Chia-Lung Chen

Bioconversion of Styrene to Poly(hydroxyalkanoate) (PHA) by the New Bacterial Strain Pseudomonas putida NBUS12

Styrene is a toxic pollutant commonly found in waste effluents from plastic processing industries. We herein identified and characterized microorganisms for bioconversion of the organic eco-pollutant styrene into a valuable biopolymer medium-chain-length poly(hydroxyalkanoate) (mcl-PHA). Twelve newly-isolated styrene-degrading Pseudomonads were obtained and partial phaC genes were detected by PCR in these isolates. These isolates assimilated styrene to produce mcl-PHA, forming PHA contents between 0.05±0.00 and 23.10±3.25% cell dry mass (% CDM). The best-performing isolate was identified as Pseudomonas putida NBUS12. A genetic analysis of 16S rDNA and phaZ genes revealed P. putida NBUS12 as a genetically-distinct strain from existing phenotypically-similar bacterial strains. This bacterium achieved a final biomass of 1.28±0.10 g L−1 and PHA content of 32.49±2.40% CDM. The extracted polymer was mainly comprised of 3-hydroxyhexanoate (C6 ), 3-hydroxyoctanoate (C8 ), 3-hydroxydecanoate (C10 ), 3-hydroxydodecanoate (C12 ), and 3-hydroxytetradecanoate (C14 ) monomers at a ratio of 2:42:1257:17:1. These results collectively suggested that P. putida NBUS12 is a promising candidate for the biotechnological conversion of styrene into mcl-PHA.

Microbial cocktail for bioconversion of green waste to reducing sugars

Green waste has been identified as a sustainable resource to convert into reducing sugars and subsequently for production of ethanol. In this study, enhancement of reducing sugar production from green waste by the different combination of pure strains was investigated. The best-defined microbial cocktail for high reducing sugars production, consisting of one fungus (Pseudallescheria sp. D42) and three bacteria (Microbacterium sp. F28, Tsukamurella sp. C35, and Bacillus sp. F4), was successfully constructed. The maximum reducing sugars yield by this fungal-bacterial cocktail was 165.2 mg/g-green waste within 24 h, which is approximate 10 times higher than the selected individual microbial strains. Without extraction and purification of specific enzymes, whole-cell-bioconversion by a defined microbial cocktail is proven as a potential alternative process for lignocellulose hydrolysis and reducing sugars production.

Co-composting of horticultural waste with fruit peels, food waste, and soybean residues

Horticultural waste was co-composted with fruit peels, food waste, and soybean residues individually to evaluate the effects of these easily available organic wastes in Singapore on the composting process and product quality. Each co-composting material was mixed with horticultural waste in the wet weight ratio of 1:1 and composted for 46 days. Results showed that all co-composting materials accelerated the degradation of total carbon and resulted in higher nutrients of nitrogen (N), phosphorous (P), and potassium (K) in the final product compared with horticultural waste alone. Mixture with fruit peels achieved the fastest total carbon loss; however, did not reach the minimum required temperature for pathogen destruction. The end product was found to be the best source for K and had a higher pH that could be used for the remediation of acidic soil. Food waste resulted in the highest available nitrate (NO3-N) content in the end product, but caused high salt content, total coliforms, and slower total carbon loss initially. Soybean residues were found to be the best co-composting material to produce compost with high N, P, and K when compared with other materials due to the highest temperature, fastest total carbon loss, fastest reduction in C/N ratio, and best conservation of nutrients.

Determination of monomeric composition in polyhydroxyalkanoates by liquid chromatography coupled with on-line mass spectrometry and off-line nuclear magnetic resonance

Polyhydroxyalkanoates (PHAs) are commercially-valuable biocompatible and biodegradable polymers with many potential medical, pharmaceutical and other industrial applications. The analysis of PHA monomeric composition is especially challenging due to the broad chemical diversity of PHA monomers and lack of analytical standards to represent the chemically-diverse PHA monomer constituents. In this study, a novel strategy based on on-line liquid chromatography-mass spectrometry (LC-MS) and off-line liquid chromatography-nuclear magnetic resonance (LC-NMR) was established to quantify seven PHA monomers with available standards and used to elucidate the structures of unknown PHA monomers. The strategy was successfully applied for the determination of monomeric composition in bacterial PHAs isolated from Pseudomonads cultivated on different carbon sources after hydrolysis. The results of this work demonstrated that the newly-developed strategy was efficient, repeatable, and could have good potential to be employed for detailed analysis of PHA monomeric composition.