AUTHOR=Gtari Maher 

TITLE=Taxogenomic status of phylogenetically distant Frankia clusters warrants their elevation to the rank of genus: A description of Protofrankia gen. nov., Parafrankia gen. nov., and Pseudofrankia gen. nov. as three novel genera within the family Frankiaceae

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.1041425

DOI=10.3389/fmicb.2022.1041425

ISSN=1664-302X

ABSTRACT=<p>The genus <italic><italic>Frankia</italic></italic> is at present the sole genus in the family <italic><italic>Frankiaceae</italic></italic> and encompasses filamentous, sporangia-forming actinomycetes principally isolated from root nodules of taxonomically disparate dicotyledonous hosts named actinorhizal plants. Multiple independent phylogenetic analyses agree with the division of the genus <italic><italic>Frankia</italic></italic> into four well-supported clusters. Within these clusters, <italic><italic>Frankia</italic></italic> strains are well defined based on host infectivity range, mode of infection, morphology, and their behaviour in culture. In this study, phylogenomics, overall genome related indices (OGRI), together with available data sets for phenotypic and host-plant ranges available for the type strains of <italic><italic>Frankia</italic></italic> species, were considered. The robustness and the deep radiation observed in <italic><italic>Frankia</italic></italic> at the subgeneric level, fulfilling the primary principle of phylogenetic systematics, were strengthened by establishing genome criteria for new genus demarcation boundaries. Therefore, the taxonomic elevation of the <italic><italic>Frankia</italic></italic> clusters to the rank of the genus is proposed. The genus <italic><italic>Frankia</italic></italic> should be revised to encompass cluster 1 species only and three novel genera, <italic><italic>Protofrankia</italic></italic> gen. nov., <italic><italic>Parafrankia</italic></italic> gen. nov., and <italic><italic>Pseudofrankia</italic></italic> gen. nov., are proposed to accommodate clusters 2, 3, and 4 species, respectively. New combinations for validly named species are also provided.</p>