Pseudonocardia yuanmoensis sp. nov., a novel actinobacterium isolated from soil in Yunnan, south-west China

A novel Gram-stain positive, aerobic, non-motile, spore-forming actinobacterium, designated YIM 75926^T, was isolated from a soil sample collected at soil forest in Yuanmo county of Yunnan province, south-west China. Its taxonomic position was investigated by a polyphasic approach. Phylogenetic analyses based on 16S rRNA gene sequences showed that the novel strain YIM 75926^T belongs to the genus Pseudonocardia and was closely related to Pseudonocardia halophobica DSM 43089^T (98.1% similarity). Strain YIM 75926^T had MK-8 (H₄) as the predominant menaquinone. The whole organism hydrolysates mainly consisted of meso-diaminopimelic acid, mannose, glucose, galactose and arabinose. The major cellular fatty acids were iso-C_16:0 (37.16%) and C_16:0 (12.43%). The DNA G+C content of strain YIM 75926^T was 70.6 mol%. The resultant phylogenetic trees further showed that strain YIM 75926^T belong to Pseudonocardia and had a distinct subclade within the evolutionary radiation of the genus Pseudonocardia. On the basis of its comparative analysis of phenotypic and genotypic characteristics, it is proposed that strain YIM 75926^T represent a novel species of the genus Pseudonocardia, named Pseudonocardia yuanmoensis sp. nov. The type strain is YIM 75926^T (=CCTCC AA 2011017^T = JCM 18055^T).     

<Emphasis Type="Italic">Pseudonocardia bannaensis</Emphasis> sp. nov., a novel actinomycete isolated from the surface-sterilized roots of <Emphasis Type="Italic">Artemisia annua</Emphasis> L.

During the course of our research on new actinobacterial sources, a novel actinomycete strain YIM 63101^T was isolated from the surface-sterilized roots of Artemisia annua L. collected from Xishuangbanna, Yunnan province, south-west China and characterized by using a polyphasic approach. The strain formed well-differentiated aerial and substrate mycelia. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain YIM 63101^T belongs to the genus Pseudonocardia, with highest similarity to “Pseudonocardia artemisiae YIM 63587^T” (99.4%). Sequence similarities between strain YIM 63101^T and the other Pseudonocardia species ranged from 97.0 (Pseudonocardia saturnea IMSNU 20052^T) to 94.0% (Pseudonocardia compacta IMSNU 20111^T). The chemotaxonomic characteristics, such as cell wall diaminopimelic acid, whole-cell sugars, fatty acid components and the major menaquinones suggested that the organism belonged to the genus Pseudonocardia. The G + C content of the genomic DNA was 69.4 mol%. Based on comparative analysis of physiological, biochemical and chemotaxonomic data, including low DNA–DNA hybridization results, it is proposed that strain YIM 63101^T represents a novel species of the genus Pseudonocardia, named Pseudonocardia bannaensis sp. nov. The type strain is YIM 63101^T (= CCTCC AA 208077 ^T = DSM 45300^T).     

<Emphasis Type="Italic">Pseudonocardia serianimatus</Emphasis> sp. nov., a novel actinomycete isolated from the surface-sterilized leaves of <Emphasis Type="Italic">Artemisia annua</Emphasis> L.

