Abstract
Rubber composed of highly unsaturated hydrocarbons, modified through addition of chemicals and vulcanization are widely used to date. However, the usage of rubber, faces many obstacles. These elastomeric materials are difficult to be re-used and recovered, leading to high post-consumer waste and vast environmental problems. Tyres, the major rubber waste source can take up to 80 years to naturally degrade. Experiments show that the latex clearing proteins (Lcp) found in Actinobacteria were reportedly critical for the initial oxidative cleavage of poly(cis-1,4-isoprene), the major polymeric unit of rubber. Although, more than 100 rubber degrading strains have been reported, only 8 Lcp proteins isolated from Nocardia (3), Gordonia (2), Streptomyces (1), Rhodococcus (1), and Solimonas (1) have been purified and biochemically characterized. Previous studies on rubber degrading strains and Lcp enzymes, implied that they are distinct. Following this, we aim to discover additional rubber degrading strains by randomly screening 940 Actinobacterial strains isolated from various locations in Sarawak on natural rubber (NR) latex agar. A total of 18 strains from 5 genera produced clearing zones on NR latex agar, and genes encoding Lcp were identified. We report here lcp genes from Microtetraspora sp. AC03309 (lcp1 and lcp2) and Dactylosporangium sp. AC04546 (lcp1, lcp2, lcp3), together with the predicted genes related to rubber degradation. In silico analysis suggested that Microtetraspora sp. AC03309 is a distinct species closely related to Microtetraspora glauca while Dactylosporangium sp. AC04546 is a species closely related to Dactylosporangium sucinum. Genome-based characterization allowed the establishment of the strains taxonomic position and provided insights into their metabolic potential especially in biodegradation of rubber. Morphological changes and the spectrophotometric detection of aldehyde and keto groups indicated the degradation of the original material in rubber samples incubated with the strains. This confirms the strains’ ability to utilize different rubber materials (fresh latex, NR product and vulcanized rubber) as the sole carbon source. Both strains exhibited different levels of biodegradation ability. Findings on tyre utilization capability by Dactylosporangium sp. AC04546 is of interest. The final aim is to find sustainable rubber treatment methods to treat rubber wastes.
Highlights
There is a great interest in developing environmentally sustainable methods to solve the rubber waste problem globally
In silico studies of their genome through genomic sequencing were used to determine the strains’ novelty. Both strains were tested for their ability to utilize natural rubber (NR) and vulcanized rubber (VR) as the sole carbon and energy source
The strains tested consisted of Actinobacteria from 9 families (15 genera) and 205 Actinobacteria strains that could not be classified based on morphology (Table 1)
Summary
There is a great interest in developing environmentally sustainable methods to solve the rubber waste problem globally. Rubber consisting of poly(cis-1,4-isoprene) or poly(trans1,4-isoprene) are highly modified through compounding and vulcanization in industrial processes and are used in more than 50,000 products today [1,2]. Rubber materials are resistant to thermal and chemical degradation. They are difficult to re-use or recycle. The majority of them are just discarded in landfills [3,4,5]. Economical, and scalable methods for converting rubber products or waste into by-products or composites that ideally can be reused are desperately needed
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