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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.

No MeSH data available.


Growth and ethanol production of Syn-HZ24 in non-sterilized outdoor cultivation systems with BICCS-based pH-rising strategy. Open square denoted cell growth; open triangle denoted pH values; open circle denoted ethanol accumulations; red dotted line denoted the ethanol production of Syn-HZ24 non-sterilized outdoor cultivation without pH-rising strategy
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Fig5: Growth and ethanol production of Syn-HZ24 in non-sterilized outdoor cultivation systems with BICCS-based pH-rising strategy. Open square denoted cell growth; open triangle denoted pH values; open circle denoted ethanol accumulations; red dotted line denoted the ethanol production of Syn-HZ24 non-sterilized outdoor cultivation without pH-rising strategy

Mentions: The BICCS-derived pH-rising strategy proved to be effective for controlling infections of the ethanol-consuming contaminant Pannonibacter phragmitetus in laboratory scale non-sterilized cultivations or artificially contaminant-inoculated cultivations, and we further explored to rescue ethanol photosynthetic production in outdoor non-sterilized environments. The BICCS was also adopted to maintain an alkaline condition (pH values around 11.0) in the culture broths of designated polyethylene membrane photobioreactors (MPBR). As shown in Fig. 5, in the first 6-day cultivations, pH values of the broth were slightly increased from 9.0 to 11.0, and maintained at this level for the following 4 days. During this process, OD730 grew to a peak value of 3.2 in day 8. Ethanol production continued and accumulated to a final titer of 0.95 g/L. In comparisons, ethanol concentration in cultivation systems taking 5% CO2 as sole carbon source (without pH-rising) reached a peak value of 0.6 g/L in day 4, and then be consumed completely in the following 6 days. Comparing with ethanol photosynthetic production of HZ24 in column photobioreactors under stable lab conditions (with continuous light intensities and constant temperatures), the carbon partitioning ratio in outdoor MPBR was significantly decreased (both the productivities and carbon partitioning ratios), which might resulted from the fluctuating environment conditions (sun light intensities, day-night cycles, and changing temperatures). In summary, our results confirmed that the pH-rising strategy successfully inhibited the infection of ethanol-consuming biocontaminant, and rescued the ethanol photosynthetic production in outdoor non-sterilized environments.Fig. 5


Rescuing ethanol photosynthetic production of cyanobacteria in non-sterilized outdoor cultivations with a bicarbonate-based pH-rising strategy
Growth and ethanol production of Syn-HZ24 in non-sterilized outdoor cultivation systems with BICCS-based pH-rising strategy. Open square denoted cell growth; open triangle denoted pH values; open circle denoted ethanol accumulations; red dotted line denoted the ethanol production of Syn-HZ24 non-sterilized outdoor cultivation without pH-rising strategy
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5391583&req=5

Fig5: Growth and ethanol production of Syn-HZ24 in non-sterilized outdoor cultivation systems with BICCS-based pH-rising strategy. Open square denoted cell growth; open triangle denoted pH values; open circle denoted ethanol accumulations; red dotted line denoted the ethanol production of Syn-HZ24 non-sterilized outdoor cultivation without pH-rising strategy
Mentions: The BICCS-derived pH-rising strategy proved to be effective for controlling infections of the ethanol-consuming contaminant Pannonibacter phragmitetus in laboratory scale non-sterilized cultivations or artificially contaminant-inoculated cultivations, and we further explored to rescue ethanol photosynthetic production in outdoor non-sterilized environments. The BICCS was also adopted to maintain an alkaline condition (pH values around 11.0) in the culture broths of designated polyethylene membrane photobioreactors (MPBR). As shown in Fig. 5, in the first 6-day cultivations, pH values of the broth were slightly increased from 9.0 to 11.0, and maintained at this level for the following 4 days. During this process, OD730 grew to a peak value of 3.2 in day 8. Ethanol production continued and accumulated to a final titer of 0.95 g/L. In comparisons, ethanol concentration in cultivation systems taking 5% CO2 as sole carbon source (without pH-rising) reached a peak value of 0.6 g/L in day 4, and then be consumed completely in the following 6 days. Comparing with ethanol photosynthetic production of HZ24 in column photobioreactors under stable lab conditions (with continuous light intensities and constant temperatures), the carbon partitioning ratio in outdoor MPBR was significantly decreased (both the productivities and carbon partitioning ratios), which might resulted from the fluctuating environment conditions (sun light intensities, day-night cycles, and changing temperatures). In summary, our results confirmed that the pH-rising strategy successfully inhibited the infection of ethanol-consuming biocontaminant, and rescued the ethanol photosynthetic production in outdoor non-sterilized environments.Fig. 5

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.