Cellular differentiation into hyphae and spores in halophilic archaea.

Several groups of bacteria have complex life cycles involving cellular differentiation and multicellular structures. For example, actinobacteria of the genus Streptomyces form multicellular vegetative hyphae, aerial hyphae, and spores. However, similar life cycles have not yet been described for archaea. Here, we show that several haloarchaea of the family Halobacteriaceae display a life cycle resembling that of Streptomyces bacteria. Strain YIM 93972 (isolated from a salt marsh) undergoes cellular differentiation into mycelia and spores. Other closely related strains are also able to form mycelia, and comparative genomic analyses point to gene signatures (apparent gain or loss of certain genes) that are shared by members of this clade within the Halobacteriaceae. Genomic, transcriptomic and proteomic analyses of non-differentiating mutants suggest that a Cdc48-family ATPase might be involved in cellular differentiation in strain YIM 93972. Additionally, a gene encoding a putative oligopeptide transporter from YIM 93972 can restore the ability to form hyphae in a Streptomyces coelicolor mutant that carries a deletion in a homologous gene cluster (bldKA-bldKE), suggesting functional equivalence. We propose strain YIM 93972 as representative of a new species in a new genus within the family Halobacteriaceae, for which the name Actinoarchaeum halophilum gen. nov., sp. nov. is herewith proposed. Our demonstration of a complex life cycle in a group of haloarchaea adds a new dimension to our understanding of the biological diversity and environmental adaptation of archaea.

Proposal of Nakamurella gen. nov. as a substitute for the bacterial genus Microsphaera Yoshimi et al. 1996 and Nakamurellaceae fam. nov. as a substitute for the illegitimate bacterial family Microsphaeraceae Rainey et al. 1997.

The bacterial genus Microsphaera Yoshimi et al. 1996 is illegitimate because of priority of the fungal genus Microsphaera (Wallr.) Lév. [Principle 2, Rule 51b(4) of the Bacteriological Code]. Therefore, a new genus name, Nakamurella, is proposed for the bacterial genus. The type species Microsphaera multipartita Yoshimi et al. 1996 becomes Nakamurella multipartita gen. nov., comb. nov. Due to the illegitimacy of the only genus in the family Microsphaeraceae Rainey et al. 1997, this family name is replaced by the new bacterial family name Nakamurellaceae.