[The functions of yhcZ gene during Bacillus thuringiensis growth]

yhcZ and yhcY genes constitute a two-component system in Bacillus subtilis and B. cereus that regulates bacterial growth. However, the exact biological function of yhcZ gene in B. thuringiensis has not been fully elucidated. In this study, we proved that HD73_5824 is an yhcZ gene in B. thuringiensis subsp. kurstaki HD73 strain by combining gene functional annotation, analysis of upstream and downstream genes arrangement, and amino acid sequence alignment. This yhcZ gene may co-regulate bacterial growth with HD73_5825 gene (yhcY gene) by constituting a two-component system. Homologous recombination technology was employed to knock out yhcZ gene of HD73, resulting in a mutant strain HD (ΔyhcZ). The HD (ΔyhcZ) strain grew slower than wild-type strain HD73 in both LB and SSM medium. Re-introduction of yhcZ gene in HD (ΔyhcZ) strain can partially restore the growth, indicating that the deletion of yhcZ gene impacts the cell growth of HD73 strain. HD (ΔyhcZ) strain grew faster than HD73 strain in M9 medium with 0.4% glucose as the sole carbon source, implying that the yhcZ gene plays an important role in glucose utilization by HD73 strain. The results of biolog assay showed that HD (ΔyhcZ) exhibits a lower average well color development compared to HD73. HD(ΔyhcZ) cells also demonstrated a decreased capacity for absorbing and utilizing D/L-serine, formic acid, D-gluconic acid, L-histamine, D-methyl lactate, and citric acid, indicating that yhcZ gene could dramatically influence carbon source utilization of HD73 strains. Additionally, HD (ΔyhcZ) was less resistant to 8% NaCl, suggesting that yhcZ gene may be involved in the expression and regulation of genes related to high-salt stress response in bacterial cells. The results above show that the yhcZ gene significantly promotes glucose and other carbon sources utilization of HD73 strain during growth. Our findings will lay a foundation not only for analyzing the regulatory mechanisms of glucose and carbon sources utilization by yhcZ gene, but also providing a reference for the further research on bacterial growth and fermentation.