Rhodococcus parequi sp. nov., a new species isolated from equine farm soil closely related to the pathogen Rhodococcus equi

We present the description of the new species, Rhodococcus parequi, found during phylogenomic investigations of a global collection of strains identified as Rhodococcus (Prescottella) equi. Strain PAM 2766T was isolated from horse-breeding farm soil in Normandy, France, and was indistinguishable from R. equi based on the usual identification tests. Whole-genome phylogenetic analyses located PAM 2766T in the same Rhodococcus sublineage as R. equi, together with Rhodococcus agglutinans, Rhodococcus defluvii, Rhodococcus soli, Rhodococcus subtropicus, Rhodococcus spongiicola and Rhodococcus xishaensis. PAM 2766T is most closely related to, but sufficiently distinct from, R. equi DSM 20307 T to be considered a separate species. The average nt identity (ANI) and average aa identity (AAI) values are 88.60% and 92.35, respectively, well below the species cutoff. The PAM 2766T draft genome is ~5.3 Mb in size with 68.98% G+C mol content. PAM 2766T is strictly aerobic and non-motile and produces smooth, creamy to buff-coloured colonies very similar to those of R. equi. It phenotypically differs from the latter by the ability to grow at 5 °C, a strongly positive urease test at 24 h and specificities in the carbon and nitrogen source utilization profile as determined by phenotype microarray screens. Our data indicate that PAM 2766T belongs to a novel species, for which the name Rhodococcus parequi sp. nov. is proposed. R. parequi was avirulent in macrophage infection assays and is assumed to be non-pathogenic. The type strain is PAM 2766T (=CETC 30995T=NCTC 14987T).

Complete genome sequence of the saprophytic actinomycete Rhodococcus (Prescottella) soli DSD51WT, closely related to the multi-host pathogen Rhodococcus (Prescottella) equi

Rhodococcus (Prescottella) soli strain DSD51WT is an aerobic, non-spore-forming, non-motile actinomycete isolated previously from soil collected from Kyoto Park, Japan, using a resuscitative technique. Here, we report the complete, circular genome sequence of R. soli DSD51WT. We employed a hybrid approach using Illumina and Oxford Nanopore platforms.

Judicial Opinion 130

Opinion 130 deals with a Request for an Opinion asking the Judicial Commission to clarify whether the genus name Rhodococcus Zopf 1891 (Approved Lists 1980) is illegitimate. The Request is approved and an answer is given. The name Rhodococcus Zopf 1891 (Approved Lists 1980) is illegitimate because it is a later homonym of the validly published cyanobacterial name Rhodococcus Hansgirg 1884. The Judicial Commission also clarifies that it has the means to resolve such cases by conserving a name over an earlier homonym. It is concluded that the name Rhodococcus Zopf 1891 (Approved Lists 1980) is significantly more important than the name Rhodococcus Hansgirg 1884 and therefore the former is conserved over the latter. This makes the name Rhodococcus Zopf 1891 (Approved Lists 1980) legitimate.

Mycobacteriales taxonomy using network analysis-aided, context-uniform phylogenomic approach for non-subjective genus demarcation

IMPORTANCE

A robust taxonomy is essential for the organized study of prokaryotes and the effective communication of microbial knowledge. The genus rank is the mainstay of biological classification as it brings together under a common name a group of closely related organisms sharing the same recent ancestry and similar characteristics. Despite the unprecedented resolution afforded by whole-genome sequencing in defining evolutionary relationships, a consensus approach for phylogenomics-based prokaryotic genus delineation remains elusive. Taxonomists use different demarcation criteria, sometimes leading to genus rank over-splitting and the creation of multiple new genera. This work reports a simple, reliable, and standardizable method that seeks to minimize subjectivity in genomics-based demarcation of prokaryotic genera, exemplified through application to the order Mycobacteriales. Formal descriptions of proposed taxonomic changes based on our study are included.

Specific preadaptations of Rhodococcus equi cooperate with its Virulence-associated protein A during macrophage infection

Gram-positive Rhodococcus equi (Prescotella equi) is a lung pathogen of foals and immunocompromised humans. Intra-macrophage multiplication requires production of the bacterial Virulence-associated protein A (VapA) which is released into the phagosome lumen. VapA pH-neutralizes intracellular compartments allowing R. equi to multiply in an atypical macrophage phagolysosome. Here, we show that VapA does not support intra-macrophage growth of several other bacterial species demonstrating that only few bacteria have the specific preadaptations needed to profit from VapA. We show that the closest relative of R. equi, environmental Rhodococcus defluvii (Prescotella defluvii), does not multiply in macrophages at 37°C even when VapA is present because of its thermosensitivity but it does so once the infection temperature is lowered providing rare experimental evidence for 'thermal restriction'. Using growth experiments with isolated macrophage lysosomes and modified infection schemes we provide evidence that R. equi resists the attack by phagolysosome contents at low pH for several hours. During this time, R. equi produces and secretes VapA which enables it to grow at the expense of lysosome constituents. We present arguments that, under natural infection conditions, R. equi is VapA-less during the initial encounter with the host. This has important implications for vaccine development.

Genome-Based Exploration of Rhodococcus Species for Plastic-Degrading Genetic Determinants Using Bioinformatic Analysis

Plastic polymer waste management is an increasingly prevalent issue. In this paper, Rhodococcus genomes were explored to predict new plastic-degrading enzymes based on recently discovered biodegrading enzymes for diverse plastic polymers. Bioinformatics prediction analyses were conducted using 124 gene products deriving from diverse microorganisms retrieved from databases, literature data, omic-approaches, and functional analyses. The whole results showed the plastic-degrading potential of Rhodococcus genus. Among the species with high plastic-degrading potential, R. erythropolis, R. equi, R. opacus, R. qingshengii, R. fascians, and R. rhodochrous appeared to be the most promising for possible plastic removal. A high number of genetic determinants related to polyester biodegradation were obtained from different Rhodococcus species. However, score calculation demonstrated that Rhodococcus species (especially R. pyridinivorans, R. qingshengii, and R. hoagii) likely possess PE-degrading enzymes. The results identified diverse oxidative systems, including multicopper oxidases, alkane monooxygenases, cytochrome P450 hydroxylases, para-nitrobenzylesterase, and carboxylesterase, and they could be promising reference sequences for the biodegradation of plastics with C-C backbone, plastics with heteroatoms in the main chain, and polyesters, respectively. Notably, the results of this study could be further exploited for biotechnological applications in biodegradative processes using diverse Rhodococcus strains and through catalytic reactions.

