lu YK, Marden J, Han M, Swingley WD, Mastrian SD, Chowdhury SR, Hao J, Helmy T, Kim S, Kurdoglu AA, Matthies HJ, Rollo D, Stothard P, Blankenship RE, Bauer CE, & Touchman JW. 2010. Metabolic flexibility revealed in the genome of the cyst-forming alpha-1 proteobacterium Rhodospirillum centenum.  BMC Genomics. 11:325.

Berleman, J., & C. E. Bauer 2005. A chemotaxis like signal transduction cascade controls a cyst developmental pathway in Rhodospirillum centenum. Mol . Microbiol. 56, 1457-1466

Berleman, J., & C. E. Bauer 2005. A chemotaxis like signal transduction cascade is involved in controlling flagella biosynthesis in Rhodospirillum centenum, Mol. Microbio. 55, 1390-1402

Berleman, J., B. Hasselbring, & C. E. Bauer 2004. Hypercyst Mutants in Rhodospirillum centenum Identify Regulatory Loci Involved in Cyst Cell Differentiation. J. Bacteriol. 186, 5834-5841 (Featured on cover).

Berleman, J. & C. E. Bauer 2004. Characterization of the cyst cell formation in the purple photosynthetic bacterium Rhodospirillum centenum. Microbiology 150, 383-390 (Featured on cover)