The diversity of root nodule bacteria associated with indigenous Lotononis spp. as determined by sodium dodecyl-sulphate polyacrylamide gel electrophoresis and 16S rDNA sequencing

Abstract

With the high rate of human population growth in Africa, it is imperative that food production be increased through improving yields and bringing more land under cultivation. Nitrogen is a key element required for plant growth and with the low input of fertilizers into African farming-systems, it is necessary to harness biological nitrogen fixation (BNF) to its fullest extent. To maximize nitrogen fixation in crop and pasture legumes under various conditions and cropping systems requires intensified research. In this study the diversity of root nodule bacteria associated with Lotononis species in South Africa was investigated. To our knowledge, no past attempts have been made to investigate the diversity of rootnodule-bacteria associated with the genus Lotonollis. Eighty nodulated plants representing thirty-two Lotononis spp. were collected from all the main geographical and climatological regions in South Africa. Isolates obtained from rootnodules were purified and characterized with sodium dodecyl-sulphate gel polyacrylamide gel electrophoresis (SDS-PAGE), supplemented at the genomic level with 16S rDNA sequence data of selected strains. Initial screening (SDS-PAGE) showed that most isolates obtained from the same plant species, grouped into various clusters within the dendrogram. A few of the isolates from similar host plants seemed to cluster with high similarity. It is thus reasonable to conclude that host specificity in the symbiotic interaction is less applicable for most species of Lotononis. When considering the geographical origins of the isolates, their diverse nature was clearly illustrated. It was showed that isolates from similar geographical regions were evenly distributed throughout the dendrogram. Some of the isolates obtained from arid environments formed closely related electrophoretic groups. It was subsequently shown that root-nodule bacteria associated with Lotononis species are not restricted to a particular rhizobial genus, but that heterogeneity is evident. Some of the isolates were also related to genera outside the Rhizobiaceae, namely Methylobacterium and Burkholderia.