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Traditionally, filamentous fungi and actinomycetes are well-known cellulolytic microorganisms that have been utilized in the commercial production of cellulase enzyme cocktails for industrial-scale degradation of plant biomass. Noticeably, the Ktedonobacteria lineage (phylum Chloroflexi) with actinomycetes-like morphology was identified and exhibited diverse carbohydrate utilization or degradation abilities. In this study, we performed genome-wide profiling of carbohydrate-active enzymes (CAZymes) in the filamentous Ktedonobacteria lineage. Numerous CAZymes (153–290 CAZymes, representing 63–131 glycoside hydrolases (GHs) per genome), including complex mixtures of endo- and exo-cellulases, were predicted in 15 available Ktedonobacteria genomes. Of note, 4–28 CAZymes were predicted to be extracellular enzymes, whereas 3–29 CAZymes were appended with carbohydrate-binding modules (CBMs) that may promote their binding to insoluble carbohydrate substrates. This number far exceeded other Chloroflexi lineages and were comparable to the cellulolytic actinomycetes. Six multi-modular extracellular GHs were cloned from the thermophilic Thermosporothrix hazakensis SK20-1T strain and heterologously expressed. The putative endo-glucanases of ThazG5-1, ThazG9, and ThazG12 exhibited strong cellulolytic activity, whereas the putative exo-glucanases ThazG6 and ThazG48 formed weak but observable halos on carboxymethyl cellulose plates, indicating their potential biotechnological application. The purified recombinant ThazG12 had near-neutral pH (optimal 6.0), high thermostability (60°C), and broad specificity against soluble and insoluble polysaccharide substrates. It also represented described a novel thermostable bacterial β-1,4-glucanase in the GH12 family. Together, this research revealed the underestimated cellulolytic potential of the Ktedonobacteria lineage and highlighted its potential biotechnological utility as a promising microbial resource for the discovery of industrially useful cellulases. [Display omitted] • The Ktedonobacteria lineage (phylum Chloroflexi) with actinomycetes-like morphology harbored numerous CAZymes. • The Ktedonobacteria lineage harbored complex mixtures of endo-/exo-cellulases with potential biotechnological application. • The thermostable (60°C) ThazG12 represented a novel bacteria-derived β-1,4-glucanase in the GH12 family. [ABSTRACT FROM AUTHOR]

Microorganisms can potentially colonise volcanic rocks using the chemical energy in reduced gases such as methane, hydrogen (H2) and carbon monoxide (CO). In this study, we analysed soil metagenomes from Chilean volcanic soils, representing three different successional stages with ages of 380, 269 and 63 years, respectively. A total of 19 metagenome-assembled genomes (MAGs) were retrieved from all stages with a higher number observed in the youngest soil (1640: 2 MAGs, 1751: 1 MAG, 1957: 16 MAGs). Genomic similarity indices showed that several MAGs had amino-acid identity (AAI) values >50% to the phyla Actinobacteria, Acidobacteria, Gemmatimonadetes, Proteobacteria and Chloroflexi. Three MAGs from the youngest site (1957) belonged to the class Ktedonobacteria (Chloroflexi). Complete cellular functions of all the MAGs were characterised, including carbon fixation, terpenoid backbone biosynthesis, formate oxidation and CO oxidation. All 19 environmental genomes contained at least one gene encoding a putative carbon monoxide dehydrogenase (CODH). Three MAGs had form I coxL operon (encoding the large subunit CO-dehydrogenase). One of these MAGs (MAG-1957-2.1, Ktedonobacterales) was highly abundant in the youngest soil. MAG-1957-2.1 also contained genes encoding a [NiFe]-hydrogenase and hyp genes encoding accessory enzymes and proteins. Little is known about the Ktedonobacterales through cultivated isolates, but some species can utilise H2 and CO for growth. Our results strongly suggest that the remote volcanic sites in Chile represent a natural habitat for Ktedonobacteria and they may use reduced gases for growth.

