Table 2.

Main characteristics and outcomes of published studies on hgcA biodiversity in environmental samples.

Method	Studied environment	Number of sequence/reads	Number of OTUs	Dominant group	Dominant Deltaproteobacteria	Reference
PCR and cloning	Florida Everglades	220	168	Deltaproteobacteria	Syntrophobacterales	Bae et al. 2014
	Wetlands	108	40	Methanomicrobia	Geobacter	Schaefer et al. 2014
	Three gorges reservoir	151	151	Unidentified	Unidentified	Du et al. 2017
	Rice paddy soils	∼ 1800	190	Proteobacteria Euryarchaeota		Liu et al. 2018a
	Laboratory and sediment slurries			Unidentified	Unidentified	Ndu et al. 2018
	Rice paddy soils	5	?	Unidentified		Vishnivetskaya et al. 2018
	Sulfate‐impacted lakes	300	174	Geobacteraceae Methanomicrobia Unidentified		Jones et al. 2019
PCR and high throughput sequencing	Boreal lakes	78,642	225	Deltaproteobacteria	Unidentified	Bravo et al. 2018a
	Lake Geneva	741,890	356	Deltaproteobacteria	Unidentified (Geobacter)	Bravo et al. 2018b
	Rice paddy soils					Liu et al. 2018a
	Boreal forest soils	1,257,577	573	Deltaproteobacteria	Unidentified (Geobacter)	Xu et al. 2019
Metagenomics	Global	823,000,000		Environmental compartment dependent		Podar et al. 2015
	Antarctic Sea‐ice and brine			Nitrospinae		Gionfriddo et al. 2016
	Rice paddy soils	901,610,484		Methanoregula spp.	Geobacter	Liu et al. 2018b
	Sulfate‐impacted lakes	885,923	27	Deltaproteobacteria		Jones et al. 2019
	Eight sites	381–102 1		Deltaproteobacteria		Christensen et al. 2019
	Tara gene catalogs oceans	111,530,851	10	Nitrospinae	Desulfovibrionales	Villar et al. 2019
Metaproteomics	EFPC and Hinds Creek, TN	15,270–16,852		Deltaproteobacteria		Christensen et al. 2019