Isolation of Bacteria from the Rhizosphere and Rhizoplane of Potato (Solanum tuberosum) Grown in Two Distinct Soils Using Semi Selective Media and Characterization of Their Biological Properties

The objective of this study was to isolate and characterize genera of bacteria that had been identified as being the most common residents in the rhizosphere of potato using cpn60 pyrosequencing analysis. Using various semi-selective media targeted to specific genera of interest, 200 isolates of bacteria were collected from rhizosphere soil and the rhizoplane of potatoes grown in soils obtained from a potato farm in Prince Edward Island and Ontario. The procedures employed were successful in selecting out representative bacteria suggested by pyrosequencing to be common in the potato rhizoplane. Results of 16S rRNA sequencing showed that 44 % of the isolates represented new species. All isolates were tested for biological and biochemical activities including phosphate solubilization, phytohormone metabolism, nitrogen fixation, antibiosis, exoenzyme production, and production of acyl-homoserine lactones. Massilia spp. and Chryseobacterium spp. showed the strongest exoenzyme activities. A greater proportion of Agrobacterium tumefaciens rhizosphere strains produced acyl-homoserine lactones compared to rhizoplane strains. Pseudomonas spp. and Lysobacter capsici had the greatest antagonistic activity on laboratory media towards six potato pathogens, and also significantly decreased disease in plants grown in pathogen-infested soil. Four isolates significantly increased growth of potato nodal explants in tissue culture. By using preliminary results derived from next generation sequencing technology and a targeted cultural technique, we were able to gain a better understanding of the biological activities of the most abundant bacterial species in the rhizosphere and rhizoplane of a cultivated crop.