Journal Article

Peculiar citric acid cycle of hydrothermal vent chemolithoautotroph <i>Hydrogenovibrio crunogenus</i>, and insights into carbon metabolism by obligate autotrophs

Ishtiaque Quasem, Alexandra N. Achille, Brittany A. Caddick, Travis A. Carter, Camille Daniels, Jennifer A. Delaney, Vedad Delic, Kimberly A. Denton, Martina C. Duran, Marianne K. Fatica, Christopher M. Ference, Julie P. Galkiewicz, Ana M. Garcia, Jacqueline D. Hendrick, Steven A. Horton, Mey S. Kun, Phoebe W. Koch, Tien Min Lee, Christie R. McCabe, Sean McHale, Lauren D. McDaniel, Damian M. Menning, Kristy J. Menning, Hamed Mirzaei-Souderjani, Salina Mostajabian, David A. Nicholson, Courtney K. Nugent, Nicholas P. Osman, Desiree I. Pappas, Andrea M. Rocha, Karyna Rosario, Haydn Rubelmann, Julie A. Schwartz, Kent W. Seeley, Christopher M. Staley, Elizabeth M. Wallace, Terianne M. Wong, Brian L. Zielinski, Thomas E. Hanson and Kathleen M. Scott

in FEMS Microbiology Letters

Volume 364, issue 14 ISSN: 0378-1097
Published online July 2017 | e-ISSN: 1574-6968 | DOI: http://dx.doi.org/10.1093/femsle/fnx148

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Abstract

The genome sequence of the obligate chemolithoautotroph Hydrogenovibrio crunogenus paradoxically predicts a complete oxidative citric acid cycle (CAC). This prediction was tested by multiple approaches including whole cell carbon assimilation to verify obligate autotrophy, phylogenetic analysis of CAC enzyme sequences and enzyme assays. Hydrogenovibrio crunogenus did not assimilate any of the organic compounds provided (acetate, succinate, glucose, yeast extract, tryptone). Enzyme activities confirmed that its CAC is mostly uncoupled from the NADH pool. 2-Oxoglutarate:ferredoxin oxidoreductase activity is absent, though pyruvate:ferredoxin oxidoreductase is present, indicating that sequence-based predictions of substrate for this oxidoreductase were incorrect, and that H. crunogenus may have an incomplete CAC. Though the H. crunogenus CAC genes encode uncommon enzymes, the taxonomic distribution of their top matches suggests that they were not horizontally acquired. Comparison of H. crunogenus CAC genes to those present in other ‘Proteobacteria’ reveals that H. crunogenus and other obligate autotrophs lack the functional redundancy for the steps of the CAC typical for facultative autotrophs and heterotrophs, providing another possible mechanism for obligate autotrophy.

Keywords: obligate autotroph; citric acid cycle; central carbon metabolism; hydrothermal vent

Journal Article.  6353 words.  Illustrated.

Subjects: Medical Microbiology and Virology ; Biotechnology ; Genetics and Genomics ; Microbiology ; Molecular and Cell Biology

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