Bacterial endosymbionts of eukaryotic hosts typically experience massive genome reduction, but the underlying evolutionary processes are often obscured by the lack of free-living relatives. Endomicrobia, a family-level lineage of host-associated bacteria in the phylum Elusimicrobiota that comprises both free-living representatives and endosymbionts of termite gut flagellates, are an excellent model to study evolution of intracellular symbionts. We reconstructed 67 metagenome-assembled genomes (MAGs) of Endomicrobiaceae among more than 1,700 MAGs from the gut microbiota of a wide range of termites. Phylogenomic analysis confirmed a sister position of representatives from termites and ruminants, and allowed to propose eight new genera in the radiation of Endomicrobiaceae. Comparative genome analysis documented progressive genome erosion in the new genus Endomicrobiellum, which comprises all flagellate endosymbionts characterized to date. Massive gene losses were accompanied by the acquisition of new functions by horizontal gene transfer, which led to a shift from a glucose-based energy metabolism to one based on sugar phosphates. The breakdown of glycolysis and many anabolic pathways for amino acids and cofactors in several subgroups was compensated by the independent acquisition of new uptake systems, including an ATP/ADP antiporter, from other gut microbiota. The putative donors are mostly flagellate endosymbionts from other bacterial phyla, including several, hitherto unknown lineages of uncultured Alphaproteobacteria, documenting the importance of horizontal gene transfer in the convergent evolution of these intracellular symbioses. The loss of almost all biosynthetic capacities in some lineages of Endomicrobiellum suggests that their originally mutualistic relationship with flagellates is on its decline.IMPORTANCEUnicellular eukaryotes are frequently colonized by bacterial and archaeal symbionts. A prominent example are the cellulolytic gut flagellates of termites, which harbor diverse but host-specific bacterial symbionts that occur exclusively in termite guts. One of these lineages, the so-called Endomicrobia, comprises both free-living and endosymbiotic representatives, which offers the unique opportunity to study the evolutionary processes underpinning the transition from a free-living to an intracellular lifestyle. Our results revealed a progressive gene loss in energy metabolism and biosynthetic pathways, compensated by the acquisition of new functions via horizontal gene transfer from other gut bacteria, and suggest the eventual breakdown of an initially mutualistic symbiosis. Evidence for convergent evolution of unrelated endosymbionts reflects adaptations to the intracellular environment of termite gut flagellates.

• Klíčová slova
• Endomicrobiaceae, Parabasalia, convergent evolution, endosymbionts, lateral gene transfer, termites,
• MeSH
• Bacteria * genetika   klasifikace   MeSH
• fylogeneze * MeSH
• genom bakteriální * MeSH
• Isoptera * mikrobiologie   parazitologie   MeSH
• metagenom MeSH
• molekulární evoluce MeSH
• přenos genů horizontální * MeSH
• střevní mikroflóra * MeSH
• symbióza * MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH

In terms of the number and diversity of living units, the prokaryotic empire is the most represented form of life on Earth, and yet it is still to a significant degree shrouded in darkness. This microbial "dark matter" hides a great deal of potential in terms of phylogenetically or metabolically diverse microorganisms, and thus it is important to acquire them in pure culture. However, do we know what microorganisms really need for their growth, and what the obstacles are to the cultivation of previously unidentified taxa? Here we review common and sometimes unexpected requirements of environmental microorganisms, especially soil-harbored bacteria, needed for their replication and cultivation. These requirements include resuscitation stimuli, physical and chemical factors aiding cultivation, growth factors, and co-cultivation in a laboratory and natural microbial neighborhood.

• Klíčová slova
• VBNC, cultivation techniques, difficult-to-culture microorganisms, dormancy, environmental microbiome, growth factors, improved cultivation, microbial ecology,
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH

