TABLE 1.

Source and size of protein sequence databases.

Database	Protein sequences	Source/Reference	Used for samples
Biogas + SwissProt	2,349,714	Schluter et al., 2008; Rademacher et al., 2012; Hanreich et al., 2013; Stolze et al., 2016	BGP
Human Gut + SwissProt	6,159,039	Qin et al., 2010 https://www.ebi.ac.uk/metagenomics/studies/ERP000108	Hgut
Soil + SwissProt	684,487	JGI sequencing project; https://gold.jgi.doe.gov/study?id=Gs0085736	Soil compost
WWTP + SwissProt	2,243,839	Albertsen et al., 2012	WWTP
SwissProt	556,196	SwissProt downloaded in November 2017 www.uniprot.org