An aerobic, non-motile, catalase-positive, Gram-stain positive actinomycete designated YIM 63233^T was isolated from the surface-sterilized leaves of Artemisia annua L. and characterized using a polyphasic taxonomic approach. Optimal growth occurred at 20–28°C, pH 6.0–7.0 and in the presence of 0–3% (w/v) NaCl. 16S rRNA gene sequence-based phylogenetic analysis showed that strain YIM 63233^T clustered with species of the genus Pseudonocardia, displaying ≥1.2% sequence divergence with recognized species of this genus (from 98.8 to 94.0%). Relatively low levels of DNA–DNA relatedness were found between strain YIM 63233^T and Pseudonocardia petroleophila IMSNU 22072^T, which supported the classification of strain YIM 63233^T within a novel species of the genus Pseudonocardia. The G + C content of genomic DNA was 72.0 mol%. Strain YIM 63233^T possessed chemotaxonomic markers that were consistent with classification in the genus Pseudonocardia, i.e. the predominant fatty acids were iso-C16:0 (32.27%), C16:0 10-methyl (8.73%) and C17:1ω8c (8.30%), whilst the predominant menaquinone was MK-8(H₄). The diagnostic diamino acid of the cell-wall peptidoglycan was meso-diaminopimelic acid. The major cell wall sugars were glucose, arabinose, galactose, mannose and rhamnose. The results of physiological and biochemical tests and DNA–DNA hybridization allowed the phenotypic and genotypic differentiation of strain YIM 63233^T from its closest phylogenetic neighbours. Therefore, the new isolate YIM 63233^T represents a novel species of the genus Pseudonocardia, for which the name Pseudonocardia serianimatus sp. nov. is proposed. The type strain is YIM 63233^T (=DSM 45302^T = CCTCC AA 208079^T).     

Pseudonocardia sichuanensis sp. nov., a novel endophytic actinomycete isolated from the root of Jatropha curcas L.

A novel isolate, designated strain KLBMP 1115^T was isolated from the surface-sterilized root of oil-seed plant Jatropha curcas L. collected from Sichuan Province, south-west China. Characterization of the isolate was based on a polyphasic approach. 16S rRNA gene sequence analysis indicated that strain KLBMP 1115^T belongs to the phylogenetic cluster of the genus Pseudonocardia and was most closely related to Pseudonocardia adelaidensis EUM 221^T (98.9%) and Pseudonocardia zijingensis DSM 44774^T (98.6%), whereas the DNA–DNA relatedness values between strain KLBMP 1115^T and the two type strains were 47.3 and 39.7%, respectively. Levels of lower similarities to the type strains of other recognized Pseudonocardia species ranged from 94.4 to 98.4%. The diagnostic diamino acid in the cell-wall peptidoglycan was meso-diaminopimelic acid. The predominant respiratory quinone was MK-8(H₄). The major fatty acids of strain KLBMP 1115^T was iso-C_16:0. The chemotaxonomic properties of strain KLBMP 1115^T were consistent with those shared by members of the genus Pseudonocardia. On the basis of the phenotypic features and the DNA–DNA hybridization data, strain KLBMP 1115^T represents a novel species of the genus Pseudonocardia, for which the name Pseudonocardia sichuanensis sp. nov. is proposed. The type strain is KLBMP 1115^T (=KCTC 19781^T = CCTCC AA 2010002^T).     

Placement of attine ant-associated Pseudonocardia in a global Pseudonocardia phylogeny (Pseudonocardiaceae, Actinomycetales): a test of two symbiont-association models

We reconstruct the phylogenetic relationships within the bacterial genus Pseudonocardia to evaluate two models explaining how and why Pseudonocardia bacteria colonize the microbial communities on the integument of fungus-gardening ant species (Attini, Formicidae). The traditional Coevolution-Codivergence model views the integument-colonizing Pseudonocardia as mutualistic microbes that are largely vertically transmitted between ant generations and that supply antibiotics that specifically suppress the garden pathogen Escovopsis. The more recent Acquisition model views Pseudonocardia as part of a larger integumental microbe community that frequently colonizes the ant integument from environmental sources (e.g., soil, plant material). Under this latter model, ant-associated Pseudonocardia may have diverse ecological roles on the ant integument (possibly ranging from pathogenic, to commensal, to mutualistic) and are not necessarily related to Escovopsis suppression. We test distinct predictions of these two models regarding the phylogenetic proximity of ant-associated and environmental Pseudonocardia. We amassed 16S-rRNA gene sequence information for 87 attine-associated and 238 environmental Pseudonocardia, aligned the sequences with the help of RNA secondary structure modeling, and reconstructed phylogenetic relationships using a maximum-likelihood approach. We present 16S-rRNA secondary structure models of representative Pseudonocardia species to improve sequence alignments and identify sequencing errors. Our phylogenetic analyses reveal close affinities and even identical sequence matches between environmental Pseudonocardia and ant-associated Pseudonocardia, as well as nesting of environmental Pseudonocardia in subgroups that were previously thought to be specialized to associate only with attine ants. The great majority of ant-associated Pseudonocardia are closely related to autotrophic Pseudonocardia and are placed in a large subgroup of Pseudonocardia that is known essentially only from cultured isolates (rather than cloned 16S sequences). The preponderance of the known ant-associated Pseudonocardia in this latter clade of culturable lineages may not necessarily reflect abundance of these Pseudonocardia types on the ants, but isolation biases when screening for Pseudonocardia (e.g., preferential isolation of autotrophic Pseudonocardia with minimum-nutrient media). The accumulated phylogenetic patterns and the possibility of isolation biases in previous work further erode support for the traditional Coevolution-Codivergence model and calls for continued revision of our understanding how and why Pseudonocardia colonize the microbial communities on the integument of fungus-gardening ant species.     

