High above the rest: standing behaviors in the amoebae of Sappinia and Thecamoeba.

Many terrestrial microbes have evolved cell behaviors that help them rise above their substrate, often to facilitate dispersal. One example of these behaviors is found in the amoebae of Sappinia pedata, which actively lift most of their cell mass above the substrate, known as standing. This standing behavior was first described in S. pedata in the 1890s from horse dung isolates but never molecularly characterized from dung. Our study expands this understanding, revealing the first molecularly confirmed S. pedata from herbivore dung in Mississippi, USA, and describing a new species, Sappinia dangeardi n. sp., with larger trophozoite cells. Additionally, we isolated another standing amoeba, Thecamoeba homeri n. sp., from soil, exhibiting a previously unreported "doughnut shape" transient behavior. In S. dangeardi n. sp., we discovered that standing is likely triggered by substrate drying, and that actin filaments actively localize in the "stalk" to support the standing cells, as observed through confocal microscopy. While the purpose of standing behaviors has not been investigated, we hypothesize it is energetically expensive and therefore a significant evolutionary strategy in these organisms. Overall, this study emphasizes behavioral adaptations to terrestrial environments within Amoebozoa, stressing the importance of diverse laboratory conditions that replicate natural habitats.

Molecular phylogenetic analyses support the validity of Ceratiomyxa porioides (Amoebozoa, Eumycetozoa) at species level.

The frequently encountered macroscopic slime molds of the genus Ceratiomyxa have long been recognized by mycologists and protistologists for hundreds of years. These organisms are amoebozoan amoebae that live and grow inside and on the surface of decaying wood. When conditions are favorable, they form subaerial sporulating structures called fruiting bodies which take on a variety of forms. These forms are typically some arrangement of column and/or branches, but one is uniquely poroid, forming folds instead. Originally, this poroid morphology was designated as its own species. However, it was not always clear what significance fruiting body morphology held in determining species. Currently, Ceratiomyxa fruticulosa var. porioides, the poroid form, is considered a taxonomic variety of Ceratiomyxa fruticulosa based on morphological designation alone. Despite its long history of observation and study, the genus Ceratiomyxa has been paid little molecular attention to alleviate these morphological issues. We have obtained the first transcriptomes of the taxon C. fruticulosa var. porioides and found single gene phylogenetic and multigene phylogenomic support to separate it from C. fruticulosa. This provides molecular evidence that fruiting body morphology does correspond to species level diversity. Therefore, we formally raise Ceratiomyxa porioides to species level.