Carbon monoxide fermentation to bioplastic: the effect of substrate adaptation on Rhodospirillum rubrum

Beatrice Mongili,Debora Fino

doi:10.1007/s13399-020-00876-x

Beatrice Mongili, Debora Fino

Open Access

https://doi.org/10.1007/s13399-020-00876-x

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Abstract

Rhodospirillum rubrum is a gram-negative bacterium that naturally takes advantage of CO and which, in the presence of acetate, accumulates carbon and energy units as polyhydroxybutyrate (PHB). Since the conversion of CO depends on a large protein membrane complex that is expressed after the exposure to carbon monoxide, this study presents the effects of a CO-based acclimation in R. rubrum on the growth trend and on the production of PHB. The strain was cultured in two consecutive fermentation cycles on 15% of CO, and the behaviour of this species, in the presence of acetate or a reducing sugar, such as fructose, was compared. The exposure of R. rubrum to CO during the first adaptation phase led to the development of a metabolically active population characterised by a greater biomass growth. The supply of fructose ensured a shorter lag-phase and a higher biomass titre, but it also determined a decrease in the biopolymer accumulation. However, R. rubrum showed the best carbon utilisation in the absence of fructose, with a growth molar yield of 48 mg mol−1, compared to the 12 mg mol−1 obtained for fructose feeding.

Highlights

The few decades will be characterised by a radical change in the economy, which will evolve from the current linear type to the new concept of circular economy
R. rubrum was fed with 15% of CO during both fermentation runs, and its growth trend supported by CO and acetate was compared with that obtained when CO and fructose were used as co-substrates
Two different concentrations of fructose, corresponding to 5 and 15 mM, were investigated in the adaptation phase to verify its effect on biomass growth

Summary

Introduction

The few decades will be characterised by a radical change in the economy, which will evolve from the current linear type to the new concept of circular economy. This change in perspective requires a substantial evolution of the supply chain network, in which by-products should be designed to take part in new production cycles as secondary raw materials. Carbon monoxide is a harmful molecule for most living beings and a greenhouse gas that affects climate change. In this scenario, anthropogenic activities play a crucial role, contributing by around 70% to the global CO emissions in the atmosphere [1].

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