Advanced approaches to produce polyhydroxyalkanoate (PHA) biopolyesters in a sustainable and economic fashion

Abstract

Polyhydroxyalkanoates (PHA), the only group of "bioplastics" sensu stricto, are accumulated by various prokaryotes as intracellular "carbonosomes". When exposed to exogenous stress or starvation, presence of these microbial polyoxoesters of hydroxyalkanoates assists microbes to survive."Bioplastics" such as PHA must be competitive with petrochemically manufactured plastics both in terms of material quality and manufacturing economics. Cost-effectiveness calculations clearly show that PHA production costs, in addition to bioreactor equipment and downstream technology, are mainly due to raw material costs. The reason for this is PHA production on an industrial scale currently relying on expensive, nutritionally relevant "1 st -generation feedstocks", such as like glucose, starch or edible oils. As a way out, carbon-rich industrial waste streams ("2 nd -generation feedstocks") can be used that are not in competition with the supply of food; this strategy not only reduces PHA production costs, but can also make a significant contribution to safeguarding food supplies in various disadvantaged parts of the world. This approach increases the economics of PHA production, improves the sustainability of the entire lifecycle of these materials, and makes them unassailable from an ethical perspective.In this context, our EU-funded projects ANIMPOL and WHEYPOL, carried out by collaborative consortia of academic and industrial partners, successfully developed PHA production processes, which resort to waste streams amply available in Europe. As real 2 nd -generation feedstocks", waste lipids and crude glycerol from animal-processing and biodiesel industry, and surplus whey from dairy and cheese making industry were used in these processes. Cost estimations made by our project partners determine PHA production prices below 3 € (WHEYPOL) and even less than 2 € (ANIMPOL), respectively, per kg; these values already reach the benchmark of economic feasibility.The presented studies clearly show that the use of selected high-carbon waste streams of (agro)industrial origin contributes significantly to the cost-effectiveness and sustainability of PHA biopolyester production on an industrial scale.

Statistical optimization and effect of mesquite honey and maize alkaline wastewater (nejayote) as substrates for cellular biomass production and polyhydroxybutyrate biosynthesis by Bacillus cereus 4N

“…Actualmente en este aspecto se está estudiando el empleo de sustratos ricos en azúcares como las melazas, mieles, jarabes y jugos, así como el empleo de sustratos lignocelulósicos como el bagazo de caña, pajas de arroz, sorgo y cáscaras de frutas o verduras. También el uso de subproductos de la industria láctea y aceitera han sido reportados para este objetivo (Nielsen et al, 2017;Koller & Braunegg, 2018). Las melazas, mieles y jarabes son fuentes de carbono económicas que favorecen la biosíntesis de PHB en el género Bacillus debido a la disposición de carbohidratos fermentables (Sathya et al, 2018), los cuales son metabolizados a través de la glicolisis y la vía de la pentosa fosfato donde las moléculas resultantes de acetil-CoA son redirigidas del ciclo de Krebs a la ruta biosintética de acumulación de PHAs.…”

“…Sin embargo, al haber una menor producción de biomasa y biopolímero en comparación con el control positivo (medio suplementado con glucosa y peptona), la formulación diseñada en este reporte puede ser mejorada evaluando distintas fuentes de nitrógeno orgánico rico en aminoácidos (harinas de soya y pescado, hidrolizados de plumas y semillas, extracto de carne, urea, licor de maíz, etc.) que complementen el uso del extracto de levadura; puesto que el nitrógeno orgánico reduce la fase de adaptación del cultivo incrementando la producción de biomasa catalíticamente activa y estimula un incremento en los radios de NADPH / NADP + , lo cual como se había mencionado anteriormente, reduce la actividad de las enzimas previas al ciclo de Krebs promoviendo una mayor acumulación de PHB (Borah et al, 2002;Benesova et al, 2017;Koller & Braunegg, 2018).…”

Switching from petro-plastics to microbial polyhydroxyalkanoates (PHA): the biotechnological escape route of choice out of the plastic predicament?

“…of the food-industrial sector on the one hand safes about 50% of the entire costs of the biopolymer production chain, and, on the other hands, provides (agro)industry a tool to upgrade their disposal products in a value-generating manner (20). Examples of (agro)industrial waste used as PHA-feedstock during the last years, albeit not yet beyond the laboratory scale, encompass molasses from sugar industry (21,22), hydrolysates of lignocellulose materials (23) like bagasse (24), wheat straw (25), rice straw (26), or wood (27,28), sugars obtained by hydrolysis of green grass (29) or saccharified ryegrass (30), empty oil palm fruit bunches (31), cellulose-digested corn stover (32), steamed soybean wastewater (33), waste glycerol from biodiesel production (34)(35)(36)(37), saturated biodiesel fractions of animal origin (38,39), waste office paper hydrolysate (40), or spent sulfite liquor obtained by chemical pulping during the paper production process (41).…”

Development of High Cell Density Cultivation Strategies for Improved Medium Chain Length Polyhydroxyalkanoate Productivity Using Pseudomonas putida LS46

“…Production costs for PHA have been estimated to be as much as fifteen-fold higher than the petrochemical counterparts (polyethylene, polypropylene) they are intended to replace [9]. Development of productive and cost-effective bioreactor cultivation processes is an important aspect of improving the economic viability and lessening the environmental impacts of PHA production [10][11][12].…”