Smaragdicoccus niigatensis gen. nov., sp. nov., a novel member of the suborder Corynebacterineae

Stalactites Core Prospect as Environmental "Microbial Ark": The Actinomycetota Diversity Paradigm, First Reported from a Greek Cave

Speleothems found in caves worldwide are considered the natural libraries of paleontology. Bacteria found in these ecosystems are generally limited to Proteobacteria and Actinomycetota, but rare microbiome and "Dark Matter" is generally under-investigated and often neglected. This research article discusses, for the first time to our knowledge, the diachronic diversity of Actinomycetota entrapped inside a cave stalactite. The planet's environmental microbial community profile of different eras can be stored in these refugia (speleothems). These speleothems could be an environmental "Microbial Ark" storing rare microbiome and "Dark Matter" bacterial communities evermore.

Antrihabitans stalagmiti sp. nov., isolated from a larva cave and a proposal to transfer Rhodococcus cavernicola Lee et al. 2020 to a new genus Spelaeibacter as Spelaeibacter cavernicola gen. nov. comb. nov

An actinobacterial strain, designated YC3-6^T, was isolated from a larva cave in Jeju, Republic of Korea. The novel isolate was found to grow at 10-30 °C, pH 5.0-10.0 and 0-4% (w/v) NaCl. The 16S rRNA gene phylogeny showed that the novel isolate formed a distinct subline within the family Nocardiaceae. Levels of 16S rRNA gene similarity indicated that the close relatives are Rhodococcus cavernicola (98.4% sequence similarity) and "Rhodococcus psychrotolerans" (98.2%) followed by Antrihabitans stalactiti (96.8%). However, the core gene-based phylogeny revealed that the novel isolate formed a tight cluster with A. stalactiti and was separated from R. cavernicola and other members of the family Nocardiaceae. The morphological and chemotaxonomic characteristics of strain YC3-6^T are in line with those of the genus Antrihabitans. Strain YC3-6^T showed an average nucleotide identity of 75.5% and a digital DDH of 20.3% with A. stalactiti. In addition, the core gene analysis showed that R. cavernicola formed a distinct subline between an Antrihabitans cluster and Aldersonia kunmingensis, and well separated from members of the genus Rhodococcus. The average amino acid identity values of R. cavernicola to closely related neighbours were 69.3-69.4% with members of the genus Antrihabitans and 67.3% with Ald. kunmingensis, while the POCP values ranged from 56.9 to 63.6%. On the basis of results obtained here, strain YC3-6^T is concluded to represent a novel species of the genus Antrihabitans, for which the name Antrihabitans stalagmiti sp. nov. (type strain, YC3-6^T = KACC 19963^T = DSM 107561^T) is proposed. Based on overall genome relatedness and chemotaxonomic differences, it is also proposed that R. cavernicola Lee et al. 2020 be transferred to a new genus Spelaeibacter as Spelaeibacter cavernicola gen. nov., comb. nov.

Verrucomicrobial methanotrophs grow on diverse C3 compounds and use a homolog of particulate methane monooxygenase to oxidize acetone

Short-chain alkanes (SCA; C2-C4) emitted from geological sources contribute to photochemical pollution and ozone production in the atmosphere. Microorganisms that oxidize SCA and thereby mitigate their release from geothermal environments have rarely been studied. In this study, propane-oxidizing cultures could not be grown from acidic geothermal samples by enrichment on propane alone, but instead required methane addition, indicating that propane was co-oxidized by methanotrophs. “Methylacidiphilum” isolates from these enrichments did not grow on propane as a sole energy source but unexpectedly did grow on C3 compounds such as 2-propanol, acetone, and acetol. A gene cluster encoding the pathway of 2-propanol oxidation to pyruvate via acetol was upregulated during growth on 2-propanol. Surprisingly, this cluster included one of three genomic operons (pmoCAB3) encoding particulate methane monooxygenase (PMO), and several physiological tests indicated that the encoded PMO3 enzyme mediates the oxidation of acetone to acetol. Acetone-grown resting cells oxidized acetone and butanone but not methane or propane, implicating a strict substrate specificity of PMO3 to ketones instead of alkanes. Another PMO-encoding operon, pmoCAB2, was induced only in methane-grown cells, and the encoded PMO2 could be responsible for co-metabolic oxidation of propane to 2-propanol. In nature, propane probably serves primarily as a supplemental growth substrate for these bacteria when growing on methane.

