Cloning, characterization and construction of htrA and htrA-like mutants of Brucella abortus and their survival in BALB/c mice

Abstract

A genomic library of Brucella abortus S2308 was screened for expression of recombinant proteins recognized by sera from mice and from cattle infected with B. abortus. A positive clone, BA1, expressing a 50 kDa peptide was recognized by both sera. Plasmid pBA1, isolated from BA1, was shown by restriction enzyme digestion to possess a 1.9 kb insert. The nucleotide sequence of the pBA1 insert revealed an open reading frame with of 1539 bases with a coding capacity of 513 amino acids and a predicted molecular weight of 50 992. The predicted amino acid sequence showed 37% identity to E. coli HtrA, a temperature inducible serine protease. A second B. abortus htrA gene, designated htrA-like, was identified on a different cloned frag ment that also encoded B. abortus recA. The nucleotide sequence of the htrA -like gene revealed an open reading frame of 1422 nucleotides with a coding capacity of 474 amino acids and a predicted molecular weight of 50 155. The deduced amino acid sequence of the htrA-like gene showed 42% and 36% identity with B. abortus and E. coli HtrAs respectively. Western blotting of E. coli lysate containing the htrA-like gene was not recognized by sera from B. abortus-infected cattle or mice. B. abortus htrA but not htrA-like relieved the temperature sensitive phenotype and permitted growth of an E. coli htrA mutant at 42°C. B. abortus htrA and htrA-like mutants were constructed and their survival and growth in BALB/c mice was compared to the parental strain S2308. Splenic levels of htrA or htrA-like mutants were initially lower but after 60 days post-infection both were higher than the parental strain. Histologic analysis of hepatic inflammatory responses suggested that an initial intense granuloma formation in the htrA group was the basis for early low splenic titers of bacteria, but that failure to maintain granulomas, as did mice given the parental strain, resulted in a marked secondary rise in splenic bacterial titers.