A stable home for an equine pathogen: valid publication of the binomial Prescottella equi gen. nov., comb. nov., and reclassification of four rhodococcal species into the genus Prescottella

Opinion 106 of the Judicial Commission has clarified the nomenclature of the taxon variously named Rhodococcus equi , ‘Prescottella equi’ and Rhodococcus hoagii . As a consequence, we present here the genus name Prescottella and that of its nomenclatural type species, Prescottella equi comb. nov., for valid publication and propose the reclassification of four rhodococcal species as novel combinations in the genus, namely Prescottella agglutinans Guo et al. 2015 comb. nov., Prescottella defluvii Kämpfer et al. 2014 comb. nov., Prescottella soli Li et al. 2015 comb. nov. and Prescottella subtropica Lee et al. 2019 comb. nov. In addition, we note that a clinical isolate, strain 86–07 (=W8901), likely represents an additional species within the genus Prescottella . Nearly a century after the original description of the type strain of the type species as Corynebacterium equi , we provide a stable home for Prescottella equi and its relatives.

Recombinant Extracellular Cholesterol Oxidase from Nocardioides simplex

Cholesterol oxidase is a highly demanded enzyme used in medicine, pharmacy, agriculture, chemistry, and biotechnology. It catalyzes oxidation of 3β-hydroxy-5-ene- to 3-keto-4-ene- steroids with the formation of hydrogen peroxide. Here, we expressed 6xHis-tagged mature form of the extracellular cholesterol oxidase (ChO) from the actinobacterium Nocardioides simplex VKM Ac-2033D (55.6 kDa) in Escherichia coli cells. The recombinant enzyme (ChO_Ns) was purified using affinity chromatography. ChO_Ns proved to be functional towards cholesterol, cholestanol, phytosterol, pregnenolone, and dehydroepiandrosterone. Its activity depended on the structure and length of the aliphatic side chain at C17 atom of the steroid nucleus and was lower with pregnenolone and dehydroepiandrosterone. The enzyme was active in a pH range of 5.25÷6.5 with the pH optimum at 6.0. Kinetic assays and storage stability tests demonstrated that the characteristics of ChO_Ns were generally comparable with or superior to those of commercial ChO from Streptomyces hygroscopicus (ChO_Sh). The results contribute to the knowledge on microbial ChOs and evidence that ChO from N. simplex VKM Ac-2033D is a promising agent for further applications.

Rhodococcus yananensis sp. nov., a novel denitrification actinobacterium isolated from microbial fermentation bed material from a pig farm

An opaque, pink-coloured, gram-positive, aerobic bacteria (designated as FBM22-1T), was isolated from microbial fermentation bed material from a pig farm in northwestern China. Optimal growth occurred at 30–37 °C, pH 7.0 and with 0.5 % NaCl (w/v). The strain had nitrification and denitrification functions. Phylogenetic analysis based on 16S rRNA gene sequences revealed that the novel isolate belonged to the genus Rhodococcus . Strain FBM22-1T was closely related to Rhodococcus zopfii NBRC 100606T and Rhodococcus rhodochrous NBRC 16069T, with 16S rRNA gene sequence similarities of 97.9 and 97.7 %, respectively. The predominant menaquinone in strain FBM22-1T was MK-8(H2). The cellular fatty acids consisted primarily of C16 : 1ω7c and/or C16 : 1 ω6c, C16 : 0 and 10-methyl C18 : 0. The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and glycolipid. The G+C content of strain FBM22-1T was 68.64 mol%. Based on the phenotypic, phylogenetic and chemotaxonomic characterization results, in combination with low values of digital DNA–DNA hybridization between strain FBM22-1T and its closest neighbours, FBM22-1T represents a novel species of the genus Rhodococcus , for which the name Rhodococcus yananensis sp. nov. is proposed; the type strain is FBM22-1T (=KCTC 49502T=CCTCC AB2020275T).

Rhodococcus oxybenzonivorans sp. nov., a benzophenone-3-degrading bacterium, isolated from stream sediment

A Gram-stain-positive, facultative aerobic, oxidase-negative, catalase-positive, non-sporulating, and non-motile bacterium, which degraded benzophenone-3, was isolated from stream sediment collected in the Republic of Korea and designated as strain S2-17T. Cells of this strain were rod-shaped during the early growth phase but became coccoid after the late exponential growth phase. Bacterial growth was observed at 15–37 °C (optimum, 25–30 °C) and pH 6.0–9.5 (optimum, pH 7.5–8.5) and in the presence of 0–9.0 % (w/v) NaCl (optimum, 0–1.0 %). Menaquinone-8 (H2) was the sole isoprenoid quinone, and C16 : 0, C17 : 1  ω8c, summed feature 3 (comprising C16 : 1  ω7c/C16 : 1  ω6c) and C18 : 1  ω9c were the major fatty acids. The cell wall of strain S2-17T contained meso-diaminopimelic acid, and arabinose, galactose and mycolic acid were found in whole-cell hydrolysates, suggesting a chemotype IV cell wall. The G+C content of the genome was 65.6 mol%. Phylogenetic analyses revealed that strain S2-17T formed a phyletic lineage within the genus Rhodococcus and was most closely related to Rhodococcus jostii DSM 44719T (99.2 % 16S rRNA gene sequence similarity). Average nucleotide identity and digital DNA–DNA hybridization values between strain S2-17T and R. jostii DSM 44719T were 82.6 and 26.5 %, respectively, indicating differences between the species. Based on its phenotypic, chemotaxonomic and molecular features, strain S2-17T represents a novel species of the genus Rhodococcus , for which the name Rhodococcus oxybenzonivorans sp. nov. is proposed. The type strain is S2-17T (=KACC 19281T=JCM 32046T).

