Biodegradation of unvulcanized natural rubber by microorganisms isolated from soil and rubber surface: A preliminary study

The Natural rubber (NR) biodegradation by three microorganisms has been evaluated: a yeast (Rhodotorula mucilaginosa) and a bacterium (Pseudomonas sp.), isolated in a liquid culture from soil, and a filamentous fungus (Alternaria alternata), isolated on a solid culture from an NR surface, were tested. The biodegradation was conducted for four months in liquid culture, at 30°C, in agitated and stationary conditions, using a Mineral Salt Medium with NR as the only carbon source. The growth behaviour of the yeast and the bacterium was evaluated by means of optical density measurements (OD₆₅₀). At the end of the incubation, the dry weight biomass of the microorganisms was measured. R. mucilaginosa showed a higher biomass production in the agitated culture, while a more efficient production was observed in static conditions for the Pseudomonas and A. alternata strains. The highest enzymatic activity of Lignin peroxidase (LiP) and Manganese-dependent peroxidase (MnP) was obtained in static conditions for A. alternata. The laccase production was probed by guaiacol oxidative polymerization on agar plates. The microorganism biodegradation capability was assessed through a combination of SEM analysis, FTIR-ATR spectroscopy, and Size Exclusion Chromatography techniques. An extended mycelium-substrate interphase and a decrease in the NR molecular weight were observed.