Diversity and salt tolerance of native Acacia rhizobia isolated from saline and non‐saline soils

Abstract

Re-establishing native vegetation in stressed soils is of considerable importance in many parts of the world, leading to significant interest in using plant-soil symbiont interactions to increase the cost-effectiveness of large-scale restoration. However, effective use of soil microbes in revegetation requires knowledge of how microbe communities vary along environmental stress gradients, as well as how such variation relates to symbiont effectiveness. In Australia, shrubby legumes dominate many ecosystems where dryland salinity is a major issue, and improving plant establishment in saline soils is a priority of regional management agencies. In this study, strains of rhizobial bacteria were isolated from a range of Acacia spp. growing in saline and non-saline soils. Replicates of each strain were grown under several salinity levels in liquid culture and characterized for growth and salt tolerance. Genetic characterization of rhizobia showed considerable variation among strains, with salt tolerance and growth generally higher in rhizobial populations derived from more saline soils. These strains showed markedly different genetic profiles and generic affiliations to those from more temperate soils, suggesting community differentiation in relation to salt stress. The identification of novel genomic species from saline soils suggests that the diversity of rhizobia associated with Australian Acacia spp. is significantly greater than previously described. Overall, the ability of some symbiotically effective strains to tolerate high salinity is promising with regard to improving host plant re-establishment in these soils.

Properties of the halophyte microbiome and their implications for plant salt tolerance

“…The genetic identification of novel species suggested that the diversity of rhizobia associated with Australian Accacia spp. is significantly greater than previously expected and documented a community differentiation in relation to salt stress (Thrall et al 2009). RuedaPuente et al (2010) detected, for the first time, Rhizobium spp.…”

“…Studies of Acacia spp. in Australia and Algeria, where the shrubby legumes dominate many ecosystems where dryland salinity is a major issue, suggested a high phylogenetic bacterial diversity (Thrall et al 2009;Boukhatem et al 2012). Based on 16S rRNA gene sequence comparisons, 48 isolates ranked into 10 phylogenetic groups representing five bacterial genera, namely, Ensifer, Mesorhizobium, Bradyrhizobium and Ochrobactrum (Boukhatem et al 2012).…”

Isolation and characterization of salt-tolerant rhizobia native to the desert<br>soils of United Arab Emirates

“…For instance, Thrall et al (2009) found that salt tolerance and growth were generally higher in rhizobial populations associated with Acacia spp., derived from saline soils than those from non-saline soils. Elanchezhian et al (2009) reported tolerance to up to1000 mM of NaCl in in vitro studies of the rhizobium species associated with Vigna marina, a wild legume found growing in sandy seashores.…”

Legumes in the reclamation of marginal soils, from cultivar and inoculant selection to transgenic approaches

“…A low-cost revegetation approach has been to inoculate different native leguminous shrubs and trees with elite strains of native rhizobia in order to re-establish plant-soil interactions in degraded lands (Thrall et al 2005). The diversity and salt tolerance of native isolated rhizobia nodulating Acacia has also been characterized in saline and non-saline Australian soils (Thrall et al 2009), and rhizobial populations derived from saline soils had higher salt tolerance and grew better. A Mesorhizobium sp.…”