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Journal of Bacteriology, April 2005, p. 2368-2376, Vol. 187, No. 7
0021-9193/05/$08.00+0     doi:10.1128/JB.187.7.2368-2376.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Pleiotropic Effect of a Histidine Kinase on Carbohydrate Metabolism in Synechocystis sp. Strain PCC 6803 and Its Requirement for Heterotrophic Growth

Abhay K. Singh and Louis A. Sherman*

Department of Biological Sciences, Purdue University, West Lafayette, Indiana

Received 8 September 2004/ Accepted 13 December 2004

The deletion of a gene coding for a histidine kinase (sll0750, Hik8) in the unicellular cyanobacterium Synechocystis sp. strain PCC 6803 resulted in a conditional lethal phenotype with a pleiotropic effect on the expression of genes involved in glucose metabolism. This mutant had comparable doubling times to wild type (WT) in continuous-light-grown photoautotrophic and mixotrophic cultures, whereas it grew poorly under mixotrophic conditions with different light and dark cycles. Growth was completely stopped, and cells eventually died, when the light duration was less than 6 h on a 24-h regimen. Northern blot analysis demonstrated that steady-state transcript levels of genes encoding key enzymes of glycolysis, gluconeogenesis, the oxidative pentose phosphate pathway, and glycogen metabolism were significantly altered in a strain with mutant hik8 ({Delta}hik8) grown with or without glucose. In some cases, differential expression was dependent on growth conditions (photoautotrophic versus mixotrophic). The enzyme activities of glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and phosphofructokinase were significantly reduced in {Delta}hik8 compared to WT. Glycogen determination indicated that {Delta}hik8 accumulated glycogen under mixotrophic conditions but was unable to utilize these reserves for heterotrophic growth. The results suggest that the loss of gap1 transcription in the absence of Hik8 was the key factor that rendered cells unable to catabolize glucose and grow heterotrophically. Additionally, the transcript levels of the phytochrome gene (cph1) and its cotranscribed response regulator gene (rcp1) were significantly reduced and its dark inducibility was lost in {Delta}hik8. The results demonstrated that Hik8 plays an important role in glucose metabolism and is necessary for heterotrophic growth.


* Corresponding author. Mailing address: Department of Biological Sciences, Purdue University, 1392 Lilly Hall of Life Sciences, West Lafayette, IN 47907. Phone: (765) 494-8106. Fax: (765) 496-1496. E-mail: lsherman{at}bilbo.bio.purdue.edu.


Journal of Bacteriology, April 2005, p. 2368-2376, Vol. 187, No. 7
0021-9193/05/$08.00+0     doi:10.1128/JB.187.7.2368-2376.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.




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