A mixed community of actinomycetes produce multiple antibiotics for the fungus farming ant <Emphasis Type="Italic">Acromyrmex octospinosus</Emphasis>

Background  

Attine ants live in an intensely studied tripartite mutualism with the fungus Leucoagaricus gongylophorus, which provides food to the ants, and with antibiotic-producing actinomycete bacteria. One hypothesis suggests that bacteria from the genus Pseudonocardia are the sole, co-evolved mutualists of attine ants and are transmitted vertically by the queens. A recent study identified a Pseudonocardia-produced antifungal, named dentigerumycin, associated with the lower attine Apterostigma dentigerum consistent with the idea that co-evolved Pseudonocardia make novel antibiotics. An alternative possibility is that attine ants sample actinomycete bacteria from the soil, selecting and maintaining those species that make useful antibiotics. Consistent with this idea, a Streptomyces species associated with the higher attine Acromyrmex octospinosus was recently shown to produce the well-known antifungal candicidin. Candicidin production is widespread in environmental isolates of Streptomyces, so this could either be an environmental contaminant or evidence of recruitment of useful actinomycetes from the environment. It should be noted that the two possibilities for actinomycete acquisition are not necessarily mutually exclusive.     

Specificity and stability of the Acromyrmex–Pseudonocardia symbiosis

The stability of mutualistic interactions is likely to be affected by the genetic diversity of symbionts that compete for the same functional niche. Fungus‐growing (attine) ants have multiple complex symbioses and thus provide ample opportunities to address questions of symbiont specificity and diversity. Among the partners are Actinobacteria of the genus Pseudonocardia that are maintained on the ant cuticle to produce antibiotics, primarily against a fungal parasite of the mutualistic gardens. The symbiosis has been assumed to be a hallmark of evolutionary stability, but this notion has been challenged by culturing and sequencing data indicating an unpredictably high diversity. We used 454 pyrosequencing of 16S rRNA to estimate the diversity of the cuticular bacterial community of the leaf‐cutting ant Acromyrmex echinatior and other fungus‐growing ants from Gamboa, Panama. Both field and laboratory samples of the same colonies were collected, the latter after colonies had been kept under laboratory conditions for up to 10 years. We show that bacterial communities are highly colony‐specific and stable over time. The majority of colonies (25/26) had a single dominant Pseudonocardia strain, and only two strains were found in the Gamboa population across 17 years, confirming an earlier study. The microbial community on newly hatched ants consisted almost exclusively of a single strain of Pseudonocardia while other Actinobacteria were identified on older, foraging ants in varying but usually much lower abundances. These findings are consistent with recent theory predicting that mixtures of antibiotic‐producing bacteria can remain mutualistic when dominated by a single vertically transmitted and resource‐demanding strain.     

