Effect of pretreatment of rubber material on its biodegradability by various rubber degrading bacteria

Abstract

The effect of pretreatment of several cis-1,4-polyisoprene containing rubbers on their biodegradability was examined. Tests were carried out with six recently isolated and characterized rubber degrading bacteria belonging to the genera Gordonia (strains Kb2, Kd2 and VH2), Mycobacterium, Micromonospora and Pseudomonas. All strains were able to use natural rubber (NR) as well as NR latex gloves as sole carbon source. Extraction of NR latex gloves by organic solvents resulted in an enhancement of growth for three of the selected strains. On the other hand, growth of Gordonia sp. (strain Kb2 and Kd2), Mycobacterium fortuitum NF4 and Micromonospora aurantiaca W2b on synthetic cis-1,4-polyisoprene did only occur after removal of the antioxidants, that are usually added during manufacture to prevent aging of the materials. Detailed degradation studies performed with Gordonia sp. Kb2 revealed an enhanced mineralization of pretreated NR latex gloves and mineralization of purified natural rubber (NR), indicating the actual mineralization of cis-1,4-polyisoprene rubber constituent even after removal of non-rubber constituent that may act as co-metabolic substrate and support microbial growth. Further analysis by scanning electron microscopy (SEM) clearly demonstrated the enhanced colonization efficiency of these bacteria towards pretreated NR latex gloves. Colonization was additionally visualized by staining of overgrown NR latex gloves with Schiff's reagent, and the purple color produced in the area of degradation was an evidence for the accumulation of aldehydes containing oligomers. Further enhancement of latex gloves degradation could be achieved after successive replacement of mineral salts medium during cultivation. Thereby, a rapid disintegration of untreated NR latex gloves material was accomplished by Gordonia sp. strain VH2. ß

Bacterial communities of tyre monofill sites: growth on tyre shreds and leachate

“…2006). In addition, additives such as carbon black and antioxidants can inhibit microbial growth (Berekaa et al. 2000; Zyska 1988).…”

“…Inorganic metals (such as zinc, cadmium and lead) and organic additives (such as accelerators) that are toxic to micro-organisms can leach from tyre material into nearby aqueous environments (Christiansson et al 2000;Nelson et al 1994;Sheehan et al 2006). In addition, additives such as carbon black and antioxidants can inhibit microbial growth (Berekaa et al 2000;Zyska 1988).…”

Construction and intergeneric conjugative transfer of a pSG5-based cosmid vector fromEscherichia colito the polyisoprene rubber degrading strainMicromonospora aurantiacaW2b

“…The non‐formation of clear zones led to negative growth on NR latex, which has been demonstrated previously[17] and in our own studies with M. aurantiaca , S. cinnamonensis and Actinoplanes missouriensis. In these studies mineralization of isoprene rubber by various actinomycetes was measured according to Berekaa et al[18]. Up to 4% mineralization of the used material could be achieved by the wild‐type strains, whereas the halo negative mutants showed no mineralization.…”

Rubber oxygenases

“…Moreover, most rubber products contain additives such as antioxidants and other stabilisers; furthermore, the polyisoprene molecule chains of most rubber items are cross-linked by sulphur bridges (vulcanised rubber). These modifications inhibit microorganisms and/or their rubber oxygenases (Berekaa et al 2000). Furthermore, the biodegradation process is limited to the surface of the rubber materials because neither microorganisms nor rubber oxygenases can penetrate the water-insoluble material.…”