Microbacterium algeriense sp. nov., a novel actinobacterium isolated from Algerian oil production waters

A non-motile, straight-rod-shaped, Gram-stain-positive and facultative anaerobic bacterium (i.e., strain G1^T) was isolated from production waters from an Algerian oilfield. Growth was observed in the presence of 0.3-3.5 % (w/v) NaCl, at 20-50 °C and at pH 6.0-9.0. Results of phylogenetic analyses based on 16S rRNA gene sequences showed that strain G1^T belonged to the genus Microbacterium. Strain G1 ^T was closely related to Microbacterium oxydans (DSM 20578^T) and Microbacterium maritypicum (DSM 12512^T) with 99.8 % sequence similarity and to Microbacterium saperdae (DSM 20169^T) with 99.6 % sequence similarity. Strain G1 ^T contained MK9, MK10, MK11, MK12 and MK13 as respiratory quinones, and phosphatidylglycerol, diphosphatidylglycerol and glycolipid as the major polar lipids. The major cellular fatty acids were anteiso-C_15:0, iso-C_16:0 and anteiso-C_17:0. The estimated DNA G+C content was 69.57 mol% based on its draft genome sequence. Genome annotation of strain G1^T predicted the presence of 3511 genes, of which 3483 were protein-coding and 47 were tRNA genes. The DNA-DNA hybridization (DDH) and average nucleotide identity (ANI) values between strain G1^T and M. oxydans (DSM 20578^T) and M. maritypicum (DSM 12512^T) were in both cases far below the respective species boundary thresholds (27.5 and 28.0 % for DDH; and 84.40 and 84.82% for ANI, respectively). Based on the data presented above, strain G1^T was considered to represent a novel species for which the name Microbacterium algeriense is proposed with the type strain G1^T (=DSM 109018^T=LMG 31276^T).

Antrihabitans stalactiti gen. nov., sp. nov., a new member of the family Nocardiaceae isolated from a cave

Two Gram-stain-positive, strictly aerobic, non-spore-forming actinobacterial strains, designated YC2-7^T and YC5-17, were isolated from the Yongcheondonggul (larva cave) in Jeju, Republic of Korea and their taxonomic ranks were examined by a polyphasic approach. The 16S rRNA gene tree showed that the novel isolates occupied an independent position separated from recognized genera of the family Nocardiaceae. In the 92 core gene-based phylogenomic analysis, strain YC2-7^T was loosely associated with the type strain of Aldersonia kummingensis with 66.2 % average amino acid identity. The 16S rRNA gene sequence simairity between the isolate and members of the family Nocardiaceae was below 96.7 %. The cell-wall peptidoglycan was meso-diaminopimelic acid as a diagnostic diamino acid. Whole-cell sugars consisted of arabinose, galactose and glucose. The predominant menaquinone was MK-8(H4, ω-cycl). The major polar lipids consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and phosphatidylinositol mannoside. The cellular fatty acids consisted mainly of saturated and unsaturated components with small amounts of tuberculostearic acid. Mycolic acids of 52-58 carbon atoms were present. The DNA G+C content of the genome was 63.8 mol%. On the basis of combination of morphological and chemotaxonomic differences, in addition to phylogenetic distinctness, the novel isolates are considered to constitute members of a novel species of a new genus in the family Nocardiaceae, for which the name Antrihabitans stalactiti gen. nov., sp. nov. is proposed. The type strain is YC2-7^T (=KACC 19965^T=DSM 108733^T).

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.

Romboutsia hominis sp. nov., the first human gut-derived representative of the genus Romboutsia, isolated from ileostoma effluent

A Gram-stain-positive, motile, rod-shaped, obligately anaerobic bacterium, designated FRIFI^T, was isolated from human ileostoma effluent and characterized. On the basis of 16S rRNA gene sequence similarity, strain FRIFI^T was most closely related to the species Romboutsia ilealis CRIB^T (97.7 %), Romboutsia lituseburensis DSM 797^T (97.6 %) and Romboutsia sedimentorum LAM201^T (96.6 %). The level of DNA-DNA relatedness between strain FRIFI^T and R. ilealis CRIB^T was 13.9±3.3 % based on DNA-DNA hybridization. Whole genome sequence-based average nucleotide identity between strain FRIFI^T and closely related Romboutsia strains ranged from 78.4-79.1 %. The genomic DNA G+C content of strain FRIFI^T was 27.8 mol%. The major cellular fatty acids of strain FRIFI^T were saturated and unsaturated straight-chain C12-C19 fatty acids as well as cyclopropane fatty acids, with C16 : 0 being the predominant fatty acid. The polar lipid profile comprised five phospholipids and six glycolipids. These results, together with differences in phenotypic features, support the proposal that strain FRIFI^T represents a novel species within the genus Romboutsia, for which the name Romboutsiahominis sp. nov. is proposed. The type strain is FRIFI^T (=DSM 28814^T=KCTC 15553^T).

