Production and Biodegradation of Polyhydroxyalkanoates PHA from Lignocellulosic Wastes

Abstract

The staggering tonnes of plastic waste, steadily destroying the environment due to its newlineinability to be degraded, have propelled the search for eco-friendly alternatives. newlinePolyhydroxyalkanoates (PHA) are natural polymers, accumulated as intracellular granules, newlinewithin the organism that function as reserve resources. PHA is completely biodegradable newlinewith physical properties comparable to their petroleum-based counterparts and thus, offer a newlinesolution to our existing plastics pollution problem. However, PHA production has proved to newlinebe an expensive one due to the costliness of the raw materials. Decades worth of studies have newlineassessed the viability of using waste streams, from various industrial sectors, as feedstocks newlinefor cost-effective manufacture of PHA. Lignocellulose, the most copious carbon cache newlineknown, has escaped exploitation due to its robust barricade, lignin. Multiple methods, newlinedeveloped to remove lignin and expose the polysaccharide layers for harvesting, generate newlinetoxic by-products. Thus, an eco-friendly approach is required. Biological pretreatment, newlineinvolving the usage of white rot fungi (WRF) for delignification, is one such approach. The newlinepresent work investigated the potential of utilizing sugar-rich hydrolysates, obtained through newlinethe biological pretreatment of lignocellulose, for the production of PHA. The research was newlinedivided into three main parts: first, the pretreatment of lignocellulosic wastes using WRF and newlinefacilitating the release of sugars; second, utilization of the released sugars for the production newlineof PHA and third, the study of biodegradation of PHA films. The novelty of this work was newlineattributed to the pretreatment approach which yielded inexpensive, sugar-rich feedstocks for newlinePHA production. Pycnoporus coccineus MScMS1 was isolated and chosen for biological newlinepretreatment of sugarcane bagasse (SB). Optimization of the process yielded ~18 mg/mL, newlinewithin 4 days and enhanced the sugar productivity to 4.5 mg/mL/day. The production of newlinePHA, by Bacillus megaterium Ti3, was found to be significantly high (plt0.05) with 1.08 g/L newlinePHA on xylose based medium. SB hydrolysates reconstituted with production medium salts newlineyielded the highest levels of PHA, 5.42 g/L, at 48 h of fermentation with equally high DCW newlineof gt50 g/L. The extracted polymer was short-chain-length (scl) poly-and#946;-hydroxybutyrate newline(PHB). The highest and faster degradation rates of the PHB/PEG blended films (gt90%) were newlinedocumented for compost soil and stagnant water in 5 weeks. Biodegradation rate of the newlineblended films was higher than that of the non-blended films. The fastest degradation of liquid newlinePHB medium was observed on day 5 by isolates KMS1 and KMS2, closely followed by newlinePsathyrella candolleana AMO on day 6 and Pycnoporus coccineus MScMS1on day 7. newline