Characterisation of global regulators that control expression of a flagella system in Rhodobacter sphaeroides

Thesis

The α-proteobacterium Rhodobacter sphaeroides expresses one flagellar system (Fla1) and two chemotaxis operons (cheOp2 and cheOp3) under laboratory conditions. It has another flagellar system (Fla2) with a proposed cognate chemotaxis operon (cheOp1) which until recently had not been seen to be expressed. Here we characterised Fla2 motility and show that cheOp1 can be expressed under Fla2-inducing conditions. Putative Fla2^+ strains AM1 and N29 were incubated on Sistrom's media and expression of the Fla2 system was confirmed with western blotting and mass spectrometry. The Fla2 motility pattern was significantly different to Fla1 when measured on soft nutrient agar and by analysing free swimming cells. Fla2^+ strains swam in a corkscrew-like pattern which may favour movement through biofilms. Fla2^+ AM1 and N29 were significantly deficient in their capacity to form biofilms compared to Fla1^+ WS8N. AM1 and N29 were found to contain mutations in cckA and plasmids expressing these mutations were able to switch expression of Fla1 in WS8N to Fla2. Expression of mutant cckA also affected cheOp2 and cheOp3 expression and induced expression of cheOp1. Some members of the α-proteobacteria are known to engage in lifestyle switches from motile to sessile growth. It is suggested that a similar switch occurs in R. sphaeroides which uses the Fla1 system for motility in liquid environments and for the initial attachments to surfaces and the Fla2 system for movement through the highly-viscous biofilm. For the first time we have also shown expression of cheOp1 which may engage in cross-talk with the cheOp2 and cheOp3-expressed chemotaxis system. These results have implications for the regulation of dual flagellar systems in the α-proteobacteria.

Authors: Thomas, S

• Publication date: 2015
• Type of award: MSc
• Level of award: Masters
• Awarding institution: University of Oxford
• Language: English
• Keywords: chemotaxis; Rhodobacter sphaeroides; Rhodobacter; flagella; Fla1; Fla2
• Subjects: Microbiology; Biochemistry