Blastococcus colisei sp. nov, isolated from an archaeological amphitheatre

Ecogenomic insights into the resilience of keystone Blastococcus Species in extreme environments: a comprehensive analysis

BACKGROUND

The stone-dwelling genus Blastococcus plays a key role in ecosystems facing extreme conditions such as drought, salinity, alkalinity, and heavy metal contamination. Despite its ecological significance, little is known about the genomic factors underpinning its adaptability and resilience in such harsh environments. This study investigates the genomic basis of Blastococcus's adaptability within its specific microniches, offering insights into its potential for biotechnological applications.

RESULTS

Comprehensive pangenome analysis revealed that Blastococcus possesses a highly dynamic genetic composition, characterized by a small core genome and a large accessory genome, indicating significant genomic plasticity. Ecogenomic assessments highlighted the genus's capabilities in substrate degradation, nutrient transport, and stress tolerance, particularly on stone surfaces and archaeological sites. The strains also exhibited plant growth-promoting traits, enhanced heavy metal resistance, and the ability to degrade environmental pollutants, positioning Blastococcus as a candidate for sustainable agriculture and bioremediation. Interestingly, no correlation was found between the ecological or plant growth-promoting traits (PGPR) of the strains and their isolation source, suggesting that these traits are not linked to their specific environments.

CONCLUSIONS

This research highlights the ecological and biotechnological potential of Blastococcus species in ecosystem health, soil fertility improvement, and stress mitigation strategies. It calls for further studies on the adaptation mechanisms of the genus, emphasizing the need to validate these findings through wet lab experiments. This study enhances our understanding of microbial ecology in extreme environments and supports the use of Blastococcus in environmental management, particularly in soil remediation and sustainable agricultural practices.

Discovery and synthesis of leaderless bacteriocins from the Actinomycetota

Leaderless bacteriocins are a unique class of bacteriocins that possess antimicrobial activity after translation and have few cases of documented resistance. Aureocin A53 and lacticin Q are considered two of the most well-studied leaderless bacteriocins. Here, we used in silico genome mining to search for novel aureocin A53-like leaderless bacteriocins in GenBank and MGnify. We identified 757 core peptides across 430 genomes with 75 species found currently without characterized leaderless bacteriocin production. These include putative novel species containing bacteriocin gene clusters (BGCs) from the genera Streptomyces (sp. NBC_00237) and Agrococcus (sp. SL85). To date, all characterized leaderless bacteriocins have been found within the phylum Bacillota, but this study identified 97 core peptides within the phylum Actinomycetota. Members of this phylum are traditionally associated with the production of antibiotics, such is the case with the genus Streptomyces. Actinomycetota is an underexplored phylum in terms of bacteriocin production with no characterized leaderless bacteriocin production to date. The two novel leaderless bacteriocins arcanocin and arachnicin from Actinomycetota members Arcanobacterium sp. and Arachnia sp., respectively, were chemically synthesized and antimicrobial activity was verified. These peptides were encoded in human gut (PRJNA485056) and oral (PRJEB43277) microbiomes, respectively. This research highlights the biosynthetic potential of Actinomycetota in terms of leaderless bacteriocin production and describes the first antimicrobial peptides encoded in the genera Arcanobacterium and Arachnia.IMPORTANCEBacteriocins are gathering attention as alternatives to current antibiotics given the increasing incidence of antimicrobial resistance. Leaderless bacteriocins are considered a commercially attractive subclass of bacteriocins due to the ability to synthesize active peptide and low levels of documented resistance. Therefore, in this work, we mined publicly available data to determine how widespread and diverse leaderless bacteriocins are within the domain of bacteria. Actinomycetota, known for its antibiotic producers but lacking described and characterized bacteriocins, proved to be a rich source of leaderless bacteriocins-97 in total. Two such peptides, arcanocin and arachnicin, were chemically synthesized and have antimicrobial activity. These bacteriocins may provide a novel source of novel antimicrobials that could aid in the development of future alternative antimicrobials and highlight that the Actinomycetota are an underexplored resource of bacteriocin peptides.