Judicial Opinions 103–111

In Opinion 103, the request to place the name Spirillum volutans Ehrenberg 1832 (Approved Lists 1980) on the list of rejected names is denied because a neotype may be designated. Similarly, because a neotype may be designated, in Opinion 104 the request to place the name Beijerinckia fluminensis Döbereiner and Ruschel 1958 (Approved Lists 1980) on the list of rejected names is denied. In Opinion 105, it is emphasized that the name Rhodoligotrophos Fukuda et al. 2012 does not contravene the Code. The request to orthographically correct Rhodoligotrophos Fukuda et al. 2012 to Rhodoligotrophus corrig. Fukuda et al. 2012 is denied. Opinion 106 addresses two Requests for an Opinion and results in the placement of the epithet hoagii in Corynebacterium hoagii (Morse 1912) Eberson 1918 (Approved Lists 1980) and Rhodococcus hoagii (Morse 1912) Kämpfer et al. 2014 on the list of rejected specific and subspecific epithets. Since this removes all known available earlier synonyms of Rhodococcus equi (Magnusson 1923) Goodfellow and Alderson 1977 (Approved Lists 1980), the request to conserve the epithet equi in this name is denied. In Opinion 107, Thermomicrobium fosteri Phillips and Perry 1976 (Approved Lists 1980) is placed on the list of rejected names as a nomen dubium et confusum. Opinion 108 denies the request to place Hyphomonas rosenbergii Weiner et al. 2000 on the list of rejected names because the information provided to the Judicial Commission is not sufficient to draw a conclusion on this matter. In Opinion 109, which addresses three Requests for an Opinion, the Judicial Commission denies the requests to place the names Bacillus aerius Shivaji et al. 2006, Bacillus aerophilus Shivaji et al. 2006 and Bacillus stratosphericus Shivaji et al. 2006 on the list of rejected names. Instead, it is concluded that these three names had not met the requirements for valid publication. Likewise, the Judicial Commission concludes in Opinion 110 that the name Actinobaculum massiliense corrig. Greub and Raoult 2006 had not met the requirements for valid publication. The Judicial Commission reaffirms in Opinion 111 that Methanocorpusculum parvum Zellner et al. 1988 is the nomenclatural type of Methanocorpusculum Zellner et al. 1988 and further emphasizes that the species was not in danger of losing this status. These Opinions were ratified by the voting members of the International Committee on Systematics of Prokaryotes.

Combination of high-throughput microfluidics and FACS technologies to leverage the numbers game in natural product discovery

High-throughput platforms facilitating screening campaigns of environmental samples are needed to discover new products of natural origin counteracting the spreading of antimicrobial resistances constantly threatening human and agricultural health. We applied a combination of droplet microfluidics and fluorescence-activated cell sorting (FACS)-based technologies to access and assess a microbial environmental sample. The cultivation performance of our microfluidics workflow was evaluated in respect to the utilized cultivation media by Illumina amplicon sequencing of a pool of millions of droplets, respectively. This enabled the rational selection of a growth medium supporting the isolation of microbial diversity from soil (five phyla affiliated to 57 genera) including a member of the acidobacterial subgroup 1 (genus Edaphobacter). In a second phase, the entire diversity covered by 1071 cultures was used for an arrayed bioprospecting campaign, resulting in > 6000 extracts tested against human pathogens and agricultural pests. After redundancy curation by using a combinatorial chemical and genomic fingerprinting approach, we assigned the causative agents present in the extracts. Utilizing UHPLC-QTOF-MS/MS-guided fractionation and microplate-based screening assays in combination with molecular networking the production of bioactive ionophorous macrotetrolides, phospholipids, the cyclic lipopetides massetolides E, F, H and serratamolide A and many derivatives thereof was shown.

Novel Glycerophospholipid, Lipo- and N-acyl Amino Acids from Bacteroidetes: Isolation, Structure Elucidation and Bioactivity

The 'core' metabolome of the Bacteroidetes genus Chitinophaga was recently discovered to consist of only seven metabolites. A structural relationship in terms of shared lipid moieties among four of them was postulated. Here, structure elucidation and characterization via ultra-high resolution mass spectrometry (UHR-MS) and nuclear magnetic resonance (NMR) spectroscopy of those four lipids (two lipoamino acids (LAAs), two lysophosphatidylethanolamines (LPEs)), as well as several other undescribed LAAs and N-acyl amino acids (NAAAs), identified during isolation were carried out. The LAAs represent closely related analogs of the literature-known LAAs, such as the glycine-serine dipeptide lipids 430 (2) and 654. Most of the here characterized LAAs (1, 5-11) are members of a so far undescribed glycine-serine-ornithine tripeptide lipid family. Moreover, this study reports three novel NAAAs (N-(5-methyl)hexanoyl tyrosine (14) and N-(7-methyl)octanoyl tyrosine (15) or phenylalanine (16)) from Olivibacter sp. FHG000416, another Bacteroidetes strain initially selected as best in-house producer for isolation of lipid 430. Antimicrobial profiling revealed most isolated LAAs (1-3) and the two LPE 'core' metabolites (12, 13) active against the Gram-negative pathogen M. catarrhalis ATCC 25238 and the Gram-positive bacterium M. luteus DSM 20030. For LAA 1, additional growth inhibition activity against B. subtilis DSM 10 was observed.

