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Substrate-dependent transcriptomic shifts in Pelotomaculum thermopropionicum grown in syntrophic co-culture with Methanothermobacter thermautotrophicus.

Kato S, Kosaka T, Watanabe K - Microb Biotechnol (2009)

Bottom Line: As it thrives on a very small energy conserved by propionate oxidation under syntrophic association with a methanogen, its catabolic pathways and regulatory mechanisms are of biological interest.Expression of the central catabolic pathway (the propionate-oxidizing methylmalonyl-CoA pathway) was found to be substrate-dependent and was largely stimulated when P. thermopropionicum was grown on propionate and lactate.These results revealed that P. thermopropionicum has complex regulatory mechanisms that alter its metabolism in response to the syntrophic partner and growth substrates.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Applied Microbiology, Marine Biotechnology Institute, Kamaishi, Iwate 026-0001, Japan.

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Effects of lactate on syntrophic methanogenesis from propionate. (A) The medium containing 20 mM propionate was inoculated with either ethanol‐ or lactate‐grown syntrophic co‐culture. (B) The medium containing 20 mM propionate was inoculated with ethanol‐grown syntrophic co‐culture and supplemented with either 4 mM ethanol or 4 mM lactate. Methane concentrations were expressed as ‘mM equivalents’ (mM eq.) by assuming that all methane was present in the aqueous phase. Values are means of three independent cultures. Error bars indicate standard deviations.
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f5: Effects of lactate on syntrophic methanogenesis from propionate. (A) The medium containing 20 mM propionate was inoculated with either ethanol‐ or lactate‐grown syntrophic co‐culture. (B) The medium containing 20 mM propionate was inoculated with ethanol‐grown syntrophic co‐culture and supplemented with either 4 mM ethanol or 4 mM lactate. Methane concentrations were expressed as ‘mM equivalents’ (mM eq.) by assuming that all methane was present in the aqueous phase. Values are means of three independent cultures. Error bars indicate standard deviations.

Mentions: Syntrophic propionate oxidation is a thermodynamically unfavorable reaction, and syntrophic propionate‐oxidizing cultures need long cultivation periods and are unstable (Boone et al., 1989; Harmsen et al., 1998; Liu et al., 1999; Imachi et al., 2000; 2002; Plugge et al., 2002). In the syntrophic co‐culture of P. thermopropionicum and M. thermautotrophicus, the long lag period was observed before the onset of propionate oxidation (Fig. 1E). In the microarray analyses, we found that the genes for propionate‐oxidizing pathway were highly upregulated in the lactate culture (Fig. 4). In addition, the growth test (Fig. 1D) showed that propionate temporally accumulated in the lactate culture and was rapidly degraded afterward. From these observations, we hypothesized that lactate may have been able to accelerate syntrophic propionate oxidation. In order to address this idea, co‐cultures of P. thermopropionicum and M. thermautotrophicus were grown on propionate, after they were pre‐grown on either ethanol or lactate (Fig. 5A). This figure shows that the lactate‐grown culture started to grow on propionate more rapidly than the ethanol‐grown culture. We also evaluated the above idea in a lactate‐supplemented experiment. In this experiment, the propionate medium was inoculated with the co‐culture pre‐grown on ethanol and supplemented with either 4 mM lactate or 4 mM ethanol (Fig. 5B). It was found that lactate showed larger effect on shortening the lag period before the onset of syntrophic propionate oxidation than ethanol. As the stimulation of the microbial growth by lactate or ethanol was same extent, the growth stimulation was not simply ascribable to an increase in cell concentrations. It has been considered that a long lag period is necessary for P. thermopropionicum to accumulate the substrates needed for the propionate activation (i.e. acetyl‐CoA), to increase cell numbers to an adequate level, and/or to express the catabolic enzymes under the energy‐limited condition (Kosaka et al., 2006). The results of the present study suggest that lactate stimulates the expression of the propionate‐oxidizing pathway, resulting in the rapid onset of syntrophic propionate oxidation.


