Publications

4369

The genus Pseudalkalibacillus, created by the reclassification of specific deep-branching Alkalihalobacillus species, exhibits polyphyletic branching. The Genome Taxonomy Database (GTDB) also assigns Pseudalkalibacillus species into two families and three genera. To clarify the evolutionary relationships and classification of Pseudalkalibacillus species, we report detailed investigations using phylogenomic and molecular signature-based approaches. In phylogenomic trees, Pseudalkalibacillus species are distributed within two family-level lineages. One of these clades, containing the type species of Pseudalkalibacillus (viz. Pseudalkalibacillus decolorationis), represents the genus Pseudalkalibacillus, groups within the family Fictibacillaceae. Ten novel conserved signature indels (CSIs) identified in this study are specific for this clade, providing a robust means for the differentiation of the emended genus Pseudalkalibacillus. The remaining Pseudalkalibacillus species form a separate family-level clade, designated as f_HBI72195 in the GTDB. Within this clade, all species except Pseudalkalibacillus caeni form a robust clade designated as Pseudalkalibacillus clade −2 in our work and g_Anaerobacillus_A in the GTDB. We have also identified 15 novel CSIs specific to this clade. As the Pseudalkalibacillus clade −2 is distinct from Pseudalkalibacillus, we propose transferring species from this clade into a new genus, Guptibacillus gen. nov. The species P. caeni branches distinctly from other Pseudalkalibacillus species, and the GTDB considers it a novel genus (g_Bacillus_BR). Six newly identified CSIs are specific to this species, and we are proposing the transfer of this species into a new genus, Exobacillus gen. nov. Two additional identified CSIs are shared by members of the novel family-level taxon (f_HBI72195) comprising the proposed genera Guptibacillus and Exobacillus, for which we are proposing the name Guptibacillaceae fam. nov. Lastly, the results presented here also show that ‘Pseudalkalibacillus hemicentroti’ and ‘Pseudalkalibacillus macyae’ are later heterotypic synonyms of Guptibacillus hwajinpoensis. These changes, which reliably depict the evolutionary relationships among Pseudalkalibacillus species, should be helpful in future studies of these organisms.

ABSTRACT Although the high-altitude limit for microbial survival in the Earth–atmosphere system has remained a scientific curiosity and topic of study, the ecological significance of long-distance microbial dispersal in the atmosphere has been perceived to have marginal relevance. Here, we report the characterization of novel plant pathogenic species of Curtobacterium that were isolated from samples collected at altitudes ranging from 1.5 to 29 km above sea level. Whole genome-based phylogenies of three strains, paired with plant challenge assays, indicate that each is a previously unrecognized species and causes disease on beans comparable to Curtobacterium flaccumfaciens . Isolates from the stratosphere (strain L6-1) and agricultural millet (G77) were identified to be the same species and designated as Curtobacterium aetherium sp. nov. C. aetherium displays high levels of tolerance to desiccation and UV radiation, which are stresses that increase in intensity with altitude. Back trajectory air mass analysis implied that the phytopathogens may have had an intercontinental source, but regional origins in the continental US cannot be excluded. The environmentally robust phytopathogens we have documented in the upper atmosphere provide new perspective on the role that high-altitude transport may play in microbial dispersal, gene flow, and the epidemiology of aerially dispersed plant disease. IMPORTANCE Enormous quantities and varieties of microorganisms are continually aerosolized and transported in the atmosphere, yet there is a limited understanding of the consequences to downwind ecosystems. While studying bacteria that survive extreme conditions at altitudes up to 29 km in the atmosphere, we discovered new species that have the capacity to cause disease in agriculturally relevant bean varieties. The hardiest isolate we characterized from the stratosphere is a member of the same species as an isolate from an agricultural source, which we have designated Curtobacterium aetherium . C. aetherium is a phytopathogen capable of enduring high-altitude and long-distance atmospheric transport while also possessing the potential to opportunistically infect crops in deposition locations.

Abstract The genus “Candidatus Kouleothrix” (Eikelboom type 1851) is the major filamentous bacterium responsible for activated sludge bulking in Japanese activated sludge plants, where it is present in many in unusually high abundances. Global surveys have shown this genus embraces several species, although the contribution each of these makes to bulking is not known. This study followed their population dynamics in a full-scale bulking sludge plant in Japan over a 12-month period, which required the development of species-specific FISH probes, used to measure their relative abundances. Six of the 9 recognised species of “Ca. Kouleothrix” were detected there, two of which (midas_s_3423 and midas_s_35412) were at consistently high abundances and responsible for increases in the sludge volume index (SVI). Their abundances were also statistically correlated with their filament lengths, which showed higher correlations with SVI increases than did species abundances. This study examined the impacts of both operational parameters and other communities on the abundances of these two species over the 12-month period and showed marked interspecies differences in responses to both. Together these findings stress the importance in studies of this kind to identify populations to species level to reveal possible important ecological differences not seen at the genus level.