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.

Rhodococcus psychrotolerans sp. nov., isolated from rhizosphere of Deschampsia antarctica

A novel actinobacterium, designated strain CMAA 1533^T, was isolated from the rhizosphere of Deschampsia antarctica collected at King George Island, Antarctic Peninsula. Strain CMAA 1533^T was found to grow over a wide range of temperatures (4-28 °C) and pH (4-10). Macroscopically, the colonies were observed to be circular shaped, smooth, brittle and opaque-cream on most of the culture media tested. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain CMAA 1533^T belongs to the family Nocardiaceae and forms a distinct phyletic line within the genus Rhodococcus. Sequence similarity calculations indicated that the novel strain is closely related to Rhodococcus degradans CCM 4446^T, Rhodococcus erythropolis NBRC 15567^T and Rhodococcus triatomae DSM 44892^T (≤ 96.9%). The organism was found to contain meso-diaminopimelic acid, galactose and arabinose in whole cell hydrolysates. Its predominant isoprenologue was identified as MK-8(H₂) and the polar lipids as diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and phosphatidylinositol mannosides. The major fatty acids were identified as Summed feature (C_16:1 ω6c and/or C_16:1 ω7c), C_16:0, C_18:1 ω9c and 10-methyl C_18:0. The G+C content of genomic DNA was determined to be 65.5 mol%. Unlike the closely related type strains, CMAA 1533^T can grow at 4 °C but not at 37 °C and was able to utilise adonitol and galactose as sole carbon sources. Based on phylogenetic, chemotaxonomic and physiological data, it is concluded that strain CMAA 1533^T (= NRRL B-65465^T = DSM 104532^T) represents a new species of the genus Rhodococcus, for which the name Rhodococcus psychrotolerans sp. nov. is proposed.

Gordonia hongkongensis sp. nov., isolated from blood culture and peritoneal dialysis effluent of patients in Hong Kong

Two bacterial strains, HKU50T and HKU46, were isolated in Hong Kong from the blood culture and the peritoneal dialysis effluent of two patients. The strains are Gram-stain-positive, acid-fast, non-motile, non-sporulating bacilli. They grow on Columbia agar with 5 % defibrinated sheep blood and brain-heart infusion agar under aerobic conditions with 5 % CO2 at 37 °C as pink-to-orange, non-haemolytic colonies. The strains are catalase-positive and oxidase-negative, and have a unique biochemical profile distinguishable from other closely related species. DNA sequencing revealed that both isolates possessed multiple intra-genomic 16S rRNA gene copies (99.8-100 % sequence identities to Gordonia lacunae NRRL B-24551T and Gordonia terrae NRRL B-16283T). Phylogenetic analysis of the 16S rRNA gene, secA1 and gyrB showed that the two isolates formed a distinct branch within the genus Gordonia and were most closely related to G. lacunae and G. terrae. DNA-DNA hybridization demonstrated ≤53.7 % and ≤49.4 % DNA relatedness between the two isolates and G. lacunae, and between the two isolates and G. terrae, respectively. Hierarchical cluster analysis of MALDI-TOF MS main spectrum profiles showed that strains HKU50T and HKU46 were closely related to each other, but were distinct from G. lacunae, G. terrae, or any other species of the genus Gordonia in the Bruker database. The chemotaxonomic traits of the two strains were highly similar, and the major fatty acids were summed feature 4 (iso-C15 : 0 2-OH/C16 : 1trans-9), C16 : 0, C18 : 1cis-9, and tuberculostearic acid. A novel species named Gordonia hongkongensis sp. nov. is proposed to accommodate strains HKU50T and HKU46, with strain HKU50T (=CCOS 955T=CIP 111027T=NBRC 111234T=NCCP 16210T) as the type strain.

