ISOLATION AND CHARACTERIZATION OF ALKALI TOLERANT BACTERIAL ISOLATES FROM INDUSTRIAL SOIL FOR POTENTIAL SELF-HEALING PAINT APPLICATIONS

Abstract

The development of micro-cracks in protective paint coatings leads to a decrease in the durability and lifespan of structures due to penetration of moisture, oxygen and other corrosive agents. Traditional repair methods generally require regular maintenance and use of artificial chemical-based sealants. This can be sustainably tackled through autonomous self-healing coatings. Urease-mediated Microbially Induced Calcium Carbonate Precipitation (MICP), a novel bio-engineering method, has recently gained popularity, mainly due to its ability to exhibit calcite precipitation upon moisture ingress, thereby effectively closing cracks without requiring any external assistance. The current study focuses on the isolation and characterization of alkali-tolerant indigenous bacterial strains and test their potential for self-healing paint applications. Soil samples collected from different industrial sites were serially diluted and cultured to obtain bacterial colonies. Three morphologically different bacterial isolates were purified and characterized under different alkaline conditions and concentrations of urea and calcium chloride. Growth behaviour was analysed at pH 8, 8.5 and 9 as well as with 1%, 2% and 3% concentrations of urea and calcium chloride to determine isolates that can survive under MICP conditions. Among the various isolates obtained, Isolate 2 exhibited better growth as compared to other isolates in the presence of alkaline and nutrient-stressed conditions. Gram staining indicated that Isolate 2 was gram positive while Isolate 1 and 3 were gram negative. Morphology and growth pattern of Isolate 2 was also similar to that of Sporosarcina pasteurii, the model organism for MICP based studies. The outcome of the study imply that the industrial soils could be a potential candidate to identify alkali tolerant bacterial strains for future bio-based self-healing coatings. Additional research on urease activity analysis, precipitation of calcium carbonate and paint compatibility assessment are needed to be done to confirm their practical applicability.