Pseudonocardia nantongensis sp. nov., a novel endophytic actinomycete isolated from the coastal halophyte Tamarix chinensis Lour

A novel isolate, designated strain KLBMP 1282^T was isolated from the surface-sterilized leaves of a coastal halophyte Tamarix chinensis Lour., collected from Nantong, Jiangsu Province, east of China. Phylogenetic analysis based on 16S rRNA gene sequences revealed that this strain belongs to the genus Pseudonocardia, being most closely related to Pseudonocardia kongjuensis LM 157^T (98.33 %), Pseudonocardia autotrophica IMSNU 20050^T (97.77 %), Pseudonocardia endophytica YIM 56035^T (97.63 %), Pseudonocardia ammonioxydans H9 ^T (97.62 %) and Pseudonocardia compacta IMSNU 20111^T (97.56 %); similarity to other type strains of the genus Pseudonocardia was <97.5 %. Chemotaxonomic data confirmed the affiliation of strain KLBMP 1282^T to the genus Pseudonocardia. Strain KLBMP 1282^T contained MK-8(H₄) as the predominant ubiquinone and iso-C_16:0 as the major fatty acid. The polar lipids detected in strain KLBMP 1282^T were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylcholine, phosphatidylmethylethanolamine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylinositol mannosides, one unknown phospholipid and four unknown glycolipids. The DNA G + C content of strain KLBMP 1282^T was 73.1 mol %. The results of DNA–DNA hybridizations and the phylogenetic analysis, together with the phenotypic and biochemical tests, allowed the differentiation of strain KLBMP 1282^T from strains of other recognized Pseudonocardia species. Therefore, strain KLBMP 1282^T represents a novel species of the genus Pseudonocardia, for which the name Pseudonocardia nantongensis sp. nov. is proposed. The type strain is KLBMP 1282^T (=KCTC 29053^T = NBRC 108677^T).     

Cadmium‐induced and trans‐generational changes in the cultivable and total seed endophytic community of Arabidopsis thaliana

Trans‐generational adaptation is important to respond rapidly to environmental challenges and increase overall plant fitness. Besides well‐known mechanisms such as epigenetic modifications, vertically transmitted endophytic bacteria might contribute to this process. The cultivable and total endophytic communities of several generations of Arabidopsis thaliana seeds harvested from plants exposed to cadmium (Cd) or not exposed were investigated. The diversity and richness of the seed endophytic community decreased with an increasing number of generations. Aeromicrobium and Pseudonocardia were identified as indicator species in seeds from Cd‐exposed plants, while Rhizobium was abundantly present in both seed types. Remarkably, Rhizobium was the only genus that was consistently detected in seeds of all generations, which suggests that the phenotypic characteristics were more important as selection criteria for which bacteria are transferred to the next plant generation than the actual genera. Production of IAA was an important trait for endophytes from both seed types, while ACC deaminase activity and Cd tolerance were mainly associated with seed endophytes from Cd‐exposed plants. Understanding how different factors influence the seed endophytic community can help us to improve seed quality and plant growth through different biotechnological applications.     

A new ether bond-splitting enzyme found in Gram-positive polyethylene glycol 6000-utilizing bacterium, <Emphasis Type="Italic">Pseudonocardia</Emphasis> sp. strain K1

Pseudonocardia sp. strain K1 is the only Gram-positive bacterium among the bacteria aerobically metabolizing polyethylene glycol (PEG). Generally, PEG is metabolized by an oxidative pathway in which a terminal alcohol group of PEG is oxidized to aldehyde and to carboxylic acid and then an ether bond is oxidatively cleaved. As the cell-free extract of Pseudonocardia sp. strain K1 has PEG dehydrogenase, PEG aldehyde dehydrogenase and diglycolic acid (DGA) dehydrogenase (DGADH) activities, all of which are constitutively formed, the strain has a metabolic pathway similar to that so far known. We purified an ether bond-splitting enzyme as DGADH. The molecular mass of the enzyme was estimated to be 55 kDa; and it consisted of two identical subunits. The enzyme oxidatively cleaved both an ether bond of PEG 3000 dicarboxylic acid and DGA. The N-terminal amino acid sequence of the purified enzyme had high homology with various superoxide dismutases and the enzyme had also superoxide dismutase activity. The atomic absorption spectrum showed that approximately one atom of Fe was included in each subunit of the enzyme. DGADH activity increased in the cells grown in a PEG medium supplemented with FeCl₃. Thus, we concluded that the enzyme purified from Pseudonocardia sp. strain K1 is a new ether bond-splitting enzyme.     