16S rRNA gene clones, and cultured representatives are a limited number. In this review, recent findings on the taxonomical and ecological significance of the class Ktedonobacteria in the phylum Chloroflexi are discussed based on the findings from both the characteristics of the cultured Ktedonobacteria and molecular-based analysis. The microorganisms characterized so far include four species in three genera, Ktedonobacter, Thermosporothrix and Thermogemmatispora, and were proposed to represent three families, Ktedonobacteraceae, Thermosporotricaceae, andThermogemmatisporaceae, and two orders, Ktedonobacterales and Thermogemmatisporales. Ktedonobacteria strainsshowed a common property of gram-positive, aerobic organisms that produce branched vegetative mycelia and formspores by budding.

Microorganisms can potentially colonise volcanic rocks using the chemical energy in reduced gases such as methane, hydrogen (H2) and carbon monoxide (CO). In this study, we analysed soil metagenomes from Chilean volcanic soils, representing three different successional stages with ages of 380, 269 and 63 years, respectively. A total of 19 metagenome-assembled genomes (MAGs) were retrieved from all stages with a higher number observed in the youngest soil (1640: 2 MAGs, 1751: 1 MAG, 1957: 16 MAGs). Genomic similarity indices showed that several MAGs had amino-acid identity (AAI) values >50% to the phyla Actinobacteria, Acidobacteria, Gemmatimonadetes, Proteobacteria and Chloroflexi. Three MAGs from the youngest site (1957) belonged to the class Ktedonobacteria (Chloroflexi). Complete cellular functions of all the MAGs were characterised, including carbon fixation, terpenoid backbone biosynthesis, formate oxidation and CO oxidation. All 19 environmental genomes contained at least one gene encoding a putative carbon monoxide dehydrogenase (CODH). Three MAGs had form I coxL operon (encoding the large subunit CO-dehydrogenase). One of these MAGs (MAG-1957-2.1, Ktedonobacterales) was highly abundant in the youngest soil. MAG-1957-2.1 also contained genes encoding a [NiFe]-hydrogenase and hyp genes encoding accessory enzymes and proteins. Little is known about the Ktedonobacterales through cultivated isolates, but some species can utilise H2 and CO for growth. Our results strongly suggest that the remote volcanic sites in Chile represent a natural habitat for Ktedonobacteria and they may use reduced gases for growth. [ABSTRACT FROM AUTHOR]

• (S)-ktedonoketone was synthesized from (R)-2-hydroxybutyric acid in 8 steps. • The first example of the synthesis of an α,β-disubstituted cyclopentenone by RCM. • Natural ktedonoketone might have (R)-configuration. The first total synthesis of (S)-ktedonoketone has been accomplished in 16% overall yield from (R)-2-hydroxybutyric acid by an eight-step sequence that features a highly diastereoselective methallylation of a chiral dioxolanone and a nucleophilic addition of α-lithiostyrene to a Weinreb's amide intermediate followed by ring-closing metathesis of the resulting enone to construct an α,β-disubstituted cyclopentenone ring system. The sign of specific rotation of synthetic (S)-ktedonoketone was opposite to that reported for the natural product. [ABSTRACT FROM AUTHOR]

Currently, actinomycetes and myxobacteria are the only bacteria believed to form sporangia. Here, we describe a sporangium-forming process identified in Dictyobacter aurantiacus strain S27 T belonging to the class Ktedonobacteria in the phylum Chloroflexi. Microscopic observations showed that strain S27 T forms a substrate mycelium and subsequently produces globose or subglobose terminal sporangia arising from the vegetative mycelia through short stalk cells. This morphogenetic differentiation is similar to that seen in members of Actinoplanes belonging to the class Actinobacteria. However, unlike in Actinoplanes, motile spores could not be observed. This is the first report of the existence of a bacterium, other than actinomycetes and myxobacteira, with a complex morphogenetic differentiation that forms sporangia and is an important microbiological discovery.

