Rhodococcus kroppenstedtii sp. nov., a novel actinobacterium isolated from a cold desert of the Himalayas, India

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.

Actinobacteria From Desert: Diversity and Biotechnological Applications

Deserts, as an unexplored extreme ecosystem, are known to harbor diverse actinobacteria with biotechnological potential. Both multidrug-resistant (MDR) pathogens and environmental issues have sharply raised the emerging demand for functional actinobacteria. From 2000 to 2021, 129 new species have been continuously reported from 35 deserts worldwide. The two largest numbers are of the members of the genera Streptomyces and Geodermatophilus, followed by other functional extremophilic strains such as alkaliphiles, halotolerant species, thermophiles, and psychrotolerant species. Improved isolation strategies for the recovery of culturable and unculturable desert actinobacteria are crucial for the exploration of their diversity and offer a better understanding of their survival mechanisms under extreme environmental stresses. The main bioprospecting processes involve isolation of target actinobacteria on selective media and incubation and selection of representatives from isolation plates for further investigations. Bioactive compounds obtained from desert actinobacteria are being continuously explored for their biotechnological potential, especially in medicine. To date, there are more than 50 novel compounds discovered from these gifted actinobacteria with potential antimicrobial activities, including anti-MDR pathogens and anti-inflammatory, antivirus, antifungal, antiallergic, antibacterial, antitumor, and cytotoxic activities. A range of plant growth-promoting abilities of the desert actinobacteria inspired great interest in their agricultural potential. In addition, several degradative, oxidative, and other functional enzymes from desert strains can be applied in the industry and the environment. This review aims to provide a comprehensive overview of desert environments as a remarkable source of diverse actinobacteria while such rich diversity offers an underexplored resource for biotechnological exploitations.

A case of peritoneal dialysis-associated peritonitis caused by Rhodococcus kroppenstedtii

BACKGROUND

Rhodococcus kroppenstedtii is an aerobic, gram-positive bacterium firstly identified in the environment, which has not been reported in human-related infection. Herein, we reported the first case of peritoneal dialysis (PD)-associated peritonitis caused by R. kroppenstedtii which was identified by whole genome sequencing.

CASE PRESENTATION

A 69-year-old man was admitted to hospital with abdominal pain and fever. Over the last 2 years, he had been undergoing continuous ambulatory peritoneal dialysis (CAPD) due to end-stage renal disease. Clinical symptom and sign in combination with laboratory examinations supported the clinical diagnosis of PD-associated peritonitis. Thus, ceftizoxime and teicoplanin were empirically used after PD effluent was collected for bacterial culture. A gram-positive bacterium was found from the PD effluent culture, which could not be identified by either Vitek 2 Compact ANC card or matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The strain was finally confirmed to be R. kroppenstedtii by whole genome sequencing (WGS) through the average nucleotide identity (ANI) analysis. With a continuous treatment with teicoplanin and imipenem for 15 days and intraperitoneal catheter removed, the infection symptom was improved evidenced by a normal body temperature, also with white blood cell count (WBC), procalcitonin (PCT) and C-reactive protein (CRP) dropped to normal levels. Peritoneal dialysis effluent culture showed a negative result. Then, hemodialysis and arteriovenous fistula angioplasty were performed, but the patient developed a progressive blood pressure loss, accompanied by multiple organ disorder, and died on Feb 25, 2020.

CONCLUSIONS

To the best of our knowledge, this is the first time to report a peritoneal dialysis-associated peritonitis caused by R. kroppenstedtii which was identified by average nucleotide identity analysis based on WGS.

Complete Genome Sequence of Rhodococcus qingshengii Strain CL-05, Isolated from Concrete

Here, we report the complete genome sequence of Rhodococcus qingshengii strain CL-05, which was isolated from pavement concrete in Newark, Delaware. The genome consists of a 6.29-Mbp chromosome and one plasmid (123,183 bp), encodes a total of 5,859 predicted proteins, and has a GC content of 62.5%.

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.

Rhizospheric Bacterial Community of Endemic Rhododendron arboreum Sm. Ssp. delavayi along Eastern Himalayan Slope in Tawang

