Biodegradation of polyurethane coatings by hydrocarbon-degrading bacteria

Five locally isolated strains designated as SBI-1, 2, 3, 4 and 5 as well as four bacterial strains provided by the U.S. Navy were cultivated on mineral salts-agar with polyurethane as the sole carbon and energy source. All the microorganisms studied grew on polyurethane (PU) except SBI-4. However, the growth inhibition of SBI-4 was temporary. With the exception of SBI-4, all microorganisms exhibited esterase activity, whether grown on enriched medium or on a mineral salts medium containing PU as sole carbon and energy source. In the mineral salts liquid medium containing polyurethane-painted aluminum coupons SBI-5 and RAG-1 grew approximately equally for about the first 120 h. Thereafter, SBI-5 continued to grow rapidly, while the growth of RAG-1 slowed or stopped. Observation that the liquid medium took on the color of the PU paint due to the release of pigment therefrom, as well as total protein concentration and optical density at 546 nm of the culture broth provided evidence of biodegradation of the PU. Incubation of the biodegrading cells for another fermentation cycle (120 h) in a freshly prepared mineral salts liquid medium containing the same PU-painted coupons continued to release colored pigment to the liquid medium, but in reduced amounts. Cells of SBI-5 were also immobilized on the polyurethane-painted coupons within a thin adherent layer of calcium alginate. Biodegradation observed with immobilized and free cells appeared to be approximately equivalent. Scanning electron microscopy of microbially treated polyurethane painted coupons revealed a reduction of the original surface rugosity.