Abstract
BackgroundEthanol photosynthetic production based on cyanobacteria cell factories utilizing CO2 and solar energy provides an attractive solution for sustainable production of green fuels. However, the scaling up processes of cyanobacteria cell factories were usually threatened or even devastated by biocontaminations, which restricted biomass or products accumulations of cyanobacteria cells. Thus it is of great significance to develop reliable biocontamination-controlling strategies for promoting ethanol photosynthetic production in large scales.ResultsThe scaling up process of a previously developed Synechocystis strain Syn-HZ24 for ethanol synthesis was severely inhibited and devastated by a specific contaminant, Pannonibacter phragmitetus, which overcame the growths of cyanobacteria cells and completely consumed the ethanol accumulation in the cultivation systems. Physiological analysis revealed that growths and ethanol-consuming activities of the contaminant were sensitive to alkaline conditions, while ethanol-synthesizing cyanobacteria strain Syn-HZ24 could tolerate alkaline pH conditions as high as 11.0, indicating that pH-increasing strategy might be a feasible approach for rescuing ethanol photosynthetic production in outdoor cultivation systems. Thus, we designed and evaluated a Bicarbonate-based Integrated Carbon Capture System (BICCS) derived pH-rising strategy to rescue the ethanol photosynthetic production in non-sterilized conditions. In lab scale artificially simulated systems, pH values of BG11 culture medium were maintained around 11.0 by 180 mM NaHCO3 and air steam, under which the infection of Pannonibacter phragmitetus was significantly restricted, recovering ethanol production of Syn-HZ24 by about 80%. As for outdoor cultivations, ethanol photosynthetic production of Syn-HZ24 was also successfully rescued by the BICCS-derived pH-rising strategy, obtaining a final ethanol concentration of 0.9 g/L after 10 days cultivation.ConclusionsIn this work, a novel product-consuming biocontamination pattern in cyanobacteria cultivations, causing devastated ethanol photosynthetic production, was identified and characterized. Physiological analysis of the essential ethanol-consuming contaminant directed the design and application of a pH-rising strategy, which effectively and selectively controlled the contamination and rescued ethanol photosynthetic production. Our work demonstrated the importance of reliable contamination control systems and strategies for large scale outdoor cultivations of cyanobacteria, and provided an inspiring paradigm for targeting effective solutions.
Highlights
Ethanol photosynthetic production based on cyanobacteria cell factories utilizing CO2 and solar energy provides an attractive solution for sustainable production of green fuels
Devastated photosynthetic ethanol production of an engineered cyanobacteria strain in non‐sterilized outdoor cultivations Previously, we have reported the development of an efficient ethanol-synthesizing cyanobacteria strain SynHZ24 (HZ24 hereafter for short) derived from Synechocystis sp
For achieving efficient ethanol photosynthetic production, pdc gene from Zymomonas mobilis (Zmpdc) encoding pyruvate decarboxylase and an endogenous gene slr1192 encoding alcohol dehydrogenase II were overexpressed in Synechocystis sp
Summary
Ethanol photosynthetic production based on cyanobacteria cell factories utilizing CO2 and solar energy provides an attractive solution for sustainable production of green fuels. The scaling up processes of cyanobacteria cell factories were usually threatened or even devastated by biocontaminations, which restricted biomass or products accumulations of cyanobacteria cells. Non-food carbohydrates, represented by lignocellulose, could provide abundant fermentation feedstock for bioethanol production; the economic competitiveness was severely restricted by the cost and energy required for pretreatments and enzymatic hydrolysis processes of the raw materials [8]. Comparing with the traditional biorefinery routes based on fermentation processes, ethanol photosynthetic production by recycling CO2 and utilizing solar energy has shown great potentials to be a more efficient and sustainable solution [9,10,11]. Despite comprehensive and systematic research and optimization on strain and cultivation process in laboratory scale, the industrialization of cyanobacteria-based ethanol photosynthetic production was still severely constrained by the lack of mature outdoor cultivation techniques and systems
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
