Production of thermostable phycocyanin in a mesophilic cyanobacterium

Anton Puzorjov,Katherine E Dunn,Alistair J Mccormick

doi:10.1016/j.mec.2021.e00175

Anton Puzorjov, Katherine E Dunn + Show 1 more

Open Access

https://doi.org/10.1016/j.mec.2021.e00175

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Abstract

Phycocyanin (PC) is a soluble phycobiliprotein found within the light-harvesting phycobilisome complex of cyanobacteria and red algae, and is considered a high-value product due to its brilliant blue colour and fluorescent properties. However, commercially available PC has a relatively low temperature stability. Thermophilic species produce more thermostable variants of PC, but are challenging and energetically expensive to cultivate. Here, we show that the PC operon from the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1 (cpcBACD) is functional in the mesophile Synechocystis sp. PCC 6803. Expression of cpcBACD in an ‘Olive’ mutant strain of Synechocystis lacking endogenous PC resulted in high yields of thermostable PC (112 ± 1 mg g−1 DW) comparable to that of endogenous PC in wild-type cells. Heterologous PC also improved the growth of the Olive mutant, which was further supported by evidence of a functional interaction with the endogenous allophycocyanin core of the phycobilisome complex. The thermostability properties of the heterologous PC were comparable to those of PC from T. elongatus, and could be purified from the Olive mutant using a low-cost heat treatment method. Finally, we developed a scalable model to calculate the energetic benefits of producing PC from T. elongatus in Synechocystis cultures. Our model showed that the higher yields and lower cultivation temperatures of Synechocystis resulted in a 3.5-fold increase in energy efficiency compared to T. elongatus, indicating that producing thermostable PC in non-native hosts is a cost-effective strategy for scaling to commercial production.

Highlights

Phycocyanin (PC) is a blue pigment-protein that forms part of the photosynthetic light-harvesting phycobilisome (PBS) complex in most cyanobacteria and red algae
Our results suggested that the presence of the T. elongatus CpcC rod linker in TeBACD allowed for the formation of a Te-PC rod complex, but this could not attach to the endogenous APC core
As Te-PC from Synechocystis showed a similar stability compared to T. elongatus, we investigated if a short heat treatment of the PC extract following cell disruption and centrifugation could be used as a rapid and low-cost method to purify Te-PC from endogenous APC (APC is typically considered a contaminant when purifying PC) (El-Mohsnawy and Abu-Khudir, 2020; Sun et al, 2012; Zhang and Chen, 1999)

Summary

Introduction

Phycocyanin (PC) is a blue pigment-protein (i.e. a phycobiliprotein) that forms part of the photosynthetic light-harvesting phycobilisome (PBS) complex in most cyanobacteria and red algae. Exposure of A. platensis PC to temperatures exceeding 45 ◦C results in progressive protein denaturation, loss of colour and a reduction in anti-oxidant properties, which limit its usage in industries including food, cos metics and textiles where processing temperatures often exceed 45 ◦C (Chaiklahan et al, 2012; Jespersen et al, 2005; Ogbonda et al, 2007; Pan-utai et al, 2018; Sarada et al, 1999). Additives and/or cross-linking agents can improve the stability of A. platensis PC (Chaiklahan et al, 2012; Martelli et al, 2014; Pan-utai et al, 2018). Additives can increase the cost of the final product and affect colour and taste, while cross-linking agents (e.g. formaldehyde) are often too toxic for human consumption (Azeredo and Waldron, 2016)

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