Isolation and Characterization of Rhizosphere Bacterial Community from cultivated plants in Mahikeng, North-West Province, South Africa
The rhizosphere is characterized by the presence of high microbial activities which are influenced by plant root exudates. This study examined bacterial diversity and physiological functions plants rhizosphere using both culture-dependent and culture-independent techniques of seven cultivated. Physico-chemical properties of soil samples revealed that the rhizobacteria adapted well to pH ranging from 7.5 to 9.1. Macronutrients (carbon, nitrogen, calcium, magnesium, phosphorous, potassium, sodium and iron) had a wide range of concentration between 0 to 4380.1 mg/kg. Concentrations of metal elements (cadmium, cobalt, chromium, copper and zinc) from all rhizosphere samples were below the amount of 3.1 mg/kg, indicating that the samples were free from metal contaminations. Sole carbon substrates utilization of bacteria in rhizosphere samples were measured as Average Well Colour Development (A WCD) and Group-wise Average Well Colour Development (AWCDg) patterns. At seventy two hours, there was no significant difference in AWCD patterns between bacteria in all samples and there was a significant difference in AWCDg patterns. Biochemical tests showed majority of isolates had similar physiological properties to members of Bacillus genus. All the bacterial isolates exhibited positive antifungal trait, fifteen solubilized phosphate and three had cyanide production traits during in vitro plant growth promotion assays. In vitro plant growth revealed that bacterial isolate RL1 (Bacillus licheniformis) produced the highest concentration of indole acetic acid (IAA) at 25 mg/ml. Bacterial isolate RG3 (Bacillus pumilus) had the highest amino cyclopropane carboxylase (ACC) deaminase activity indicated by the high production of α-ketobutyrate produced at 4.8 mg/ml. There were significant differences in shoot length at P ≤ 5% level of significance and there was no significant difference in the number of leaves across all three inoculated plants at P ≥ 5% level of significance. Sequence and phylogenetic analysis of identified culture-dependent bacteria revealed a homologous similarity of 94 to 100% between isolates sequences and GenBank sequences. From this, 81% of the sequences were closely related to Firmicutes, 13% to Actinobacteria and 6% to Proteobacteria. From cultureindependent method, only 8 PCR-DGGE bands were detected, the 200 bp sequences in the 16S rRNA fragment showed 91 to 100% homologous similarity to GenBank sequences. Their 16S rRNA sequences was closely related to 50% uncultured bacterium clones, 25% Firmicutes, 13% Proteobacteria and 12% Bacteroidetes sequences. Both culture-dependent and cultureindependent techniques were precise in the identification and description of bacterial community in rhizosphere.