A comparative study on the phylogenetic diversity of culturable actinobacteria isolated from five marine sponge species

A cultivation-based approach was employed to compare the culturable actinobacterial diversity associated with five marine sponge species (Craniella australiensis, Halichondria rugosa, Reniochalina sp., Sponge sp., and Stelletta tenuis). The phylogenetic affiliation of the actinobacterial isolates was assessed by 16S rDNA-RFLP analysis. A total of 181 actinobacterial strains were isolated using five different culture media (denoted as M1–M5). The type of medium exhibited significant effects on the number of actinobacteria recovered, with the highest number of isolates on M3 (63 isolates) and the lowest on M1 (12 isolates). The genera isolated were also different, with the recovery of three genera on M2 and M3, and only a single genus on M1. The number of actinobacteria isolated from the five sponge species was significantly different, with a count of 83, 36, 30, 17, and 15 isolates from S. tenuis, H. rugosa, Sponge sp., Reniochalina sp., and C. australiensis, respectively. M3 was the best isolation medium for recovery of actinobacteria from S. tenuis, H. rugosa, and Sponge sp., while no specific medium preference was observed for the recovery of actinobacteria from Reniochalina sp., and C. australiensis. The RFLP fingerprinting of 16S rDNA genes digested with HhaI revealed six different patterns, in which 16 representative 16S rDNAs were fully sequenced. Phylogenetic analysis indicated that 12 strains belong to the group Streptomyces, three strains belong to Pseudonocardia, and one strain belongs to Nocardia. Two strains C14 (from C. australiensis) and N13 (from Sponge sp.) have only 96.26% and 96.27% similarity to earlier published sequences, and are therefore potential candidates for new species. The highest diversity of three actinobacteria genera was obtained from Sponge sp., though the number of isolates was low. Two genera of actinobacteria, Streptomyces, and Pseudonocardia, were isolated from both S. tenuis and C. australiensis. Only the genus of Streptomyces was isolated from H. rugosa and Reniochalina sp. Sponge species have been demonstrated here to vary as sources of culturable actinobacterial diversity, and the methods for sampling such diversity presented may be useful for improved sampling of such diversity.     

Identification and genetic diversity analysis of strain Pseudomonas syringae S5: A pathogen responsible for bacteriosis in Avena sativa plants

The genus Pseudomonas includes pathogenic species P. syringae, which can be found in various agricultural environments and which can affect a wide variety of plants, causing significant economic losses when the environmental conditions for its proliferation are optimal. Comprehensive characterizations of phytopathogenic bacteria belonging to the genus Pseudomonas are scarce in Argentina. In this work, the tabtoxin‐producing strain Pseudomonas S5, isolated from oat, was identi?ed as a P. syringae through biochemical tests such as the LOPAT test, and genetic tests such as the analysis of the small subunit ribosomal RNA gene (16S rRNA) sequence and repetitive elements, using BOX and ERIC primers. It was also determined that this phytopathogen is potentially capable of infecting other crops of agricultural importance for our region, such as soybean. This ability to infect different hosts gives it an adaptive advantage that allows it to endure seasonal changes in the environment where it lives. Our work contributes to the physiological classification of the phytopathogen P. syringae S5 isolated from our region, as well as to the knowledge about its range of potential hosts.     

