Ultraviolet Resistance of Microorganisms Isolated from Uranium-Rich Minerals from Perus, Brazil

The district of Perus, located in the city of São Paulo, Brazil, is renowned for its weathered granitic-pegmatitic masses, which harbor a significant number of uraniferous minerals that contribute to ionizing radiation levels up to 20 times higher than the background levels. In this study, aseptically collected mineral samples from the area were utilized to isolate 15 microorganisms, which were subjected to pre-screening tests involving UV-C and UV-B radiation. The microorganisms that exhibited the highest resistance to ultraviolet (UV) radiation were selected for the construction of survival curves for UV-C, broad-band UV-B, and solar simulation resistance testing. Subsequently, the four strains that demonstrated superior survival capabilities under UV radiation exposure were chosen for 16S rRNA gene sequencing. Among these, Nocardioides sp. O4R and Nocardioides sp. MA2R demonstrated the most promising outcomes in the UV radiation resistance assessments, showcasing comparable performance to the well-established radioresistant model organism Deinococcus radiodurans. These findings underscore the potential of naturally occurring high-radiation environments as valuable resources for the investigation of UV-resistant microorganisms. Astrobiology 24, 783-794.

The rhizosphere microbiome of 51 potato cultivars with diverse plant growth characteristics

Rhizosphere microbial communities play a substantial role in plant productivity. We studied the rhizosphere bacteria and fungi of 51 distinct potato cultivars grown under similar greenhouse conditions using a metabarcoding approach. As expected, individual cultivars were the most important determining factor of the rhizosphere microbial composition; however, differences were also obtained when grouping cultivars according to their growth characteristics. We showed that plant growth characteristics were related to deterministic and stochastic assembly processes of bacterial and fungal communities, respectively. The bacterial genera Arthrobacter and Massilia (known to produce indole acetic acid and siderophores) exhibited greater relative abundance in high- and medium-performing cultivars. Bacterial co-occurrence networks were larger in the rhizosphere of these cultivars and were characterized by a distinctive combination of plant beneficial Proteobacteria and Actinobacteria along with a module of diazotrophs namely Azospira, Azoarcus, and Azohydromonas. Conversely, the network within low-performing cultivars revealed the lowest nodes, hub taxa, edges density, robustness, and the highest average path length resulting in reduced microbial associations, which may potentially limit their effectiveness in promoting plant growth. Our findings established a clear pattern between plant productivity and the rhizosphere microbiome composition and structure for the investigated potato cultivars, offering insights for future management practices.

Nocardioides potassii sp. nov., isolated from weathered potash tailings soil

A Gram-positive, aerobic actinomycete, designated strain KLBMP 9356^T, was isolated from weathered potash tailings soil sampled in Xuzhou, Jiangsu Province, PR China. The colonies were cream-coloured, convex and rounded. The optimal growth conditions of strain KLBMP 9356^T were 1 % (w/v) NaCl, 28 °C and pH 7. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain KLBMP 9356^T showed the highest similarity to Nocardioides zhouii CGMCC 1.11084^T (98.9 %) and Nocardioides glacieisoli CGMCC 1.11097^T (98.7 %). Results from two tree-making algorithms supported the position that strain KLBMP 9356^T forms a stable clade with N. zhouii CGMCC 1.11084^T and N. glacieisoli CGMCC 1.11097^T. Strain KLBMP 9356^T exhibited low digital DNA-DNA hybridization values with N. zhouii CGMCC 1.11084T (27.6 %) and N. glacieisoli CGMCC 1.11097^T (31.4 %). The average nucleotide identity values between strain KLBMP 9356^T and N. zhouii CGMCC 1.11084^T and N. glacieisoli CGMCC 1.11097^T were 83.8% and 85.9%, respectively. The peptidoglycan in the cell wall of the novel strain was ll-2,6-diaminopimelic acid and the predominant menaquinone was MK-8(H₄). The major fatty acids (>10 %) were C_17:1ω8c and C_18:1ω9c. The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol, lyso-phospatidylglycerol and phosphatidylinositol. The genomic DNA G+C content was 71.6 mol%. Based on its morphological, chemotaxonomic and phylogenetic characteristics, strain KLBMP 9356^T represents a novel species of the genus Nocardioides, for which the name Nocardioides potassii sp. nov. is proposed. The type strain is KLBMP 9356^T (=CGMCC 4.7738^T=NBRC 115493^T).

