Bacillus species: The dominant bacteria of the rhizosphere of established tea bushes

A number of species belonging to the genus Bacillus were found to be well adapted to the rhizoplane and rhizosphere of established tea bushes. Amongst the species, Bacillus subtilis and B. mycoides appeared to be closely associated with tea roots. The two species comprised a major part of the bacterial population, even during unfavourable periods. In extreme winter months the population of B. subtilis and B. mycoides were recorded upto 3.9 X 10(6) and 10(7) cells/g rhizosphere soil, respectively. The soil temperature during this period was in the range of 0 to 5 degrees C. Under laboratory conditions pure cultures of these Bacillus species did not grow upto 14 degrees C. While the pH of tea rhizosphere soil samples ranged from 4.3 to 6.3, these two species were able to grow at 28 degrees C in a much wider range of pH (4 to 12.0-12.5) under laboratory conditions. Survival of these bacterial species under adverse environmental conditions was probably due to their spore forming property. Various species of Bacillus behaved antagonistically amongst themselves, indicating perhaps to their bacteriocinogenic property. The observations also indicate that the tea bushes tend to make the soil acidic.