Publications

4857

Dichloromethane (DCM; CH2Cl2) is a widespread pollutant with anthropogenic and natural sources. Anaerobic DCM-dechlorinating bacteria use the Wood–Ljungdahl pathway, yet dechlorination reaction mechanisms remain unclear and the enzyme(s) responsible for carbon-chlorine bond cleavage have not been definitively identified. Of the three bacterial taxa known to carry out anaerobic dechlorination of DCM, ‘Candidatus Formimonas warabiya’ strain DCMF is the only organism that can also ferment non-chlorinated substrates, including quaternary amines (i.e., choline and glycine betaine) and methanol. Strain DCMF is present within enrichment culture DFE, which was derived from an organochlorine-contaminated aquifer. We utilized the metabolic versatility of strain DCMF to carry out comparative metaproteomics of cultures grown with DCM or glycine betaine. This revealed differential abundance of numerous proteins, including a methyltransferase gene cluster (the mec cassette) that was significantly more abundant during DCM degradation, as well as highly conserved amongst anaerobic DCM-degrading bacteria. This lends strong support to its involvement in DCM dechlorination. A putative glycine betaine methyltransferase was also discovered, adding to the limited knowledge about the fate of this widespread osmolyte in anoxic subsurface environments. Furthermore, the metagenome of enrichment culture DFE was assembled, resulting in five high quality and two low quality draft metagenome-assembled genomes. Metaproteogenomic analysis did not reveal any genes or proteins for utilization of DCM or glycine betaine in the cohabiting bacteria, supporting the previously held idea that they persist via necromass utilization.

AbstractMicrobes in marine sediments play crucial roles in global carbon and nutrient cycling. However, our understanding of microbial diversity and physiology on the ocean floor is limited. Here, we use phylogenomic analyses of thousands of metagenome-assembled genomes (MAGs) from coastal and deep-sea sediments to identify 55 MAGs that are phylogenetically distinct from previously described bacterial phyla. We propose that these MAGs belong to 4 novel bacterial phyla (Blakebacterota, Orphanbacterota, Arandabacterota, and Joyebacterota) and a previously proposed phylum (AABM5-125-24), all of them within the FCB superphylum. Comparison of their rRNA genes with public databases reveals that these phyla are globally distributed in different habitats, including marine, freshwater, and terrestrial environments. Genomic analyses suggest these organisms are capable of mediating key steps in sedimentary biogeochemistry, including anaerobic degradation of polysaccharides and proteins, and respiration of sulfur and nitrogen. Interestingly, these genomes code for an unusually high proportion (~9% on average, up to 20% per genome) of protein families lacking representatives in public databases. Genes encoding hundreds of these protein families colocalize with genes predicted to be involved in sulfur reduction, nitrogen cycling, energy conservation, and degradation of organic compounds. Our findings advance our understanding of bacterial diversity, the ecological roles of these bacteria, and potential links between novel gene families and metabolic processes in the oceans.

Abstract A new distribution map is provided for Candidatus Liberibacter africanus Jagoueix, Bové & Garnier. Alphaproteobacteria: Rhizobiales: Phyllobacteriaceae. Hosts: Citrus spp.

AbstractBackgroundAce Lake is a marine-derived, stratified lake in the Vestfold Hills of East Antarctica with an upper oxic and lower anoxic zone. Cyanobacteria are known to reside throughout the water column. ASynechococcus-like species becomes the most abundant member in the upper sunlit waters during summer while persisting annually even in the absence of sunlight and at depth in the anoxic zone. Here, we analysed ~ 300 Gb of Ace Lake metagenome data including 59Synechococcus-like metagenome-assembled genomes (MAGs) to determine depth-related variation in cyanobacterial population structure. Metagenome data were also analysed to investigate viruses associated with this cyanobacterium and the host’s capacity to defend against or evade viruses.ResultsA singleSynechococcus-like species was found to exist in Ace Lake,CandidatusRegnicoccus frigidus sp. nov., consisting of one phylotype more abundant in the oxic zone and a second phylotype prevalent in the oxic-anoxic interface and surrounding depths. An important aspect of genomic variation pertained to nitrogen utilisation, with the capacity to perform cyanide assimilation and asparagine synthesis reflecting the depth distribution of available sources of nitrogen. Both specialist (host specific) and generalist (broad host range) viruses were identified with a predicted ability to infectCa.Regnicoccus frigidus. Host-virus interactions were characterised by a depth-dependent distribution of virus type (e.g. highest abundance of specialist viruses in the oxic zone) and host phylotype capacity to defend against (e.g. restriction-modification, retron and BREX systems) and evade viruses (cell surface proteins and cell wall biosynthesis and modification enzymes).ConclusionIn Ace Lake, specific environmental factors such as the seasonal availability of sunlight affects microbial abundances and the associated processes that the microbial community performs. Here, we find that the population structure forCa.Regnicoccus frigidus has evolved differently to the other dominant phototroph in the lake,CandidatusChlorobium antarcticum. The geography (i.e. Antarctica), limnology (e.g. stratification) and abiotic (e.g. sunlight) and biotic (e.g. microbial interactions) factors determine the types of niches that develop in the lake. While the lake community has become increasingly well studied, metagenome-based studies are revealing that niche adaptation can take many paths; these paths need to be determined in order to make reasonable predictions about the consequences of future ecosystem perturbations.