Nocardioides palaemonis sp. nov. and Tessaracoccus palaemonis sp. nov., isolated from the gastrointestinal tract of lake prawn

Two novel Gram-stain-positive, non-motile and non-spore-forming bacterial strains, designated J2M5^T and J1M15^T, were isolated from the gastrointestinal tract of a lake prawn Palaemon paucidens. Strain J2M5^T was an obligately aerobic bacterium that formed milky-coloured colonies and showed a rod-coccus cell cycle, while strain J1M15^T was a facultatively aerobic bacterium that formed orangish-yellow-coloured colonies and showed rod-shaped cells. Strains J2M5^T and J1M15^T showed the highest 16S rRNA gene sequence similarity to Nocardioides ganghwensis JC2055^T (98.63 %) and Tessaracoccus flavescens SST-39^T (98.08 %), respectively. The whole-genome sequence of strain J2M5^T was 4.52 Mbp in size and the genomic G+C content directly calculated from the genome sequence of strain J2M5^T was 72.5 mol%. The whole-genome sequence of strain J1M15^T was 3.20 Mbp in size and the genomic G+C content directly calculated from the genome sequence of strain J1M15^T was 69.6mol %. Strains J2M5^T and J1M15^T showed high OrthoANI similarity to N. ganghwensis JC2055^T (83.6 %) and T. flavescens (77.2 %), respectively. We analysed the genome sequences of strains J2M5^T and J1M15^T in terms of carbohydrate-active enzymes, antibiotic resistance genes and virulence factor genes. Strains J2M5^T and J1M15^T contained MK-8 (H₄) and MK-9 (H₄) as the predominant respiratory quinones, respectively. The major polar lipids of both strains were phosphatidylglycerol and diphosphatidylglycerol. Additionally, strain J2M5^T possessed phosphatidylcholine, phosphatidylserine and phosphatidylethanolamine. The cellular sugar components of strain J2M5^T were ribose, mannose, glucose and galactose, and its cellular amino acid components were l-alanine and l-lysine. The cellular sugar components of strain J1M15^T were rhamnose, ribose, mannose and glucose, and its cellular amino acid component was l-alanine. The major cellular fatty acids of strains J2M5^T and J1M15^T were iso-C_{16 : 0} and anteiso-C_15 : 0, respectively. The multiple taxonomic analyses indicated that strains J2M5^T and J1M15^T represent novel species of the genus Nocardioides and Tessaracoccus, respectively. We propose the names Nocardioides palaemonis sp. nov. and Tessaracoccus palaemonis sp. nov. for strain J2M5^T (=KCTC 49461^T=CCUG 74767^T) and strain J1M15^T (=KCTC 49462^T=CCUG 74766^T), respectively.

Uncovering the biodiversity and biosynthetic potentials of rare actinomycetes

Background

Antibiotic resistance is on the rise, and new antibiotic research has slowed in recent years, necessitating the discovery of possibly novel microbial resources capable of producing bioactive compounds. Microbial infections are gaining resistance to existing antibiotics, emphasizing the need for novel medicinal molecules to be discovered as soon as possible. Because the possibilities of isolating undiscovered actinomycetes strains have decreased, the quest for novel products has shifted to rare actinomycetes genera from regular environments or the identification of new species identified in unusual habitats.

Main body of the abstract

The non-streptomyces actinobacteria are known as rare actinomycetes that are extremely difficult to cultivate. Rare actinomycetes are known to produce a variety of secondary metabolites with varying medicinal value. In this review, we reported the diversity of rare actinomycetes in several habitat including soil, plants, aquatic environment, caves, insects and extreme environments. We also reported some isolation methods to easily recover rare Actinobacteria from various sources guided with some procedures to identify the rare Actinobacteria isolates. Finally, we reported the biosynthetic potential of rare actinomycetes and its role in the production of unique secondary metabolites that could be used in medicine, agriculture, and industry. These microbial resources will be of interest to humanity, as antibiotics, insecticides, anticancer, antioxidants, to mention but a few.

Short conclusion

Rare actinomycetes are increasingly being investigated for new medicinal compounds that could help to address existing human health challenges such as newly emerging infectious illnesses, antibiotic resistance, and metabolic disorders. The bioactive secondary metabolites from uncommon actinomycetes are the subject of this review, which focuses on their diversity in different habitats, isolation, identification and biosynthetic potentials.

