Conditional essentiality of the 11-subunit complex I-like enzyme in strict anaerobes: the case of Desulfitobacterium hafniense strain DCB-2

TL;DR

This study explores the role of a complex I-like enzyme in the energy metabolism of a strict anaerobe, showing it is essential for certain growth conditions.

Contribution

The study reveals the conditional essentiality of a complex I-like enzyme in a strict anaerobe using experimental and proteomic approaches.

Findings

The complex I-like enzyme is essential for growth with lactate and pyruvate but not with H2 as an electron donor.

Seven potential redox partners were identified with expression patterns similar to Nuo homologues.

A model is proposed where the enzyme serves as an electron entry point for cytoplasmic substrates like lactate or pyruvate.

Abstract

In oxidative phosphorylation, respiratory complex I serves as an entry point in the electron transport chain for electrons generated in catabolic processes in the form of NADH. An ancestral version of the complex, lacking the NADH-oxidising module, is encoded in a significant number of bacterial genomes. Amongst them is Desulfitobacterium hafniense, a strict anaerobe capable of conserving energy via organohalide respiration. This study investigates the role of the complex I-like enzyme in D. hafniense energy metabolism using rotenone as a specific complex I inhibitor under different growth conditions. The investigation revealed that the complex I-like enzyme was essential for growth with lactate and pyruvate but not in conditions involving H2 as an electron donor. In addition, a previously published proteomic dataset of strain DCB-2 was analysed to reveal the predominance of the complex under different growth conditions and to identify potential redox partners. This approach revealed seven candidates with expression patterns similar to Nuo homologues, suggesting the use of diverse electron sources. Based on these results, we propose a model where the complex I-like enzyme serves as an electron entry point into the respiratory chain for substrates delivering electrons within the cytoplasm, such as lactate or pyruvate, with ferredoxins shuttling electrons to the complex.

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