Consists of one species, Methylosemipumilus turicensis (GCF_000953015.1), that was initially proposed as ‘Candidatus Methylopumilus turicensis’ in Salcher et. al. 2015 and later changed to Methylosemipumilus turicensis in Salcher et al. 2019. Also known as PRD01a001B from 16S rRNA gene based studies. Methylosemipumilus has a relatively small genome size (<1.8 Mb) but not as small as Methylopumilus (1.3-1.4 Mb), which – together with improved genomic analyses – led to the reclassification to Methylosemipumilus. The closest cultivated relatives are Methylotenera sp. L2L1 (GCF_000744605.1) with an average amino acid identity of 67.45% and average nucleotide identity of 70.55% and Methylovorus sp. MP688 (GCF_000183115.1) with an AAI of 69.37% and an ANI of 69.42%, while the genus Methylopumilus is more distantly related (AAI of 61.5-62.2% and ANI of 66.4-66.9%). Methylosemipumilus are aerobic methylotrophs containing pathways for methanol oxidation (Xox), the RuMP cycle and the tetrahydromethanopterin (H4MPT) pathway for formaldehyde oxidation. Methylosemipumilus are found in the plankton of lakes in relatively low abundances. The so far only strain was isolated via dilution-to extinction cultivation by using autoclaved lake water, no growth is observed in rich medium or on agar plates (Salcher et al. 2015). Therefore, the strain was not submitted to a culture collection because these bacteria are hard to maintain, i.e., they are very slowly growing, reach low densities in liquid culture, and do not grow on agar plates.