Presence of the Weakly Pathogenic Fusarium poae in the Fusarium Head Blight Disease Complex Hampers Biocontrol and Chemical Control of the Virulent Fusarium graminearum Pathogen

Fusarium head blight (FHB) in wheat (Triticum aestivum L.) is caused by a consortium of mutually interacting Fusarium species. In the field, the weakly pathogenic F. poae often thrives on the infection sites of the virulent F. graminearum. In this ecological context, we investigated the efficacy of chemical and biocontrol agents against F. graminearum in wheat ears. For this purpose, one fungicide comprising prothioconazole + spiroxamine and two bacterial biocontrol strains, Streptomyces rimosus LMG 19352 and Rhodococcus sp. R-43120 were tested for their efficacy to reduce FHB symptoms and mycotoxin (deoxynivalenol, DON) production by F. graminearum in presence or absence of F. poae. Results showed that the fungicide and both actinobacterial strains reduced FHB symptoms and concomitant DON levels in wheat ears inoculated with F. graminearum. Where Streptomyces rimosus appeared to have direct antagonistic effects, Rhodococcus and the fungicide mediated suppression of F. graminearum was linked to the archetypal salicylic acid and jasmonic acid defense pathways that involve the activation of LOX1, LOX2 and ICS. Remarkably, this chemical- and biocontrol efficacy was significantly reduced when F. poae was co-inoculated with F. graminearum. This reduced efficacy was linked to a suppression of the plant's intrinsic defense system and increased levels of DON. In conclusion, our study shows that control strategies against the virulent F. graminearum in the disease complex causing FHB are hampered by the presence of the weakly pathogenic F. poae. This study provides generic insights in the complexity of control strategies against plant diseases caused by multiple pathogens.

Comparative Genomics of the Rhodococcus Genus Shows Wide Distribution of Biodegradation Traits

The genus Rhodococcus exhibits great potential for bioremediation applications due to its huge metabolic diversity, including biotransformation of aromatic and aliphatic compounds. Comparative genomic studies of this genus are limited to a small number of genomes, while the high number of sequenced strains to date could provide more information about the Rhodococcus diversity. Phylogenomic analysis of 327 Rhodococcus genomes and clustering of intergenomic distances identified 42 phylogenomic groups and 83 species-level clusters. Rarefaction models show that these numbers are likely to increase as new Rhodococcus strains are sequenced. The Rhodococcus genus possesses a small “hard” core genome consisting of 381 orthologous groups (OGs), while a “soft” core genome of 1253 OGs is reached with 99.16% of the genomes. Models of sequentially randomly added genomes show that a small number of genomes are enough to explain most of the shared diversity of the Rhodococcus strains, while the “open” pangenome and strain-specific genome evidence that the diversity of the genus will increase, as new genomes still add more OGs to the whole genomic set. Most rhodococci possess genes involved in the degradation of aliphatic and aromatic compounds, while short-chain alkane degradation is restricted to a certain number of groups, among which a specific particulate methane monooxygenase (pMMO) is only found in Rhodococcus sp. WAY2. The analysis of Rieske 2Fe-2S dioxygenases among rhodococci genomes revealed that most of these enzymes remain uncharacterized.

Rhodococcus oryzae sp. nov., a novel actinobacterium isolated from rhizosphere soil of rice (Oryza sativa L.)

A Gram-stain-positive, non-motile, creamy-white actinobacterium, which has an elementary branching rod-coccus life cycle was isolated from the rhizosphere soil of rice (Oryza sativa L.) collected from Northeast Agricultural University in Harbin, Heilongjiang province, north-east PR China, and its taxonomic status was examined by using a polyphasic approach. Results from the 16S rRNA gene sequence study showed that the isolate, designated strain NEAU-CX67^T, belonged to the genus Rhodococcus and formed a cluster with Rhodococcus maanshanensis DSM 44675^T, Rhodococcus kronopolitis NEAU-ML12^T and Rhodococcus tukisamuensis JCM 11308^T (98.3, 98.1 and 97.7% gene sequence similarity, respectively). The major fatty acids were C_16 : 0, 10-methyl C_18 : 0, C_18 : 1 ω9c and C_16 : 1 ω7c. The polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and phosphatidylinositol mannoside. The major isoprenoid quinone was MK-8(H₂). Whole-cell hydrolysates contained meso-diaminopimelic acid. Arabinose, galactose and ribose were detected as diagnostic sugars from whole-cell hydrolysates. Mycolic acids were detected. The genomic DNA G+C content of strain NEAU-CX67^T was 64.6 mol%. Strain NEAU-CX67^T exhibited low average nucleotide identity and digital DNA-DNA hybridization values with R. maanshanensis DSM 44675^T (92.1 and 45.4 %) and R. tukisamuensis JCM 11308^T (81.9 and 24.4 %). On the basis of results of phylogenetic, genotypic, physiological and chemotaxonomic analysis, strain NEAU-CX67^T is considered to represent a novel species of the genus Rhodococcus for which the name Rhodococcus oryzae sp. nov. is proposed. The type strain is NEAU-CX67^T (=DSM 107701^T=CCTCC AB 2018233^T).

