Establishing Mixotrophic Growth of Cupriavidus necator H16 on CO2 and Volatile Fatty Acids

Kamran Jawed,Katalin Kovács,Rajesh Reddy Bommareddy,Victor Uhunoma Irorere,Nigel P Minton

doi:10.3390/fermentation8030125

Abstract

The facultative chemolithoautotroph Cupriavidus necator H16 is able to grow aerobically either with organic substrates or H2 and CO2 s and it can accumulate large amounts of (up to 90%) poly (3-hydroxybutyrate), a polyhydroxyalkanoate (PHA) biopolymer. The ability of this organism to co-utilize volatile fatty acids (VFAs) and CO2 as sources of carbon under mixotrophic growth conditions was investigated and PHA production was monitored. PHA accumulation was assessed under aerobic conditions, with either individual VFAs or in mixtures, under three different conditions—with CO2 as additional carbon source, without CO2 and with CO2 and H2 as additional sources of carbon and energy. VFAs utilisation rates were slower in the presence of CO2. PHA production was significantly higher when cultures were grown mixotrophically and with H2 as an additional energy source compared to heterotrophic or mixotrophic growth conditions, without H2. Furthermore, a two-step VFA feeding regime was found to be the most effective method for PHA accumulation. It was used for PHA production mixotrophically using CO2, H2 and VFA mixture derived from an anaerobic digestor (AD). The data obtained demonstrated that process parameters need to be carefully monitored to avoid VFA toxicity and low product accumulation.

Highlights

Up to 348 million tons of plastics are produced each year, a figure significantly higher than the weight of the human adult population [1,2]
We found that cells were able to utilise each volatile fatty acids (VFAs) as the sole carbon and energy source up to a certain concentration, with an observed increase in the lag phase with increasing concentrations of VFAs and an increase in their chain length (Figure 1)
Circular economy strategies are essential to driving decarbonisation, and as such, utilisation of CO2 and other waste carbon sources as feedstocks to replace petrochemical based chemical synthesis are at the heart of these efforts

Summary

Introduction

Up to 348 million tons of plastics are produced each year, a figure significantly higher than the weight of the human adult population [1,2]. An estimated 99 million Mt of mismanaged plastic waste (MPW) was generated in 2015 [3]. MPW is regarded as plastic waste that has been littered, inadequately disposed or released from uncontrolled landfill sites [4]. Between 1950 and 2015, only 9% of plastic waste generated was recycled, while 12% were incinerated, with almost 80% left to go to landfills and the natural environment [5]. 18% with the EU topping the chart at 30% [5]. This has led to significant pollution of aquatic and terrestrial habitats, owing to their recalcitrant nature, causing significant damage to the environment, human health, coastal life, amongst others [3].

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Results

Conclusion