Analysis of soil bacteria in Ngere Tea catchment area of Murang'a County, Kenya

Abstract

Bacteria are a very diverse group of organisms in soil, with major taxonomic groups being represented in most soils. The extent of the diversity of microorganisms in soil is seen to be critical to the maintenance of soil health, since a wide range of bacteria are involved in the important soil functions. The objectives of this study were to isolate, characterise and identify groups of bacteria that are associated with soil fertility in tea growing areas of Ngere. Thirty eight isolates were obtained using two categories of media, namely dilute nutrient broth agar and Tryptone soy agar. Ngere tea soils had a pH range of 3.9 to 5.0 and organic carbon content that ranged from 3% to 19%. The isolates were characterized using cultural and biochemical techniques. The Gram stain reaction showed that 53% of the isolates were Gram positive while 47% were Gram negative, and they grew well at pH ranging from 5 ­ 6.5 and temperature range of 25oC to 35oC. Identification was done by Polymerase Chain Reaction (PCR) amplification of the 16S rDNA region, sequencing and phylogenetic analysis. BLAST analysis of the partial sequences showed that 45 % were from the genus Bacillus within the Firmicutes in the domain bacteria with similarities between 83 % and 99 %, 23% and belonged to the genus Pseudomonas with similarities between 94 % and 99 %. The genus Enterobacter represented 13% with similarities between 83 % and 90 %. Other genera such Burkholderia, Chryseobacterium, Acinetobacter and Serratia constituted 9 % with similarity of 88% to 99 %. D66 showed identity of 95 - 97 % similarity with the previously known sequences in the GenBank database. This represents novel species of organisms within Ngere tea soils. IsolatesD63, S49, D16, D5, S48, D51, D80, D1, D79 and S31 showed identity of 80 -93 % similarity, representing novel genera of organisms within the tea soils. This study demonstrated that Ngere tea soils harbours diverse bacteria with specific biochemical properties like the ability to reduce nitrate to nitrite, nitrogen fixation, ability to produce urease enzyme that splits urea into carbon dioxide and ammonia, ability to hydrolyse starch and to solubilisation phosphate suggests their involvement in the nutrient recycling within the tea soils hence improving soil fertility. Thus these can be used as indicators of soil health or as biofertilizres.