Isolation and Identification of Zn solubilising bacteria and Evaluation of various Carrier Efficacy in Superior Isolate Survival

Zinc (Zn) is one of the micronutrient that is in calcareous soils in low solubility forms. One of the ways of supplying Zn of the plant in these conditions is the use of microorganisms as biofertilizer. A suitable carrier is needed to supply these fertilizers. Therefore, this study was performed to isolation and identification of Zn solubilizing bacteria from soil and to evaluate the survival of the superior strain in various carriers during nine months in a completely randomized two-factor design (carrier and Time) was performed with three replications. Solid carriers included perlite, peat moss, sawdust, sugar beet waste, manure, vermicompost, azolla, biochar (azolla and apple), bran and talc. In this study, bacterial inoculants prepared with the same initial population after storage at room temperature were compared for the survival of the bacteria. For counting the bacteria in microbial carriers, MPN counting method was used in each month. The results showed that out of 24 samples of the rhizosphere soil, 15 strains of Zn-solubilizing bacteria were isolated and purified. Five isolates found to be the most efficient in solubilizing insoluble Zn compounds were examined for molecular identification. Based on gene 16S rRNA sequencing, three of the isolates belonged to the genus of Pseudomonas, and two to Enterobacter. The highest solubility index (2.28) was related to Pseudomonas fluorescens strains which were used for inoculation of microbial carriers by Ur 22 strain. The results of bacterial count in carriers showed that among the tested carriers, the highest population counted after nine months in carrier of apple biochar (5.07 log cfu g-1) and azolla biochar (5.07 log cfu g-1), and the lowest population was obtained in talc carrier (2.11 log cfu g-1). In general, it can be said that among the tested carriers, Biochar is recommended due to its good properties and cost-effectiveness.