Production of thermostable phycocyanin in a mesophilic cyanobacterium

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.

Characterization of Molecular Diversity and Organization of Phycobilisomes in Thermophilic Cyanobacteria

“…In addition, molecular diversity can shed light on the evolution and structural characteristics (e.g., structural rigidity and thermostability) of PBPs [ 16 , 17 ]. The complexity of molecular components for PBS can also provide insights into metabolic engineering in mesophilic species since the heterologous production of mature PBPs is significantly challenging [ 18 ].…”

Gene expression and organization of thylakoid protein complexes in the PSII‐less mutant of Synechocystis sp. PCC 6803

“…Decoupling of PBS also takes place in response to blue light (Luimstra et al, 2020 ) or HL (Tamary et al, 2012 ), which cause excitation imbalance and PSII photoinhibition, respectively. The observed increase in the decoupled PBS in the mutant was accompanied by lower overall PC abundance (Figures 1 and 2 ), further supported by a lower 650‐ to 665‐nm peak in 77‐K fluorescence emission corresponding to uncoupled PC and APC (Figure 3c ) (Elanskaya et al, 2018 ; Puzorjov et al, 2021 ).…”

Light and carbon: Synthetic biology toward new cyanobacteria-based living biomaterials

“…recently used CyanoGate to insert a phycobiliprotein gene (used to produce a high commodity dye derived from light harvesting complexes) from a thermophilic cyanobacteria into Synechocystis sp. PCC 6803, a mesophilic species more amenable to industrial production of the dye [ 87 ].…”