Residual effects of successive exposure of soybean Bradyrhizobium strains to aluminium on solid defined medium

Abstract

The aim of these studies was to investigate whether residual toxic effects of exposing soybean root nodule bacteria to Al in a solid defined media (SDM) alter tolerance to Al, survival, sensitivity to antibiotics, N2 fixation effectiveness and genetic diversity of Bradyrhizobium strains. After being exposed four times to Al, strains showed variation in Al tolerance but there was no evidence of change in their original Al tolerance, sensitivity to the antibiotics or genetic diversity. Exposure of Bradyrhizobium strains to SDM plus Al did not alter biological N2 fixation effectiveness of five strains. Strain SEMIA 587 showed a reduction in its N2 fixation effectiveness but it seems that it was just a superficial toxic effect because one single passage through the plant eliminated this effect. Residual Al did not cause increases in Al tolerance and reductions in the survival and N2 fixation effectiveness of Bradyrhizobium strains USDA 143, SEMIA 586, SEMIA 5019, SEMIA 5039 and SEMIA 5073. It also did not alter the resistance to antibiotics of strains USDA 143, SEMIA 5039 and SEMIA 5073, and the genetic diversity of the strains SEMIA 587 and SEMIA 5019.

Seleção de rizóbios nativos para guandu, caupi e feijão-de-porco nos tabuleiros costeiros de Sergipe

“…Não houve relação entre a reação ácida ou alcalina em meio de cultura contendo manitol (Tabela 1) como fonte de C e a tolerância ao alumínio. Diferenças entre estirpes de rizóbio quanto à tolerância ao Al têm sido relatadas (Ayanaba et al, 1983;Hungria & Vargas, 2000;Campo & Wood, 2001), contudo, os mecanismos envolvidos nessa tolerância ainda não estão totalmente esclarecidos. Estudos compilados por Johnson & Wood (1990) e Wood (1995 indicaram que a ação dos íons Al ocorreria pela sua ligação ao DNA, interferindo na divisão celular.…”

“…Do mesmo modo, concentrações tóxicas de Al ocorrem em diversos solos intemperizados dos trópicos e afetam todas as etapas da FBN (Hungria & Vargas, 2000). Contudo, existe variabilidade entre estirpes de rizóbio quanto à tolerância a temperaturas elevadas e ao Al tóxico (Ayanaba et al, 1983;La Favre & Eaglesham, 1986;Karanja & Wood, 1988;Wood, 1995;Hungria et al, 1997;Hungria & Vargas, 2000;Campo & Wood, 2001).…”