Many metazoan species carry symbiotic bacteria which play a mutualistic, commensal, or parasitic role. Cas9 proteins are highly enriched in pathogenic and commensal bacteria. Marine iguanas have mutualistic and commensal relationships with several other animals. The GUT cells live as commensal organisms and outcompete other phenotypes. Cats have either a mutualistic or commensal relationship with humans. Porins are also an important factor for complement inhibition for both pathogenic and commensal species. Their long co-evolution with other species has led to mimetic, commensal, parasitic, and mutualistic relationships. This mutualistic relationship is unusual in propionibacteria, which are largely commensal. All of these receptors are used for iron acquisition for both pathogenic and commensal species. A mucus layer protects the large intestine from attacks from colonic commensal bacteria. "Scotoplanes" sp, like other sea cucumbers, host parasitic and commensal organisms. Those that neither help nor harm humans are called commensal organisms. Other causes include overgrowth of the commensal flora of the vagina. Oral rinse technique can distinguish between commensal candidal carriage and candidiasis. Saker nests support a species-rich assemblage of commensal insects.