The phylum deferribacteres and the genus caldithrix

Abstract

The phylum Deferribacteres sensu stricto has been characterized in 2001 and currently groups 6 genera and 10 species of Gram-negative, anaerobic bacteria, i.e., Calditerrivibrio, Deferribacter, Denitrovibrio, Flexistipes, Geovibrio, and Mucispirillum. Caldithrix, which is currently an unclassified genus, sometimes described as phylogenetically related to Deferribacteres but it probably represents another phylum. The genome sizes of Deferribacteres are rather small ranging from 2.22 to 3.22 Mb with two rrn operons and a variable G+C content ranging from 28.7 to 50.2 mol%. Caldithrix abyssi presents a chromosome of 4.96 Mb, and the G+C % in the genus Caldithrix is about 43 mol%. Members of Deferribacteres and Caldithrix are Gram-negative rods or vibrio-shaped cells that do not form endospores, preferentially anaerobes (rarely microaerophilic), neutrophilic mesophilic to thermophilic. Mainly chemoorganotrophs, they can use various types of electron donors and acceptors, or other types of metabolism (chemolithotrophic or fermentative). Most of them are halophile or halotolerant explaining that they were frequently found in marine niches particularly in thermophilic, halophilic, and sulfide-rich conditions such as those found in deep hydrothermal vents. They were also found in oil reservoirs and polluted soils. Among Deferribacteres, Mucispirillum sp. displayed a particular lifestyle associated with gut mucus in rodents where it might contribute to pathogenesis in inflammatory conditions. No members of Deferribacteres are associated to human beings in health or disease.