Microbiology (medical)

AbstractProtists frequently host diverse bacterial symbionts, in particular those affiliated with the order Holosporales (Alphaproteobacteria). All characterised members of this bacterial lineage have been retrieved in obligate association with a wide range of eukaryotes, especially multiple protist lineages (e.g. amoebozoans, ciliates, cercozoans, euglenids, and nucleariids), as well as some metazoans (especially arthropods and related ecdysozoans). While the genus Paramecium and other ciliates have been deeply investigated for the presence of symbionts, known members of the family “Candidatus Paracaedibacteraceae” (Holosporales) are currently underrepresented in such hosts. Herein, we report the description of “Candidatus Intestinibacterium parameciiphilum” within the family “Candidatus Paracaedibacteraceae”, inhabiting the cytoplasm of Paramecium biaurelia. This novel bacterium is almost twice as big as its relative “Candidatus Intestinibacterium nucleariae” from the opisthokont Nuclearia and does not present a surrounding halo. Based on phylogenetic analyses of 16S rRNA gene sequences, we identified six further potential species-level lineages within the genus. Based on the provenance of the respective samples, we investigated the environmental distribution of the representatives of “Candidatus Intestinibacterium” species. Obtained results are consistent with an obligate endosymbiotic lifestyle, with protists, in particular freshwater ones, as hosts. Thus, available data suggest that association with freshwater protists could be the ancestral condition for the members of the “Candidatus Intestinibacterium” genus.

Bathyarchaeia are widespread in various anoxic ecosystems and are considered one of the most abundant microbial groups on the earth. There are only a few reports of laboratory cultivation of Bathyarchaeia, and none of the representatives of this class has been isolated in pure culture. Here, we report a sustainable cultivation of the Bathyarchaeia archaeon (strain M17CTs) enriched from anaerobic sediment of a coastal lake. The cells of strain M17CTs were small non-motile cocci, 0.4–0.7 μm in diameter. The cytoplasmic membrane was surrounded by an S-layer and covered with an outermost electron-dense sheath. Strain M17CTs is strictly anaerobic mesophile. It grows at 10–45°C (optimum 37°C), at pH 6.0–10.0 (optimum 8.0), and at NaCl concentrations of 0–60 g l−1 (optimum 20 g l−1). Growth occurred in the presence of methoxylated aromatic compounds (3,4-dimethoxybenzoate and vanillate) together with complex proteinaceous substrates. Dimethyl sulfoxide and nitrate stimulated growth. The phylogenomic analysis placed strain M17CTs to BIN-L-1 genus-level lineage from the BA1 family-level lineage and B26-1 order-level lineage (former subgroup-8) within the class Bathyarchaeia. The complete genome of strain M17CTs had a size of 2.15 Mb with a DNA G + C content of 38.1%. Based on phylogenomic position and phenotypic and genomic properties, we propose to assign strain M17CTs to a new species of a novel genus Bathyarchaeum tardum gen. nov., sp. nov. within the class Bathyarchaeia. This is the first sustainably cultivated representative of Bathyarchaeia. We propose under SeqCode the complete genome sequence of strain M17CTs (CP122380) as a nomenclatural type of Bathyarchaeum tardum, which should be considered as a type for the genus Bathyarchaeum, which is proposed as a type for the family Bathyarchaeaceae, order Bathyarchaeales, and of the class Bathyarchaeia.

IntroductionCandidate Phyla Radiation (CPR) and more specifically Candidatus Saccharibacteria (TM7) have now been established as ubiquitous members of the human oral microbiota. Additionally, CPR have been reported in the gastrointestinal and urogenital tracts. However, the exploration of new human niches has been limited to date.MethodsIn this study, we performed a prospective and retrospective screening of TM7 in human samples using standard PCR, real-time PCR, scanning electron microscopy (SEM) and shotgun metagenomics.ResultsUsing Real-time PCR and standard PCR, oral samples presented the highest TM7 prevalence followed by fecal samples, breast milk samples, vaginal samples and urine samples. Surprisingly, TM7 were also detected in infectious samples, namely cardiac valves and blood cultures at a low prevalence (under 3%). Moreover, we observed CPR-like structures using SEM in all sample types except cardiac valves. The reconstruction of TM7 genomes in oral and fecal samples from shotgun metagenomics reads further confirmed their high prevalence in some samples.ConclusionThis study confirmed, through their detection in multiple human samples, that TM7 are human commensals that can also be found in clinical settings. Their detection in clinical samples warrants further studies to explore their role in a pathological setting.

In this paper, a comprehensive overview of the ‘Candidatus Liberibacter solanacearum’ presence in Europe was provided. The analyzed findings revealed that, since the first appearance of this pathogen in Finland and Spain in 2008, it has spread to 13 new European countries. Therefore, ‘Ca. L. solanacearum’ has spread very quickly across the European continent, as evident from the emergence of new host plants within the Apiaceae, Urticaceae, and Polygonaceae families, as well as new haplotypes of this pathogen. Thus far, 5 of the 15 ‘Ca. L. solanacearum’ haplotypes determined across the globe have been confirmed in Europe (haplotypes C, D, E, U, and H). Fully competent ‘Ca. L. solanacearum’ vectors include Bactericera cockerelli, Trioza apicalis, and B. trigonica; however, only T. apicalis and B. trigonica are presently established in Europe and are very important for plants from the Apiaceae family in particular. Moreover, psyllid species such as B. tremblayi, T. urticae, and T. anthrisci have also been confirmed positive for ‘Ca. L. solanacearum’. Constant monitoring of its spread in the field (in both symptomatic and asymptomatic plants), use of sensitive molecular diagnostic techniques, and application of timely management strategies are, therefore, of utmost importance for the control of this destructive pathogen.