Blastococcus montanus sp. nov., a multi-stress-resistant and bacteriostatic-producing bacterium isolated from the Flaming Mountain, Xinjiang,China

A bacterial strain designated HT6-4T was isolated from soil samples collected from the Flaming Mountain, Xinjiang, PR China. The purpose of this study was to describe a novel species and its characteristics, through genome sequencing and analysis of the relationship between the members of the genus Blastococcus, and explore the antiradiation, antioxidation and antibacterial capabilities of strain HT6-4T. The polyphasic study confirmed the affiliation of strain HT6-4T with the genus Blastococcus. Strain HT6-4T was aerobic, Gram-stain-positive, non-budding, non-motile, catalase-positive and oxidase-negative. It grew at 10-37 °C, pH 5.0-8.0 and 0-4% (w/v) NaCl. Colonies were circular, smooth and bright orange in colour. In addition, strain HT6-4T was drought tolerant. The predominant menaquinone was MK-9, with MK-8 as the minor component. The polar lipids of strain HT6-4T were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, phosphatidylinositol, phospholipids, an unidentified aminolipid and two unidentified phospholipids. Whole-cell hydrolysates contain meso-diaminopimelic acid as the diagnostic diamino acid and ribose and galactose as diagnostic sugars. Its major fatty acids were iso-C16 :  0, C17 :  1 ω8c and C18 :  1 ω9c. The genome of strain HT6-4T was 4.30 Mb in the whole-genome shotgun project. The G+C content was 73.9 mol%. The phylogenetic analysis based on the 16S rRNA gene sequence showed that strain HT6-4T was closely related to Blastococcus jejuensis KST3-10T(97.9%), Blastococcus capsensis BMG 804T(97.8%), Blastococcus aggregatus DSM 4725T(97.5%), Blastococcus saxobsidens BC 444T(97.5%), Blastococcus xanthinilyticus BMG 862T(97.5%) and Blastococcus litoris GP-S2-8T(97.5%). The average nucleotide identity (OrthoANI) and digital DNA-DNA hybridization (dDDH) values among strain HT6-4T and B. jejuensis KST3-10T, B. capsensis BMG 804T, B. aggregatus DSM 4725T, B. saxobsidens BC 444T, B. xanthinilyticus BMG 862T and B. litoris GP-S2-8T were below the species delimitation thresholds. The genome of strain HT6-4T contained antiradiation genes, antioxidant genes and antibacterial genes. Based on its morphological, physiological and chemical taxonomic characteristics, strain HT6-4T (=KCTC 59234T =GDMCC 1.4386T) should be classified as a novel species of the genus Blastococcus with the proposed name Blastococcus montanus sp. nov.

Blastococcus brunescens sp. nov., a member of the Geodermatophilaceae isolated from sandstone collected from the Sahara Desert in Tunisia

The taxonomic position of strain BMG 8361T, isolated from sandstone collected in the Sahara Desert of Southern Tunisia, was refined through a polyphasic taxonomic investigation. Colonies of BMG 8361T were pale-orange coloured, irregular with a dry surface and produced a diffusible pink or brown pigment depending on media. The Gram-positive cells were catalase-positive and oxidase-negative. The strain exhibited growth at 10-40 °C and pH values ranging from 5.5 to 9.0, with optima at 28-35 °C and pH 6.5-8.0. Additionally, BMG 8361T demonstrated the ability to grow in the presence of up to 1 % NaCl (w/v) concentration. The peptidoglycan of the cell wall contained meso-diaminopimelic acid, glucose, galactose, xylose, ribose, and rhamnose. The predominant menaquinones consisted of MK-9(H4) and MK-9. The main polar lipids were phosphatidylcholine, phosphatidylinositol, glycophosphatidylinositol, diphosphatidylglycerol, phosphatidylethanolamine, and two unidentified lipids. Major cellular fatty acids were iso-C16 : 0, iso-C16 : 1 h, and C17 : 1  ω8c. Phylogenetic analyses based on both the 16S rRNA gene and whole-genome sequences assigned strain BMG 8361T within the genus Blastococcus. The highest pairwise sequence similarity observed in the 16S rRNA gene was 99.5 % with Blastococcus haudaquaticus AT 7-14T. However, when considering digital DNA-DNA hybridization and average nucleotide identity, the highest values, 48.4 and 86.58 %, respectively, were obtained with Blastococcus colisei BMG 822T. These values significantly undershoot the recommended thresholds for establishing new species, corroborating the robust support for the distinctive taxonomic status of strain BMG 8361T within the genus Blastococcus. In conjunction with the phenotyping results, this compelling evidence leads to the proposal of a novel species we named Blastococcus brunescens sp. nov. with BMG 8361T (=DSM 46845T=CECT 8880T) as the type strain.

