Isolation and characterization of thermophilic microorganisms able to grow on cellulose acetate

Cellulose acetate (CA) can be successfully used for producing compostable plastics. It is biodegradable under composting conditions, but neither the mechanism of degradation nor the involved microorganisms are known. We isolated five thermophilic strains from compost which were identified by molecular characterisation as belonging to the family Thermomonosporaceae, probably to the genus Actinomadura. The strains are able to grow at 50 degreesC on minimal plates supplemented with CA (DS=2) or microcrystalline cellulose in powder. The degradation of CA is visible by the clarification of the area surrounding the mycelium. The strains grow at 37 degreesC on cellulose but not on CA. At 20 and 58 degreesC no growth is detected on both substrates. The strains are viable after a 2-week incubation period at 65 degreesC. Neutral and basic pHs are the best for CA degradation, while poor results are obtained under acidic conditions. The best degradation of CA is obtained using nitrate as nitrogen source. Solid-state respiration tests, performed using sterile vermiculite as a matrix, confirmed that the strains are able to mineralise the CA. The strains failed to grow in CA under liquid conditions.