Information on rhizosphere microbiome of endemic plants from high mountain ecosystems against those of cultivated plantations is inadequate. Comparative bacterial profiles of endemic medicinal plant Rhododendron arboreum Sm. subsp. delavayi rhizosphere pertaining to four altitudinal zonation Pankang Thang (PTSO), Nagula, Y-junction and Bum La (Indo-China border; in triplicates each) along cold adapted Eastern slope of Himalayan Tawang region, India is described here. Significant differences in DGGE profile between below ground bulk vs. rhizospheric community profile associated with the plant was identified. Tagged 16S amplicon sequencing from PTSO (3912 m) to Bum La (4509 m), revealed that soil pH, total nitrogen (TN), organic matter (OM) significantly influenced the underlying bacterial community structure at different altitudes. The relative abundance of Acidobacteria was inversely related to pH, as opposed to TN which was positively correlated to Acidobacteria and Proteobacteria abundance. TN was also the significant predictor for less abundant taxonomic groups Chloroflexi, Gemmatimonadetes, and Nitrospirae. Bum La soil harbored less bacterial diversity compared to other sites at lower altitudes. The most abundant phyla at 3% genetic difference were Acidobacteria, Actinobacteria, and Proteobacteria amongst others. Analysis of similarity indicated greater similarity within lower altitudinal than higher altitudinal group (ANOSIM, R = 0.287, p = 0.02). Constraining the ordination with the edaphic factor explained 83.13% of variation. Unique phylotypes of Bradyrhizobium and uncultured Rhizobiales were found in significant proportions at the four regions. With over 1% relative abundance Actinobacteria (42.6%), Acidobacteria (24.02%), Proteobacteria (16.00%), AD3 (9.23%), WPS-2 (5.1%), and Chloroflexi (1.48%) dominated the core microbiome.

Rhodococcus enclensis sp. nov., a novel member of the genus Rhodococcus

A novel actinobacterial strain, designated, NIO-1009(T), was isolated from a marine sediment sample collected from Chorao Island, Goa, India. Phylogenetic analysis comparisons based on 16S rRNA gene sequences between strain NIO-1009(T) and other members of the genus Rhodococcus revealed that strain NIO-1009(T) had the closest sequence similarity to Rhodococcus kroppenstedtii DSM 44908(T) and Rhodococcus corynebacterioides DSM 20151(T) with 99.2 and 99.1%, respectively. Furthermore, DNA-DNA hybridization results showed that R. kroppenstedtii DSM 44908(T) and R. corynebacterioides DSM 20151(T) were 39.5 (3.0%) and 41.7 (2.0%) with strain NIO-1009(T), respectively, which were well below the 70% limit for any novel species proposal. Phylogenetically strain NIO-1009(T) forms a stable clade with and R. kroppenstedtii DSM 44908(T) and R. corynebacterioides DSM 20151(T) with 100% bootstrap values. Strain NIO-1009(T) contained meso-diaminopimelic acid as the diagnostic diamino acid and galactose and arabinose as the cell wall sugars. The major fatty acids were C(16 : 0), C(18 : 1)ω9c, C(16 : 1)(ω6c and/or ω7c) and 10-methyl C(18 : 0). The only menaquinone detected was MK-8(H2), while the major polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol, phosphatidylinositol mannoside and one unknown phospholipid. The G+C content of the genomic DNA was 66.9 mol%. The phenotypic and genotypic data showed that strain NIO-1009(T) warrants recognition as a novel species of the genus Rhodococcus for which the name Rhodococcus enclensis sp. nov., is proposed; the type strain is NIO-1009(T) ( = NCIM 5452(T) = DSM 45688(T)).

Paenisporosarcina indica sp. nov., a psychrophilic bacterium from a glacier, and reclassification of Sporosarcina antarctica Yu et al., 2008 as Paenisporosarcina antarctica comb. nov. and emended description of the genus Paenisporosarcina

A Gram-stain-positive, aerobic, spore-forming, rod-shaped bacterium, PN2T, was isolated from a soil sample collected near the Pindari glacier. It contained anteiso-C15 : 0, iso-C15 : 0 and C16 : 1ω7c alcohol as the predominant fatty acids, MK-7 as the major menaquinone and A4α type (l-Lys–d-Glu) peptidoglycan. Based on these characteristics, strain PN2T was assigned to the genus Paenisporosarcina . Phylogenetic analysis based on 16S rRNA gene sequence placed strain PN2T within the genus Paenisporosarcina and showed a sequence similarity of 98.5–99.0 % with members of this genus. Paenisporosarcina macmurdoensis CMS 21wT, Paenisporosarcina quisquiliarum SK 55T and Sporosarcina antarctica N-05T were identified as the most closely related species with 16S rRNA gene sequence similarities of 98.6 %, 99.0 % and 98.4 %, respectively. The values for DNA–DNA relatedness between strain PN2T and P. macmurdoensis , P. quisquiliarum and S. antarctica were below the 70 % threshold value (32.0 %, 42.0 % and 38.0 % respectively). In addition, strain PN2T exhibited a number of phenotypic differences from P. macmurdoensis , P. quisquiliarum and S. antarctica . Based on the cumulative differences, strain PN2T was identified as representing a novel species and the name Paenisporosarcina indica sp. nov. was proposed. The type strain of Paenisporosarcina indica sp. nov. is PN2T (LMG 23933T = JCM 15114T). Furthermore, based on the morphological and chemotaxonomic characteristics, the species Sporosarcina antarctica was reclassified as a species of the genus Paenisporosarcina and renamed Paenisporosarcina antarctica comb. nov. In addition, an emended description of the genus Paenisporosarcina is presented.

