The candidate phyla radiation (CPR) has been described as an obligatory group of ultrasmall bacteria associated with host bacteria. They phylogenetically represent a subdivision of bacteria distinct from other living organisms. Using polyphasic approaches, we screened human faecal samples for the detection of Saccharibacteria. The new sequences obtained by sequencing were compared to the complete CPR genomes available to date. Then, we attempted a co-culture of CPR-bacteria and non-CPR bacteria from human faecal samples. We finally aimed to evaluate the prevalence and distribution of these Saccharibacteria sequences in human sources in 16S amplicon datasets. We were able to reconstitute two high-quality Saccharibacteria genomes named Minimicrobia massiliensis and Minimicrobia timonensis. We have established, for the first time in human digestive samples, the coculture of Candidatus Saccharibacteria with two different bacterial hosts. Finally, we showed that 12.8% (610/4,756) of samples sequenced in our laboratory were positive for operational taxonomic units (OTUs) assigned to M.massiliensis. and significantly enriched in human respiratory and oral microbiota. Here, we reported the first genomes and coculture of Saccharibacteria from human gut specimens. This study opens a new field, particularly in the study of the involvement of CPR in the human intestinal microbiota.
Hemotropic mycoplasmas, previously classified in the genus Eperythrozoon, have been reported as causing human infections in Brazil, China, Japan, and Spain.
In 2017, we detected DNA from Candidatus Mycoplasma haemohominis in the blood of a Melanesian patient from New Caledonia presenting with febrile splenomegaly, weight loss, life-threatening autoimmune hemolytic anemia, and hemophagocytosis. The full genome of the bacterium was sequenced from a blood isolate. Subsequently, we retrospectively (2011–2017) and prospectively (2018–2019) tested patients who had been hospitalized with a similar clinico-biological picture. In addition, as these patients had been in contact with frugivorous bats (authorized under conditions for hunting and eating in New Caledonia), we investigated the role of these animals and their biting flies by testing them for hemotropic mycoplasmas.
There were 15 patients found to be infected by this hemotropic mycoplasma. Among them, 4 (27%) died following splenectomy performed either for spontaneous spleen rupture or to cure refractory autoimmune hemolytic anemia. The bacterium was cultivated from the patient’s blood. The full genome of the Neocaledonian Candidatus M. haemohominis strain differed from that of a recently identified Japanese strain. Of 40 tested Pteropus bats, 40% were positive; 100% of collected bat flies Cyclopodia horsfieldi (Nycteribiidae, Diptera) were positive. Human, bat, and dipteran strains were highly similar.
The bacterium being widely distributed in bats, Candidatus M. haemohominis, should be regarded as a potential cause of severe infections in humans.