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A novel actinobacterial strain, designated SYSU K12189T, was isolated from a soil sample collected from a Karst cave in Xingyi county, Guizhou province, south-western China. The taxonomic position of the strain was investigated using a polyphasic approach. Cells of the strain were observed to be aerobic and Gram-stain positive. On the basis of 16S rRNA gene sequence similarities and phylogenetic analysis, strain SYSU K12189T is closely related to the type strains of the genus Microlunatus, Microlunatus parietis 12-Be-011T (98.5% sequence similarity), Microlunatus nigridraconis CPCC 203993T (98.4%) and Microlunatus cavernae YIM C01117T (96.6%), and is therefore considered to represent a member of the genus Microlunatus. DNA–DNA hybridization values between strain SYSU K12189T and related type strains of the genus Microlunatus were < 70%. In addition, LL-diaminopimelic acid was found to be the diagnostic diamino acid in the cell wall peptidoglycan. The major isoprenoid quinone was identified as MK-9(H4), while the major fatty acids (> 10%) were found to be anteiso-C15:0, iso-C15:0, iso-C16:0 and iso-C14:0. The polar lipids were found to contain diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, three glycolipids and two unidentified lipids. The genomic DNA G+C content of strain SYSU K12189T was determined to be 69.4 mol%. On the basis of phenotypic, genotypic and phylogenetic data, strain SYSU K12189T is concluded to represent a novel species of the genus Microlunatus, for which the name Microlunatus speluncae sp. nov. is proposed. The type strain is SYSU K12189T (= KCTC 39847T = DSM 103947T).

Uranium tailing is a serious pollution challenge for the environment. Based on metagenomic sequencing analysis, we explored the functional and structural diversity of the microbial community in six soil samples taken at different soil depths from uranium-contaminated and uncontaminated areas. Kyoto Encyclopedia of Genes and Genomes Orthology (KO) groups were obtained using a Basic Local Alignment Search Tool search based on the universal protein resource database. The KO-pathway network was then constructed using the selected KOs. Finally, alpha and beta diversity analyses were performed to explore the differences in soil bacterial diversity between the radioactive soil and uncontaminated soil. In total, 30–68 million high-quality reads were obtained. Sequence assembly yielded 286,615 contigs; and these contigs mostly annotated to 1699 KOs. The KO distributions were similar among the six soil samples. Moreover, the proportion of the metabolism of other amino acids (e.g., beta-alanine, taurine, and hypotaurine) and signal transduction was significantly lower in radioactive soil than in uncontaminated soil, whereas the proportion of membrane transport and carbohydrate metabolism was higher. Additionally, KOs were mostly enriched in ATP-binding cassette transporters and two-component systems. According to diversity analyses, Actinobacteria and Proteobacteria were the dominant phyla in radioactive and uncontaminated soil, and Robiginitalea, Microlunatus, and Alicyclobacillus were the dominant genera in radioactive soil. Taken together, these results demonstrate that soil microbial community, structure, and functions show significant changes in uranium-contaminated soil. The dominant categories such as Actinobacteria and Proteobacteria may be applied in environmental governance for uranium-contaminated soil in southern China.

Marine sponge-associated actinomycetes are considered as promising sources for the discovery of novel biologically active compounds. In the present study, a total of 64 actinomycetes were isolated from 12 different marine sponge species that had been collected offshore the islands of Milos and Crete, Greece, eastern Mediterranean. The isolates were affiliated to 23 genera representing 8 different suborders based on nearly full length 16S rRNA gene sequencing. Four putatively novel species belonging to genera Geodermatophilus, Microlunatus, Rhodococcus and Actinomycetospora were identified based on a 16S rRNA gene sequence similarity of < 98.5% to currently described strains. Eight actinomycete isolates showed bioactivities against Trypanosma brucei brucei TC221 with half maximal inhibitory concentration (IC50) values <20 μg/mL. Thirty four isolates from the Milos collection and 12 isolates from the Crete collection were subjected to metabolomic analysis using high resolution LC-MS and NMR for dereplication purposes. Two isolates belonging to the genera Streptomyces (SBT348) and Micromonospora (SBT687) were prioritized based on their distinct chemistry profiles as well as their anti-trypanosomal activities. These findings demonstrated the feasibility and efficacy of utilizing metabolomics tools to prioritize chemically unique strains from microorganism collections and further highlight sponges as rich source for novel and bioactive actinomycetes.

