RECOMBINANT CO-EXPRESSION OF THE ECTOINE BIOSYNTHESIS GENE CLUSTER ectABC IN HALOMONAS FROM QINGHAI LAKE

Halomonas is capable of synthesizing organic compatible solutes ectoine in response to high osmotic pressure. To reveal the possibility of heterologous co-expression of ectoine biosynthesis genes, intracellular ectoine in Halomonas sp. QHL1 strain was determined by HPLC under different salt gradients. The entire ectABC gene cluster for ectoine synthesis was cloned using genome walking and expressed in the heterologous recombinant E. coli BL21. The results showed that the concentration of ectoine accumulated in the cells had a positive correlation with the extracellular Na+ concentration and reached a maximum value (167.1 mg/g cell dry weight) at 1.0 mol/L Na+, and high concentration of Na+ strongly inhibited the bacteria growth. The entire ectABC gene cluster in QHL1 strain was 3580 bp, containing structural gene ectA (579 bp), ectB (1269 bp) and ectC (390 bp). Based on bioinformatics prediction analysis, two putative promoters (70 and 38-controlled promoter) and several conserved motifs with unknown function were identified in the upstream of ect-operon. The recombinant plasmid pET-28a (+)-ectABC was successfully constructed, and the results of heterologous expression indicated that these three genes could be simultaneously translated to protein EctA (27.2 kD), EctB (52.5 kD) and EctC (20.8 kD). These results contribute further improvements in ectoine high yield and hypohaline biotechnological process optimization, and also provided a framework for future genetic manipulation of systems metabolic engineering.