Overall, LDPE attack by R. opacus R7 emerges as a dynamic process shaped by substrate accessibility and cultivation strategy, highlighting its potential as a platform for controlled plastic biodegradation.
Abstract
Background
Polyethylene (PE) is the most widely produced polyolefin and represents a major contributor to plastic waste, largely due to its chemical stability and resistance to biological degradation. PE biodegradation is typically characterized as a series of oxidative metabolic processes rather than mineralization. An urgent priority is the development of integrated experimental setups that bring together physiological, biochemical, and molecular analyses under controlled cultivation conditions to unlock the metabolic traits of PE biodegradation. This study aims to elucidate the molecular mechanisms of commercial low-molecular-weight PE (LDPE) attack by Rhodococcus opacus R7 through an integrated genome-to-function approach, including growth and extracellular laccase assays, intracellular lipid quantification, gas chromatography coupled with mass spectrometry (GC-MS) analysis of compounds associated with untreated LDPE, and transcriptional profiling of oxidative enzymes.
Results
LDPE utilization was evaluated under multiple cultivation strategies (1% single-dose vs. 0.4% fed-batch), inoculum conditions, and polymer types (untreated or UV-pretreated) over 28 days. Fed-batch LDPE (0.4%) supported slightly higher viable cell numbers than fixed-dose LDPE (1%), while prolonged PE pre-adaptation did not enhance growth. Extracellular laccase activity was detected under all conditions, but was more influenced by the physiological status of the inoculum than by PE concentration or pretreatment. Lipid accumulation was early detected in case of 1% PE, while the fed-batch conditions reflected the growth phase and physiological responses. GC-MS analyses revealed that LDPE oxidation products vary compared to abiotic and control samples. Specifically, fixed-dose LDPE favored a progressive change in the pattern-profile of carboxylic acids and medium- to long-chain alkanes, while fed-batch LDPE produced a heterogeneous mixture, including alcohols and ketones, consistent with a continuous and asynchronous transformation of the polymer. The fed-batch condition induced a broader and earlier transcriptional activation of oxidative genes, including seven laccase-like multicopper oxidases (LMCOs), alkane monooxygenase (alkB), benzoate dioxygenase (benA), and cytochrome P450 hydroxylase. Long-chain n-alkanes, particularly tetracosane (C24), strongly induced oxidative enzymes, suggesting their role as metabolic signals during PE degradation.
Conclusions
Overall, LDPE attack by R. opacus R7 emerges as a dynamic process shaped by substrate accessibility and cultivation strategy, highlighting its potential as a platform for controlled plastic biodegradation.
Results indicate that functional differentiation and cooperative interactions contribute to enhanced LDPE degradation by Z123, which provides mechanistic insights into consortium-based plastic biodegradation and supports the rational design of microbial platforms for plastic waste management.
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This review provides the current state of PHAs production from wild yeast strains and the various approaches that have been used to improve yield, and discusses the performance, challenges, and limitations of various synthetic biology and metabolic engineering strategies in yeast strains for PHAs production.
K. Mohanrasu, R. Selvakumar, I. Grainge et al.· International Journal of Bio...· 0 citations
Polyhydroxyalkanoates (PHAs) are biodegradable microbial polyesters that may reduce dependence on petroleum-derived plastics, but broader use remains constrained by production costs and tightly controlled cultivation. Thermophilic microorganisms have attracted increasing attention as promising PHA producers because they can be cultivated at elevated temperatures, reducing contamination risks and operational costs. In this study, a thermophilic Geobacillus sp. strain SL28 isolated from a Vietnamese hot spring was evaluated for its PHA-producing capability. Temperature, initial pH, carbon and nitrogen sources, C/N ratio, and cultivation time were examined. Intracellular inclusions were assessed by Sudan Black B and Nile Blue A staining and transmission electron microscopy, whereas the recovered polymer was characterized by FE-SEM, Fourier-transform infrared spectroscopy (FTIR), gas chromatography–mass spectrometry (GC–MS), 1H- and 13C-nuclear magnetic resonance (NMR) spectroscopy, capillary viscometry, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and tensile testing. Under the optimized cultivation conditions identified by one-factor experimentation (50 °C, pH 7.0, sucrose, peptone, C/N 25:1, and 72 h), SL28 reached a dry cell weight of 2.215 ± 0.16 g/L and a PHA concentration of 1.383 ± 0.04 g/L, equivalent to 62.57 ± 2.82% of DCW. Structural characterization confirmed that the recovered polymer was poly(3-hydroxybutyrate) (PHB). The purified PHB also exhibited favorable thermal stability, a relatively high molecular weight, and satisfactory mechanical properties. These results demonstrate the potential of thermophilic Geobacillus sp. SL28 as a promising candidate for PHB production.
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