Streptomyces genisteinicus sp. nov., a novel genistein-producing actinomycete isolated from a Chinese medicinal plant and proposal of Streptomyces michiganensis Corbaz et al. 1957 as a later heterotypic synonym of Streptomyces xanthochromogenes Arishima et al. 1956

A novel genistein-producing actinobacterial strain, designated strain CRPJ-33^T, was isolated from the healthy leaves of a medicinal plant Xanthium sibiricum collected from Hunan Province, PR China. 16S rRNA gene sequence analysis indicated strain CRPJ-33^T belonged to the genus Streptomyces and had 99.7, 99.0, 98.9, 98.9, 98.8 and 98.7% sequence similarities to Streptomyces zhihengii YIM T102^T, Streptomyces eurocidicus NRRL B-1676^T, Streptomyces xanthochromogenes NRRL B-5410^T, Streptomyces michiganensis NBRC 12797^T, Streptomyces mauvecolor LMG 20100^T and Streptomyces lavendofoliae NBRC 12882^T, respectively. Phylogenetic analysis of 16S rRNA gene sequences showed that strain CRPJ-33^T was most closely related to S. zhihengii YIM T102^T. However, digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values between them were much less than the recommended threshold values. Furthermore, differential comparisons of the phenotypic characteristics were enough to distinguish strain CRPJ-33^T from S. zhihengii YIM T102^T. Meanwhile, the ANI and dDDH values or MLSA distances between strain CRPJ-33^T and other type strains, which exhibited ≥98.7 % 16S rRNA gene sequence similarities to strain CRPJ-33^T, were far away from the recommended threshold values. Based on these results, it is thought that strain CRPJ-33^T should represent a novel species of the genus Streptomyces, for which the name Streptomyces genisteinicus sp. nov. is proposed. The type strain is CRPJ-33^T (=MCCC 1K04965^T=JCM 34526^T). In addition, the phenotypic, chemotaxonomic and genotypic characteristics, as well as phylogenetic information revealed that the type strains of S. xanthochromogenes and S. michiganensis should belong to same genomic species. Consequently, it is proposed that S. michiganensis is a heterotypic synonym of S. xanthochromogenes for which an emended description is given.

Exploration of Intrinsic Microbial Community Modulators in the Rice Endosphere Indicates a Key Role of Distinct Bacterial Taxa Across Different Cultivars

Microbial communities associated with the plant phyllosphere and endosphere can have both beneficial as well as detrimental effects on their hosts. There is an ongoing debate to which extend the phyllosphere and endosphere microbiome assembly is controlled by the host plant how pronounced cultivar effects are. We investigated the bacterial and fungal communities from the phyllosphere and endosphere of 10 different rice cultivars grown under identical environmental conditions in the frame of a targeted approach to identify drivers of community assembly. The results indicated that the endophytic bacterial communities were clearly separated into two groups. The α-diversity and microbial network complexity within Group I were significantly lower than in Group II. Moreover, the genera Nocardioides, Microvirga, and Gaiella were significantly more abundant in Group II and only present in the interaction networks of this group. These three genera were significantly correlated with α- and β-diversity of the endophytic bacterial community and thus identified as major drivers of the endosphere community. We have identified keystone taxa that shape endophytic bacterial communities of different rice cultivars. Our overall findings provide new insights into plant-microbe interactions, and may contribute to targeted improvements of rice varieties in the future.

Marine Rare Actinomycetes: A Promising Source of Structurally Diverse and Unique Novel Natural Products

Rare actinomycetes are prolific in the marine environment; however, knowledge about their diversity, distribution and biochemistry is limited. Marine rare actinomycetes represent a rather untapped source of chemically diverse secondary metabolites and novel bioactive compounds. In this review, we aim to summarize the present knowledge on the isolation, diversity, distribution and natural product discovery of marine rare actinomycetes reported from mid-2013 to 2017. A total of 97 new species, representing 9 novel genera and belonging to 27 families of marine rare actinomycetes have been reported, with the highest numbers of novel isolates from the families Pseudonocardiaceae, Demequinaceae, Micromonosporaceae and Nocardioidaceae. Additionally, this study reviewed 167 new bioactive compounds produced by 58 different rare actinomycete species representing 24 genera. Most of the compounds produced by the marine rare actinomycetes present antibacterial, antifungal, antiparasitic, anticancer or antimalarial activities. The highest numbers of natural products were derived from the genera Nocardiopsis, Micromonospora, Salinispora and Pseudonocardia. Members of the genus Micromonospora were revealed to be the richest source of chemically diverse and unique bioactive natural products.

