Analysis of the Viability of Oil-Oxidizing Microorganisms After Long-Term Storage and the Effect of Humate Concentration on Their Activity

This study evaluated the viability of oil-oxidizing microorganisms after long-term refrigerated storage. It determined how different concentrations of potassium humate affect their growth, activity, and bioremediation potential in oil-contaminated soil. Four bacterial strains, S3, S4, S6, and A1, previously isolated from oil-contaminated soils, were examined after one year of storage. Their viability was assessed by cultivation in meat-peptone broth and on meat-peptone agar, followed by visual observation, microscopy, Gram staining, and spectrophotometric measurement of optical density at 600 nm. Potassium humate obtained from oxidized brown coal was tested at concentrations of 0.5%, 1%, 5%, and 10%. The efficiency of soil purification was evaluated by measuring the mass fraction of petroleum products during a 90-day experiment. After storage, strains S3, S4, and A1 retained viability and showed active growth, whereas S6 did not recover under standard cultivation conditions. The response to humate depended on both strain and concentration. S3 recorded the highest optical density at 10% humate, while A1 showed growth at 1% and 10%. In the soil experiment, S4 with potassium humate achieved the greatest reduction of petroleum products, reaching 77.11% purification after 90 days. S3 with humate and Bakoyl with humate also showed high efficiencies of 75.49% and 76.07%, respectively. The results confirm that potassium humate can enhance the activity of selected oil-oxidizing microorganisms and support the development of combined biopreparations for reclaiming oil-contaminated soils.