Isolation and characterization of actinobacteria ectosymbionts from Acromyrmex subterraneus brunneus (Hymenoptera, Formicidae)

The ectosymbiont actinobacterium Pseudonocardia was isolated from the integument of Acromyrmex leaf-cutter ants and seems to play a crucial role in maintaining asepsis of the nest. Currently, there has been an intensive search for Pseudonocardia associated with several attine species, but few studies have indicated that other actinobacteria may be associated with these ants as well. We therefore characterized the culturable actinobacteria community associated with the integument of the fungus-growing ant Acromyrmex subterraneus brunneus Forel, 1893 (Hymenoptera: Formicidae). Ectosymbionts were isolated using four different media and characterized by morphological and molecular (16S rDNA) methods. A total of 20 strains were isolated, of which 17 were characterized as Streptomyces spp., and one isolate each as Pseudonocardia, Kitassatospora and Propionicimonas. Unlike other Acromyrmex species, A. subterraneus brunneus is associated with a diversity of actinobacteria. Even though Pseudonocardia is present on this leaf-cutting ant’s integument, the number and diversity of Streptomyces spp. found differs from those of previous studies with other attine ants and suggest that different culturing approaches are needed to characterize the true diversity of microbes colonizing the integument of attine ants. Moreover, understanding the diversity of the culturable actinobacteria associated with A. subterraneus brunneus should increase our knowledge of the evolutionary relationship of this intricate symbiotic association.     

Symbiont Interactions in a Tripartite Mutualism: Exploring the Presence and Impact of Antagonism between Two Fungus-Growing Ant Mutualists

Mutualistic associations are shaped by the interplay of cooperation and conflict among the partners involved, and it is becoming increasingly clear that within many mutualisms multiple partners simultaneously engage in beneficial interactions. Consequently, a more complete understanding of the dynamics within multipartite mutualism communities is essential for understanding the origin, specificity, and stability of mutualisms. Fungus-growing ants cultivate fungi for food and maintain antibiotic-producing Pseudonocardia actinobacteria on their cuticle that help defend the cultivar fungus from specialized parasites. Within both ant-fungus and ant-bacterium mutualisms, mixing of genetically distinct strains can lead to antagonistic interactions (i.e., competitive conflict), which may prevent the ants from rearing multiple strains of either of the mutualistic symbionts within individual colonies. The success of different ant-cultivar-bacterium combinations could ultimately be governed by antagonistic interactions between the two mutualists, either as inhibition of the cultivar by Pseudonocardia or vice versa. Here we explore cultivar-Pseudonocardia antagonism by evaluating in vitro interactions between strains of the two mutualists, and find frequent antagonistic interactions both from cultivars towards Pseudonocardia and vice versa. To test whether such in vitro antagonistic interactions affect ant colonies in vivo, we performed sub-colony experiments using species of Acromyrmex leaf-cutting ants. We created novel ant-fungus-bacterium pairings in which there was antagonism from one, both, or neither of the ants'' microbial mutualists, and evaluated the effect of directional antagonism on cultivar biomass and Pseudonocardia abundance on the cuticle of workers within sub-colonies. Despite the presence of frequent in vitro growth suppression between cultivars and Pseudonocardia, antagonism from Pseudonocardia towards the cultivar did not reduce sub-colony fungus garden biomass, nor did cultivar antagonism towards Pseudonocardia reduce bacteria abundance on the cuticle of sub-colony workers. Our findings suggest that inter-mutualist antagonism does not limit what combinations of cultivar and Pseudonocardia strains Acromyrmex fungus-growing ants can maintain within nests.     

