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Characterization of Acid-Aluminium Sensitive Mutants of Soybean Symbiont Bradyrhizobium japonicum Generated by Transposon Mutagenesis

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Author(s): ARIS TRI WAHYUDI | ANDINI PURNAWIJAYA | DINI NURDIANI | TEDJA IMAS

Journal: Microbiology Indonesia
ISSN 1978-3477

Volume: 1;
Issue: 2;
Start page: 81;
Date: 2007;
Original page

Keywords: Bradyrhizobium japonicum | acid-aluminium tolerance | transposon mutagenesis | aluminium absorption | phosphate intracellular

ABSTRACT
Acid-aluminium sensitive mutants of symbiotic bacterium Bradyrhizobium japonicum BJ11 (designated as AAS11) and KDR15 (designated as AAS15) were constructed by mini-Tn5 transposon mutagenesis to study genes involved in acid-aluminium tolerance (AAT) in B. japonicum. Transposon delivery was carried out through conjugation between B. japonicum strains as recipients and Escherichia coli S17-1 (ë pir) carrying pUTmini-Tn5Km1 as a donor strain. The result showed that frequency of transconjugation was in the range of 6.7 x 10-7 to 7.1 x 10-6 cell per recipients. AAS11 and AAS15 mutants did not grow on Ayanaba media (pH 4.5) containing 50 M Aluminium. These mutants remained able to form root nodules of Siratro (Macroptilium arthropurpureum) plants revealing genes interrupted by transposon which were responsible for acid-Al tolerance did not correlate with the nodulation genes. Strains tolerant to acid-aluminium and their mutants with a wild type sensitive to acidaluminium were characterized by accumulating phosphate and aluminium absorption. Compared to the wild type acid-aluminium tolerant B. japonicum, there was approximately a three- to eight-times decrease in phosphate accumulation and a five- to seven-times increase in aluminium absorption by these mutants. These results suggest that aluminium and phosphate contents in the bacterial cells may be involved in mechanisms of acid-Al tolerance of B. japonicum grown in acid-aluminium stress conditions.
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