CRISPR/Cas9-based gene deletion and targeted metabolomics reveal ectoine flux reprogramming in Halomonas campaniensis

Ectoine and betaine are widely used compatible solutes. In Halomonas campaniensis XH26, the hom gene is involved in betaine biosynthesis, and the doeA gene participates in ectoine degradation. Deletion of hom and doeA may lead to poorly understood changes in metabolic flux within the ectoine biosynthesis pathway. The metabolically deficient XH26/Δhom and XH26/Δhom/ΔdoeA strains were constructed using a CRISPR/Cas9 approach. Comparative analyses of colony morphology, growth characteristics, and intracellular ectoine yield were conducted to evaluate the regulatory roles of the hom and doeA genes. RT-qPCR and targeted metabolomics were used to assess changes in gene expression related to ectoine biosynthesis and shifts in central carbon metabolic flux. The metabolically deficient strains XH26/Δhom and XH26/Δhom/ΔdoeA were constructed. Compared to the strain XH26, both mutant strains exhibited smaller colony diameters and shorter, broader cells. Intracellular ectoine yield increased by 13.3 % and 33.3 %, respectively, while betaine yield significantly decreased by 73.08 % and 76.92 %. RT-qPCR analysis revealed the significant upregulation of asd, lysC, ectA, ectB, and ectC, suggesting an enhanced metabolic flux toward ectoine biosynthesis. Targeted metabolomics indicated that the differentially abundant metabolites were mainly involved in four key energy metabolism pathways. These results indicate that knocking out the key genes hom and doeA in the ectoine biosynthesis pathway led to the restructuring of carbon metabolic flux in H. campaniensis. More carbon entered the ectoine biosynthesis pathway, resulting in the enhanced production of ectoine and a concomitant reduction in its degradation. These findings offer theoretical support for engineering high-yield ectoine-producing strains.