Zur Kenntnis thermophiler Actinomyceten

Zusammenfassung Für Thermomonospora curvata und Streptomyces rectus=Actinomyces thermophilus sensu Gilbert werden Neotypen vorgeschlagen. Für Streptomyces thermoviolaceus ssp. thermoviolaceus und ssp. apingens, S. thermovulgaris, Pseudonocardia thermophila und Microbispora bispora werden Typusstämme ausgewählt. Thermomonospora curvata wird als Typusart für die Gattung Thermomonospora gewählt. Die Gattung Thermopolyspora wird Synonym von Microbispora. Von den Thermopolyspora-Arten kommt nur Th. bispora zur Gattung Microbispora. Für Th. polyspora, Th. flexuosa und Th. rectivirgula ist später eine neue Gattung aufzustellen.Folgende Sporenfeinstruktur wurde für die thermophilen Arten festgestellt: Bei Streptomyces thermovulgaris, Pseudonocardia thermophila und Microbispora bispora sind die Spore glatt, sie sind stachelig bei Streptomyces rectus und Thermomonospora curvata und warzig bei Streptomyces thermoviolaceus. Die Warzen sind in der Mitte vertieft.Ultradünnschnitte wurden von den Sporen von Thermomonospora curvata hergestellt. Die Stacheln werden durch die Falten einer Hülle gebildet, welche locker die dickwandige, glatte Spore umgibt. Die Ähnlichkeit der Bilder mit Microellobosporia ist vielleicht ein Hinweis auf eine mögliche Verwandtschaft der beiden Gattungen.Bei Pseudonocardia thermophila wurden das Mycelwachstum und die Sporenbildung im einzelnen verfolgt. Sowohl die Substrat- als auch die Lufthyphen sin septiert. Viererlei Sporen werden gebildet: Zerfallssporen im Substratmycel, Zerfallssporen im Luftmycel, Segmentationssporen in den Lufthyphen=Entstehung nach dem Pseudonocardia-Typ und Sporenbildung in den Lufthyphen nach dem Streptomyces-Typ.Fünf Formen der Luftsporenbildung werden diskutiert: der Streptomyces-Typ, der Microbispora-Typ, der Thermomonospora-Typ, der Pseudonocardia-Typ und die Sporenbildung, wie sie Krassilnikov u. Agre für Thermopolyspora-Arten beschrieben.

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Studies on thermophilic actinomycetes

Summary Typecultures are designated for the species Streptomyces thermoviolaceus ssp. thernoviolaceus and ssp. apingens, S. thermovulgaris, Pseudonocardia thermophila and Microbispora bispora; neotypes are proposed for Thermonospora curvata and Streptomyces rectus=Actinomyces thermophilus sensu Gilbert. Thermonospora curvata is chosen as type species of the genus Thermonospora. The genus Thermopolyspora becomes a synonym of Microbispora. A new genus will have to be erected for Thermopolyspora polyspora, Th. flexuosa and Th. rectivirgula, which do not fit into the genus Microbispora.The fine structure of the spores of some thermophilic species is described. Streptomyces thermovulgaris, Pseudonocardia thermophila and Microbispora bispora have smooth spore walls; spines are developed in Streptomyces rectus and Thermomonospora curvata, and warts in Streptomyces thermoviolaceus. The warts have been found to possess a median depression.Ultrathin sections were cut of the spores and hyphae of Thermomonospora curvata. The spine bearing layer forms a loose sheath around the smooth, thick wall of the spore as is reported in Microellobosporia. This may indicate relationship between these two genera.In Pseudonocardia thermophila the development of the substrate and aerial mycelia and the spore formation has been studied in detail. Both the substrate and aerial hyphae are septate. Four kinds of spores were observed: fragmentation spores in the substrate hyphae, fragmentation spores in the aerial hyphae, segmentation spores in the aerial hyphae produced according to the Pseudonocardia-type, and spores formed in the aerial hyphae according to the Streptomyces-type.Among the non-sporangiate actinomycetes five types of aerial spore formation are discussed, the Streptomyces-type, Microbispora-type, Thermomonospora-type, Pseudonocardia-type, and the formation of spores described by Krassilnikov and Agre for two species of Thermopolyspora.

     

A review on the genus Metarhizium as an entomopathogenic microbial biocontrol agent with emphasis on its use and utility in Mexico

Metarhizium is a genus of entomopathogenic fungi that was initially classified into three species and varieties. More recently, DNA sequencing has improved the phylogenetic resolution of Metarhizium which now includes 30 species. The insect host ranges vary within the genus and some species such as M. robertsii have broad host ranges, while others such as M. acridum show a narrow host range and are restricted to the order Orthoptera. Metarhizium spp. are ubiquitous naturally occurring soil inhabiting fungi, and some are rhizosphere colonisers and their diversity has been attributed to various selective factors (habitat type, climatic conditions, specific associations with plants and insect hosts). Metarhizium have been used for the biological control of insect pests that affect economically important agricultural crops and have been tested under laboratory and field conditions for the control of insect vectors of human disease, showing the effectiveness of the fungus against the target pest. In Mexico, Metarhizium species have been used for the control of insect pests such as the spittlebug (Hemiptera: Cercopidae), and locusts (Orthoptera) that affect crops such as corn, bean and sugarcane. Biosafety studies, such as dermal and intragastric tests in mammalian models have also been carried out to ensure safety to humans and other animals. Metarhizium shows great promise as an alternative to chemical insecticides that has relatively low impact on human health and the environment. Key features of Metarhizium for biocontrol of insects are outlined with special reference to their utility in Mexico.     