Rhodococcus nanhaiensis sp. nov., an actinobacterium isolated from marine sediment

In this study, two strains (SCSIO 10187(T) and SCSIO 10197) were isolated from a sediment sample collected from the South China Sea and characterized by using a polyphasic approach. Growth was observed at 15-35 °C (optimum 28 °C) and pH 5.0-8.0 (optimum pH 6.0). Based on 16S rRNA gene sequence analysis, the strains were identified as members of the genus Rhodococcus. Phylogenetic analysis showed that the two strains clustered together and the 16S rRNA gene sequence similarities between them and other members of the genus Rhodococcus were 93.2-97.7 %. The menaquinone type was MK-8(H(2)). Major cellular fatty acids were C(16 : 0), C(18 : 1)ω9c, C(17 : 0), 10-methyl C(18 : 0), C(18 : 0), C(19 : 0) and C(17 : 1)ω8c. The polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and phosphatidylinositol mannoside. The DNA G+C contents of strains SCSIO 10187(T) and SCSIO 10197 were 63.7 and 63.2 mol%, respectively. The combined genotypic and phenotypic data showed that the two strains represent a novel species of the genus Rhodococcus, for which the name Rhodococcus nanhaiensis is proposed; the type strain is SCSIO 10187(T) ( = DSM 45608(T) = CCTCC AB 2011024(T)), with SCSIO 10197 ( = DSM 45609 = CCTCC AB 2011025) as a reference strain.

Rhodococcus artemisiae sp. nov., an endophytic actinobacterium isolated from the pharmaceutical plant Artemisia annua L

A Gram-positive, non-motile actinobacterium, designated YIM 65754T, was isolated from the stem of Artemisia annua L., collected from Yunnan province, south-west China. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain YIM 65754T comprised an evolutionary lineage within the genus Rhodococcus. The isolate clustered with Rhodococcus pyridinivorans PDB9T, Rhodococcus gordoniae W 4937T and Rhodococcus rhodochrous DSM 43241T, with which it shared 98.4, 97.9 and 97.8 % 16S rRNA gene sequence similarities, respectively. However, DNA-DNA relatedness demonstrated that strain YIM 65754T was distinct from its closest phylogenetic neighbours. The cell-wall peptidoglycan contained meso-diaminopimelic acid, arabinose, galactose, mannose and glucose (cell-wall chemotype IV). The major menaquinone was MK-8(H2) and the predominant fatty acids were C16:0 (27.83 %), iso-C15:0 2-OH and/or C16:1ω7c (20.21 %) and 10-methyl C18:0 (17.50 %). The DNA G+C content was 66.2 mol%. On the basis of phenotypic, chemotaxonomic and phylogenetic evidence, the isolate represents a novel species of the genus Rhodococcus, for which the name Rhodococcus artemisiae sp. nov. is proposed; the type strain is YIM 65754T (=CCTCC AA 209042T=DSM 45380T).

The genome of a pathogenic rhodococcus: cooptive virulence underpinned by key gene acquisitions

We report the genome of the facultative intracellular parasite Rhodococcus equi, the only animal pathogen within the biotechnologically important actinobacterial genus Rhodococcus. The 5.0-Mb R. equi 103S genome is significantly smaller than those of environmental rhodococci. This is due to genome expansion in nonpathogenic species, via a linear gain of paralogous genes and an accelerated genetic flux, rather than reductive evolution in R. equi. The 103S genome lacks the extensive catabolic and secondary metabolic complement of environmental rhodococci, and it displays unique adaptations for host colonization and competition in the short-chain fatty acid–rich intestine and manure of herbivores—two main R. equi reservoirs. Except for a few horizontally acquired (HGT) pathogenicity loci, including a cytoadhesive pilus determinant (rpl) and the virulence plasmid vap pathogenicity island (PAI) required for intramacrophage survival, most of the potential virulence-associated genes identified in R. equi are conserved in environmental rhodococci or have homologs in nonpathogenic Actinobacteria. This suggests a mechanism of virulence evolution based on the cooption of existing core actinobacterial traits, triggered by key host niche–adaptive HGT events. We tested this hypothesis by investigating R. equi virulence plasmid-chromosome crosstalk, by global transcription profiling and expression network analysis. Two chromosomal genes conserved in environmental rhodococci, encoding putative chorismate mutase and anthranilate synthase enzymes involved in aromatic amino acid biosynthesis, were strongly coregulated with vap PAI virulence genes and required for optimal proliferation in macrophages. The regulatory integration of chromosomal metabolic genes under the control of the HGT–acquired plasmid PAI is thus an important element in the cooptive virulence of R. equi.

