Kalymmatonema
gen. nov. (Scytonemataceae, Cyanobacteria): A desert soil crust genus previously identified as
Scytonema hyalinum
, with description of seven species new to science
Abstract
Numerous cyanobacterial strains previously identified as
Scytonema hyalinum
were determined to be phylogenetically distant from the type species of
Scytonema, S. hofmannii
. Morphological and molecular evidence suggests this distinct clade necessitates placement in a new genus, and we have described
Kalymmatonema
gen. nov. herein.
Kalymmatonema
has been demonstrated to exhibit five ribosomal operons, all of which differed in both sequence and secondary structure of conserved helical domains in the 16S–23S internal transcribed spacer rRNA region. Four of these operon copies were highly similar in 16S and 23S rRNA gene sequences, whereas the divergent fifth copy is thought to represent a whole‐operon horizontal gene transfer event. Through in‐depth analysis, we were able to recognize seven species new to science, the type species
K. desertorum
sp. nov.,
K. arcangelii
comb. nov.,
K. chimaera
sp. nov.,
K. ethiopiense
sp. nov.,
K. gypsitolerans
sp. nov.,
K. mateoae
sp. nov., and
K. oahuense
sp. nov. We also created the new combination,
K. hyalinum
comb. nov., in order to include the original
Scytonema hyalinum
in this new genus based upon the common morphological feature of a mucilaginous apical cap on the trichomes.
Kalymmatonema
displays a complex evolution of its ribosomal operons, with evidence not only of horizontal gene transfer but also of internal rearrangements and mobile genetic elements that have transposed the tRNA‐containing region of the ITS rRNA region among the four similar operons. Additional investigation of the evolutionary history of this interesting genus will likely lead to a better understanding of the processes shaping ribosomal evolution in cyanobacteria.