Sequence analysis and functional studies of a chromosomal region of alkaliphilic Bacillus firmus 0F4 encoding an ABC-type transporter with similarity of sequence and Na+ exclusion capacity to the Bacillus subtilis NatAB transporter

Yi Wei, Arthur A. Guffanti, Terry Ann Krulwich

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Abstract

A 14.1-kb DNA fragment was cloned from a lambda library containing inserts of DNA from alkaliphilic Bacillus firmus OF4 on the basis of its hybridization to a probe from a previously sequenced alkaliphile homolog of the natA gene from Bacillus subtilis. Sequence analysis of the entire fragment revealed that, as in B. subtilis, the natA gene was part of a putative gene locus encoding an ABC-type transporter. In the alkaliphile, the transporter involved three genes, designated natCAB, that are part of a larger operon of unknown function. This is in contrast to the two-gene natAB operon and to another homolog from B. subtilis, the yhaQP genes. Like natAB, however, the alkaliphile natCAB catalyzes Na+ extrusion as assessed in a mutant of Escherichia coli that is deficient in Na+ extrusion. The full 14.1-kb fragment of alkaliphile DNA sequenced in this study contained several probable operons as well as likely monocistronic units. Among the 17 predicted ORFs apart from natCAB were acsA, a homolog of a halobacterial gene encoding acetylCoA synthetase; sspA, a homolog of a small acid-soluble spore protein; and malK, an ATP-binding component that was unaccompanied by candidates for other real transport genes but was able to complement a malK-deficient mutant of E. coli. No strong candidates for genes encoding a secondary Na+/H+ antiporter were found in the fragment, either from the sequence analysis or from analyses of complementation of E. coli mutants by subclones of the 14.1-kb piece. There were a total of 12 ORFs whose closest and significant homologs were genes from B. subtilis; of these, one-third were in apparently different contexts, as assessed by the sequence of the neighboring genes, than the B. subtilis homologs.

Original languageEnglish
Pages (from-to)113-120
Number of pages8
JournalExtremophiles
Volume3
Issue number2
DOIs
StatePublished - May 1999

Keywords

  • ABC transporter
  • Alkaliphile
  • Bacillus firmus
  • Na extrusion
  • NatCAB
  • malK

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