Isolation and Characterisation of Indigenous Zinc Solubilising Microbes and their Probiotic Potentiality in Aquatic Ecosystems of Malawi

Abstract

In this study, zinc solubilizing microorganisms (ZnSM) were isolated from the rhizospheres of aquatic plants, water and benthic soils of Malawi aquatic ecosystem with the aim of having cheap and environmental friendly biofertiliser that have probiotics traits in Malawi. Several studies have shown potentiality of indigenous ZnSM in biofertiliser development, but little is known about the presence of indigenous ZnSM and having probiotic traits in Malawi aquatic ecosystem.  Isolates were screened for solubilisation traits using basal medium with three amendments of insoluble zinc (zinc carbonate, oxide and phosphate) supplemented by the characterization of plant-growth-promoting (PGP) and probiotic traits. Molecular characterization using 16S rRNA gene and biochemical test were used in identification and characterisation. Isolates candidacy was based on solubilisation index (SI) of above 1.5 complimented by production by diverse plant growth promoting and probiotic traits. Eight isolate namely Serratia marcescens, Enterobacter wuhouensis, Serratia surfactantfaciens, Serratia nematodiphila, Alcaligenes faecalis, Bacillus altitudinis and Klebsiella pasteurii were selected as potential candidates for development of zinc based biofertiliser. The study revealed that zinc solubilising microbes have great potential in probiotic development evidenced by production of amylase. The study has revealed and showed that Bacillus altitudinis strain had no site specificity and had highest potential in biofertiliser and probiotic development shown by solubilisation index of 4.7, 3.4 and 4 for zinc oxide, carbonate and phosphate respectively. Isolates solubilisation quantification was based on the type of inorganic zinc indicating that some of these microbes may be site specific based on the type of inorganic zinc available. The pH of the culture broth was found to be decreased in the range of 3.33 to 3.35 indicating that solubilisation is based on acid extrudes by the microbes. The study has given an insight of potentiality of indigenous microbes from aquatic ecosystem in the development of biofertiliser and probiotics in Malawi.