The genus Clostridium belongs to the family Clostridiaceae. However, many species with the genus name Clostridium are found in different families and even crossing into a different phylum. Motivated by recently completed genome sequences, we propose the reclassification of two separate clades that include misclassified Clostridium species which phylogenetically lie within the family Lachnospiraceae, known for being benign members of gut microbiomes and for their plant-degrading capabilities. We use several phylogenetic and phylogenomic perspectives as well as phenotypic comparisons to gain insight into the evolutionary history of these taxa. One clade, which includes Clostridium clostridioforme, Clostridium aldenense, Clostridium asparagiforme, Clostridium bolteae, Clostridium citroniae and Clostridium lavalense, we propose to reclassify as Enterocloster gen. nov., and reclassify the species as Enterocloster clostridioformis comb. nov., Enterocloster aldensis comb. nov., Enterocloster asparagiformis comb. nov., Enterocloster bolteae comb. nov., Enterocloster citroniae comb. nov. and Enterocloster lavalensis comb. nov. The other clade comprises Clostridium sphenoides, Clostridium aerotolerans, Clostridium algidixylanolyticum, Clostridium amygdalinum, Clostridium celerecrescens, Clostridium indolis, Clostridium saccharolyticum, Clostridium xylanolyticum and Desulfotomaculum guttoideum, and we propose to reclassify it as Lacrimispora gen. nov., including reclassification of the members as Lacrimispora sphenoides comb. nov., Lacrimispora aerotolerans comb. nov., Lacrimispora algidixylanolytica comb. nov., Lacrimispora amygdalina comb. nov., Lacrimispora celerecrescens comb. nov., Lacrimispora indolis comb. nov., Lacrimispora saccharolytica comb. nov. and Lacrimispora xylanolytica comb. nov. We emend the description of D. guttoideum to reflect that it is a later heterotypic synonym of Clostridiums phenoides, which we have reclassified as Lacrimispora sphenoides.
Keywords: Clostridium; Lachnospiraceae; butyrate; cluster XIVa; gut microbiome; novel genus.