The Variability of the Predominant Culturable Plant Growth-Promoting Rhizobacterial Diversity in the Acidic Tea Rhizosphere Soils in the Eastern Black Sea Region

The purpose of this study was to investigate the diversity of cultivable nitrogen fixing, phosphate solubilising and total bacteria originated from 580 rhizospheric acidic soils samples of tea plants grown at 62 locations. Based on FAME profiles of over 1428 rhizoplane bacteria, 63 bacterial genera were identified with a similarity index > 0.3, but 56.4% of the identified isolates belonged to six genera: Bacillus (37.02%), Pseudomonas (12.67%), Stenotrophomonas (5.71%), Paenibacillus (6.58%), Arthrobacter (4.35%) and Brevibacillus (3.98%). Most of the total, N2-fixing and P-solubilizing bacteria isolated were Gram positive (59.9, 58.8 and 56.3%) and Gram negative constituted only 40.1, 41.2 and 43.7%. Among different groups, Firmicutes, Gammaproteobacteria and Actinobacteria comprised the largest groups contributing to about 50.3 and 46.6%, 30.8 and 32.5%, and 8.3 and 9.6% of the total N2-fixing and P-solubilizing isolates, respectively. B. cereus, P. fluorescens, B. megaterium, S. maltophilia, P. putida, B. licheniformis, B. pumilus, B. subtilis and P. polymyxa were the most frequent N2-fixing and P-solubilizing species in the acidic tea rhizosohere soils. In these studies were evaluated to represent the dominant culturable diversity of diazotrophs and phosphobacteria, and thus potentially beneficial to the growth and survival of tea plants in that specific acidic ecosystem of eastern Black Sea region.