Abstract Objective ‘Candidatus Liberibacter asiaticus’ (CLas) is associated with the devastating citrus ‘greening’ disease. All attempts to achieve axenic growth and complete Koch’s postulates with CLas have failed to date, at best yielding complex cocultures with very low CLas titers detectable only by PCR. Reductive genome evolution has rendered all pathogenic ‘Ca. Liberibacter’ spp. deficient in multiple key biosynthetic, metabolic and structural pathways that are highly unlikely to be rescued in vitro by media supplementation alone. By contrast, Liberibacter crescens (Lcr) is axenically cultured and its genome is both syntenic and highly similar to CLas. Our objective is to achieve replicative axenic growth of CLas via addition of missing culturability-related Lcr genes. Results Bioinformatic analyses identified 405 unique ORFs in Lcr but missing (or truncated) in all 24 sequenced CLas strains. Site-directed mutagenesis confirmed and extended published EZ-Tn5 mutagenesis data, allowing elimination of 310 of these 405 genes as nonessential, leaving 95 experimentally validated Lcr genes as essential for CLas growth in axenic culture. Experimental conditions for conjugation of large GFP-expressing plasmids from Escherichia coli to Lcr were successfully established for the first time, providing a practical method for transfer of large groups of ‘essential’ Lcr genes to CLas.

Abstract The previously uncultured phylum “Candidatus Eremiobacterota” is globally distributed and often abundant in oligotrophic environments. Although it includes lineages with the genetic potential for photosynthesis, one of the most important metabolic pathways on Earth, the absence of pure cultures has limited further insights into its ecological and physiological traits. We report the first successful isolation of a “Ca. Eremiobacterota” strain from a fumarolic ice cave on Mt. Erebus volcano (Antarctica). Polyphasic analysis revealed that this organism is an aerobic anoxygenic photoheterotrophic bacterium with a unique lifestyle, including bacteriochlorophyll a production, CO2 fixation, a high CO2 requirement, and phototactic motility using type IV-pili, all of which are highly adapted to polar and fumarolic environments. The cells are rods or filaments with a vesicular type intracytoplasmic membrane system. The genome encodes novel anoxygenic Type II photochemical reaction centers and bacteriochlorophyll synthesis proteins, forming a deeply branched monophyletic clade distinct from known phototrophs. The first cultured strain of the eighth phototrophic bacterial phylum which we name Vulcanimicrobium alpinus gen. nov., sp. nov. advances our understanding of ecology and evolution of photosynthesis.

AbstractThe endosymbiotic Wolbachia is one of the most common intracellular bacteria known in arthropods and nematodes. Its ability for reproductive manipulation can cause unequal inheritance to male and female offspring, allowing the manipulator to spread, but potentially also impact the evolutionary dynamics of infected hosts. Estimated to be present in up to 66% of insect species, little is known about the phenotypic impact of Wolbachia within the order Coleoptera. Here, we describe the reproductive manipulation by the Wolbachia strain wSur harboured by the sawtoothed grain beetle Oryzaephilus surinamensis (Coleoptera, Silvanidae), through a combination of genomics approaches and bioassays. The Wolbachia strain wSur belongs to supergroup B that contains well‐described reproductive manipulators of insects and encodes a pair of cytoplasmic incompatibility factor (cif) genes, as well as multiple homologues of the WO‐mediated killing (wmk) gene. A phylogenetic comparison with wmk homologues of wMel of Drosophila melanogaster identified 18 wmk copies in wSur, including one that is closely related to the wMel male‐killing homologue. However, further analysis of this particular wmk gene revealed an eight‐nucleotide deletion leading to a stop‐codon and subsequent reading frame shift midsequence, probably rendering it nonfunctional. Concordantly, utilizing a Wolbachia‐deprived O. surinamensis population and controlled mating pairs of wSur‐infected and noninfected partners, we found no experimental evidence for male‐killing. However, a significant ~50% reduction of hatching rates in hybrid crosses of uninfected females with infected males indicates that wSur is causing cytoplasmic incompatibility. Thus, Wolbachia also represents an important determinant of host fitness in Coleoptera.