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.

Nocardia halotolerans sp. nov., a halotolerant actinomycete isolated from saline soil

A novel halotolerant actinomycete, strain Chem15T, was isolated from soil around Inche-Broun hypersaline wetland; its taxonomic position was determined based on a polyphasic approach. Strain Chem15T was strictly aerobic and tolerated NaCl up to 12.5 %. The optimum temperature and pH for growth were 28–30 °C and pH 7.0–7.5, respectively. The cell wall of strain Chem15T contained meso-diaminopimelic acid as diamino acid and galactose, arabinose and ribose as whole-cell sugars. The major phospholipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and phosphatidylinositol mannosides. The cellular fatty acids profile consisted of C16 : 0, iso-C18 : 0, C18 : 0 10-methyl and C18 : 1ω9c, and the major respiratory quinone was MK-8(H4cycl). The G+C content of the genomic DNA was 68.0 mol%. The novel strain constituted a distinct phyletic line within the genus Nocardia, based on 16S rRNA gene sequence analysis, and was closely associated with Nocardia sungurluensis DSM 45714T and Nocardia alba DSM 44684T (98.2 and 98.1 % 16S rRNA gene sequence similarity, respectively). However DNA–DNA relatedness and phenotypic data demonstrated that strain Chem15T was clearly different from closely related species of the genus Nocardia. It is concluded that the organism should be classified as a representative of a novel species of the genus Nocardia, for which the name Nocardia halotolerans sp. nov. is proposed. The type strain is Chem15T ( = IBRC-M 10490T = LMG 28544T).

Tomitella cavernea sp. nov., an actinomycete isolated from soil

A Gram-staining-positive, aerobic, non-spore-forming, irregular rod-shaped actinobacterium, designated YIM C00895(T), was isolated from a soil sample collected from Jiuxiang Scenic Region, Yunnan province, south-west China. The strain was able to grow at 10-28 °C, pH 6.0-10.0 and 0-11% NaCl (w/v). Phylogenetic analysis based on 16S rRNA (95.3%) gene sequences revealed the highest similarity to Tomitella biformata AHU1821(T). The whole-cell hydrolysates of strain YIM C00895(T) contained meso-diaminopimelic acid, arabinose and galactose, indicating chemotype IV. The muramic acids in the peptidoglycan were glycolated. The polar lipids consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylinositol mannosides and an unidentified glycolipid. MK-9(H2) was the predominant menaquinone. The major fatty acids were C14 : 0, C16 : 0, C16 : 1 and C18 : 1ω9c and tuberculostearic acid (10-methyl C18 : 0) was present in relatively small amounts (4.5%). TLC analysis of its cellular mycolic acids showed a similar profile to Tomitella biformata DSM 45403(T). The DNA G+C content of the strain was 67.5 mol%. The results of physiological and biochemical tests allowed strain YIM C00895(T) to be differentiated phenotypically from Tomitella biformata DSM 45403(T). On the basis of evidence from this polyphasic study, the novel species Tomitella cavernea sp. nov. is proposed. The type strain of Tomitella cavernea is YIM C00895(T) ( = DSM 45788(T)  = JCM 18542(T)).

Characterization of Romboutsia ilealis gen. nov., sp. nov., isolated from the gastro-intestinal tract of a rat, and proposal for the reclassification of five closely related members of the genus Clostridium into the genera Romboutsia gen. nov., Intestinibacter gen. nov., Terrisporobacter gen. nov. and Asaccharospora gen. nov

