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Methanospirillum Respiratory mRNA Biomarkers Correlate with Hydrogenotrophic Methanogenesis Rate during Growth and Competition for Hydrogen in an Organochlorine-Respiring Mixed Culture
journal contribution
posted on 2013-01-02, 00:00 authored by Annette R. Rowe, Cresten B. Mansfeldt, Gretchen L. Heavner, Ruth E. RichardsonMolecular biomarkers hold promise for inferring rates
of key metabolic
activities in complex microbial systems. However, few studies have
assessed biomarker levels for simultaneously occurring (and potentially
competing) respirations. In this study, methanogenesis biomarkers
for Methanospirillum hungatei were developed, tested,
and compared to Dehalococcoides mccartyi biomarkers
in a well-characterized mixed culture. Proteomic analyses of mixed
culture samples (n = 4) confirmed expression of many M. hungatei methanogenesis enzymes. The mRNAs for two oxidoreductases
detected were explored as quantitative biomarkers of hydrogenotrophic
methanogenesis: a coenzyme F420-reducing hydrogenase (FrcA)
and an iron sulfur protein (MvrD). As shown previously in D. mccartyi, M. hungatei transcript levels
correlated linearly with measured (R = 0.97 for FrcA, R = 0.91 for MvrD; n = 7) or calculated
respiration rate (R = 0.81 for FrcA, R = 0.62 for MvrD; n = 35) across two orders of magnitude
on a log–log scale. The average abundance of MvrD transcripts
was consistently two orders of magnitude lower than FrcA, regardless
of experimental condition. In experiments where M. hungatei was competing for hydrogen with D. mccartyi, transcripts
for the key respiratory hydrogenase HupL were generally less abundant
per mL than FrcA and more abundant than MvrD. With no chlorinated
electron acceptor added, HupL transcripts fell below both targets.
These biomarkers hold promise for the prediction of in situ rates
of respiration for these microbes, even when growing in mixed culture
and utilizing a shared substrate which has important implications
for both engineered and environmental systems. However, the differences
in overall biomarker abundances suggest that the strength of any particular
mRNA biomarker relies upon empirically established quantitative trends
under a range of pertinent conditions.
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Keywords
respiration rateHupL transcriptsmethanogenesis biomarkershungatei methanogenesis enzymesmRNA biomarkerbiomarker abundancesMethanospirillum Respiratory mRNA Biomarkers Correlatehydrogenase HupLbiomarker levelsHydrogenotrophic Methanogenesis Ratehydrogenotrophic methanogenesisMvrD transcriptsculture samplesMethanospirillum hungateiinferring rateshungatei transcript levelsiron sulfur proteinProteomic analyseschlorinated electron acceptorFrcADehalococcoides mccartyi biomarkers
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