Reticulibacter mediterranei gen. nov., sp. nov., within the new family Reticulibacteraceae fam. nov., and Ktedonospora formicarum gen. nov., sp. nov., Ktedonobacter robiniae sp. nov., Dictyobacter formicarum sp. nov. and Dictyobacter arantiisoli sp. nov., belonging to the class Ktedonobacteria

Dictyobacter halimunensis sp. nov., a new member of the phylum Chloroflexota, from forest soil in a geothermal area

Three Gram-stain-positive aerobic bacteria, characterized by branched mycelia with putative sporangia, were isolated from forest soil inside a decayed bamboo stem from a geothermal area in West Java, Indonesia. The strain S3.2.2.5T grew at 15-37 °C (optimum 30 °C), at pH 5.0-7.0 (optimum 7.0) and in the presence of 0-1% NaCl (optimum 0%). Strain S3.2.2.5T was able to hydrolyse cellulose, xylan, starch and skim milk. The cell-wall sugars were composed of xylose and mannose, and the peptidoglycan hydrolysates contained d-glutamic acid, glycine, d-alanine, l-alanine, β-alanine and l-ornithine. The major fatty acids (>10%) were anteiso-C17:0, iso-C17:0, C16:1 2-OH and iso-C16:1. The major polar lipids were phosphatidylinositol, phosphatidylglycerol, diphosphatidylglycerol, unidentified glycolipids and unidentified phospholipids. The major menaquinone was MK-9 (H2). The results of the analysis of the phylogenetic tree based on the 16S rRNA gene indicated that these three isolates belong to the genus Dictyobacter and they were most closely related to the type strain of species Dictyobacter aurantiacus S-27T (97.41-98.00%). The strain S3.2.2.5T exhibited a genome size of 9.41 Mbp, which was significantly larger than the known Dictyobacter species. The G+C content was 54.3 mol%. The average nucleotide identity (90.77%) and the digital DNA-DNA hybridization values (42.6%) between strain S3.2.2.5T and D. aurantiacus S-27T were below the threshold value for species delineation. Based on the phenotypic, chemotaxonomic and molecular characteristics of strain S3.2.2.5T, a novel species of the genus Dictyobacter, for which the name Dictyobacter halimunensis sp. nov., is proposed. The type strain is S3.2.2.5T (= UICC B-128T = CGMCC 1.61913T = KCTC 43728T).

The biotechnological potential of the Chloroflexota phylum

In the next decades, the increasing material and energetic demand to support population growth and higher standards of living will amplify the current pressures on ecosystems and will call for greater investments in infrastructures and modern technologies. A valid approach to overcome such future challenges is the employment of sustainable bio-based technologies that explore the metabolic richness of microorganisms. Collectively, the metabolic capabilities of Chloroflexota, spanning aerobic and anaerobic conditions, thermophilic adaptability, anoxygenic photosynthesis, and utilization of toxic compounds as electron acceptors, underscore the phylum's resilience and ecological significance. These diverse metabolic strategies, driven by the interplay between temperature, oxygen availability, and energy metabolism, exemplify the complex adaptations that enabled Chloroflexota to colonize a wide range of ecological niches. In demonstrating the metabolic richness of the Chloroflexota phylum, specific members exemplify the diverse capabilities of these microorganisms: Chloroflexus aurantiacus showcases adaptability through its thermophilic and phototrophic growth, whereas members of the Anaerolineae class are known for their role in the degradation of complex organic compounds, contributing significantly to the carbon cycle in anaerobic environments, highlighting the phylum's potential for biotechnological exploitation in varying environmental conditions. In this context, the metabolic diversity of Chloroflexota must be considered a promising asset for a large range of applications. Currently, this bacterial phylum is organized into eight classes possessing different metabolic strategies to survive and thrive in a wide variety of extreme environments. This review correlates the ecological role of Chloroflexota in such environments with the potential application of their metabolisms in biotechnological approaches.

Microbial communities from weathered outcrops of a sulfide-rich ultramafic intrusion, and implications for mine waste management

The Duluth Complex (DC) contains sulfide-rich magmatic intrusions that represent one of the largest known economic deposits of copper, nickel, and platinum group elements. Previous work showed that microbial communities associated with experimentally-weathered DC waste rock and tailings were dominated by uncultivated taxa and organisms not typically associated with mine waste. However, those experiments were designed for kinetic testing and do not necessarily represent the conditions expected for long-term environmental weathering. We used 16S rRNA gene methods to characterize the microbial communities present on the surfaces of naturally-weathered and historically disturbed outcrops of DC material. Rock surfaces were dominated by diverse uncultured Ktedonobacteria, Acetobacteria, and Actinobacteria, with abundant algae and other phototrophs. These communities were distinct from microbial assemblages from experimentally-weathered DC rocks, suggesting different energy and nutrient resources in environmental samples. Sulfide mineral incubations performed with and without algae showed that photosynthetic microorganisms could have an inhibitory effect on autotrophic populations, resulting in slightly lower sulfate release and differences in dominant microorganisms. The microbial assemblages from these weathered outcrops show how communities develop during weathering of sulfide-rich DC rocks and represent baseline data that could evaluate the effectiveness of future reclamation of waste produced by large-scale mining operations.