From Organic Wastes to Bioplastics: Feasibility of Nonsterile Poly(3-hydroxybutyrate) Production by Zobellella denitrificans ZD1

Abstract

Poly(3-hydroxybutyrate) (PHB)—a renewable and biodegradable polymer—is a promising alternative to nonbiodegradable synthetic plastics that are derived from petrochemicals. The methods currently employed for PHB production are costly, in part, due to the expensive cultivation feedstocks and the need to sterilize the culture medium, which is energy-intensive. This study investigates the feasibility of nonsterile PHB production from several saline organic wastes using a salt-tolerant strain, Zobellella denitrificans ZD1 (referred to as strain ZD1). Factors such as the pH, salinity, carbon/nitrogen (C/N) ratio, nitrogen source, and electron acceptor that might affect the growth of strain ZD1 and its PHB production were determined. Our results showed successful nonsterile PHB production by growing the strain ZD1 on nonsterile synthetic crude glycerol, high-strength saline wastewater, and real municipal wastewater-activated sludge under saline conditions. The PHB production was significantly enhanced when the levels of salts and nitrate-nitrogen in the culture medium were increased. This study suggested a promising low-cost nonsterile PHB production strategy from organic wastes using strain ZD1.

A Novel Recirculating Aquaculture System for Sustainable Aquaculture: Enabling Wastewater Reuse and Conversion of Waste-to-Immune-Stimulating Fish Feed

“…As successful demonstration of nonsterile cultivation of Z. denitrificans ZD1 from activated sludge, synthetic high-strength wastewater, and synthetic crude glycerol under saline conditions has been previously reported, it is feasible to produce PHB-rich Z. denitrificans ZD1 biomass from nonsterile agro-industrial wastes/wastewaters in this study.…”

“…The 3% NaCl in these solutions provided an ideal condition for the nonsterile cultivation of PHB-rich Z. denitrificans ZD1, and thus there was no need for sterilization …”

“…Such microorganisms, used as animal feed, are also called single-cell proteins (SCPs) because they are rich in proteins and contain readily digestible nutrients (e.g., lipids and minerals) for animal consumption. − Conventional SCPs are phototrophic microorganisms such as algae and purple phototrophic bacteria that are cultivated with energy-intensive illumination to low cell densities. , On the contrary, the production of heterotrophs as SCPs is more energy-efficient; for example, it only requires ∼230-MJ C/electron donor to produce 1 kg of biomass. ,, Zobellella denitrificans ZD1 is a heterotrophic hyper-PHB-accumulating (up to 84%) bacterium, capable of growing on different saline and nonsaline organic wastes. , Accordingly, a novel strategy is to concurrently produce PHB-rich Z. denitrificans ZD1 biomass as SCP from AW and wastes and high-quality treated wastewater for reuse.…”

Integrated Biotechnology Management of Biosolids: Sustainable Ways to Produce Value—Added Products

“…PHA content in waste activated sludge (WAS) has been reported to range from 0.3 to 22.7 mg (Crutchik et al, 2020). Asiri et al (2020) investigated the bioaugmentation of Zobellella denitrificans in sludge under saline conditions for the production of PHB, the most commonly used PHA. C/N ratio, electron acceptors and saline factors affected the growth of Z. denitrificans and subsequent production of PHB.…”

“…C/N ratio, electron acceptors and saline factors affected the growth of Z. denitrificans and subsequent production of PHB. Increasing the saline conditions from no NaCl to 3% NaCl, the PHB production increased to 0.56 mg/L from 0.38 mg/L (Asiri et al, 2020). Mixing organic municipal solid waste and sewage sludge in a threestep mixed microbial culture (MMC) was investigated.…”