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Natural rubber Natural rubber (NR) is made from the latex of the Hevea brasiliensis also known as the rubber tree. It is mainly composed of cis-1,4 polyisoprene which has a molecular mass of about 106 Da. This could also be chemically synthesized and produce the substance known as Isoprene Rubber (IR). (Linos et. al, 2000). Since 1914, natural rubber has been a classic subject of biodegradation studies. (Rose and Steinbuchel, 2005). This is due to the high rate of its yearly manufacture which is several million tons, as mentioned in the study of Bereeka 2006, and its slow rate of natural degradation as reviewed by Rose and Steinbechul, 2005. In fact, a number of studies abound concerning its degradation. And it has been learned that both bacteria and fungi can participate in such process. Throughout all the investigations and experimentations done, two categories of rubber-degrading microbes according mainly on growth characteristics have been established. Based on a review of Rose and Steinbuchel 2005, which recapped the aforementioned groups, the microbes that can degrade rubber can be categorized as clear zone-forming around their colonies and non-halo forming whenever isolated and cultured in latex overlay plate, which is made by overlaying a layer of latex agar medium on a basal salt medium agar. The former category was identified to mainly consist of actinomycetes species. They are said to biodegrade or metabolize rubber by secreting enzymes and other substances and also they are dubbed to be slow degraders since they rarely show an abundant cell mass when grown on natural rubber directly. On the other hand, members of the second group do not form halos on latex overlay plates. They, unlike the first group, grow more when directly grown on natural rubber. In a way, their growth on rubber could be described in an adhesive manner. The second group is said to demonstrate a relatively stronger growth on rubber. Species comprising this category are the Corynebacterium- Nocardia-Mycobacterium group. They consist of the Gordonia polyisoprenivorans strains VH2 and Y2K, G. westfalica strain Kb1, and Mycobacterium fortuitum strain NF4. As demonstrated by a particular study by Linos et al. (2000), the mechanisms that the microbes undergo when biodegrading is colonization, biofilm formation and aldehyde group formation after cultivating it on the surface of latex gloves. Such is revealed after undergoing the Schiff reagent’s test. This is further examined under a scanning electron microscope. In their methodology they have indicated that the preliminary screening method to be used in finding potential rubber-degrading bacteria is by growing such bacteria or microbe on the latex overlay or by latex film on the mineral agar plates. Growth and colonization of the microbe in this medium would indicate its utilization of rubber as its sole carbon source; hence, making it as a potential rubber-degrader.
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