Acidiphilium is a genus in the phylum Pseudomonadota (Bacteria).^[1] As the name suggests, this comprises a nutritionally diverse genus of bacteria adapted to life in extremely acidic conditions, and often exhibiting FeIII (ferric iron) reduction.

The name Acidiphilium derives from:
Neo-Latin noun acidum (from Latin adjective acidus, sour), an acid; Neo-Latin neuter gender adjective philum (from Greek neuter gender adjective philon (φίλον)), friend, loving; Neo-Latin neuter gender noun Acidiphilium (sic), acid lover.^[2]

The genus contains 6 species (including basonyms and synonyms), namely^[2]

• A. acidophilum ( (Harrison 1983) Hiraishi et al. 1998; Neo-Latin noun acidum (from Latin adjective acidus, sour), an acid; Neo-Latin neuter gender adjective philum (from Greek neuter gender adjective philon (φίλον)), friend, loving; Neo-Latin neuter gender adjective acidophilum, acid loving.), this species used to known as Thiobacillus acidophilus^[3]
• A. angustum ( Wichlacz et al. 1986; Latin neuter gender adj, angustum, narrow, small, with respect to nutritional versatility.)^[4]
• A. cryptum ( Harrison 1981, (Type species of the genus).; Neo-Latin neuter gender adjective cryptum (from Greek noun adjective krupton [sic]), hidden.)^[5]
• A. multivorum ( Wakao et al. 1995; Latin adjective multus, many; Latin v. voro, to eat, devour; Neo-Latin neuter gender adjective multivorum, devouring many kinds of substances.)^[6]
• A. organovorum ( Lobos et al. 1986; Neo-Latin pref. organo- (from Greek adjective organikos, of or pertaining to an organ), pertaining to organic chemical compounds; Latin v. voro, to eat, devour; Neo-Latin neuter gender adjective organovorum, devouring organic compounds.)^[7]
• A. rubrum ( Wichlacz et al. 1986; Latin adjective ruber -bra -brum, red; Latin neuter gender adjective rubrum, red colored.)^[4]Acidocella aminolytica and Acidocella facilis used to be in this genus.^[8]

• Bacterial taxonomy
• Microbiology