Conservation of Rhodococcus equi (Magnusson 1923) Goodfellow and Alderson 1977 and rejection of Rhodococcus hoagii (Morse 1912) Kämpfer et al. 2014

A recent taxonomic study confirmed the synonymy of Rhodococcus equi (Magnusson 1923) Goodfellow and Alderson 1977 and Corynebacterium hoagii (Morse 1912) Eberson 1918. As a result, both R. equi and C. hoagii were reclassified as Rhodococcus hoagii comb. nov. in application of the principle of priority of the Prokaryotic Code. Because R. equi is a well-known animal and zoonotic human pathogen, and a bacterial name solidly established in the veterinary and medical literature, we and others argued that the nomenclatural change may cause error and confusion and be potentially perilous. We have now additionally found that the nomenclatural type of the basonym C. hoagii, ATCC 7005T, does not correspond with the original description of the species C. hoagii in the early literature. Its inclusion as the C. hoagii type on the Approved Lists 1980 results in a change in the characters of the taxon and in C. hoagii designating two different bacteria. Moreover, ATCC 7005, the only strain in circulation under the name C. hoagii, does not have a well documented history; it is unclear why it was deposited as C. hoagii and a possible mix-up with a Corynebacterium (Rhodococcus) equi isolate is a reasonable assumption. We therefore request the rejection of Rhodococcus hoagii as a nomen ambiguum, nomen dubium and nomen perplexum in addition to nomen periculosum, and conservation of the name Rhodococcus equi, according to Rules 56ab of the Code.

Analysis of the biodegradative and adaptive potential of the novel polychlorinated biphenyl degrader Rhodococcus sp. WAY2 revealed by its complete genome sequence

The complete genome sequence of Rhodococcus sp. WAY2 (WAY2) consists of a circular chromosome, three linear replicons and a small circular plasmid. The linear replicons contain typical actinobacterial invertron-type telomeres with the central CGTXCGC motif. Comparative phylogenetic analysis of the 16S rRNA gene along with phylogenomic analysis based on the genome-to-genome blast distance phylogeny (GBDP) algorithm and digital DNA–DNA hybridization (dDDH) with other Rhodococcus type strains resulted in a clear differentiation of WAY2, which is likely a new species. The genome of WAY2 contains five distinct clusters of bph, etb and nah genes, putatively involved in the degradation of several aromatic compounds. These clusters are distributed throughout the linear plasmids. The high sequence homology of the ring-hydroxylating subunits of these systems with other known enzymes has allowed us to model the range of aromatic substrates they could degrade. Further functional characterization revealed that WAY2 was able to grow with biphenyl, naphthalene and xylene as sole carbon and energy sources, and could oxidize multiple aromatic compounds, including ethylbenzene, phenanthrene, dibenzofuran and toluene. In addition, WAY2 was able to co-metabolize 23 polychlorinated biphenyl congeners, consistent with the five different ring-hydroxylating systems encoded by its genome. WAY2 could also use n-alkanes of various chain-lengths as a sole carbon source, probably due to the presence of alkB and ladA gene copies, which are only found in its chromosome. These results show that WAY2 has a potential to be used for the biodegradation of multiple organic compounds.

Rhodococcus hoagii bloodstream infection in an allogeneic hematopoietic stem cell transplantation patient: Case report and review of literature

We report a case of bloodstream infection caused by R. hoagii in a woman with acute myeloid leukemia, 37-years-old, who received an allogeneic hematopoietic stem cell transplant. She developed cutaneous and gastrointestinal tract graft versus host disease, respectively on day 29 and day 69. On day 157 she developed to acute severe respiratory failure. Rhodococcus sp was identified by MALDI-TOF and 16S rRNA sequencing from blood culture as Rhodococcus hoagii. The patient was a nurse that lived in urban areas, and stated no recent trips to countryside areas neither contacted with animals. Despite of the treatment with antibiotics with action against R. hoagii such as linezolid and meropenem the patient evolved to multiorgan dysfunction and death. Our case-report emphasizes the importance of early diagnosis and the use of 16S rRNA sequencing to confirmed the identification of species of Rhodococcus infection.

Rhodococcus subtropicus sp. nov., a new actinobacterium isolated from a cave

A novel Gram-stain-positive actinobacterial strain, designated C9-28^T, was isolated from soil sampled in a natural cave on Jeju Island, Republic of Korea. Strain C9-28^T morphologically exhibited a rod-coccus life cycle and grew at 10-37 °C (optimum, 30 °C), pH 6-9 (optimum, pH 7) and 0-3 % (optimum, absence of NaCl). In the maximum-likelihood tree based on 16S rRNA gene sequences, strain C9-28^T formed a sublineage between a Rhodococcus equi-Rhodococcus soli-Rhodococcus agglutinans clade and the type strain of Rhodococcus defluvii. The closest relatives of strain C9-28^T were the type strains of R. defluvii (98.88 % 16S rRNA gene sequence similarity), R. equi (98.88 %) and R. soli (98.60 %). The phylogenomic tree based on whole genome sequences supported the distinct position of the novel strain within the genus Rhodococcus. The following chemotaxonomic characteristics also supported the assignment to the genus: meso-diaminopimelic acid; arabinose and galactose in whole-cell hydrolysates; the predominant menaquinone of MK-8(H₂); and polar lipids including diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol, phosphatidylinositol mannoside, three unidentified glycolipids and two unidentified lipids. The predominant cellular fatty acids were C_16 : 0, summed feature 3 (C_16 : 1ω7c and/or C_16 : 1ω6c), C_18 : 1ω9c and C_14 : 0. Based on the values of average nucleotide identity and digital DNA-DNA hybridization from whole genome sequences, and in vitro DNA-DNA hybridization between the isolate and the closest relatives, strain C9-28^T (=KACC 19823^T=DSM 107559^T) represents a novel species of the genus Rhodococcus, for which the name Rhodococcussubtropicus sp. nov. is proposed.

