Abstract
The inexhaustible nature and biodegradability of bioplastics like polyhydroxyalkanoates (PHAs) make them suitable assets to replace synthetic plastics. The eventual fate of these eco-friendly and non-toxic bioplastics relies upon the endeavors towards satisfying cost and, in addition, execution necessity. In this study, we utilized and statistically optimized different food (kitchen-/agro-) waste as a sole carbon/nitrogen source for the production of PHA at a reduced cost, indicating a proficient waste administration procedure. Seven different types of kitchen-/agro-waste were used as unique carbon source and four different types of nitrogen source were used to study their impact on PHA production by Bacillus subtilis MTCC 144. Among four different studied production media, mineral salt medium (MSM) (biomass: 37.7 g/L; cell dry weight: 1.8 g/L; and PHA: 1.54 g/L) was found most suitable for PHA production. Further, carbon and nitrogen components of MSM were optimized using one-factor-at-a-time experiments, and found that watermelon rind (PHA = 12.97 g/L) and pulse peel (PHA = 13.5 g/L) were the most suitable carbon and nitrogen sources, respectively, in terms of PHA (78.60%) recovery. The concentrations of these factors (sources) were statistically optimized using response surface methodology coupled with the genetic algorithm approach. Additionally, in order to enhance microbial PHA production, the interaction of citrate synthase, a key enzyme in the TCA cycle, with different known inhibitors was studied using in silico molecular docking approach. The inhibition of citrate synthase induces the blockage of the tricarboxylic cycle (TCA), thereby increasing the concentration of acetyl-CoA that helps in enhanced PHA production. Molecular docking of citrate synthase with different inhibitors of PubChem database revealed that hesperidin (PubChem compound CID ID 10621), generally present in citrus fruits, is the most efficient inhibitor of the TCA cycle with the binding score of –11.4 and warrants experimental validation. Overall, this study provides an efficient food waste management approach by reducing the production cost and enhancing the production of PHA, thereby lessening our reliance on petroleum-based plastics.
Highlights
The discovery of synthetic plastic was a boon for societal development, but excessive and indiscriminate use of this material in every sector tremendously increased the amount of non-biodegradable waste material all over the world, and it has become a curse for our environment
Bacillus subtilis is a well-known PHA producer [26]; here in this study, B. subtilis MTCC 144 was exploited for PHA production considering two phase production schemes during the experiments
Petroleum resources are depleting, there is an urgent need of an alternative of these petroleum-based synthetic plastics, and PHAs are an exceptional substitute over synthetic plastics as they are biodegradable, non-toxic, and sustainable
Summary
Due to its non-degradable nature, it is accumulating continuously in the environment and has put an adverse effect on all of our biological systems, including habitat [1]. All of these activities lead to imbalance of our ecosystem. Proper disposal of synthetic plastics is a major issue, as these are xenobiotic in nature and resistant to microbial degradation processes. Synthetic plastics persist in our ecosystem for several years as their molecular size is very big, which is the major reason for the resistance towards microbial degradation [2]. The widely used methods of getting rid of synthetic plastics are either incineration or recycling. Incineration generates a surplus amount of CO2 , along with some highly toxic gases that are accountable for global warming and air pollution; whereas, the recycling process is extremely expensive [3]
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