The ability of Microlunatus phosphovorus to accumulate large amounts of polyphosphate (Poly-P) plays an important role in removing soluble phosphorus from wastewater. Strain JN459, isolated from a sewage system, was previously demonstrated to be Microlunatus phosphovorus. In this study, we analyzed the phosphorus-accumulating and phosphorus-releasing characteristics of strain JN459. Our analyses indicate that strain JN459 accumulates Poly-P under aerobic conditions but releases phosphorus under anaerobic conditions. To determine the mechanisms underlying Poly-P metabolism in strain JN459, we compared transcriptional profiles under aerobic and anaerobic conditions. Significant differences were detected in the expression levels of genes associated with Poly-P metabolism between aerobic and anaerobic conditions, including ppk (MLP_47700, MLP_50300 and MLP_05750), ppgk (MLP_05430 and MLP_26610), ppx (MLP_44770), pap (MLP_23310) and ppnk (MLP_17420). The high expression of polyphosphate glucokinase (MLP_05430) and polyphosphate/ATP-dependent NAD kinase (MLP_17420) indicated that both of them might be responsible for utilizing Poly-P as the energy resource for growth under anaerobic conditions. These findings enhance our understanding of phosphate metabolism in a major bacterial species involved in wastewater phosphorus reduction.

Several previous studies indicated that Actinobacteria may be enriched in soils with elevated content of heavy metals. In this study, we have developed a method for the in-depth analysis of actinobacterial communities in soil through phylum-targeted high-throughput sequencing and used it to address this question and examine the community composition in grassland soils along a gradient of heavy metal contamination (Cu, Zn, Cd, Pb). The use of the 16Sact111r primer specific for Actinobacteria resulted in a dataset obtained by pyrosequencing where over 98 % of the sequences belonged to Actinobacteria. The diversity within the Actinobacterial community was not affected by the heavy metals, but the contamination was the most important factor affecting community composition. The most significant changes in community composition were due to the content of Cu and Pb, while the effects of Zn and Cd were relatively minor. For the most abundant actinobacterial taxa, the abundance of taxa identified as members of the genera Acidothermus, Streptomyces, Pseudonocardia, Janibacter and Microlunatus increased with increasing metal content, while those belonging to Jatrophihabitans and Actinoallomurus decreased. The genus Ilumatobacter contained operational taxonomic units (OTUs) that responded to heavy metals both positively and negatively. This study also confirmed that Actinobacteria appear to be less affected by heavy metals than other bacteria. Because several Actinobacteria were also identified in playing a significant role in cellulose and lignocellulose decomposition in soil, they potentially represent important decomposers of organic matter in such environments.

Continuous cropping has a negative effect on soybean yield. In this study, a positioning experiment was conducted starting in 2015, with three treatments: maize–soybean rotation (SMR), 2-year maize, 2-year soybean rotation cropping (SC2), and 8-year soybean continuous cropping (SC8). We determined soybean yields (2015–2022) and analyzed soil microbial communities, functions, and metabolites composition in the 0–20 cm tillage layer using metagenomics technology and GC–MS technology during soybean flowering in 2022. Results indicated that continuous cropping (SC8) significantly reduced soybean yield compared to crop rotation (SMR) during the experimental period, while SC8 showed higher yield than SC2 in 2022. Compared to SMR, SC8 significantly increased soil N content and significantly decreased pH and TP, AP, and AK content. However, the pH and AK contents of SC8 were significantly higher than those of SC2. LeFSe analysis showed that Friedmanniella, Microlunatus, Nitrososphaera, Rubrobacter, Geodermatophilus, Nitriliruptor were enriched in SC8. Gaiella, Sphaerobacter, Methyloceanibacter were enriched in SC2. Sphingomonas, Cryobacterium, Marmoricola, Haliangium, Arthrobacter, Ramlibacter, Rhizobacter, Pseudolabrys, Methylibium, Variovorax were enriched in SMR. And the relative abundance of Cryobacterium, Marmoricola, Haliangium, Arthrobacter, Ramlibacter, Rhizobacter, Methylibium, Variovorax was significantly positively correlated with yield, while the relative abundance of Gaiella and Sphaerobacter was significantly negatively correlated with yield. SC8 significantly increased the abundance of genes in nitrogen metabolism and significantly decreased the abundance of genes related to phosphorus and potassium metabolism compared with SMR. However, the abundance of genes in potassium metabolism was significantly higher in SC8 than in SC2. Metabolomic analysis showed that compared to SMR, SC8 decreased the abundance of carbohydrates, ketones, and lipid. However, the abundance of carbohydrates, ketones, and lipid was significantly higher in SC8 than in SC2. Mantel test showed that soil pH and AK significantly affected soil microbial community, function, and metabolite composition. Correlation analysis showed significant correlation between soil metabolites and microorganisms, metabolic functions.