Genomic analysis of a novel Rhodococcus (Prescottella) equi isolate from a bovine host

Rhodococcus (Prescottella) equi causes pneumonia-like infections in foals with high mortality rates and can also infect a number of other animals. R. equi is also emerging as an opportunistic human pathogen. In this study, we have sequenced the genome of a novel R. equi isolate, B0269, isolated from the faeces of a bovine host. Comparative genomic analyses with seven other published R. equi genomes, including those from equine or human sources, revealed a pangenome comprising of 6876 genes with 4141 genes in the core genome. Two hundred and 75 genes were specific to the bovine isolate, mostly encoding hypothetical proteins of unknown function. However, these genes include four copies of terA and five copies of terD genes that may be involved in responding to chemical stress. Virulence characteristics in R. equi are associated with the presence of large plasmids carrying a pathogenicity island, including genes from the vap multigene family. A BLAST search of the protein sequences from known virulence-associated plasmids (pVAPA, pVAPB and pVAPN) revealed a similar plasmid backbone on two contigs in bovine isolate B0269; however, no homologues of the main virulence-associated genes, vapA, vapB or vapN, were identified. In summary, this study confirms that R. equi genomes are highly conserved and reports the presence of an apparently novel plasmid in the bovine isolate B0269 that needs further characterisation to understand its potential involvement in virulence properties.

The pathogenic actinobacterium Rhodococcus equi: what's in a name?

Rhodococcus equi is the only recognized animal pathogenic species within an extended genus of metabolically versatile Actinobacteria of considerable biotechnological interest. Best known as a horse pathogen, R. equi is commonly isolated from other animal species, particularly pigs and ruminants, and causes severe opportunistic infections in people. As typical in the rhodococci, R. equi niche specialization is extrachromosomally determined, via a conjugative virulence plasmid that promotes intramacrophage survival. Progress in the molecular understanding of R. equi and its recent rise as a novel paradigm of multihost adaptation has been accompanied by an unusual nomenclatural instability, with a confusing succession of names: "Prescottia equi", "Prescotella equi", Corynebacterium hoagii and Rhodococcus hoagii. This article reviews current advances in the genomics, biology and virulence of this pathogenic actinobacterium with a unique mechanism of plasmid-transferable animal host tropism. It also discusses the taxonomic and nomenclatural issues around R. equi in the light of recent phylogenomic evidence that confirms its membership as a bona fide Rhodococcus.

Advanced Rhodococcus Biocatalysts for Environmental Biotechnologies

The review is devoted to biocatalysts based on actinobacteria of the genus Rhodococcus, which are promising for environmental biotechnologies. In the review, biotechnological advantages of Rhodococcus bacteria are evaluated, approaches used to develop robust and efficient biocatalysts are discussed, and their relevant applications are given. We focus on Rhodococcus cell immobilization in detail (methods of immobilization, criteria for strains and carriers, and optimization of process parameters) as the most efficient approach for stabilizing biocatalysts. It is shown that advanced Rhodococcus biocatalysts with improved working characteristics, enhanced stress tolerance, high catalytic activities, human and environment friendly, and commercially viable are developed, which are suitable for wastewater treatment, bioremediation, and biofuel production.

Molecular analysis of the chromosomal 16S rRNA gene and vapA plasmid gene of Polish field strains of R. equi

Rhodococcus equi (R. hoagii) is an opportunistic pathogen commonly found in foals up to 6 months old and animal environment. The R. equi genome contains genetically stable chromosomal DNA and an 80–90 kb plasmid containing vapA gene, responsible for virulence. Most reports from around the world focus on the determination of R. equi plasmid profiles. Few studies have attempted to determine differences in nucleotide sequences between virulent strains of R. equi isolated from foals and breeding environment. The aim of the study was to perform a molecular analysis of a fragment of the chromosomal gene encoding the 16S rRNA subunit and the vapA plasmid gene of virulent R. equi strains isolated on Polish studs from foals and from the breeding environment of horses. The sequencing method was used to compare the primary structure of fragments of the chromosomal and plasmid DNA of the virulent R. equi strains. The sequences of 22 clinical and 18 environmental R. equi isolates were compared with the sequences of the gene fragments of reference strains available in the NCBI GenBank database. All sequenced 16S rRNA amplicons of Polish field strains were identical and showed 99.5% similarity to the four randomly selected sequences of this gene fragment in the GenBank database. The results confirm that fragments of the 16S rRNA gene of R. equi strains are highly conserved and do not undergo variation in field conditions. Analysis of the sequencing results for the vapA gene fragment of the strains used in our study revealed two polymorphic variants and clear differences between the sequences of strains isolated from foals and from soil samples. Presumably, R. equi strains present in the breeding environment are more exposed than clinical strains to adverse external factors. This may result in changes in the DNA sequence due to natural selection.

Current taxonomy of Rhodococcus species and their role in infections

Rhodococcus is a genus of obligate aerobic, Gram-positive, partially acid-fast, catalase-positive, non-motile, and none-endospore bacteria. The genus Rhodococcus was first introduced by Zopf. This bacterium can be isolated from various sources of the environment and can grow well in non-selective medium. A large number of phenotypic characterizations are used to compare different species of the genus Rhodococcus, and these tests are not suitable for accurate identification at the genus and species level. Among nucleic acid-based methods, the most powerful target gene for revealing reliable phylogenetic relationships is 16S ribosomal RNA gene (16S rRNA gene) sequence analysis, but this gene is unable to differentiation some of Rhodococcus species. To date, whole genome sequencing analysis has solved taxonomic complexities in this genus. Rhodococcus equi is the major cause of foal pneumonia, and its implication in human health is related to cases in immunocompromised patients. Macrolide family together with rifampicin is one of the most effective antibiotic agents for treatment rhodococcal infections.