A Gram-positive staining, rod-shaped, non-motile, spore-forming obligately anaerobic bacterium, designated CRIBT, was isolated from the gastro-intestinal tract of a rat and characterized. The major cellular fatty acids of strain CRIBT were saturated and unsaturated straight-chain C12-C19 fatty acids, with C16:0 being the predominant fatty acid. The polar lipid profile comprised six glycolipids, four phospholipids and one lipid that did not stain with any of the specific spray reagents used. The only quinone was MK-6. The predominating cell-wall sugars were glucose and galactose. The peptidoglycan type of strain CRIBT was A1σ lanthionine-direct. The genomic DNA G+C content of strain CRIBT was 28.1 mol%. On the basis of 16S rRNA gene sequence similarity, strain CRIBT was most closely related to a number of species of the genus Clostridium, including Clostridium lituseburense (97.2%), Clostridium glycolicum (96.2%), Clostridium mayombei (96.2%), Clostridium bartlettii (96.0%) and Clostridium irregulare (95.5%). All these species show very low 16S rRNA gene sequence similarity (<85%) to the type strain of Clostridium butyricum, the type species of the genus Clostridium. DNA-DNA hybridization with closely related reference strains indicated reassociation values below 32%. On the basis of phenotypic and genetic studies, a novel genus, Romboutsia gen. nov., is proposed. The novel isolate CRIBT (=DSM 25109T=NIZO 4048T) is proposed as the type strain of the type species, Romboutsia ilealis gen. nov., sp. nov., of the proposed novel genus. It is proposed that C. lituseburense is transferred to this genus as Romboutsia lituseburensis comb. nov. Furthermore, the reclassification into novel genera is proposed for C. bartlettii, as Intestinibacter bartlettii gen. nov., comb. nov. (type species of the genus), C. glycolicum, as Terrisporobacter glycolicus gen. nov., comb. nov. (type species of the genus), C. mayombei, as Terrisporobacter mayombei gen. nov., comb. nov., and C. irregulare, as Asaccharospora irregularis gen. nov., comb. nov. (type species of the genus), on the basis of additional data collected in this study. In addition, an emendation of the species Peptostreptococcus anaerobius and the order Eubacteriales is provided.

Mycolic acids: structures, biosynthesis, and beyond

Mycolic acids are major and specific lipid components of the mycobacterial cell envelope and are essential for the survival of members of the genus Mycobacterium that contains the causative agents of both tuberculosis and leprosy. In the alarming context of the emergence of multidrug-resistant, extremely drug-resistant, and totally drug-resistant tuberculosis, understanding the biosynthesis of these critical determinants of the mycobacterial physiology is an important goal to achieve, because it may open an avenue for the development of novel antimycobacterial agents. This review focuses on the chemistry, structures, and known inhibitors of mycolic acids and describes progress in deciphering the mycolic acid biosynthetic pathway. The functional and key biological roles of these molecules are also discussed, providing a historical perspective in this dynamic area.

Phenotypic and genotypic characterization of Rhodococcus equi isolated from sputum

INTRODUCTION

Rhodococcus equi is an opportunistic pathogen, causing rhodococcosis, a condition that can be confused with tuberculosis. Often, without identifying M. tuberculosis, physicians initiate empiric treatment for tuberculosis. R. equi and M. tuberculosis have different susceptibility to drugs. Identification of R. equi is based on a variety of phenotypic, chromatographic, and genotypic characteristics.

OBJECTIVE

This study aimed to characterize bacterial isolates from sputum samples suggestive of R. equi.

METHODS

The phenotypic identification included biochemical assays; thin-layer chromatography (TLC) and polymerase chain reaction (PCR) were used for genotypic identification.

RESULTS

Among 78 Gram-positive and partially acid-fast bacilli isolated from the sputum of tuberculosis-suspected patients, 51 were phenotypically and genotypically characterized as R. equi based on literature data. Mycolic acid analysis showed that all suspected R. equi had compounds with a retention factor (R(f)) between 0.4-0.5. Genotypic characterization indicated the presence of the choE gene 959bp fragments in 51 isolates CAMP test positive. Twenty-two CAMP test negative isolates were negative for the choE gene. Five isolates presumptively identified as R. equi, CAMP test positive, were choE gene negative, and probably belonged to other bacterial species.

CONCLUSIONS

The phenotypic and molecular techniques used constitute a good methodological tool to identify R. equi.

Tomitella biformata gen. nov., sp. nov., a new member of the suborder Corynebacterineae isolated from a permafrost ice wedge

