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Manganese-mediated resistance to aluminium and antibiotics in strains of Azospirillum brasilense and their interaction with rice genotypes in acid soil
Published online by Cambridge University Press: 27 March 2009
Summary
Manganese-tolerant strains Mnr-1 and Mnr-5 of Azospirillum brasilense (RAU 1075) were isolated through step-wise transfer to higher levels of manganese chloride. One of the strains (Mnr-5) showed more growth at low pH and greater nitrogenase activity in 10 mM MnCl2. 4H2O than parental and Mnr-1 strains. These tolerant strains also showed cross-resistance to antibiotics such as gentamycin and neomycin but not to streptomycin. Mn-adapted strains also tolerated elevated levels of aluminium (2·5–3·5 mg/kg) and the stability of the Mn-resistance required the presence of Mn2+ ions in the growth medium. It has been demonstrated that the effect of inoculation with Mn-adapted strains was variable with different genotypes of rice in acid soil and that initial low level of nitrogen was essential for maximum associative N2-fixation.
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