Impact of additives of commercial rubber compounds on the microbial and enzymatic degradation of poly(cis-1,4-isoprene)

Much fundamental research has already been performed to understand the mechanism of microbial rubber degradation. Due to the increasing amount of rubber waste, biotechnical methods to degrade that particular waste are strongly needed. The present study evaluates whether a microbial or an enzymatic process is more suitable for efficient biodegradation, due to less sensitivity towards rubber additives. Therefore we investigated the impact of 15 different frequently used rubber additives on cells of the potent rubber degrader Gordonia polyisoprenivorans VH2 and the enzyme Lcp1(VH2). For this, cells were grown on poly(cis-1,4-isoprene) in presence of these rubber additives. Furthermore, the effect of those additives on the enzymatic cleavage of poly(cis-1,4-isoprene) by Lcp1(VH2) was determined by in vitro studies. It was observed that additives, used to accelerate the vulcanization process, like N-cyclohexyl-2-benzothiazolesulfenamide and zinc-bis(N,N-dibenzyl-dithiocarbamate), are diminishing the growth of the microorganism depending on their concentrationhigher toxicity with increasing concentration. In contrast, sulfur prevents cell growth, but does not affect Lcp1(VH2). Stearic acid and paraffin wax were found to be consumed by G. polyisoprenivorans VH2. Plasticizers mainly prevent growth, but do not interfere with the enzyme activity. This study identified antioxidants as the most interfering group of additives for microbial and enzymatic rubber degradation. It was found that the in vitro degradation by Lcp1(VH2) is much more resistant and less sensitive towards the investigated rubber additives, when compared to the in vivo approach. Therefore, an enzymatic process might be a promising method to enhance rubber degradation.