RESUMO

The plant growth-promoting rhizobacterium, Ochrobactrum sp. 11a displays a high intrinsic salinity tolerance and has been used in this work to study the molecular basis of bacterial responses to high concentrations of NaCl. A collection of Ochrobactrum sp. 11a mutants was generated by Tn5-B21 mutagenesis and screened for sensitivity to salinity. One clone, designated PBP and unable to grow on glutamate mannitol salt agar medium supplemented with 300 mM NaCl was selected and further characterized. The PBP mutant carries a single transposon insertion in a gene showing a high degree of identity to the serine-type d-alanyl-d-alanine carboxypeptidase gene of Ochrobactrum anthropi. Interestingly, the expression of this gene was shown to be upregulated by salt in the PBP mutant. Moreover, evidence is presented for the requirement of the gene product for adaptation to high-salt conditions as well as to overcome the toxicity of LiCl, KCl, sucrose, polyethylene glycol (PEG), AlCl(3), CuSO(4), and ZnSO(4). In addition to the altered tolerance to both ionic and osmotic stresses, the PBP mutant exhibited changes in colony and cell morphology, exopolysaccharide production, and an increased sensitivity to detergents.

Assuntos

Resposta ao Choque Térmico , Íons , Ochrobactrum/crescimento & desenvolvimento , Pressão Osmótica , Tolerância ao Sal , D-Ala-D-Ala Carboxipeptidase Tipo Serina/metabolismo , Sequência de Aminoácidos , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Meios de Cultura , Elementos de DNA Transponíveis , Regulação Bacteriana da Expressão Gênica , Íons/farmacologia , Dados de Sequência Molecular , Mutagênese , Mutação , Ochrobactrum/enzimologia , Ochrobactrum/genética , Ochrobactrum/fisiologia , Proteínas de Ligação às Penicilinas/genética , Proteínas de Ligação às Penicilinas/metabolismo , Análise de Sequência de DNA , D-Ala-D-Ala Carboxipeptidase Tipo Serina/genética , Cloreto de Sódio/farmacologia