A genomic library derived from the deep-sea bacterium Photobacterium profun
dum SS9 was conjugally delivered into a previously isolated pressure-sensit
ive SS9 mutant, designated EC1002 (E. Chi and D. H. Bartlett, J. Bacteriol.
175:7533-7540, 1993), and exconjugants were screened for the ability to gr
ow at 280-atm hydrostatic pressure. Several clones were identified that had
restored high-pressure growth. The complementing DNA was localized and in
all cases found to possess strong homology to recD, a DNA recombination and
repair gene. EC1002 was found to be deficient in plasmid stability, a phen
otype also seen in Escherichia coli recD mutants. The defect in EC1002 was
localized to a point mutation that created a stop codon within the recD gen
e. Two additional recD mutants were constructed by gene disruption and were
both found to possess a pressure sensitive growth phenotype, although the
magnitude of the defect depended on the extent of 3' truncation of the recD
coding sequence. Surprisingly, the introduction of the SS9 recD gene into
an E. coli recD mutant had two dramatic effects. At high pressure, SS9 recD
enabled growth in the E. coli mutant strain under conditions of plasmid an
tibiotic resistance selection and prevented cell filamentation. Both of the
se effects were recessive to wild-type E. coli recD. These results suggest
that the SS9 recD gene plays an essential role in SS9 growth at high pressu
re and that it may be possible to identify additional aspects of RecD funct
ion through the characterization of this activity.