Abstract
ABSTRACTEfficient N2-fixing Leguminosae nodulating bacteria resistant to As may facilitate plant growth on As-contaminated sites. In order to identify bacteria holding these features, 24 strains were isolated from nodules of the trap species Crotalaria spectabilis (12) and Stizolobium aterrimum (12) growing on an As-contaminated gold mine site. 16S rRNA gene sequencing revealed that most of the strains belonged to the group of α-Proteobacteria, being representatives of the genera Bradyrhizobium, Rhizobium, Inquilinus, Labrys, Bosea, Starkeya, and Methylobacterium. Strains of the first four genera showed symbiotic efficiency with their original host, and demonstrated in vitro specific plant-growth-promoting (PGP) traits (production of organic acids, indole-3-acetic-acid and siderophores, 1-aminocyclopropane-1-carboxylate deaminase activity, and Ca3(PO4)2 solubilization), and increased resistance to As, Zn, and Cd. In addition, these strains and some type and reference rhizobia strains exhibited a wide resistance spectrum to β-lactam antibiotics. Both intrinsic PGP abilities and multi-element resistance of rhizobia are promising for exploiting the symbiosis with different legume plants on trace-element-contaminated soils.
Highlights
Soil microorganisms delivering ecosystem services have been recognized as important allies for phytotechnologies
Intrinsic plant-growth promoting abilities and multi-element resistance of rhizobia are promising for exploiting the symbiosis with different legume-plants on trace element contaminated soils
All strains isolated from nodules of C. spectabilis (12) and S. aterrimum (12)
Summary
Soil microorganisms delivering ecosystem services (e.g. biological N2 fixation - BFN) have been recognized as important allies for phytotechnologies. Their ability to improve the nutritional status of the plant, positively influence the tolerance of plants to excess of trace elements. The symbiosis rhizobia-legume can replace ammonium-based fertilizers, and reduce risks on soil acidification, which might increase availability of trace elements. Contamination is ‘inactivated’ in place, preventing further spreading and transfer into food chains (2,5,6,7,8). This all contributes to an attenuation of the impacts of the contaminants on site and on adjacent ecosystems (2,8)
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