Biosynthesis of Polyhydroxyalkanoates (PHAs) by the Valorization of Biomass and Synthetic Waste

Synthetic pollutants are a looming threat to the entire ecosystem, including wildlife, the environment, and human health. Polyhydroxyalkanoates (PHAs) are natural biodegradable microbial polymers with a promising potential to replace synthetic plastics. This research is focused on devising a sustainable approach to produce PHAs by a new microbial strain using untreated synthetic plastics and lignocellulosic biomass. For experiments, 47 soil samples and 18 effluent samples were collected from various areas of Punjab, Pakistan. The samples were primarily screened for PHA detection on agar medium containing Nile blue A stain. The PHA positive bacterial isolates showed prominent orange–yellow fluorescence on irradiation with UV light. They were further screened for PHA estimation by submerged fermentation in the culture broth. Bacterial isolate 16a produced maximum PHA and was identified by 16S rRNA sequencing. It was identified as Stenotrophomonas maltophilia HA-16 ({"type":"entrez-nucleotide","attrs":{"text":"MN240936","term_id":"1712425297","term_text":"MN240936"}}MN240936), reported first time for PHA production. Basic fermentation parameters, such as incubation time, temperature, and pH were optimized for PHA production. Wood chips, cardboard cutouts, plastic bottle cutouts, shredded polystyrene cups, and plastic bags were optimized as alternative sustainable carbon sources for the production of PHAs. A vital finding of this study was the yield obtained by using plastic bags, i.e., 68.24 ± 0.27%. The effective use of plastic and lignocellulosic waste in the cultivation medium for the microbial production of PHA by a novel bacterial strain is discussed in the current study.     

Sodium Dodecyl Sulphate, a Strong Inducer of Thermostable Glucanhydrolase Secretion from a Derepressed Mutant Strain of Bacillus alcalophilus GCBNA-4

In the present study, we report the optimisation of batch conditions for improved α-1,4-glucan-glucanohydrolase (GGH) secretion by a nitrous acid (NA)-treated Bacillus alcalophilus. The wild (isolate GCB-18) and NA-derivative (mutant GCBNA-4) were grown in a medium containing 10 g/L nutrient broth, 10 g/L starch, 5 g/L lactose, 2 g/L ammonium sulphate, 2 g/L CaCl₂ and phosphate buffer (pH 7.6). Sodium dodecyl sulphate (SDS) was used as an enzyme inducer while batch fermentations were carried out at 40 °C. The mutant produced GGH in 40 h which was 15-fold higher than the wild in presence of SDS. Thermodynamic studies revealed that the mutant culture exhibited the capability for improved enzyme activity over a broad range of temperature (35–70 °C). The enzyme was purified by cation-exchange column chromatography with ～80 % recovery. The performance of fuzzy-logic system control was found to be highly promising for the improved substrate conversion rate. The correlation (1.045E?+?0025) among variables demonstrated the model terms as highly significant indicating commercial utility of the culture used (P?<?0.05).