Gram-reaction-positive, aerobic, non-spore-forming, irregular rod-shaped bacteria, designated AHU1821T and AHU1820, were isolated from an ice wedge in the Fox permafrost tunnel, Alaska. The strains were psychrophilic, growing at −5 to 27 °C. Phylogenetic analysis of the 16S rRNA and gyrB gene sequences indicated that the ice-wedge isolates formed a clade distinct from other mycolic-acid-containing bacteria within the suborder Corynebacterineae. The cell wall of strains AHU1821T and AHU1820 contained meso-diaminopimelic acid, arabinose and galactose, indicating chemotype IV. The muramic acids in the peptidoglycan were glycolated. The predominant menaquinone was MK-9(H2). The polar lipids consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylinositol mannosides and an unidentified glycolipid. The major fatty acids were hexadecenoic acid (C16 : 1), hexadecanoic acid (C16 : 0), octadecenoic acid (C18 : 1) and tetradecanoic acid (C14 : 0). Tuberculostearic acid was present in relatively small amounts (1 %). Strains AHU1821T and AHU1820 contained mycolic acids with 42–52 carbons. The DNA G+C content of the two strains was 69.3–71.6 mol% (T m). 16S rRNA, rpoB and recA gene sequences were identical between strains AHU1821T and AHU1820 and those of the gyrB gene showed 99.9 % similarity. Based on phylogenetic and phenotypic evidence, strains AHU1821T and AHU1820 represent a single novel species of a novel genus, for which the name Tomitella biformata gen. nov., sp. nov. is proposed. The type strain of Tomitella biformata is AHU1821T (=DSM 45403T =NBRC 106253T).

Williamsia faeni sp. nov., an actinomycete isolated from a hay meadow

The taxonomic status of an actinomycete isolated from soil collected from a hay meadow was determined using a polyphasic approach. The strain, designated N1350(T), had morphological and chemotaxonomic properties consistent with its classification in the genus Williamsia and formed a distinct phyletic line within the clade comprising the type strains of species of the genus Williamsia in the 16S rRNA gene tree. Strain N1350(T) shared highest 16S rRNA gene sequence similarities with Williamsia marianensis MT8(T) (98.1 %) and Williamsia muralis MA140-96(T) (98.3 %). However, strain N1350(T) was readily distinguished from the type strains of Williamsia species using a combination of phenotypic properties. On the basis of these data, strain N1350(T) is considered to represent a novel species of the genus Williamsia. The name proposed for this taxon is Williamsia faeni sp. nov., with the type strain N1350(T) (=DSM 45372(T) =NCIMB 14575(T) =NRRL B-24794(T)).

Hoyosella altamirensis gen. nov., sp. nov., a new member of the order Actinomycetales isolated from a cave biofilm

A novel actinomycete, strain OFN S31(T), was isolated from a complex biofilm in the Altamira Cave, Spain. A polyphasic study was carried out to clarify the taxonomic position of this strain. Phylogenetic analysis with 16S rRNA gene sequences of representatives of the genera Corynebacterium, Dietzia, Gordonia, Millisia, Mycobacterium, Nocardia, Rhodococcus, Segniliparus, Skermania, Tsukamurella and Williamsia indicated that strain OFN S31(T) formed a distinct taxon in the 16S rRNA gene tree that was more closely associated with the Mycobacterium clade. The type strain of Mycobacterium fallax was the closest relative of strain OFN S31(T) (95.6 % similarity). The cell wall contained meso-diaminopimelic acid, arabinose and galactose, which are characteristic components of cell-wall chemotype IV of actinomycetes. The sugars of the peptidoglycan were acetylated. The polar lipid pattern was composed of phosphatidylinositol, phosphatidylglycerol, phosphatidylethanolamine and diphosphatidylglycerol. Strain OFN S31(T) is characterized by the absence of mycelium and mycolic acids. Strain OFN S31(T) had MK-8 as the major menaquinone. The DNA G+C content was 49.3 mol%, the lowest found among all taxa included in the suborder Corynebacterineae. Based on morphological, chemotaxonomic, phenotypic and genetic characteristics, strain OFN S31(T) is considered to represent a novel species of a new genus, for which the name Hoyosella altamirensis gen. nov., sp. nov. is proposed. The type strain of Hoyosella altamirensis is strain OFN S31(T) (=CIP 109864(T) =DSM 45258(T)).

The genus Dietzia: a new home for some known and emerging opportunist pathogens

The genus Dietzia has only been established fairly recently. The Gram morphology and colony appearance of the species of this genus is remarkably similar to Rhodococcus equi. In the absence of simple, accurate methods for their identification, Dietzia spp. might have been misidentified as a Rhodococcus spp. and/or considered to be contaminants only. This MiniReview is designed to summarize current evidence on the clinical significance of Dietzia species, to consider their potential role as human pathogens, and to outline approaches that can be used to accurately classify and identify members of the genus, with the overall aim of alerting the medical microbiological community to a little known genus that contains clinically significant organisms.