Abstract Numerous bacteria in the human gut microbiome remain unknown and/or have yet to be cultured. While collections of human gut bacteria have been published, few strains are accessible to the scientific community. We have therefore created a publicly available collection of bacterial strains isolated from the human gut. The Human intestinal Bacteria Collection (HiBC) ( https://www.hibc.rwth-aachen.de ) contains 340 strains representing 198 species within 29 families and 7 phyla, of which 29 previously unknown species are taxonomically described and named. These included two butyrate-producing species of Faecalibacterium and new dominant species associated with health and inflammatory bowel disease, Ruminococcoides intestinale and Blautia intestinihominis , respectively. Plasmids were prolific within the HiBC isolates, with almost half (46%) of strains containing plasmids, with a maximum of six within a strain. This included a broadly occurring plasmid (pBAC) that exists in three diverse forms across Bacteroidales species. Megaplasmids were identified within two strains, the pMMCAT megaplasmid is globally present within multiple Bacteroidales species. This collection of easily searchable and publicly available gut bacterial isolates will facilitate functional studies of the gut microbiome.

Abstract Defining the minimal genetic requirements for cellular life remains a fundamental question in biology. Genomic exploration continually reveals novel microbial lineages, often exhibiting extreme genome reduction, particularly within symbiotic relationships. Here, we report the discovery ofCandidatusSukunaarchaeum mirabile, a novel archaeon with an unprecedentedly small genome of only 238 kbp —less than half the size of the smallest previously known archaeal genome— from a dinoflagellate-associated microbial community. Phylogenetic analyses place Sukunaarchaeum as a deeply branching lineage within the tree of Archaea, representing a novel major branch distinct from established phyla. Environmental sequence data indicate that sequences closely related to Sukunaarchaeum form a diverse and previously overlooked clade in microbial surveys. Its genome is profoundly stripped-down, lacking virtually all recognizable metabolic pathways, and primarily encoding the machinery for its replicative core: DNA replication, transcription, and translation. This suggests an unprecedented level of metabolic dependence on a host, a condition that challenges the functional distinctions between minimal cellular life and viruses. The discovery of Sukunaarchaeum pushes the conventional boundaries of cellular life and highlights the vast unexplored biological novelty within microbial interactions, suggesting that further exploration of symbiotic systems may reveal even more extraordinary life forms, reshaping our understanding of cellular evolution. Graphical Abstract

Objectives This study examined feline haemoplasmas ( Mycoplasma haemofelis , ‘ Candidatus Mycoplasma haemominutum’ [ C Mhm] and ‘ Candidatus Mycoplasma turicensis’) infecting Thai domestic cats, using the 16S and 23S rRNA genes as genetic markers. Methods Blood samples from 20 cats were obtained from a diagnostic laboratory and nucleic acids were extracted from each sample using a commercial kit. PCR targeting the 16S rRNA gene was used to screen haemoplasmas in the samples. Positive PCR samples were further sequenced using the 16S and 23S rRNA genes. The sequences from each genetic marker were analysed using Nucleotide BLAST, phylogeny and genetic network analyses. Results Among the 20 samples, five were infected with haemoplasmas. In the 16S rRNA gene sequencing, four sequences were assigned to C Mhm and the remaining sequence was likely to be a closely related species of C Mhm. In the 23S rRNA gene sequencing, four sequences from the same samples used for 16S rRNA gene sequencing were identified as C Mhm and one sequence could be a putative novel haemoplasma species closely related to C Mhm. Conclusions and relevance Only C Mhm and its closely related species were identified in this study. Although C Mhm has been recognised as a low-virulence parasite, cases of severe anaemia in cats infected with C Mhm have been found. Thus, such cases could be confirmed via the analysis of 16S and 23S rRNA genes. Furthermore, molecular detection and genetic analyses of feline haemoplasmas in additional cat blood samples should be conducted using PCR assay and DNA sequencing based on universal primers of 16S rRNA and 23S rRNA genes to enable more specific identification.