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Critical Involvement of Environmental Carbon Dioxide Fixation to Drive Wax Ester Fermentation in Euglena

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ABSTRACT

Accumulation profiles of wax esters in Euglena gracilis Z were studied under several environmental conditions. The highest amount of total wax esters accumulated under hypoxia in the dark, and C28 (myristyl-myristate, C14:0-C14:0) was prevalent among all conditions investigated. The wax ester production was almost completely suppressed under anoxia in the light, and supplying exogenous inorganic carbon sources restored wax ester fermentation, indicating the need for external carbon sources for the wax ester fermentation. 13C-labeling experiments revealed specific isotopic enrichment in the odd-numbered fatty acids derived from wax esters, indicating that the exogenously-supplied CO2 was incorporated into wax esters via the propionyl-CoA pathway through the reverse tricarboxylic acid (TCA) cycle. The addition of 3-mercaptopicolinic acid, a phosphoenolpyruvate carboxykinase (PEPCK) inhibitor, significantly affected the incorporation of 13C into citrate and malate as the biosynthetic intermediates of the odd-numbered fatty acids, suggesting the involvement of PEPCK reaction to drive wax ester fermentation. Additionally, the 13C-enrichment pattern of succinate suggested that the CO2 assimilation might proceed through alternative pathways in addition to the PEPCK reaction. The current results indicate that the mechanisms of anoxic CO2 assimilation are an important target to reinforce wax ester fermentation in Euglena.

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Major wax ester components in hypoxic E. gracilis Z cells.Light-grown cells in the late log phase were transferred to hypoxic culture by stopping the culture agitation. Error bars indicate standard deviation from triplicate cultures.
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pone.0162827.g002: Major wax ester components in hypoxic E. gracilis Z cells.Light-grown cells in the late log phase were transferred to hypoxic culture by stopping the culture agitation. Error bars indicate standard deviation from triplicate cultures.

Mentions: The wax ester fermentation in Euglena under photosynthetic conditions has rarely been addressed, presumably because the photosynthetic O2 generation could impede hypoxia and wax ester fermentation. Thus, we compared the accumulation profiles of wax esters between the light-grown and the dark-grown E. gracilis Z under the hypoxic conditions (Fig 2). The dark-grown cells accumulated larger amounts of wax esters than the light-grown cells. The decrease in the wax ester synthesis with increasing O2 concentration has been reported for E. gracilis SM-ZK and E. gracilis T [9, 24]. It is possible that the reduced levels of wax ester accumulation under the hypoxic-light conditions (Fig 2) may be due to a possible increase in O2 partial tension in the culture medium. The distribution of the five major wax esters (Figs 1 and 2), which altogether accounted for more than 70% of the total amounts synthesized under the hypoxic-light and hypoxic-dark conditions. Among all the samples, C14:0-C14:0 was most abundant followed by C14:0-C15:0, and the other three species existed in similar proportions (Fig 2). The similar wax ester profiles suggested that the light conditions mainly affected the amounts but not the varieties of lipid constituents of the wax esters lipid constituents.


Critical Involvement of Environmental Carbon Dioxide Fixation to Drive Wax Ester Fermentation in Euglena
Major wax ester components in hypoxic E. gracilis Z cells.Light-grown cells in the late log phase were transferred to hypoxic culture by stopping the culture agitation. Error bars indicate standard deviation from triplicate cultures.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5036851&req=5

pone.0162827.g002: Major wax ester components in hypoxic E. gracilis Z cells.Light-grown cells in the late log phase were transferred to hypoxic culture by stopping the culture agitation. Error bars indicate standard deviation from triplicate cultures.
Mentions: The wax ester fermentation in Euglena under photosynthetic conditions has rarely been addressed, presumably because the photosynthetic O2 generation could impede hypoxia and wax ester fermentation. Thus, we compared the accumulation profiles of wax esters between the light-grown and the dark-grown E. gracilis Z under the hypoxic conditions (Fig 2). The dark-grown cells accumulated larger amounts of wax esters than the light-grown cells. The decrease in the wax ester synthesis with increasing O2 concentration has been reported for E. gracilis SM-ZK and E. gracilis T [9, 24]. It is possible that the reduced levels of wax ester accumulation under the hypoxic-light conditions (Fig 2) may be due to a possible increase in O2 partial tension in the culture medium. The distribution of the five major wax esters (Figs 1 and 2), which altogether accounted for more than 70% of the total amounts synthesized under the hypoxic-light and hypoxic-dark conditions. Among all the samples, C14:0-C14:0 was most abundant followed by C14:0-C15:0, and the other three species existed in similar proportions (Fig 2). The similar wax ester profiles suggested that the light conditions mainly affected the amounts but not the varieties of lipid constituents of the wax esters lipid constituents.

View Article: PubMed Central - PubMed

ABSTRACT

Accumulation profiles of wax esters in Euglena gracilis Z were studied under several environmental conditions. The highest amount of total wax esters accumulated under hypoxia in the dark, and C28 (myristyl-myristate, C14:0-C14:0) was prevalent among all conditions investigated. The wax ester production was almost completely suppressed under anoxia in the light, and supplying exogenous inorganic carbon sources restored wax ester fermentation, indicating the need for external carbon sources for the wax ester fermentation. 13C-labeling experiments revealed specific isotopic enrichment in the odd-numbered fatty acids derived from wax esters, indicating that the exogenously-supplied CO2 was incorporated into wax esters via the propionyl-CoA pathway through the reverse tricarboxylic acid (TCA) cycle. The addition of 3-mercaptopicolinic acid, a phosphoenolpyruvate carboxykinase (PEPCK) inhibitor, significantly affected the incorporation of 13C into citrate and malate as the biosynthetic intermediates of the odd-numbered fatty acids, suggesting the involvement of PEPCK reaction to drive wax ester fermentation. Additionally, the 13C-enrichment pattern of succinate suggested that the CO2 assimilation might proceed through alternative pathways in addition to the PEPCK reaction. The current results indicate that the mechanisms of anoxic CO2 assimilation are an important target to reinforce wax ester fermentation in Euglena.

No MeSH data available.


Related in: MedlinePlus