Rhodococcus is a prototypic genus within the Actinobacteria, one of the largest microbial groups on Earth. Many of the ubiquitous rhodococcal species are biotechnologically useful due to their metabolic versatility and biodegradative properties. We have deciphered the genome of a facultatively parasitic Rhodococcus, the animal and human pathogen R. equi. Comparative genomic analyses of related species provide a unique opportunity to increase our understanding of niche-adaptive genome evolution and specialization. The environmental rhodococci have much larger genomes, richer in metabolic and degradative pathways, due to gene duplication and acquisition, not genome contraction in R. equi. This probably reflects that the host-associated R. equi habitat is more stable and favorable than the chemically diverse but nutrient-poor environmental niches of nonpathogenic rhodococci, necessitating metabolically more complex, expanded genomes. Our work also highlights that the recruitment or cooption of core microbial traits, following the horizontal acquistion of a few critical genes that provide access to the host niche, is an important mechanism in actinobacterial virulence evolution. Gene cooption is a key evolutionary mechanism allowing rapid adaptive change and novel trait acquisition. Recognizing the contribution of cooption to virulence provides a rational framework for understanding and interpreting the emergence and evolution of microbial pathogenicity.

Microbial communities in subpermafrost saline fracture water at the Lupin Au mine, Nunavut, Canada

We report the first investigation of a deep subpermafrost microbial ecosystem, a terrestrial analog for the Martian subsurface. Our multidisciplinary team analyzed fracture water collected at 890 and 1,130 m depths beneath a 540-m-thick permafrost layer at the Lupin Au mine (Nunavut, Canada). 14C, 3H, and noble gas isotope analyses suggest that the Na-Ca-Cl, suboxic, fracture water represents a mixture of geologically ancient brine, approximately25-kyr-old, meteoric water and a minor modern talik-water component. Microbial planktonic concentrations were approximately10(3) cells mL(-1). Analysis of the 16S rRNA gene from extracted DNA and enrichment cultures revealed 42 unique operational taxonomic units in 11 genera with Desulfosporosinus, Halothiobacillus, and Pseudomonas representing the most prominent phylotypes and failed to detect Archaea. The abundance of terminally branched and midchain-branched saturated fatty acids (5 to 15 mol%) was consistent with the abundance of Gram-positive bacteria in the clone libraries. Geochemical data, the ubiquinone (UQ) abundance (3 to 11 mol%), and the presence of both aerobic and anaerobic bacteria indicated that the environment was suboxic, not anoxic. Stable sulfur isotope analyses of the fracture water detected the presence of microbial sulfate reduction, and analyses of the vein-filling pyrite indicated that it was in isotopic equilibrium with the dissolved sulfide. Free energy calculations revealed that sulfate reduction and sulfide oxidation via denitrification and not methanogenesis were the most thermodynamically viable consistent with the principal metabolisms inferred from the 16S rRNA community composition and with CH4 isotopic compositions. The sulfate-reducing bacteria most likely colonized the subsurface during the Pleistocene or earlier, whereas aerobic bacteria may have entered the fracture water networks either during deglaciation prior to permafrost formation 9,000 years ago or from the nearby talik through the hydrologic gradient created during mine dewatering. Although the absence of methanogens from this subsurface ecosystem is somewhat surprising, it may be attributable to an energy bottleneck that restricts their migration from surface permafrost deposits where they are frequently reported. These results have implications for the biological origin of CH4 on Mars.

Rhodococcus kyotonensis sp. nov., a novel actinomycete isolated from soil

A polyphasic study was undertaken to establish the taxonomic position of an isolate, strain DS472(T), from soil in Kyoto, Japan. Phylogenetic analysis, based on the 16S rRNA gene sequences, revealed that this strain constitutes a new subline within the genus Rhodococcus, with Rhodococcus yunnanensis YIM 70056(T) and Rhodococcus fascians DSM 20669(T) as its nearest phylogenetic neighbours (98.2 and 97.8 % sequence similarity, respectively). DNA-DNA hybridization experiments revealed 36 and 29 % relatedness between the isolate and its phylogenetic relatives, R. yunnanensis and R. fascians, respectively. Chemotaxonomic characteristics, including the major quinone MK-8(H(2)), predominant fatty acids C(16 : 0), C(18 : 1)omega9c and 10-methyl C(18 : 0), the presence of cell-wall chemotype IV and mycolic acids, were consistent with the properties of members of the genus Rhodococcus. The DNA G+C content was 64.5 mol%. On the basis of both phenotypic and genotypic evidence, strain DS472(T) represents a novel species of the genus Rhodococcus, for which the name Rhodococcus kyotonensis sp. nov. is proposed. The type strain is strain DS472(T) (=IAM 15415(T)=CCTCC AB206088(T)).