MOLECULAR CHARACTERIZATION AND MINERALIZATION POTENTIAL OF PHOSPHORUS SOLUBILIZING BACTERIA COLONIZING COMMON BEAN (Phaseolus vulgaris L.) RHIZOSPHERE IN WESTERN KENYA

Abstract

Phosphorous solubilizing bacteria (PSB) are a category of microbes that transform insoluble phosphates in soil into soluble forms that crops can utilize for growth and development. Phosphorous in natural soils is abundant, but since it is poorly soluble, it is not readily available to plants. Introducing phosphorous-solubilizing microbes, such as bacteria, is a safer way of improving soluble forms of phosphorous as compared to chemical fertilizers. Due to environmental issues and concerns about consumer health, the pervasive use of chemical fertilizers to provide nutrients in agriculture, especially the use of phosphorous and nitrogenous fertilizers, is currently under investigation. In soil and plant rhizospheres, multiple phosphorous solubilizing bacteria have been revealed, each with its own different capacity to solubilize phosphates. The solubilization potentials of these bacteria, on the other end, varies by genetic and molecular characteristics. The objective of this study were to determine the mineralization potential of phosphorus solubilizing bacteria, their molecular variations and plant growth promoting characteristics in growth and development of the common bean Phaseolus vulgaris.L, which were used as an indicator plant. The phosphate solubilization potential of each PSB isolates were evaluated under agar and broth medium of National Botanical Research Institute's phosphate (NBRIP) that was supplemented with Tricalcium Phosphate (TCP). The experimental design was complete randomized design and descriptive statistics was used to present the findings of the study. The strains, KV1 and KB5 (B5) were found to be the most effective phosphorus solubilizers with 3.69 solubility index and 4.16 solubility indices respectively: they converted total of amount soluble phosphate concentration in the broth medium (1471 P (ug/Ml) and 1395 P(ug/mL)) respectively. The least performing isolate was KBU with 2.34 solubility index. 16S ribosomal RNA gene sequencing and NCBI blasting closely identified the isolates KK3 as Enterobacter mori, KB5 as Pseudomonas kribbensis, KV1 as Enterobacter asburiae, KB3 as Enterobacter mori, KK1 as Enterobacter cloacae, KBU as Enterobacter tabaci and KB2 as Enterobacter bugandensis.The most efficient phosphate solubilizing isolate were used to test the improvement of plant growth parameters of Rosecoco and Mwetemania bean varieties and significant differences was determined using ANOVA and means were separated using Turkey Honest at 5 % level. PSB strains found in common bean rhizospheres varied in solubilization and genetically and that KVI and B5 were the most promising high efficiency strains that can be used to unravel the insufficiency of phosphorus and as a biofertilizer for sustainable crop production. Isolating and defining compatible PSB, along with comparing and analyzing the genetic factors would be a major step in developing an efficient biofertilizer for safer, economically sustainable agricultural systems, as well as protecting soil from hazardous chemical fertilizers.