Immobilization of Cells of Hydrocarbon-oxidizing Bacteria for Petroleum Bioremediation Using New Materials

While liquid biopreparations for water and soil bioremediation are convenient and economically attractive, microbial survival under standard environmental conditions is poor. Microbial immobilization is a common and efficient method to preserve high viable cell titers. We tested the effect of three new materials on the survival of various hydrocarbon oxidizers during long-term storage. The suspended (planktonic) cultures stored under the same conditions served as a control when assessing the viability of immobilized cultures after long-term storage. The cells of Acinetobacter seifertii, Pseudomonas extremaustralis, P. aeruginosa, Rhodococcus erythropolis, and Dietzia maris grown with microcapsules (MCs) of chitosan-modified polyurea (represented by crumpled spheres, 40–200 µm in diameter) attached abundantly to the MC surface. After several months of storage with MCs, CFU titers were two to five times higher than in the control. Cultivation of P. aeruginosa and R. erythropolis with polylactide (PLA) MCs (represented by slightly crumpled thin-walled spheres 25–100 µm in size) resulted in the formation of thick biofilms on MC surface. After 30-day storage with these MCs, CFU titers of R. erytropolis were up to one thousand times higher than in the control. In the presence of PLA MCs, the respiration rates of both cultures were five to eight times higher than in the control without MCs. The reasons of the better survival of immobilized cells are being discussed. After storage for up to 12 months, CFU titers of bacteria (R. erythropolis, A. seifertii, P. aeruginosa, P. extremaustralis) and yeasts (Yarrovia lipolytica) immobilized in the gel based on silanol derivatives of humic substances were ten to one hundred times higher than in the control. After 4-month storage, hydrocarbon degradation by the stabilized cultures began earlier and was faster and more complete than in the control. The tested materials may be used to extend the storage time for the preparations of biotechnologically important bacteria and for application for petroleum bioremediation.