The Asian citrus psyllid Diaphorina citri (Insecta: Hemiptera: Psylloidea), a serious pest of citrus species worldwide, harbors vertically transmitted intracellular mutualists, Candidatus Profftella armatura (Profftella_DC, Gammaproteobacteria: Burkholderiales) and Candidatus Carsonella ruddii (Carsonella_DC, Gammaproteobacteria: Oceanospirillales). Whereas Carsonella_DC is a typical nutritional symbiont, Profftella_DC is a unique defensive symbiont with organelle-like features, including intracellular localization within the host, perfect infection in host populations, vertical transmission over evolutionary time, and drastic genome reduction down to much less than 1 Mb. Large parts of the 460-kb genome of Profftella_DC are devoted to genes for synthesizing a polyketide toxin; diaphorin. To better understand the evolution of this unusual symbiont, the present study analyzed the genome of Profftella_Dco, a sister lineage to Profftella_DC, using Diaphorina cf. continua, a host psyllid congeneric with D. citri. The genome of coresiding Carsonella (Carsonella_Dco) was also analyzed. The analysis revealed nearly perfect synteny conservation in these genomes with their counterparts from D. citri. The substitution rate analysis further demonstrated genomic stability of Profftella which is comparable to that of Carsonella. Profftella_Dco and Profftella_DC shared all genes for the biosynthesis of diaphorin, hemolysin, riboflavin, biotin, and carotenoids, underlining multiple roles of Profftella, which may contribute to stabilizing symbiotic relationships with the host. However, acyl carrier proteins were extensively amplified in polyketide synthases DipP and DipT for diaphorin synthesis in Profftella_Dco. This level of acyl carrier protein augmentation, unprecedented in modular polyketide synthases of any known organism, is not thought to influence the polyketide structure but may improve the synthesis efficiency.

• Klíčová slova
• Diaphorina, defensive symbiont, diaphorin, hemolysin, reduced genome, secondary metabolite,
• MeSH
• biologická evoluce * MeSH
• Gammaproteobacteria chemie   genetika   metabolismus   MeSH
• genom bakteriální * MeSH
• Hemiptera mikrobiologie   MeSH
• hemolyziny chemie   genetika   metabolismus   MeSH
• karotenoidy metabolismus   MeSH
• mutační rychlost MeSH
• polyketidy metabolismus   MeSH
• sekvence aminokyselin MeSH
• symbióza MeSH
• vitaminy genetika   metabolismus   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• srovnávací studie MeSH
• Názvy látek
• hemolyziny MeSH
• karotenoidy MeSH
• polyketidy MeSH
• vitaminy MeSH

Animals interact with a diverse array of both beneficial and detrimental microorganisms. In insects, these symbioses in many cases allow feeding on nutritionally unbalanced diets. It is, however, still not clear how are obligate symbioses maintained at the cellular level for up to several hundred million years. Exact mechanisms driving host-symbiont interactions are only understood for a handful of model species and data on blood-feeding hosts with intracellular bacteria are particularly scarce. Here, we analyzed interactions between an obligately blood-sucking parasite of sheep, the louse fly Melophagus ovinus, and its obligate endosymbiont, Arsenophonus melophagi. We assembled a reference transcriptome for the insect host and used dual RNA-Seq with five biological replicates to compare expression in the midgut cells specialized for housing symbiotic bacteria (bacteriocytes) to the rest of the gut (foregut-hindgut). We found strong evidence for the importance of zinc in the system likely caused by symbionts using zinc-dependent proteases when acquiring amino acids, and for different immunity mechanisms controlling the symbionts than in closely related tsetse flies. Our results show that cellular and nutritional interactions between this blood-sucking insect and its symbionts are less intimate than what was previously found in most plant-sap sucking insects. This finding is likely interconnected to several features observed in symbionts in blood-sucking arthropods, particularly their midgut intracellular localization, intracytoplasmic presence, less severe genome reduction, and relatively recent associations caused by frequent evolutionary losses and replacements.

• Klíčová slova
• B-vitamins, RNA-Seq, immunity, interactions, parasites, symbiotic bacteria, zinc,
• MeSH
• Bacteria klasifikace   genetika   izolace a purifikace   MeSH
• biologická evoluce MeSH
• Diptera genetika   mikrobiologie   MeSH
• DNA bakterií analýza   genetika   MeSH
• fylogeneze MeSH
• hmyzí geny * MeSH
• infekce přenášené vektorem MeSH
• interakce hostitele a patogenu MeSH
• ovce parazitologie   MeSH
• střevní mikroflóra * MeSH
• symbióza MeSH
• transkriptom MeSH
• trávicí systém mikrobiologie   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• DNA bakterií MeSH

