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

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ABSTRACT

Background: Ethanol 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.

Results: The 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.

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

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Related in: MedlinePlus

Evaluation of the contamination-controlling effects of BICCS based pH-rising strategy for ethanol photosynthetic production of Syn-HZ24. a Ethanol production of Syn-HZ24 cultivated in sterilized (red open squares), non-sterilized (blue triangles), and Pannonibacter phragmitetus inoculated BG11 culture medium bubbled with 5% CO2 as main carbon source. Red crosses denoted the pH values during the cultivation process. b CFU dynamics of Synechocystis (open square) and Pannonibacter (closed circle) cultivated in BG11 culture medium bubbled with 5% CO2–air steam without pH-rising strategy. c Ethanol production of Syn-HZ24 cultivated in sterilized (red open squares), non-sterilized (blue triangles), and Pannonibacter phragmitetus inoculated BG11 culture medium with BICCS-based pH-rising strategy. Red crosses denoted the pH values during the cultivation processes. pH values were allowed to increase to 11 physiologically and then constantly maintained at 11 with 180 mM NaHCO3 and air stream. d CFU dynamics of Synechocystis (open square) and Pannonibacter (closed circle) cultivated in BG11 culture medium with the BICCS-based pH-rising strategy. pH values of the cultivation process were maintained in the range from 10 to 11
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Fig4: Evaluation of the contamination-controlling effects of BICCS based pH-rising strategy for ethanol photosynthetic production of Syn-HZ24. a Ethanol production of Syn-HZ24 cultivated in sterilized (red open squares), non-sterilized (blue triangles), and Pannonibacter phragmitetus inoculated BG11 culture medium bubbled with 5% CO2 as main carbon source. Red crosses denoted the pH values during the cultivation process. b CFU dynamics of Synechocystis (open square) and Pannonibacter (closed circle) cultivated in BG11 culture medium bubbled with 5% CO2–air steam without pH-rising strategy. c Ethanol production of Syn-HZ24 cultivated in sterilized (red open squares), non-sterilized (blue triangles), and Pannonibacter phragmitetus inoculated BG11 culture medium with BICCS-based pH-rising strategy. Red crosses denoted the pH values during the cultivation processes. pH values were allowed to increase to 11 physiologically and then constantly maintained at 11 with 180 mM NaHCO3 and air stream. d CFU dynamics of Synechocystis (open square) and Pannonibacter (closed circle) cultivated in BG11 culture medium with the BICCS-based pH-rising strategy. pH values of the cultivation process were maintained in the range from 10 to 11

Mentions: For mimics of the infected cultivations, purified Pannonibacter phragmitetus cells would be artificially inoculated in sterilized BG11 culture medium. As shown in Fig. 4a, when no pH-rising strategy was adopted, about 0.9 g/L ethanol was obtained in the cultivation systems with sterilized BG11 culture medium, while the inoculation of Pannonibacter phragmitetus cells completely devastated the ethanol production, similar with the cultivations with non-sterilized culture medium, meaning that infection of the isolated Pannonibacter phragmitetus strain could be the main reason responsible for devastation of photosynthetic ethanol production in this case. During the 10-day cultivation, pH values of the cultivations were maintained in the range from 7.0 to 8.0, under which concentrations of Pannonibacter phragmitetus cells artificially inoculated into the systems increased from 1.4–1.5 × 108 to 2.8–3.2 × 109 cells/mL, while cell concentrations of HZ24 were increased from 1.6–1.8 × 108 to 9 × 108 cells/mL, much slower than that of Pannonibacter phragmitetus (Fig. 4b).Fig. 4


Rescuing ethanol photosynthetic production of cyanobacteria in non-sterilized outdoor cultivations with a bicarbonate-based pH-rising strategy
Evaluation of the contamination-controlling effects of BICCS based pH-rising strategy for ethanol photosynthetic production of Syn-HZ24. a Ethanol production of Syn-HZ24 cultivated in sterilized (red open squares), non-sterilized (blue triangles), and Pannonibacter phragmitetus inoculated BG11 culture medium bubbled with 5% CO2 as main carbon source. Red crosses denoted the pH values during the cultivation process. b CFU dynamics of Synechocystis (open square) and Pannonibacter (closed circle) cultivated in BG11 culture medium bubbled with 5% CO2–air steam without pH-rising strategy. c Ethanol production of Syn-HZ24 cultivated in sterilized (red open squares), non-sterilized (blue triangles), and Pannonibacter phragmitetus inoculated BG11 culture medium with BICCS-based pH-rising strategy. Red crosses denoted the pH values during the cultivation processes. pH values were allowed to increase to 11 physiologically and then constantly maintained at 11 with 180 mM NaHCO3 and air stream. d CFU dynamics of Synechocystis (open square) and Pannonibacter (closed circle) cultivated in BG11 culture medium with the BICCS-based pH-rising strategy. pH values of the cultivation process were maintained in the range from 10 to 11
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5391583&req=5

Fig4: Evaluation of the contamination-controlling effects of BICCS based pH-rising strategy for ethanol photosynthetic production of Syn-HZ24. a Ethanol production of Syn-HZ24 cultivated in sterilized (red open squares), non-sterilized (blue triangles), and Pannonibacter phragmitetus inoculated BG11 culture medium bubbled with 5% CO2 as main carbon source. Red crosses denoted the pH values during the cultivation process. b CFU dynamics of Synechocystis (open square) and Pannonibacter (closed circle) cultivated in BG11 culture medium bubbled with 5% CO2–air steam without pH-rising strategy. c Ethanol production of Syn-HZ24 cultivated in sterilized (red open squares), non-sterilized (blue triangles), and Pannonibacter phragmitetus inoculated BG11 culture medium with BICCS-based pH-rising strategy. Red crosses denoted the pH values during the cultivation processes. pH values were allowed to increase to 11 physiologically and then constantly maintained at 11 with 180 mM NaHCO3 and air stream. d CFU dynamics of Synechocystis (open square) and Pannonibacter (closed circle) cultivated in BG11 culture medium with the BICCS-based pH-rising strategy. pH values of the cultivation process were maintained in the range from 10 to 11
Mentions: For mimics of the infected cultivations, purified Pannonibacter phragmitetus cells would be artificially inoculated in sterilized BG11 culture medium. As shown in Fig. 4a, when no pH-rising strategy was adopted, about 0.9 g/L ethanol was obtained in the cultivation systems with sterilized BG11 culture medium, while the inoculation of Pannonibacter phragmitetus cells completely devastated the ethanol production, similar with the cultivations with non-sterilized culture medium, meaning that infection of the isolated Pannonibacter phragmitetus strain could be the main reason responsible for devastation of photosynthetic ethanol production in this case. During the 10-day cultivation, pH values of the cultivations were maintained in the range from 7.0 to 8.0, under which concentrations of Pannonibacter phragmitetus cells artificially inoculated into the systems increased from 1.4–1.5 × 108 to 2.8–3.2 × 109 cells/mL, while cell concentrations of HZ24 were increased from 1.6–1.8 × 108 to 9 × 108 cells/mL, much slower than that of Pannonibacter phragmitetus (Fig. 4b).Fig. 4

View Article: PubMed Central - PubMed

ABSTRACT

Background: Ethanol 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.

Results: The 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.

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

No MeSH data available.


Related in: MedlinePlus