Genomic characterization of eight Ensifer strains isolated from pristine caves and a whole genome phylogeny of Ensifer (Sinorhizobium)

Ensifer canadensis sp. nov. strain T173T isolated from Melilotus albus (sweet clover) in Canada possesses recombinant plasmid pT173b harbouring symbiosis and type IV secretion system genes apparently acquired from Ensifer medicae

A bacterial strain, designated T173^T, was previously isolated from a root-nodule of a Melilotus albus plant growing in Canada and identified as a novel Ensifer lineage that shared a clade with the non-symbiotic species, Ensifer adhaerens. Strain T173^T was also previously found to harbour a symbiosis plasmid and to elicit root-nodules on Medicago and Melilotus species but not fix nitrogen. Here we present data for the genomic and taxonomic description of strain T173^T. Phylogenetic analyses including the analysis of whole genome sequences and multiple locus sequence analysis (MLSA) of 53 concatenated ribosome protein subunit (rps) gene sequences confirmed placement of strain T173^T in a highly supported lineage distinct from named Ensifer species with E. morelensis Lc04^T as the closest relative. The highest digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values of genome sequences of strain T173^T compared with closest relatives (35.7 and 87.9%, respectively) are well below the respective threshold values of 70% and 95-96% for bacterial species circumscription. The genome of strain T173^T has a size of 8,094,229 bp with a DNA G + C content of 61.0 mol%. Six replicons were detected: a chromosome (4,051,102 bp) and five plasmids harbouring plasmid replication and segregation (repABC) genes. These plasmids were also found to possess five apparent conjugation systems based on analysis of TraA (relaxase), TrbE/VirB4 (part of the Type IV secretion system (T4SS)) and TraG/VirD4 (coupling protein). Ribosomal RNA operons encoding 16S, 23S, and 5S rRNAs that are usually restricted to bacterial chromosomes were detected on plasmids pT173d and pT173e (946,878 and 1,913,930 bp, respectively) as well as on the chromosome of strain T173^T. Moreover, plasmid pT173b (204,278 bp) was found to harbour T4SS and symbiosis genes, including nodulation (nod, noe, nol) and nitrogen fixation (nif, fix) genes that were apparently acquired from E. medicae by horizontal transfer. Data for morphological, physiological and symbiotic characteristics complement the sequence-based characterization of strain T173^T. The data presented support the description of a new species for which the name Ensifer canadensis sp. nov. is proposed with strain T173^T (= LMG 32374^T = HAMBI 3766^T) as the species type strain.

Microbial communities in carbonate precipitates from drip waters in Nerja Cave, Spain

Research on cave microorganisms has mainly focused on the microbial communities thriving on speleothems, rocks and sediments; however, drip water bacteria and calcite precipitation has received less attention. In this study, microbial communities of carbonate precipitates from drip waters in Nerja, a show cave close to the sea in southeastern Spain, were investigated. We observed a pronounced difference in the bacterial composition of the precipitates, depending on the galleries and halls. The most abundant phylum in the precipitates of the halls close to the cave entrance was Proteobacteria, due to the low depth of this sector, the direct influence of a garden on the top soil and the infiltration of waters into the cave, as well as the abundance of members of the order Hyphomicrobiales, dispersing from plant roots, and other Betaproteobacteria and Gammaproteobacteria, common soil inhabitants. The influence of marine aerosols explained the presence of Marinobacter, Idiomarina, Thalassobaculum, Altererythrobacter and other bacteria due to the short distance from the cave to the sea. Nineteen out of forty six genera identified in the cave have been reported to precipitate carbonate and likely have a role in mineral deposition.

Genomic characterization of bacteria from the ultra-oligotrophic Madison aquifer: insight into the archetypical LuxI/LuxR and identification of novel LuxR solos

OBJECTIVES

To characterize the bacterial community of Wind Cave's Madison aquifer through whole-genome sequencing, and to better understand the bacterial ecology by identifying genes involved in acyl-homoserine lactone (AHL) based quorum-sensing (QS) systems.

