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Journal of Bacteriology, October 2009, p. 6383-6393, Vol. 191, No. 20
0021-9193/09/$08.00+0     doi:10.1128/JB.00576-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Importance of Proteins Controlling Initiation of DNA Replication in the Growth of the High-Pressure-Loving Bacterium Photobacterium profundum SS9{triangledown}

Ziad W. El-Hajj,1 Theodora Tryfona,1,{dagger} David J. Allcock,1,2 Fariha Hasan,1,{ddagger} Federico M. Lauro,3,§ Lindsay Sawyer,1 Douglas H. Bartlett,3 and Gail P. Ferguson2*

Institute of Cell Biology and Centre for Science at Extreme Conditions, School of Biological Sciences, King's Buildings, University of Edinburgh, Edinburgh EH9 3JR, United Kingdom,1 School of Medicine & Dentistry, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, United Kingdom,2 Marine Biology Research Division, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093-02023

Received 1 May 2009/ Accepted 11 August 2009

The molecular mechanism(s) by which deep-sea bacteria grow optimally under high hydrostatic pressure at low temperatures is poorly understood. To gain further insight into the mechanism(s), a previous study screened transposon mutant libraries of the deep-sea bacterium Photobacterium profundum SS9 and identified mutants which exhibited alterations in growth at high pressure relative to that of the parent strain. Two of these mutants, FL23 (PBPRA3229::mini-Tn10) and FL28 (PBPRA1039::mini-Tn10), were found to have high-pressure sensitivity and enhanced-growth phenotypes, respectively. The PBPRA3229 and PBPRA1039 genes encode proteins which are highly similar to Escherichia coli DiaA, a positive regulator, and SeqA, a negative regulator, respectively, of the initiation of DNA replication. In this study, we investigated the hypothesis that PBPRA3229 and PBPRA1039 encode DiaA and SeqA homologs, respectively. Consistent with this, we determined that the plasmid-carried PBPRA3229 and PBPRA1039 genes restored synchrony to the initiation of DNA replication in E. coli mutants lacking DiaA and SeqA, respectively. Additionally, PBPRA3229 restored the cold sensitivity phenotype of an E. coli dnaA(Cs) diaA double mutant whereas PBPRA1039 suppressed the cold sensitivity phenotype of an E. coli dnaA(Cs) single mutant. Taken together, these findings show that the genes disrupted in FL23 and FL28 encode DiaA and SeqA homologs, respectively. Consequently, our findings add support to a model whereby high pressure affects the initiation of DNA replication in P. profundum SS9 and either the presence of a positive regulator (DiaA) or the removal of a negative regulator (SeqA) promotes growth under these conditions.

* Corresponding author. Mailing address: School of Medicine & Dentistry, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, United Kingdom. Phone: 44 1224 559147. Fax: 44 1224 555766. E-mail: g.ferguson{at}abdn.ac.uk

{triangledown} Published ahead of print on 21 August 2009.

{dagger} Present address: School of Biological Sciences, Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, United Kingdom.

{ddagger} Present address: Department of Microbiology, Quiaid-I-Azam University, Islamabad, Pakistan.

§ Present address: Environmental Microbiology Initiative, School of Biotechnology & Biomolecular Sciences, The University of New South Wales, Sydney, Australia 2052.

Journal of Bacteriology, October 2009, p. 6383-6393, Vol. 191, No. 20
0021-9193/09/$08.00+0     doi:10.1128/JB.00576-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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