Genome-Based Taxonomic Classification of the Phylum Actinobacteria

The application of phylogenetic taxonomic procedures led to improvements in the classification of bacteria assigned to the phylum Actinobacteria but even so there remains a need to further clarify relationships within a taxon that encompasses organisms of agricultural, biotechnological, clinical, and ecological importance. Classification of the morphologically diverse bacteria belonging to this large phylum based on a limited number of features has proved to be difficult, not least when taxonomic decisions rested heavily on interpretation of poorly resolved 16S rRNA gene trees. Here, draft genome sequences of a large collection of actinobacterial type strains were used to infer phylogenetic trees from genome-scale data using principles drawn from phylogenetic systematics. The majority of taxa were found to be monophyletic but several orders, families, and genera, as well as many species and a few subspecies were shown to be in need of revision leading to proposals for the recognition of 2 orders, 10 families, and 17 genera, as well as the transfer of over 100 species to other genera. In addition, emended descriptions are given for many species mainly involving the addition of data on genome size and DNA G+C content, the former can be considered to be a valuable taxonomic marker in actinobacterial systematics. Many of the incongruities detected when the results of the present study were compared with existing classifications had been recognized from 16S rRNA gene trees though whole-genome phylogenies proved to be much better resolved. The few significant incongruities found between 16S/23S rRNA and whole genome trees underline the pitfalls inherent in phylogenies based upon single gene sequences. Similarly good congruence was found between the discontinuous distribution of phenotypic properties and taxa delineated in the phylogenetic trees though diverse non-monophyletic taxa appeared to be based on the use of plesiomorphic character states as diagnostic features.

Nocardiosis from 1888 to 2017

The genus Nocardia is an aerobic bacterium, Gram-positive and catalase positive that is in Nocardiaceae family. This bacterium first described by Edmond Nocard in 1888 and is not in human commensal bacteria. To date, nocardiosis incidence is increasing due to increase population growth rate, increase in patients with immune disorder diseases and immunocompromised patients. We surveyed taxonomic position, isolation methods, phenotypic and molecular identification at the genus and species levels, antibiogram, treatment and epidemiology in the world from 1888 to 2017.

Next-generation systematics: An innovative approach to resolve the structure of complex prokaryotic taxa

Prokaryotic systematics provides the fundamental framework for microbiological research but remains a discipline that relies on a labour- and time-intensive polyphasic taxonomic approach, including DNA-DNA hybridization, variation in 16S rRNA gene sequence and phenotypic characteristics. These techniques suffer from poor resolution in distinguishing between closely related species and often result in misclassification and misidentification of strains. Moreover, guidelines are unclear for the delineation of bacterial genera. Here, we have applied an innovative phylogenetic and taxogenomic approach to a heterogeneous actinobacterial taxon, Rhodococcus, to identify boundaries for intrageneric and supraspecific classification. Seven species-groups were identified within the genus Rhodococcus that are as distantly related to one another as they are to representatives of other mycolic acid containing actinobacteria and can thus be equated with the rank of genus. It was also evident that strains assigned to rhodococcal species-groups are underspeciated with many misclassified using conventional taxonomic criteria. The phylogenetic and taxogenomic methods used in this study provide data of theoretical value for the circumscription of generic and species boundaries and are also of practical significance as they provide a robust basis for the classification and identification of rhodococci of agricultural, industrial and medical/veterinary significance.

Pangenome and Phylogenomic Analysis of the Pathogenic Actinobacterium Rhodococcus equi

We report a comparative study of 29 representative genomes of the animal pathogen Rhodococcus equi The analyses showed that R. equi is genetically homogeneous and clonal, with a large core genome accounting for ≈80% of an isolates' gene content. An open pangenome, even distribution of accessory genes among the isolates, and absence of significant core-genome recombination, indicated that gene gain/loss is a main driver of R. equi genome evolution. Traits previously predicted to be important in R. equi physiology, virulence and niche adaptation were part of the core genome. This included the lack of a phosphoenolpyruvate:carbohydrate transport system (PTS), unique among the rhodococci except for the closely related Rhodococcus defluvii, reflecting selective PTS gene loss in the R. equi-R. defluvii sublineage. Thought to be asaccharolytic, rbsCB and glcP non-PTS sugar permease homologues were identified in the core genome and, albeit inefficiently, R. equi utilized their putative substrates, ribose and (irregularly) glucose. There was no correlation between R. equi whole-genome phylogeny and host or geographical source, with evidence of global spread of genomovars. The distribution of host-associated virulence plasmid types was consistent with the exchange of the plasmids (and corresponding host shifts) across the R. equi population, and human infection being zoonotically acquired. Phylogenomic analyses demonstrated that R. equi occupies a central position in the Rhodococcus phylogeny, not supporting the recently proposed transfer of the species to a new genus.

Rhodococcus antrifimi sp. nov., isolated from dried bat dung of a cave

A Gram-reaction-positive, high DNA G+C content, non-motile actinobacterium, strain D7-21T, was isolated from dried bat dung inside a natural cave and its taxonomic status was examined by using a polyphasic approach. The 16S rRNA gene sequence study showed that the isolate belonged to the genus Rhodococcus and formed a cluster with Rhodococcus defluvii (98.98 % gene similarity), Rhodococcus equi (98.62 %) and Rhodococcus kunmingensis (97.66 %). Whole-cell hydrolysates contained meso-diaminopimelic acid, arabinose and galactose as the diagnostic diamino acid and sugars. MK-8(H2) was the predominant menaquinone. The major polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol, phosphatidylinositol mannoside, an unknown phosphoglycolipid and an unknown glycolipid. Mycolic acids were present. The major fatty acids were C16 : 0, C18 : 1ω9c and 10-methyl C18 : 0. The DNA G+C content was 70.1 mol%. A battery of phenotypic features and DNA–DNA relatedness data support that strain D7-21T ( = KCTC 29469T = DSM 46727T) represents a novel species of the genus Rhodococcus, for which Rhodococcus antrifimi sp. nov. is proposed.