Plumage colour variations in the Agapornis genus: a review

The genus Agapornis consists of nine small African parrot species that are globally well known as pets, but are also found in their native habitat. Illegal trapping, poaching and habitat destruction are the main threats these birds face in the wild. In aviculture, Agapornis breeding is highly popular all across the globe. Birds are mainly selected based on their plumage colour variations but very little molecular research has been conducted on this topic. There are 30 known colour variations amongst the nine species and most of these are inherited as Mendelian traits. However, to date none of the genes or polymorphisms linked to these variations have been identified or verified. Due to unethical breeding practices, the need for the development of molecular tests such as identification verification tests or species identity tests is growing. Future research is paramount to ensure the conservation of wild populations as well as aiding breeders in improving breeding strategies.     

Pseudonocardia hispaniensis sp. nov., a novel actinomycete isolated from industrial wastewater activated sludge

A novel actinomycete, designated PA3^T, was isolated from an oil refinery wastewater treatment plant, located in Palos de la Frontera, Huelva, Spain, and characterized taxonomically by using a polyphasic approach. Phylogenetic analysis based on 16S rRNA gene sequences showed that the isolate formed a distinct subclade in the Pseudonocardia tree together with Pseudonocardia asaccharolytica DSM 44247^T. The chemotaxonomic properties of the isolate, for example, the presence of MK-8 (H₄) as the predominant menaquinone and iso-C_16:0 as the major fatty acid, are consistent with its classification in the genus Pseudonocardia. DNA:DNA pairing experiments between the isolate and the type strain of P. asaccharolytica DSM 44247^T showed that they belonged to separate genomic species. The two strains were readily distinguished using a combination of phenotypic properties. Consequently, it is proposed that isolate PA3^T represents a novel species for which the name Pseudonocardia hispaniensis sp. nov. is proposed. The type strain is PA3^T (= CCM 8391^T = CECT 8030^T).     

Disease defence through generations: leaf‐cutter ants and their symbiotic bacteria

Microbial ecology of animals is taking on significance in the modern dialogue for the biology of species. Similar to a nuclear genome, the entire bacterial assemblage maintains an ancestral signal of the host's evolution leading to cophylogeny between the host and the microbes they harbour (Brucker & Bordenstein 2012b). The stability of such associations is of great interest as they provide a means for species to acquire new traits and genetic diversity that their own genomes lack (McFall‐Ngai et al. 2013). The role of gut microbiota, for example, in host health and nutrition is widely recognized and a shared characteristic among animals. The role of bacteria colonizing the outside surfaces of animals is less well understood, but rather than random colonization, these microbes on skin, cuticles, scales and feathers in many cases provide benefits to the host. The symbiosis of leaf‐cutter ants, their fungus gardens and their microbiota is a fascinating and complex system. Whether culture‐independent bacterial diversity on the cuticle of leaf‐cutter ants is high or highly constrained by subcuticular gland secretions is one prominent question. In this issue of Molecular Ecology, Andersen et al. (2013) show that leaf‐cutting ants, Acromyrmex echinatior, maintain a dominant and colony‐specific bacterium called Pseudonocardia on their cuticles (the laterocervical plates in particular). This bacterium is involved in protecting the ants and their fungal gardens from disease. Other fungus‐gardening attine species as well as soil and vegetation can harbour Pseudonocardia. However, it was previously unknown how stable the bacterial strain–ant colony association was through the lifetime of the colony.