Microbial community structure and functional diversity of nitrogen-fixing bacteria associated with Colophospermum mopane

Abstract

Colophospermum mopane is an indigenous legume tree that grows in Southern Africa and is one of the predominant trees of the woodland vegetation. In order to increase knowledge about its ecology, especially how C. mopane thrives in the nitrogen-poor soils of the region, we analyzed the root-associated bacteria to assess the active diazotrophic diversity and total microbial diversity by culture-dependent and independent techniques. Root nodules were not detected but in some samples the lateral roots showed an outgrowth-like protuberance, that were not likely to have functions related to legume root nodules. The bacterial isolates recovered were related to Actinobacteria, Firmicutes and Proteobacteria. The total microbial diversity was dominated by Actinobacteria-related phylotypes, while the active diazotrophic diversity showed that the majority of the sequences were related to the order Rhizobiales but also to Spirochaetes, Firmicutes, Bacteroidetes and Deltaproteobacteria. Several isolates showed characteristics of plant growth-promoting bacteria. These findings increase the spectrum of possible phylotypes that can be found in legume trees that are typically nodulated by Alpha- and Betaproteobacteria, and reveal for the first time a surprising diversity of nitrogen-fixing bacteria active in legume tree roots.

Associative nitrogen fixation in nodules of the conifer Lepidothamnus fonkii (Podocarpaceae) inhabiting ombrotrophic bogs in southern Patagonia

“…2). Such diazotrophs were also detected in other studies on root-associated BNF of trees, but the diversity of active diazotrophs was much higher in these studies, indicating a non-specific association of diazotrophs with tree roots4243. In our study, however, the expression of Bradyrhizobiaceae and Burkholderiaceae related nifH was essentially only detected in peat, indicating that free-living Bradyrhizobiaceae and Burkholderiaceae contribute to BNF in peat rather than to BNF in root nodules of L. fonkii .…”

Genetic diversity of rhizobia and plant growth promoting rhizobacteria of soil under the influence of Piliostigma reticulatum (DC.) Hochst and their impact on shrub growth

“…This is certainly the case of strains PZS_B03, PZG_S16 (belonging to the Bacillus genus), PZS_A04 and PZG_S12 (belonging to the Peanibacillus genus). In fact, the Bacillus genus also comprised a high percentage of endophytic bacteria associated with the roots of Colophospermum mopane (Burbano et al, 2015). Comparison of the results of this study and those of Burbano et al, showed that PEB from P. reticulatum were more diversified than those associated with the roots of C. mopane and Cohnella sp.…”

“…More than 60% of these bacterial species were denoted non-symbiotic bacteria. A similar study carried out by Burbano et al (2015) found fewer families of bacteria associated with Colophospermum mopane. As P. recticulatum, Colophospermum mopane also belongs to the family of non-nodulate plants (LPWG, 2017).…”

Insect outbreaks alter nutrient dynamics in a southern African savanna: patchy defoliation of Colophospermum mopane savanna by Imbrasia belina larvae

“…), but N‐fixing actinomycetes may form an association (Burbano et al . ). It is usually monodominant thereby exerting a strong influence on biogeochemical cycling through its seasonal pattern of leaf flush, leaffall, and decomposition (Dekker & Smit ).…”