Abstract Background Nudibranchs comprise a group of > 6000 marine soft-bodied mollusk species known to use secondary metabolites (natural products) for chemical defense. The full diversity of these metabolites and whether symbiotic microbes are responsible for their synthesis remains unexplored. Another issue in searching for undiscovered natural products is that computational analysis of genomes of uncultured microbes can result in detection of novel biosynthetic gene clusters; however, their in vivo functionality is not guaranteed which limits further exploration of their pharmaceutical or industrial potential. To overcome these challenges, we used a fluorescent pantetheine probe, which produces a fluorescent CoA-analog employed in biosynthesis of secondary metabolites, to label and capture bacterial symbionts actively producing these compounds in the mantle of the nudibranch Doriopsilla fulva. Results We recovered the genome of Candidatus Doriopsillibacter californiensis from the Ca. Tethybacterales order, an uncultured lineage of sponge symbionts not found in nudibranchs previously. It forms part of the core skin microbiome of D. fulva and is nearly absent in its internal organs. We showed that crude extracts of D. fulva contained secondary metabolites that were consistent with the presence of a beta-lactone encoded in Ca. D. californiensis genome. Beta-lactones represent an underexplored group of secondary metabolites with pharmaceutical potential that have not been reported in nudibranchs previously. Conclusions Altogether, this study shows how probe-based, targeted sorting approaches can capture bacterial symbionts producing secondary metabolites in vivo.

Huanglongbing (HLB), also known as citrus greening, is an insidious disease in citrus and has become a threat to the sustainability of the citrus industry worldwide. In the U.S., Candidatus Liberibacter asiaticus (CLas) is the pathogen that is associated with HLB, an unculturable, phloem-limited bacteria, vectored by the Asian Citrus Psyllid (ACP, Diaphorina citri). There is no known cure nor treatment to effectively control HLB, and current control methods are primarily based on the use of insecticides and antibiotics, where effectiveness is limited and may have negative impacts on beneficial and non-target organisms. Thus, there is an urgent need for the development of effective and sustainable treatment options to reduce or eliminate CLas from infected trees. In the present study, we screened citrus-derived endophytes, their cell-free culture supernatants (CFCS), and crude plant extracts for antimicrobial activity against two culturable surrogates of CLas, Sinorhizobium meliloti and Liberibacter crescens. Candidates considered high-potential antimicrobial agents were assessed directly against CLas in vitro, using a propidium monoazide–based assay. As compared to the negative controls, statistically significant reductions of viable CLas cells were observed for each of the five bacterial CFCS. Subsequent 16S rRNA gene sequencing revealed that each of the five bacterial isolates were most closely related to Bacillus amyloliquefaciens, a species dominating the market of biological control products. As such, the aboveground endosphere of asymptomatic survivor citrus trees, grown in an organic orchard, were found to host bacterial endophytes capable of effectively disrupting CLas cell membranes. These results concur with the theory that native members of the citrus microbiome play a role in the development of HLB. Here, we identify five strains of Bacillus amyloliquefaciens demonstrating notable potential to be used as sources of novel antimicrobials for the sustainable management of HLB.

AbstractMethanogenic and methanotrophic archaea produce and consume the greenhouse gas methane, respectively, using the reversible enzyme methyl-coenzyme M reductase (Mcr). Recently, Mcr variants that can activate multicarbon alkanes have been recovered from archaeal enrichment cultures. These enzymes, called alkyl-coenzyme M reductase (Acrs), are widespread in the environment but remain poorly understood. Here we produced anoxic cultures degrading mid-chain petroleum n-alkanes between pentane (C5) and tetradecane (C14) at 70 °C using oil-rich Guaymas Basin sediments. In these cultures, archaea of the genus Candidatus Alkanophaga activate the alkanes with Acrs and completely oxidize the alkyl groups to CO2. Ca. Alkanophaga form a deep-branching sister clade to the methanotrophs ANME-1 and are closely related to the short-chain alkane oxidizers Ca. Syntrophoarchaeum. Incapable of sulfate reduction, Ca. Alkanophaga shuttle electrons released from alkane oxidation to the sulfate-reducing Ca. Thermodesulfobacterium syntrophicum. These syntrophic consortia are potential key players in petroleum degradation in heated oil reservoirs.

‘Candidatus Phytoplasma solani’ (stolbur phytoplasma) is associated with rubbery taproot disease (RTD) of sugar beet (Beta vulgaris L.), while Macrophomina phaseolina is considered the most important root rot pathogen of this plant in Serbia. The high prevalence of M. phaseolina root rot reported on sugar beet in Serbia, unmatched elsewhere in the world, coupled with the notorious tendency of RTD-affected sugar beet to rot, has prompted research into the relationship between the two diseases. This study investigates the correlation between the occurrence of sugar beet RTD and the presence of root rot fungal pathogens in a semi-field ‘Ca. P. solani’ transmission experiment with the cixiid vector Reptalus quinquecostatus (Dufour), in addition to naturally infected sugar beet in the open field. Our results showed that: (i) Reptalus quinquecostatus transmitted ‘Ca. P. solani’ to sugar beet which induced typical RTD root symptoms; (ii) Macrophomina phaseolina root rot was exclusively present in ‘Ca. P. solani’-infected sugar beet in both the semi-field experiment and naturally infected sugar beet; and that (iii) even under environmental conditions favorable to the pathogen, M. phaseolina did not infect sugar beet, unless the plants had been previously infected with phytoplasma.