Biostimulation of carbonate precipitation process in soil for copper immobilization

The urease-based microbially induced carbonate precipitation (MICP) is known as effective remediation strategy in soil metals remediation; however, all related studies confined to bioaugmentation. In the present study, biostimulation process was adopted for the first time in accelerating MICP in copper (Cu) immobilization in soil. The abundance, composition, and diversity of the bacterial community after biostimulation were assessed with MiSeq Illumina sequencing analysis that confirmed number and types of ureolytic and calcifying bacteria grown significantly leading to MICP process, compared to untreated soil. The results demonstrated that biostimulation induced calcite precipitation in soil that immobilized Cu mainly in carbonated fraction of soil, while soluble-exchangeable fraction decreased from 45.54 mg kg^-1 to 1.55 mg kg^-1 Cu in soil. Scanning electron microscopy (SEM) cum energy-dispersive X-ray spectroscopy (EDX) evaluated structure and elemental composition in Cu immobilization after biostimulation. Fourier Transform-Infra Red (FTIR) spectroscopy depicted functional chemical groups involved in copper immobilization, while X-Ray Diffraction (XRD) identified main crystalline phases or biominerals formed during biostimulation in order to carryout Cu remediation from soil.

Nocardioides silvaticus sp. nov., isolated from forest soil

A Gram-stain-positive, non-motile, rod-shaped bacterial strain S-34^T was isolated from forest soil. According to 16S rRNA gene sequence analysis, strain S-34^T was related to Nocardioides members and showed the highest similarities to Nocardioides thalensis NCCP-696^T (97.3 %) and Nocardioides panacisoliGsoil 346^T (97.0 %), Nocardioides litorisoli X-2^T (96.5 %) and Nocardioides immobilis FLL521^T (96.4 %). Phylogenetic trees showed that strain S-34^T fell within the cluster containing strain S-34^T and N. immobilis FLL521^T. The levels of DNA-DNA relatedness between strain S-34^T and N. thalensis CCTCC AB 2016296^T and between strain S-34^T and N. panacisoli KCTC 19470^T were 50.6 and 58.8 %, respectively. The genome orthoANI value between strain S-34^T and N. immobilis CCTCC AB 2017083^T was 82.4 %. Strain S-34^T had ll-diaminopimelic acid in the cell-wall peptidoglycan, diphosphatidylglycerol, phosphatidylglycerol, four unknown phospholipids and one unknown lipid as the polar lipids, meanquinone-8(H4) as the only respiratory quinone and iso-C16 : 0, C17:1ω8c, C17:1ω6c, C17 : 0 and C17 : 0 10-methyl (tbsa) as the major fatty acids. The genome length of strain S-34^T was 4.53 Mb containing 52 contigs and with a DNA G+C content of 71.2 mol%. Strain S-34^T could be distinguished from the other Nocardioides members mainly based on the data of phylogenetic analyses, DNA-DNA hybridization, polar lipids and some biochemical differences. Therefore, strain S-34^T represents a novel species of the genus Nocardioides, for which the name Nocardioidessilvaticus sp. nov. is proposed. The type strain is S-34^T (=KCTC 49137^T=CCTCC AB 2018079^T).

Nocardioides astragali sp. nov., isolated from a nodule of wild Astragalus chrysopterus in northwestern China

