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Journal of Bacteriology, October 2002, p. 5590-5598, Vol. 184, No. 20
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.20.5590-5598.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Tactic Responses to Oxygen in the Phototrophic Bacterium Rhodobacter sphaeroides WS8N

Simona Romagnoli,{dagger} Helen L. Packer,{ddagger}, and Judith P. Armitage*

Microbiology Unit, Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom

Received 3 April 2002/ Accepted 18 July 2002

The temporal and spatial behavior of a number of mutants of the photosynthetic, facultative anaerobe Rhodobacter sphaeroides to both step changes and to gradients of oxygen was analyzed. Wild-type cells, grown under a range of conditions, showed microaerophilic behavior, accumulating in a 1.3-mm band about 1.3 mm from the meniscus of capillaries. Evidence suggests this is the result of two signaling pathways. The strength of any response depended on the growth and incubation conditions. Deletion of either the complete chemosensory operons 1 and 2 plus the response regulator genes cheY4 and cheY5 or cheA2 alone led to the loss of all aerotactic responses, although the cells still swam normally. The Prr system of R. sphaeroides responds to electron flow through the alternative high-affinity cytochrome oxidase, cbb3, controlling expression of a wide range of metabolic pathways. Mutants with deletions of either the complete Prr operon or the histidine kinase, PrrB, accumulated up to the meniscus but still formed a thick band 1.3 mm from the aerobic interface. This indicates that the negative aerotactic response to high oxygen levels depends on PrrB, but the mutant cells still retain the positive response. Tethered PrrB- cells also showed no response to a step-down in oxygen concentration, although those with deletions of the whole operon showed some response. In gradients of oxygen where the concentration was reduced at 0.4 µM/s, tethered wild-type cells showed two different phases of response, with an increase in stopping frequency when the oxygen concentration fell from 80 to 50% dissolved oxygen and a decrease in stopping at 50 to 20% dissolved oxygen, with cells returning to their normal stopping frequency in 0% oxygen. PrrB and CheA2 mutants showed no response, while PrrCBA mutants still showed some response.

* Corresponding author. Mailing address: Microbiology Unit, Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom. Phone: 44 1865 275297. Fax: 44 1865 275299. E-mail: judith.armitage{at}bioch.ox.ac.uk.

{dagger} Present address: Department of Microbiology, Ohio State University, Columbus, OH 43210-1292.

{ddagger} Present address: School of Biological and Molecular Sciences, Oxford Brookes University, Oxford OX3 0BP, United Kingdom.

Journal of Bacteriology, October 2002, p. 5590-5598, Vol. 184, No. 20
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.20.5590-5598.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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