Understanding unipolar growth within the rod-shaped bacterium Rhizobium leguminosarum

Wright, Hannah Jane (2023) Understanding unipolar growth within the rod-shaped bacterium Rhizobium leguminosarum. Doctoral thesis, University of East Anglia.

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Abstract

Unipolar growth within the alphaproteobacterial family Rhizobiaceae is believed to be coordinated by a largely unknown suite of proteins distinct from those required for dispersed cell elongation (a growth mechanism widely observed amongst other Gram-negative rods). Recent studies within Agrobacterium and Sinorhizobium have identified several growth-associated polar proteins, yet the mechanisms underpinning unipolar growth within other Rhizobiaceae genera remain poorly understood. In this thesis, Rhizobium leguminosarum homologs of the chromosome partitioning ATPase ParA1 and pole-organising protein PopZ, and a novel Rhizobium cytoskeletal element (Rcy), were identified as candidate growth-associated polar proteins. Their involvement during unipolar growth was then investigated by studying the impact of their deletion and overexpression on cell growth and morphology, and by observing the localisation of ParA1-, PopZ-, and Rcy-EGFP fusion proteins.

The findings of this work support the classification of PopZ as a polarity protein, proposed here to possibly localise to the R. leguminosarum growth pole. Both PopZ and ParA1 help to maintain rod morphology in R. leguminosarum, possibly by facilitating spatial coordination of cell growth and division. Overexpression of PopZ was associated with minicell formation, while ParA1 overexpression was correlated with asymmetric cell division and occasional cellular branching. Within this thesis, the candidate cytoskeletal element Rcy was characterised as a unipolar-localised protein, hypothesised to determine the site of cell growth at the growth pole. Overexpression of Rcy within R. leguminosarum resulted in the formation of enlarged spherical and irregularly shaped cells containing multiple Rcy foci around the perimeter of the cell. Furthermore, difficulties recovering rcy knockout mutants suggest that this protein may be essential for cell viability. Overall, this work highlights the involvement of ParA1, PopZ and Rcy in the coordination of Rhizobium growth and division, shedding light on the proteins which may regulate unipolar growth and the maintenance of rod morphology within the Rhizobiaceae.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Biological Sciences
Depositing User:	Nicola Veasy
Date Deposited:	12 Nov 2024 15:25
Last Modified:	12 Nov 2024 15:25
URI:	https://ueaeprints.uea.ac.uk/id/eprint/97660
DOI:

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