A Gram-positive, non-motile, rod-shaped bacterial strain, designated HH06^T, was isolated from a nodule of Astragalus chrysopterus in northwestern China. Phylogenetic analysis of the 16S rRNA gene sequence showed that the strain is closely related to Nocardioides alpinus Cr7-14^T and Nocardioides furvisabuli DSM 18445^T with 98.5 and 98.1% similiarity, respectively. Growth was observed at 4–28 °C in R2A medium (optimum at 25 °C), at 10–30 °C in YMA and LB medium (optimum in both at 28 °C) and at pH 5.0–10.0 in R2A medium (optimum at pH 7.0–8.0). The cell wall peptidoglycan was found to contain LL-diaminopimelic acid as the principal diamino acid and MK-8(H4) was identified as the predominant menaquinone. The major polar lipids were identified as phosphatidylinositol, phosphatidylglycerol, diphosphatidylglycerol, phosphatidylcholine, two unidentified glycolipids and two unidentified polar lipids. The major fatty acids were identified as iso-C_16:0 (32.8%) and C_18:1ω9c (15.1%). The DNA G+C content of strain HH06^T was determined to be 71.4 mol%. Based on phenotypic, chemotaxonomic, phylogenetic properties and DNA–DNA relatedness, it is concluded that strain HH06^T represents a novel species of the genus Nocardioides, for which the name Nocardioides astragali sp. nov. is proposed. The type strain is HH06^T (= CGMCC 4.7327^T = NBRC 112322^T).

Nocardioides sonneratiae sp. nov., an endophytic actinomycete isolated from a branch of Sonneratia apetala

A Gram-staining-positive, aerobic non-spore-forming and short-rod-shaped endophytic actinomycete was isolated from a branch of Sonneratia apetala, designated strain BGMRC0092T and investigated in detail data to determine its taxonomic position. On the basis of the 16S rRNA gene sequence analysis, the results of the phylogenetic analyses indicated that BGMRC0092T was most closely related to Nocardioides alpinus Cr7-14T (96.9 %), Nocardioides oleivorans DSM16090T (96.4 %) and Nocardiodes exalbidus RC825T (96.3 %). The predominant cellular fatty acids of BGMRC0092T were iso-C16 : 0 and C18 : 1ω8c. The major menaquinone was MK-8(H4). The diagnostic diamino acid in the cell-wall peptidoglycan was ll-2,6-diaminopimelic acid. The predominant cell-wall sugars were composed of galactose, mannose, rhamnose and xylose. The polar lipid pattern contained diphosphatidylglycerol, phosphatidylglycerol, phosphatidylcholine, one unknown phospholipid and three unknown polar lipids. The DNA G+C content was 69.3 mol%. On the basis of phenotypic and chemotaxonomic characteristics and the results of phylogenetic analysis, BGMRC0092T represents a novel species of the genus Nocardioides, for which the name Nocardioides sonneratiae sp. nov. is proposed. The type strain is Nocardioides sonneratiae BGMRC0092T (=KCTC 39565T=NBRC 110251 T=DSM 100390T).

Nocardioides thalensis sp. nov., isolated from a desert

A novel actinobacterial strain, designated NCCP-696T, was isolated from the Thal desert in Punjab, Pakistan, and characterized by using a polyphasic taxonomy approach. Phylogenetic analyses based on 16S rRNA gene sequences showed that strain NCCP-696T belongs to the genus Nocardioides and showed the highest level of sequence similarity with respect to Nocardioides panacisoliGsoil 346T (98.2 %) and less than 96.4 % to the strains of other species of the genus Nocardioides. Cells of strain NCCP-696T were Gram-positive, aerobic, non-motile rods and formed cream-coloured colonies. The strain was positive for oxidase and catalase. Growth occurred at 20-42 °C (optimum 30-37 °C) at pH 5.5-9.0 (optimum pH 7.0) and with 0-4 % NaCl (optimum 0-2 %, w/v). Strain NCCP-696T contained Iso-C16 : 0, C18 : 1ω9c, C17 : 1ω8c and C17 : 0 as the predominant fatty acids and was found to have LL-2,6-diaminopimelic acid in the cell-wall peptidoglycan. The polar lipid profile consisted of phosphatidylinositol, phosphatidylglycerol and one unknown phospholipid. The major menaquinone was MK-8(H4) (98.7 %) while a minor amount (1.3 %) of MK-9(H2) was also detected. The DNA G+C content of the genomic DNA was 71.6 mol%. The DNA-DNA hybridization value of the isolate against the closely related type strain Nocardioides panacisoliGsoil 346T was 56.3±1.4. On the basis of the phylogenetic inference, chemotaxonomic characteristics and phenotypic data, strain NCCP-696T should be classified as a novel species, for which the name Nocardioides thalensis sp. nov. is proposed. The type strain is NCCP-696T (=DSM 103833T=CCTCC AB 2016296T).