Detmer Sipkema

1 Introduction Anaerobic microbes capable of utilising carbon monoxide (CO) as a carbon and energy source, known as carboxydotrophs, are commonly found in hydrothermal environments (Brady et al. 2015; DePoy et al. 2020; Fukuyama et al. 2020; Omae et al. 2019; Slobodkina et al. 2022; Sokolova et al. 2005). Most of the thermophilic carboxydotrophs are hydrogenogenic, that is, they produce H2 as the main product via the water-gas shift reaction (CO + H2O → CO2 + H2) (Diender et al. 2015; Fukuyama et al.

INTRODUCTION Since the beginning of this century, biological dark matter has been brought to light at an ever-increasing speed. Metagenomic sequencing of environmental samples from across the globe have shown the same pattern over and over again: The large majority of bacteria as observed through the presence of their DNA has never been obtained in culture (Dat et al., 2021; Hug et al., 2016; Parks et al., 2018), also coined as the ‘great plate count anomaly’ (Staley & Konopka, 1985).

Abstract Genomic and functional analyses of bacterial sponge symbionts belonging to the uncultivated candidate genus ‘Entotheonella’ has revealed them as the prolific producers of bioactive compounds previously identified from their invertebrate hosts. These studies also suggested ‘Entotheonella’ as the first members of a new candidate phylum, ‘Tectomicrobia’. Here we analyzed the phylogenetic structure and environmental distribution of this as-yet sparsely populated phylum-like lineage.