Adaptation of Pseudomonas sp. AKS2 in biofilm on low-density polyethylene surface: an effective strategy for efficient survival and polymer degradation

Background: Pseudomonas sp. AKS2 can efficiently degrade low-density polyethylene (LDPE). It has been shown that this degradation of LDPE by AKS2 is correlated to its ability to form biofilm on the polymer surface. However, the underlying mechanism of this biofilm-mediated degradation remains unclear. Since bioremediation potential of an organism is related to its adaptability in a given environment, we hypothesized that AKS2 cells undergo successful adaptation in biofilm on LDPE, which leads to higher level of LDPE degradation. To verify this, the current study investigated a number of parameters of AKS2 cells in biofilm that are known to be involved in adaptation process. Results: Successful adaptation always develops a viable microbial population. So we examined the viability of AKS2 cells in biofilm. We observed the presence of viable population in the biofilm. To gain an insight, the growth of AKS2 cells in biofilm on LDPE at different time points was examined. Results showed a better reproductive competence and more colonization for AKS2 biofilm cells than planktonic cells, indicating the increased fitness of AKS2 biofilm cells than their planktonic counterpart. Towards understanding fitness, we determined the hydrolytic activity, different carbon source utilization potentials, functional diversity and homogeneity of AKS2 biofilm cells. Results showed increased hydrolytic activity (approximately 31%), higher metabolic potential, higher functional diversity (approximately 27%) and homogeneity for biofilm-harvested cells than planktonic cells. We also examined cellular surface hydrophobicity, which is important for cellular attachment to LDPE surface. Consistent with the above results, the cell surface hydrophobicity of biofilm-harvested AKS2 cells was found to be higher (approximately 26%) compared to that of their planktonic counterpart. All these results demonstrated the occurrence of physiological as well as structural adaptations of AKS2 cells in biofilm on LDPE surface that resulted in better attachment, better utilization of polymer and better growth of AKS2 cells, leading to the development of a stable colony on LDPE surface. Conclusions: The present study shows that AKS2 cells in biofilm on LDPE surface undergo successful adaptation that leads to enhanced LDPE degradation, and thus, it helps us to understand the underlying mechanism of biofilm-mediated polymer degradation process by AKS2 cells.