Classification of strain CCM 4446T as Rhodococcus degradans sp. nov

Strain CCM 4446T, with notable biodegradation capabilities, was investigated in this study in order to elucidate its taxonomic position. Chemotaxonomic analyses of quinones, polar lipids, mycolic acids, polyamines and the diamino acid of the cell-wall peptidoglycan corresponded with characteristics of the genus Rhodococcus. Phylogenetic analysis, based on the 16S rRNA gene sequence, assigned strain CCM 4446T to the genus Rhodococcus and placed it in the Rhodococcus erythropolis 16S rRNA gene clade. Further analysis of catA and gyrB gene sequences, automated ribotyping with EcoRI restriction endonuclease, whole-cell protein profiling, DNA-DNA hybridization and extensive biotyping enabled differentiation of strain CCM 4446T from all phylogenetically closely related species, i.e., Rhodococcus baikonurensis, Rhodococcus qingshengii, Rhodococcus erythropolis and Rhodococcus globerulus. The results obtained show that the strain investigated represents a novel species within the genus Rhodococcus, for which the name Rhodococcus degradans sp. nov., is proposed. The type strain is CCM 4446T ( = LMG 28633T).

Rhodococcus lactis sp. nov., an actinobacterium isolated from sludge of a dairy waste treatment plant

A Gram-stain-positive, non-motile and aerobic bacterium, designated strain DW151BT, was isolated from a sludge sample of a dairy industry effluent treatment plant. 16S rRNA gene sequence analysis of strain DW151BT placed it within the genus Rhodococcus. It displayed significant similarity with recognized species of the genus: Rhodococcus pyridinivorans PDB9T (98.8 %), Rhodococcus gordoniae W 4937T (98.6 %), Rhodococcus rhodochrous DSM 43241T (98.5 %) and Rhodococcus artemisiae YIM 65754T (97.5 %). However, strain DW151BT differed from phylogenetically closely related species in various phenotypic properties. The cellular polar lipid profile consisted of diphosphatidylglycerol (DPG), phosphatidylethanolamine (PE) and phosphatidylinositol (PI) as major lipids, MK-8(H2) was the major menaquinone and meso-diaminopimelic acid was the cell-wall peptidoglycan. The fatty acid profile consisted of C16 : 0, C18 : 1cis9 and C16 : 1cis9 as main components. The presence of C16 : 0 and diphosphatidylglycerol as major fatty acid and polar lipid, respectively, was in accordance with chemotaxonomic markers of the genus Rhodococcus. The DNA G+C content of strain DW151BT was 69.9 mol%, a value within the limits reported for the members of this genus. Furthermore, strain DW151BT showed low similarity at the whole genome level in DNA-DNA hybridization experiments with phylogenetically closely related strains. Considering the low similarity at the genome level and differences in phenotypic properties, strain DW151BT is considered to represent a novel species of the genus Rhodococcus, for which the name Rhodococcus lactis sp. nov. is proposed. The type strain is DW151BT ( = MTCC 12279T = DSM 45625T).

Rhodococcus soli sp. nov., an actinobacterium isolated from soil using a resuscitative technique

A Gram-positive, aerobic, non-motile, non-spore forming strain, designated DSD51W(T), was isolated using a resuscitative technique from a soil sample collected from Kyoto park, Japan, and characterized by using a polyphasic approach. The morphological and chemotaxonomic properties of the isolate were typical of those of members of the genus Rhodococcus. Strain DSD51W(T) was found to form a coherent cluster with Rhodococcus hoagii ATCC 7005(T), Rhodococcus equi NBRC 101255(T), Rhodococcus defluvii Call(T) and Rhodococcus kunmingensis YIM 45607(T) as its closest phylogenetic neighbours in 16S rRNA gene sequence analysis. However, the DNA-DNA hybridization values with the above strains were 58.2 ± 2.2, 58.4 ± 1.9, 45.1 ± 1.4 and 40.3 ± 4.7 %, respectively. In combination with differences in physiological and biochemical properties, strain DSD51W(T) can be concluded to represent a novel species of the genus Rhodococcus, for which the name Rhodococcus soli sp. nov. is proposed, with the type strain DSD51W(T) (=KCTC 29259(T) = JCM 19627(T) = DSM 46662(T) = KACC 17838(T)).

Genomic analyses confirm close relatedness between Rhodococcus defluvii and Rhodococcus equi (Rhodococcus hoagii)

Rhodococcus defluvii strain Ca11(T) was isolated from a bioreactor involved in extensive phosphorus removal. We have sequenced the whole genome of this strain, and our comparative genomic and phylogenetic analyses confirm its close relatedness with Rhodococcus equi (Rhodococcus hoagii) strains, which share >80 % of the gene content. The R. equi virulence plasmid is absent though most of the chromosomal R. equi virulence-associated genes are present in R. defluvii Ca11(T). These data suggest that although R. defluvii is an environmental organism, it has the potential to colonize animal hosts.

Rhodococcus aerolatus sp. nov., isolated from subarctic rainwater

A Gram-stain-positive, rod-shaped and non-motile strain, designated PAMC 27367(T), was isolated from rainwater collected on the Bering Sea. Analysis of the 16S rRNA gene sequence of the strain showed an affiliation with the genus Rhodococcus. Phylogenetic analyses revealed that strain PAMC 27367(T) formed a robust clade with the type strains of Rhodococcus rhodnii, Rhodococcus aetherivorans and Rhodococcus ruber with 16S rRNA gene sequence similarities of 96.3 %, 95.8 % and 95.5 %, respectively. Cells of the strain grew optimally at 25 °C and at pH 6.5-7.0 in the presence of 0-2 % (w/v) sea salts. The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylinositol mannoside and three unknown phospholipids. The major cellular fatty acids (>10 %) were iso-C16 : 0, C17 : 1ω8c and 10-methyl C17 : 0. Cell wall analysis showed that strain PAMC 27367(T) contained meso-diaminopimelic acid. The genomic DNA G+C content was 77.1 mol%. Based on the phylogenetic, chemotaxonomic and phenotypic data presented here, we propose a novel species with the name Rhodococcus aerolatus sp. nov., with PAMC 27367(T) ( = KCTC 29240(T) = JCM 19485(T)) as the type strain.