Abstract
In the context of sustainable bioremediation of Low-density polyethylene (LDPE), in this study, several strategies were explored to enhance the LDPE degradation by the bacterium Enterobacter cloacae AKS7. Initially, Mineral oil and Tween 80 were used to test whether they could modulate microbial colonization and polymer degradation by AKS7. Results indicated Mineral oil could increase microbial colonization and LDPE degradation whereas Tween 80 compromised the same. Since LDPE holds hydrophobic characteristics, the organism showing higher cell-surface hydrophobicity could adhere efficiently to the polymer. Thus, the organism AKS7 was grown in media with different concentrations of glucose and ammonium sulphate to exhibit differences in cell-surface hydrophobicity. We noticed that with increasing cell-surface hydrophobicity, the microbial colonization and LDPE degradation got enhanced considerably. The observations indicated that cell-surface hydrophobicity promoted microbial colonization to LDPE that increased the degree of biodegradation. Besides, LDPE films were photo-oxidized before microbial exposure which showed that AKS7 could degrade ultra-violet (UV) treated LDPE more proficiently compared to the UV-untreated polymer. Moreover, AKS7 could colonize more effectively to the UV-treated LDPE in contrast to the untreated LDPE. Furthermore, it was observed that UV exposure increased the carbonyl bond index of the polymer which got utilized by the organism efficiently thereby increasing the polymer degradation. Hence, the observations indicated that effective microbial colonization to UV-treated LDPE films exhibited a promising metabolic activity that could show an enhanced degradation of LDPE. Therefore, AKS7 warrants to be considered as a promising organism for enhanced degradation of LDPE.
Highlights
In 1970, Leo Baekeland coined the term “plastic” and introduced the world’s first synthetic plastic named “Bakelite”
Microbial colonization to Low-density polyethylene (LDPE) had been found to promote the extent of biodegradation considerably as the closer association between bacteria and polymer could lead to better utilization of the polymer by the bacteria[4]
Literature survey revealed that chemical compounds like Mineral oil and Tween 80 were found to influence the microbial colonization of LDPE noticeably[10]
Summary
In 1970, Leo Baekeland coined the term “plastic” and introduced the world’s first synthetic plastic named “Bakelite”. Since plastic-waste management methods are time-consuming, expensive, and labour intensive, the need of the hour is to look for various methods for effective polymer degradation In this regard, it was reported that molecular weight, structure, crystallinity, density, mechanical, optical, and dielectric properties of plastic molecules could modulate the degree of degradation of LDPE considerably[5,6,7]. Though in our previous report, a considerable level of LDPE biodegradation was spotted by Enterobacter cloacae AKS7, the extent of degradation needs to be increased to manage the huge accumulation of LDPE based polymers. Towards this direction, several strategies were undertaken to enhance the degree of LDPE degradation by Enterobacter cloacae AKS7. The results of the current report revealed that without being exposed to genetic manipulation, the bacteria Enterobacter cloacae AKS7 could modulate the degree of utilization of LDPE either by changing the surface hydrophobicity of the bacterial or by altering the structure of the polymer
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