Substrate-dependent transcriptomic shifts in Pelotomaculum thermopropionicum grown in syntrophic co-culture with Methanothermobacter thermautotrophicus.

Kato S, Kosaka T, Watanabe K - Microb Biotechnol (2009)

Effects of lactate on syntrophic methanogenesis from propionate. (A) The medium containing 20 mM propionate was inoculated with either ethanol‐ or lactate‐grown syntrophic co‐culture. (B) The medium containing 20 mM propionate was inoculated with ethanol‐grown syntrophic co‐culture and supplemented with either 4 mM ethanol or 4 mM lactate. Methane concentrations were expressed as ‘mM equivalents’ (mM eq.) by assuming that all methane was present in the aqueous phase. Values are means of three independent cultures. Error bars indicate standard deviations.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3815365&req=5

f5: Effects of lactate on syntrophic methanogenesis from propionate. (A) The medium containing 20 mM propionate was inoculated with either ethanol‐ or lactate‐grown syntrophic co‐culture. (B) The medium containing 20 mM propionate was inoculated with ethanol‐grown syntrophic co‐culture and supplemented with either 4 mM ethanol or 4 mM lactate. Methane concentrations were expressed as ‘mM equivalents’ (mM eq.) by assuming that all methane was present in the aqueous phase. Values are means of three independent cultures. Error bars indicate standard deviations.
Mentions: Syntrophic propionate oxidation is a thermodynamically unfavorable reaction, and syntrophic propionate‐oxidizing cultures need long cultivation periods and are unstable (Boone et al., 1989; Harmsen et al., 1998; Liu et al., 1999; Imachi et al., 2000; 2002; Plugge et al., 2002). In the syntrophic co‐culture of P. thermopropionicum and M. thermautotrophicus, the long lag period was observed before the onset of propionate oxidation (Fig. 1E). In the microarray analyses, we found that the genes for propionate‐oxidizing pathway were highly upregulated in the lactate culture (Fig. 4). In addition, the growth test (Fig. 1D) showed that propionate temporally accumulated in the lactate culture and was rapidly degraded afterward. From these observations, we hypothesized that lactate may have been able to accelerate syntrophic propionate oxidation. In order to address this idea, co‐cultures of P. thermopropionicum and M. thermautotrophicus were grown on propionate, after they were pre‐grown on either ethanol or lactate (Fig. 5A). This figure shows that the lactate‐grown culture started to grow on propionate more rapidly than the ethanol‐grown culture. We also evaluated the above idea in a lactate‐supplemented experiment. In this experiment, the propionate medium was inoculated with the co‐culture pre‐grown on ethanol and supplemented with either 4 mM lactate or 4 mM ethanol (Fig. 5B). It was found that lactate showed larger effect on shortening the lag period before the onset of syntrophic propionate oxidation than ethanol. As the stimulation of the microbial growth by lactate or ethanol was same extent, the growth stimulation was not simply ascribable to an increase in cell concentrations. It has been considered that a long lag period is necessary for P. thermopropionicum to accumulate the substrates needed for the propionate activation (i.e. acetyl‐CoA), to increase cell numbers to an adequate level, and/or to express the catabolic enzymes under the energy‐limited condition (Kosaka et al., 2006). The results of the present study suggest that lactate stimulates the expression of the propionate‐oxidizing pathway, resulting in the rapid onset of syntrophic propionate oxidation.

Bottom Line: As it thrives on a very small energy conserved by propionate oxidation under syntrophic association with a methanogen, its catabolic pathways and regulatory mechanisms are of biological interest.Expression of the central catabolic pathway (the propionate-oxidizing methylmalonyl-CoA pathway) was found to be substrate-dependent and was largely stimulated when P. thermopropionicum was grown on propionate and lactate.These results revealed that P. thermopropionicum has complex regulatory mechanisms that alter its metabolism in response to the syntrophic partner and growth substrates.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Applied Microbiology, Marine Biotechnology Institute, Kamaishi, Iwate 026-0001, Japan.

Show MeSH
Related in: MedlinePlus