Three mesophilic, Gram-stain-positive, aerobic bacterial strains, designated Uno3 T , Uno11 T and Uno16 T , were isolated from a soil-like granular micro-organism mass (termed Tengu-no-mugimeshi) collected from Tsumagoi, Gunma, Japan. They grow at 11-37 °C and pH 4.0-8.0, form branched mycelia, and have a G+C content between 49.4-50.3 mol%. The major menaquinone and fatty acid of Uno3 T are MK-9 and iso-C16 : 0, respectively, whereas Uno11 T and Uno16 T share MK-9 (H2) and C16 : 1-2OH. The major cell-wall sugars are mannose (Uno3 T and Uno11 T ) and glucose (Uno16 T ). Phylogenetic analysis based on 16S rRNA gene sequences indicated that these three strains belong to the order Ktedonobacterales and are most closely related to Dictyobacter aurantiacus S-27 T (sequence similarity of 91.3, 96.4 and 95.5 %). Average nucleotide identity values were <79.9 % among Uno11 T , Uno16 T and D. aurantiacus S-27 T , well below the 95-96 % species circumscription threshold. Based on phenotypic features and phylogenetic positions, we propose that Uno3 T represents a novel genus and species, Tengunoibacter tsumagoiensis gen. nov., sp. nov. (type strain Uno3 T =NBRC 113152 T =LMG 30471 T =BCRC 81113 T ) within the new family Dictyobacteraceae fam. nov. Strains Uno11 T and Uno16 T are also considered to represent novel species: Dictyobacterkobayashii sp. nov. (type strain Uno11 T =NBRC 113153 T =LMG 30472 T =BCRC 81114 T ) and Dictyobacteralpinus sp. nov. (type strain Uno16 T =NBRC 113154 T =BCRC 81115 T ). We also propose an emended description of the genus Dictyobacter, classifying it within family Dictyobacteraceae, and provide emended descriptions of the genera Dictyobacter and Ktedonobacter.

Two thermophilic, aerobic, Gram-stain-positive Ktedonobacteria strains, A1-2 T and A3-2 T , were isolated from geothermal soil in Japan. The strains formed orange-coloured colonies on 10-fold diluted Reasoner's 2A medium, followed by formation of branched aerial mycelium with multiple grape-like spores. Both strains hydrolysed casein, carboxymethyl cellulose, starch, chitin and xylan, but did not liquify gelatin. Strain A1-2 T utilised sucrose and gellan gum and was inhibited by inositol, while strain A3-2 T utilised only gellan gum and was not inhibited by inositol. The DNA G+C contents of strain A1-2 T and A3-2 T were 63.2 and 63.1 mol%, respectively. Chemotaxonomic data (major fatty acid, iso-C17 : 0; major menaquinone, MK-9(H2); cell-wall amino acids, ornithine, serine, glycine, glutamic acid, alanine and β-alanine; polar lipids, phosphatidylinositol, phosphatidylglycerol, diphosphatidylglycerol, one unidentified lipid, one unidentified phosphoglycolipid and three unidentified glycolipids; major cell-wall sugars, mannose, arabinose and xylose) indicate that both strains belong to the genus Thermogemmatispora. 16S rRNA gene sequence analysis indicated that strain A1-2  T was most closely related to the type strains of Thermogemmatispora onikobensis (97.7 % sequence similarity), and that strain A3-2 T was most closely related to the type strains of Thermogemmatispora carboxidivorans(97.2%), but DNA-DNA hybridization shows relatedness values of <67 % with previously described type strains. Moreover, 16S rRNA gene sequence similarity and DNA-DNA relatedness between strain A1-2 T and strain A3-2 T were 96.0 and 33.4%, respectively, suggesting that the two strains are genetically distinct. The two strains are proposed as Thermogemmatispora aurantia sp. nov. and Thermogemmatispora argillosa sp. nov.