5 years ago

Thermodynamically diverse syntrophic aromatic compound catabolism

Takashi Narihiro, Kyohei Kuroda, Miaomiao Liu, Wen-Tso Liu, Ran Mei, Masaru Konishi Nobu
Specialized organotrophic Bacteria “syntrophs” and methanogenic Archaea “methanogens” form a unique metabolic interaction to accomplish cooperative mineralization of organic compounds to CH4 and CO2. Due to challenges in cultivation of syntrophs, mechanisms for how their organotrophic catabolism circumvents thermodynamic restrictions remain unclear. In this study, we investigate two communities hosting diverse syntrophic aromatic compound metabolizers (Syntrophus, Syntrophorhabdus, Pelotomaculum, and an uncultivated Syntrophorhabdacaeae member) to uncover their catabolic diversity and flexibility. Although syntrophs have been generally presumed to metabolize aromatic compounds to acetate, CO2, H2, and formate, combined metagenomics and metatranscriptomics show that uncultured syntrophs utilize unconventional alternative metabolic pathways in situ producing butyrate, cyclohexanecarboxylate, and benzoate as catabolic byproducts. In addition, we also find parallel utilization of diverse H2 and formate generating pathways to facilitate interactions with partner methanogens. Based on thermodynamic calculations, these pathways may enable syntrophs to combat thermodynamic restrictions. In addition, when fed with specific substrates (i.e., benzoate, terephthalate, or trimellitate), each syntroph population expresses different pathways, suggesting ecological diversification among syntrophs. These findings suggest we may be drastically underestimating the biochemical capabilities, strategies, and diversity of syntrophic bacteria thriving at the thermodynamic limit. This article is protected by copyright. All rights reserved.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1111/1462-2920.13922

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