Abstract

We previously characterized a gene (originally named org35, renamed cstA) encoding aPAS/PAC sensor hybrid histidine kinase (HK) which interacts with Azospirilum brasilenseNifA in a yeast two-hybrid system. The predicted CstA is a hybrid sensor kinase, comprising two N-terminal PAS domains, a histidine kinase core domain and a response regulator receiver (RR) domain. To determine the function of the cstA, two mutants wereconstructed including two in-frame deletion mutants ΔHK and ΔRR. A microscopic analysis revealed that both cstA mutants developed mature cyst cells more quickly than the wild type. Moreover, cstA mutants are affected in colony morphology which are essential for A. brasilense cells to differentiate into cyst-like forms. These observations suggested that cstA is involved in cyst development in A. brasilense.

  Key words: Two-component system protein, ·cyst development, ·nitrogen fixation,·Azospirillum brasilense.

Abbreviation

HK, Histidine kinase; RR, regulator receiver; PHB, poly-hydroxybutyric acid; TDFs, transcript-derived fragments; Ap, antibiotics ampicilline; Km, kanamycin; Tc, tetracycline; Nx, nalidixic acid; Sp, spectinomycin; DNA, deoxyribonucleic acid; PCR, polymerase chain reaction; MSM,MSM, minimal salts medium; EPS, exopolysaccharides