Originally published as Genetics Published Articles Ahead of Print on June 14, 2005.

Genetics, Vol. 170, 1473-1484, August 2005, Copyright © 2005
doi:10.1534/genetics.104.038943

RecD Plays an Essential Function During Growth at Low Temperature in the Antarctic Bacterium Pseudomonas syringae Lz4W

K. Regha^1,2, Ajit K. Satapathy¹ and Malay K. Ray³

Centre for Cellular and Molecular Biology, Hyderabad 500007, India

³ Corresponding author: Centre for Cellular and Molecular Biology, Uppal Rd., Hyderabad 500007, India.
E-mail: malay{at}ccmb.res.in

The Antarctic psychrotrophic bacterium Pseudomonas syringae Lz4W has been used as a model system to identify genes that are required for growth at low temperature. Transposon mutagenesis was carried out to isolate mutant(s) of the bacterium that are defective for growth at 4° but normal at 22°. In one such cold-sensitive mutant (CS1), the transposon-disrupted gene was identified to be a homolog of the recD gene of several bacteria. Trans-complementation and freshly targeted gene disruption studies reconfirmed that the inactivation of the recD gene leads to a cold-sensitive phenotype. We cloned, sequenced, and analyzed 11.2 kbp of DNA from recD and its flanking region from the bacterium. recD was the last gene of a putative recCBD operon. The RecD ORF was 694 amino acids long and 40% identical (52% similar) to the Escherichia coli protein, and it could complement the E. coli recD mutation. The recD gene of E. coli, however, could not complement the cold-sensitive phenotype of the CS1 mutant. Interestingly, the CS1 strain showed greater sensitivity toward the DNA-damaging agents, mitomycin C and UV. The inactivation of recD in P. syringae also led to cell death and accumulation of DNA fragments of 25–30 kbp in size at low temperature (4°). We propose that during growth at a very low temperature the Antarctic P. syringae is subjected to DNA damage, which requires direct participation of a unique RecD function. Additional results suggest that a truncated recD encoding the N-terminal segment of (1–576) amino acids is sufficient to support growth of P. syringae at low temperature.

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