[Cloning and characterization of ectABC cluster from Bacillus alcalophilus DTY1]

Bacillus alcalophilus DTY1, one moderate halophytic bacterium isolated from saline soil in Loess Plateau of China, was characterized with efficient production of ectoine. In this study, the gene cluster ectABC taking in charge of biosynthesizing ectoine was cloned from the genomic library of strain DTY1. Nucleotide sequencing indicated that ectA, ectB and ectC were predicted to encode peptides of 169, 428 and 132 amino acids, respectively. The deduced amino acid sequences of EctA, EctB and EctC share 59%, 81% and 81% identity to 2,4-diaminobutyric acid acetyltransferase, 2,4-diaminobutyric acid transaminase and ectoine synthase of B. halodurans C-125, respectively. A fragment containing ectABC genes was introduced into B. cereus Z, which made the transgenic Z cells increased tolerance to salt, remarkably. HPLC analysis of ectoine in the transgenic Z cells revealed that 70.1 mg/g ectoine was detected in 1.0% NaCl medium and 118.6 mg/g ectoine in 5.0% NaCl medium. Furthermore, as the concentration of salt increased, transgenic Z cells accumulated more ectoine. These results suggest that ectoine is an important facet in B. alcalophilus DTY1 to high-osmolarity surroundings, and the expression of ectABC is induced by salt strength.