Bacterial endosymbionts evolve under strong host-driven selection. Factors influencing host evolution might affect symbionts in similar ways, potentially leading to correlations between the molecular evolutionary rates of hosts and symbionts. Although there is evidence of rate correlations between mitochondrial and nuclear genes, similar investigations of hosts and symbionts are lacking. Here, we demonstrate a correlation in molecular rates between the genomes of an endosymbiont (Blattabacterium cuenoti) and the mitochondrial genomes of their hosts (cockroaches). We used partial genome data for multiple strains of B. cuenoti to compare phylogenetic relationships and evolutionary rates for 55 cockroach/symbiont pairs. The phylogenies inferred for B. cuenoti and the mitochondrial genomes of their hosts were largely congruent, as expected from their identical maternal and cytoplasmic mode of inheritance. We found a correlation between evolutionary rates of the two genomes, based on comparisons of root-to-tip distances and on comparisons of the branch lengths of phylogenetically independent species pairs. Our results underscore the profound effects that long-term symbiosis can have on the biology of each symbiotic partner.

• Klíčová slova
• Blattabacterium cuenoti, cockroach, host–symbiont interaction, molecular evolution, phylogeny, substitution rate,
• MeSH
• fylogeneze MeSH
• genom bakteriální MeSH
• genom mitochondriální * MeSH
• molekulární evoluce MeSH
• švábi * MeSH
• symbióza MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Legionellaceae are intracellular bacteria known as important human pathogens. In the environment, they are mainly found in biofilms associated with amoebas. In contrast to the gammaproteobacterial family Enterobacteriaceae, which established a broad spectrum of symbioses with many insect taxa, the only instance of legionella-like symbiont has been reported from lice of the genus Polyplax. Here, we sequenced the complete genome of this symbiont and compared its main characteristics to other Legionella species and insect symbionts. Based on rigorous multigene phylogenetic analyses, we confirm this bacterium as a member of the genus Legionella and propose the name Candidatus Legionella polyplacis, sp.n. We show that the genome of Ca. Legionella polyplacis underwent massive degeneration, including considerable size reduction (529.746 bp, 484 protein coding genes) and a severe decrease in GC content (23%). We identify several possible constraints underlying the evolution of this bacterium. On one hand, Ca. Legionella polyplacis and the louse symbionts Riesia and Puchtella experienced convergent evolution, perhaps due to adaptation to similar hosts. On the other hand, some metabolic differences are likely to reflect different phylogenetic positions of the symbionts and hence availability of particular metabolic function in the ancestor. This is exemplified by different arrangements of thiamine metabolism in Ca. Legionella polyplacis and Riesia. Finally, horizontal gene transfer is shown to play a significant role in the adaptive and diversification process. Particularly, we show that Ca. L. polyplacis horizontally acquired a complete biotin operon (bioADCHFB) that likely assisted this bacterium when becoming an obligate mutualist.

• Klíčová slova
• genome evolution, horizontal gene transfer, symbiosis,
• MeSH
• Anoplura genetika   mikrobiologie   MeSH
• fyziologická adaptace MeSH
• genom bakteriální genetika   MeSH
• koevoluce MeSH
• Legionella klasifikace   genetika   fyziologie   MeSH
• molekulární evoluce * MeSH
• přenos genů horizontální MeSH
• sekvenční analýza DNA MeSH
• symbióza MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH

Stable endosymbiosis of a bacterium into a host cell promotes cellular and genomic complexity. The mealybug Planococcus citri has two bacterial endosymbionts with an unusual nested arrangement: the γ-proteobacterium Moranella endobia lives in the cytoplasm of the β-proteobacterium Tremblaya princeps These two bacteria, along with genes horizontally transferred from other bacteria to the P. citri genome, encode gene sets that form an interdependent metabolic patchwork. Here, we test the stability of this three-way symbiosis by sequencing host and symbiont genomes for five diverse mealybug species and find marked fluidity over evolutionary time. Although Tremblaya is the result of a single infection in the ancestor of mealybugs, the γ-proteobacterial symbionts result from multiple replacements of inferred different ages from related but distinct bacterial lineages. Our data show that symbiont replacement can happen even in the most intricate symbiotic arrangements and that preexisting horizontally transferred genes can remain stable on genomes in the face of extensive symbiont turnover.

• Klíčová slova
• Sodalis, horizontal gene transfer, organelle, scale insect,
• MeSH
• Betaproteobacteria genetika   růst a vývoj   MeSH
• fylogeneze MeSH
• Gammaproteobacteria genetika   růst a vývoj   MeSH
• genom bakteriální MeSH
• Planococcus (hmyz) genetika   mikrobiologie   MeSH
• přenos genů horizontální genetika   MeSH
• sekvenční analýza DNA MeSH
• symbióza genetika   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH