Mesobacillus

Members of the genus Mesobacillus are either aerobic or facultatively anaerobic. They mostly demonstrate endospore formation under adverse environmental or nutritional conditions. Species can be found in a variety of environments, ranging from soil, human gut, groundwater, wastewater systems, hypersalinic lakes and thermal aquifers. Cells can be either motile or non-motile. Some specific species are high salt tolerant and even require high salt concentration for growth (ie. Mesobacillus persicus).[10] Mesobacillus can survive in temperatures ranging from 10°C to 45°C, but optimal growth occurs in the range of 25-37°C.

Genome sequence analyses have identified three conserved signature indels (CSIs) uniquely found in members of Mesobacillus in the proteins PhoH family protein, TrkA family potassium uptake protein and a hypothetical protein.[1] These molecular markers provide a reliable means to distinguish Mesobacillus species from other Bacillaceae genera and bacteria.

As of May 2021, there are a total of 14 species with validly published names in the genus Mesobacillus.[3] In phylogenetic trees constructed based on concatenated sequences from various datasets of conserved proteins and 16S rRNA sequences, members of this genus group together and forms a monophyletic branch.[1] This grouping is also reflected n the Genome Taxonomy Database (GTDB). [11]

The non-validly published species "Bacillus mediterraneensis" has been found to branch with other members of Mesobacillus as well as share molecular markers unique to the clade.[9] However, transfer of these species into Mesobacillus was not proposed due to the lack of strain culture information. This indicates the requirement for additional analyses of this clade as more genomic and strain information become available.