Biodegradation Of Natural Rubber Products And Characterization Of Related Genes In Streptomyces sp. strain CFMR 7 (JCM 30950)
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Date
2017-08
Authors
Jayaram, Nanthini
Journal Title
Journal ISSN
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Publisher
Universiti Sains Malaysia
Abstract
The existing methods of disposing and recycling of rubber products are difficult, expensive and not environmentally friendly. In this study, a Streptomyces sp., which has been identified as a potential rubber degrading strain from previous study, was further characterized. The rubber degrading activity of this strain was tested with latex products such as car tyre, latex glove, latex condom and fresh latex stripes. The degradation behaviour was unequivocally demonstrated by SEM micrographs with respect to colonisation behaviour, disintegration of rubber material and bio-film formation after 3, 6 and 9 months of inoculation. FTIR – ATR spectroscopy analysis on these inoculated products revealed insights into the biodegradation mechanism of this strain whereby, a decrease in the number of cis-1,4 double bonds in the polyisoprene chain and the appearance of both ketone and aldehyde groups formation were confirmed. In the presence of strain Streptomyces sp. CFMR 7, GPC analysis revealed a significant shift in the molecular weight distribution to lower values. Increased shift was observed over the periods of 3, 6 and 9 months during cultivation. No shift in the molecular weight distribution was observed for non-inoculated control. These results clearly showed that Streptomyces sp. CFMR 7 was able to cleave the carbon backbone of poly (cis-1,4-isoprene). Upon the
confirmation of rubber degrading ability of this strain on different natural rubber products, the strain was subjected to whole genome sequencing. The genome of this strain was sequenced using single molecule sequencing technology (SMRT) with the PacBio®RS II system yielding∼147 × coverage. De novo assembly was carried out using the Hierarchical Genome Assembly Process (HGAP) workflow. This workflow resulted in two contigs: a linear chromosome with 8,207,733 bases and a linear plasmid with 99,537 bases. The annotation for this genome was conducted with RAST (Rapid Annotation using Subsystem Technology (RAST) and National Centre for Biotechnology Information (NCBI). The results revealed that the chromosome of this strain contains 71% GC content, 64 tRNA genes, 18 rRNA genes and 7075 predicted coding sequences (CDS) while the plasmid has 72% of GC content and 93 predicted coding sequences (CDS). From the genome analysis, it was noted that Streptomyces sp. CFMR 7 harbours three full length latex clearing protein (lcp) genes. Genes encoding oxidoreductase α-subunit (oxiA) and oxidoreductase β-subunit (oxiB) were also found downstream of two lcp genes which are located adjacent to each other. In silico analysis reveals genes that have been identified to be involved in the microbial degradation of rubber in the Streptomyces sp. strain CFMR 7. The complete genome sequences of Streptomyces sp. strain CFMR 7 has been deposited in GenBank under accession numbers CP011522 (Chromosome) and CP011523 (Plasmid). Although there were many Streptomyces sp. whole genomes sequenced prior to this genome sequencing, none was specially sequenced for its rubber degrading ability. From the study, it was confirmed that Streptomyces sp. CFMR 7 is able to degrade both vulcanized and non-vulcanized natural rubber products and it also harbours the genes that are responsible for the natural rubber degradation.
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Keywords
Biodegradation of natural rubber products , and characterization of related genes