The widespread use of harmful fungicides in the agricultural sector has led to a demand for safer alternatives to protect against crop pathogens. The domestic apple is the second most highly consumed fruit in the world and encounters several pre- and post-harvest fungal and bacterial phytopathogens. The goal of this study was to explore the uncharacterized microbiome of a wild apple, Malus trilobata, as a potential source of novel biocontrol agents for two post-harvest fungi that affect commercial apples: Botrytis cinerea and Penicillium expansum. We sampled microflora associated with the leaves, bulk soil, and roots of Malus trilobata in two regions of Lebanon: Ehden reserve in the north and Dhour EL Choueir near Beirut. The two regions have different soil types Dhour EL Choueir and samples from the two regions showed very different microbial compositions, with greater microbial diversity among those from Ehden reserve. Molecular characterization revealed a wide variety of genera displaying activity against the two fungal pathogens, including several with previously unknown antifungal activity: Bosea, Microlunatus, Microbacterium, Mycetecola, Rhizobium and Paraphoma. In total, 92 strains inhibited Penicillium expansum (39%) and 87 strains inhibited Botrytis cinerea (38%) out of 237 screened. Further chemical and genetic characterization of one or more selected strains could pave the way for future development of new biocontrol agents for post-harvest applications.

Phosphorous (P) is widely used in agriculture; yet, P fertilizers are a nonrenewable resource. Thus, mechanisms to improve soil P bioavailability need to be found. Legumes are efficient in P acquisition and, therefore, could be used to develop new technologies to improve soil P bioavailability. Here, we studied different species and varieties of legumes and their rhizosphere microbiome responses to low-P stress. Some varieties of common beans, cowpeas, and peas displayed a similar biomass with and without P fertilization. The rhizosphere microbiome of those varieties grown without P was composed of unique microbes displaying different levels of P solubilization and mineralization. When those varieties were amended with P, some of the microbes involved in P solubilization and mineralization decreased in abundance, but other microbes were insensitive to P fertilization. The microbes that decreased in abundance upon P fertilization belonged to groups that are commonly used as biofertilizers such as Pseudomonas and Azospirillum. The microbes that were not affected by P fertilization constitute unique species involved in P mineralization such as Arenimonas daejeonensis, Hyphomicrobium hollandicum, Paenibacillus oenotherae, and Microlunatus speluncae. These P-insensitive microbes could be used to optimize P utilization and drive future sustainable agricultural practices to reduce human dependency on a nonrenewable resource.

The presence of the olive tree in Tuscany, Italy, in its forms that have survived to the present day as an essential component of the landscape dates back many centuries. Global change is now threatening it. Therefore, it is important to find markers to enhance the olive tree environment in terms of its resilience. The aim of the research was to investigate the composition of soil bacteriomes in contrasting geochemical environments using a geochemistry approach based on the behavior of the REEs, inherited from parent rock material. Bacteriome assemblages and REE content were analyzed in 48 topsoils developed in six geochemical Tuscan environments. Combined geochemical, geoinformatic, and bioinformatic techniques highlighted the existence of four bacteriome assemblages depending on Light-REEs. Further results showed that the soil bioavailable fraction of REEs was related to parent rock materials, pH, and bacteriome composition. The most abundant bacteria were Microlunatus in graded fluvio-lacustrine soils, Gaiella in graded arenaceous soils, Bradyrizhobium in pyroclastic soils, and Rubrobacter in soils on gentle slopes of calcareous and carbonatic lithologies. This research represents a starting point to define new indicators able to assess the resilience of the olive trees in the Mediterranean landscape and characterize the territory of extra virgin olive oils.

Extreme meteorological events and anthropogenic influences determine important variations in microbial community composition. To know the extent of these variations, it is necessary to delve deeper into the geogenic factors to be considered as a baseline. The purpose of this study was to assess the effect of topographic characteristics and soil geochemistry on the spatial distribution of three Actinobacteria genera considered as molecular biomarkers of landforms belonging to Mediterranean environments. Given the important role that Actinobacteria play in the ecosystem, we performed a spatial distribution model of the genera Rubrobacter, Gaiella, and Microlunatus and investigated the fungi/bacteria ratio in a machine learning (ML)-based framework. Variable importance provided insight into the controlling factor of geomicrobial spatial distribution. The spatial distribution of the predicted Actinobacteria genera generally follows topographic constraints, mostly altitude. Rubrobacter was related to the slope aspect and lithium; Microlunatus was related to the topographic wetness index (TWI) and normalized difference water index (NDWI), as well as the fungi/bacteria ratio; and Gaiella was related to flow path and metals. Our results provide new information on the adaptation of Actinobacteria in Mediterranean areas and show the potential of using ML frameworks for the spatial prediction of OTUs distribution.