关键词: 茎瘤固氮根瘤菌ORS571, TlpA1, 原核表达, ITC, 生物膜, 絮凝

Abstract: Chemotaxis plays an important role in the initial stage of symbiosis between rhizobium and host. TlpA1 is an important transmembrane chemoreceptor in A. caulinodans ORS571, but its sensing mechanism is not clear. To study the mechanism of the interaction between receptor protein TlpA1 and chemotaxin, and the biological function of TlpA1 in A.caulinodans ORS571. The N-terminal expression plasmid was constructed by the blunt end ligation, and the target protein was expressed and purified in Escherichia coli. The interaction between protein and chemotaxin was detected by isothermal titration calorimetry. The phenotypes, such as biofilm formation and cell flocculation, were investigated. The results showed that the receptor protein TlpA1 bound to succinic acid through its extracellular part (29～183 amino acids). Under the condition of nitrogen fixation, the biofilm formation of ΔTlpA1 mutant decreased about 38% compared with wild type. And there was no significant difference in flocculation between the ΔTlpA1 mutant and wild type. The transmembrane chemoreceptors TlpA1 could regulate the biofilm formation of A. caulinodans ORS571 by sensing of succinic acid, but could not regulate the flocculation of A. caulinodans ORS571.

Key words: Azorhizobium caulinodans ORS571, TlpA1, prokaryotic expression, ITC, biofilm, flocculation