RESULTS

Genome-based taxonomic classification revealed the microbial richness present in the pristine Madison aquifer. The strains were found to span eleven genera and fourteen species, of which eight had uncertain taxonomic classifications. The genomes of strains SD129 and SD340 were found to contain the archetypical AHL QS system composed of two genes, luxI and luxR. Surprisingly, the genomes of strains SD115, SD129, SD274 and SD316 were found to contain one to three luxR orphans (solos). Strain SD129, besides possessing an archetypical AHL QS luxI-luxR pair, also contained two luxR solos, while strain SD316 contained three LuxR solos and no luxI-luxR pairs. The ligand-binding domain of two LuxR solos, one each from strains SD129 and SD316, were found to contain novel substitutions not previously reported, thus may represent two LuxR orphans that detection and response to unknown self-produced signal(s), or to signal(s) produced by other organisms.

Colored Microbial Coatings in Show Caves from the Galapagos Islands (Ecuador): First Microbiological Approach

The Galapagos Islands (Ecuador) have a unique ecosystem on Earth due to their outstanding biodiversity and geological features. This also extends to their subterranean heritage, such as volcanic caves, with plenty of secondary mineral deposits, including coralloid-type speleothems and moonmilk deposits. In this study, the bacterial communities associated with speleothems from two lava tubes of Santa Cruz Island were investigated. Field emission scanning electron microscopy (FESEM) was carried out for the morphological characterization and detection of microbial features associated with moonmilk and coralloid speleothems from Bellavista and Royal Palm Caves. Microbial cells, especially filamentous bacteria in close association with extracellular polymeric substances (EPS), were abundant in both types of speleothems. Furthermore, reticulated filaments and Actinobacteria-like cells were observed by FESEM. The analysis of 16S rDNA revealed the presence of different bacterial phylotypes, many of them associated with the carbon, nitrogen, iron and sulfur cycles, and some others with pollutants. This study gives insights into subsurface microbial diversity of the Galapagos Islands and further shows the interest of the conservation of these subterranean geoheritage sites used as show caves.

New insights into the molecular physiology of sulfoxide reduction in bacteria

Sulfoxides occur in biology as products of the S-oxygenation of small molecules as well as in peptides and proteins and their formation is often associated with oxidative stress and can affect biological function. In bacteria, sulfoxide damage can be reversed by different types of enzymes. Thioredoxin-dependent peptide methionine sulfoxide reductases (MSR proteins) repair oxidized methionine residues and are found in all Domains of life. In bacteria MSR proteins are often found in the cytoplasm but in some bacteria, including pathogenic Neisseria, Streptococci, and Haemophilus they are extracytoplasmic. Mutants lacking MSR proteins are often sensitive to oxidative stress and in pathogens exhibit decreased virulence as indicated by reduced survival in host cell or animal model systems. Molybdenum enzymes are also known to reduce S-oxides and traditionally their physiological role was considered to be in anaerobic respiration using dimethylsulfoxide (DMSO) as an electron acceptor. However, it now appears that some enzymes (MtsZ) of the DMSO reductase family of Mo enzymes use methionine sulfoxide as preferred physiological substrate and thus may be involved in scavenging/recycling of this amino acid. Similarly, an enzyme (MsrP/YedY) of the sulfite oxidase family of Mo enzymes has been shown to be involved in repair of methionine sulfoxides in periplasmic proteins. Again, some mutants deficient in Mo-dependent sulfoxide reductases exhibit reduced virulence, and there is evidence that these Mo enzymes and some MSR systems are induced by hypochlorite produced by the innate immune system. This review describes recent advances in the understanding of the molecular microbiology of MSR systems and the broadening of the role of Mo-dependent sulfoxide reductase to encompass functions beyond anaerobic respiration.