Rescuing ethanol photosynthetic production of cyanobacteria in non-sterilized outdoor cultivations with a bicarbonate-based pH-rising strategy

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.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-017-0765-5) contains supplementary material, which is available to authorized users.

Effect of Organic Solvents on Microalgae Growth, Metabolism and Industrial Bioproduct Extraction: A Review

“…Maintaining alkaline conditions (pH = 11) was reported to prevent development of bacteria and a loss of ethanol during outdoor cultivation of ethanol-producing Synechocystis sp. [ 177 ]. However, it should be remembered, that extreme cultivation conditions can also have inhibitory effect on microalgal cultures.…”

Metal Oxide Mediated Extracellular NADPH Regeneration Improves Ethanol Production by Engineered Synechocystis sp. PCC 6803

“…PCC 6803 and pyruvate decarboxylase ( PDC1 : GenBank accession number MK868028) from Saccharomyces cerevisiae into pEERM vector under the control of psbA1 promoter (Data S1; Englund et al, 2015; Velmurugan and Incharoensakdi, 2018). The engineered strain was cultivated in 250 mL Erlenmeyer flasks containing 100 mL BG-11 medium (pH 7.5) supplemented with 30 μg/mL chloramphenicol under continuous illumination of 100 μE/m 2 /s at 28 ± 1°C with atmospheric CO 2 supply upon shaking at 160 rpm (Rippka et al, 1979; Zhu et al, 2017).…”

Building a bio-based industry in the Middle East through harnessing the potential of the Red Sea biodiversity

“…One of the major challenges in developing Cyanobacteria-based, non-sterilized outdoor cultivations will be possible contaminations with other microorganisms living in the Red Sea (Raitsos et al 2013 ). Strategies have been developed to eliminate specific contaminants of cyanobacterial outdoor cultivations, such as the bicarbonate-based pH-rising strategy (Zhu et al 2017 ). Along these lines, specific solutions will have to be developed to handle the local contaminants.…”