Blastococcus carthaginiensis sp. nov., isolated from a monument sampled in Carthage, Tunisia

A comprehensive polyphasic investigation was conducted to elucidate the taxonomic position of an actinobacterium, designated BMG 814T, which was isolated from the historic ruins of Carthage city in Tunisia. It grew as pink-orange pigmented colonies and displayed versatile growth capabilities, thriving within a temperature range of 20-40 °C, across a pH spectrum ranging from pH 5.5 to 10 and in the presence of up to 4 % NaCl. Chemotaxonomic investigations unveiled specific cell components, including diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, glycophosphatidylinositol, an unidentified aminoglycophospholipid, six unidentified aminolipids, two unidentified phospholipids and one unidentified lipid in its polar lipid profile. Furthermore, galactose, glucose and ribose were identified as the primary cell-wall sugars. Major menaquinones identified were MK-9(H4), MK-9(H2) and MK-9, while major fatty acids comprised iso-C15 : 0, iso-C16 : 0, C17 : 1  ω8c and C18 : 1  ω9c. Through phylogenetic analysis based on the 16S rRNA gene sequence, the strain was positioned within the genus Blastococcus, with Blastococcus capsiensis BMG 804T showing the closest relationship (99.1 %). In light of this, draft genomes for both strains, BMG 814T and BMG 804T, were sequenced in this study, and comparative analysis revealed that strain BMG 814T exhibited digital DNA-DNA hybridization and average nucleotide identity values below the recommended thresholds for demarcating new species with all available genomes of type strains of validly names species. Based on the polyphasic taxonomy assessment, strain BMG 814T (=DSM 46848T=CECT 8878T) was proposed as the type strain of a novel species named Blastococcus carthaginiensis sp. nov.

Genotype-phenotype correlations within the Geodermatophilaceae

The integration of genomic information into microbial systematics along with physiological and chemotaxonomic parameters provides for a reliable classification of prokaryotes. In silico analysis of chemotaxonomic traits is now being introduced to replace characteristics traditionally determined in the laboratory with the dual goal of both increasing the speed of the description of taxa and the accuracy and consistency of taxonomic reports. Genomics has already successfully been applied in the taxonomic rearrangement of Geodermatophilaceae (Actinomycetota) but in the light of new genomic data the taxonomy of the family needs to be revisited. In conjunction with the taxonomic characterisation of four strains phylogenetically located within the family, we conducted a phylogenetic analysis of the whole proteomes of the sequenced type strains and established genotype-phenotype correlations for traits related to chemotaxonomy, cell morphology and metabolism. Results indicated that the four isolates under study represent four novel species within the genus Blastococcus. Additionally, the genera Blastococcus, Geodermatophilus and Modestobacter were shown to be paraphyletic. Consequently, the new genera Trujillonella, Pleomorpha and Goekera were proposed within the Geodermatophilaceae and Blastococcus endophyticus was reclassified as Trujillonella endophytica comb. nov., Geodermatophilus daqingensis as Pleomorpha daqingensis comb. nov. and Modestobacter deserti as Goekera deserti comb. nov. Accordingly, we also proposed emended descriptions of Blastococcus aggregatus, Blastococcus jejuensis, Blastococcus saxobsidens and Blastococcus xanthilyniticus. In silico chemotaxonomic results were overall consistent with wet-lab results. Even though in silico discriminatory levels varied depending on the respective chemotaxonomic trait, this approach is promising for effectively replacing and/or complementing chemotaxonomic analyses at taxonomic ranks above the species level. Finally, interesting but previously overlooked insights regarding morphology and ecology were revealed by the presence of a repertoire of genes related to flagellum synthesis, chemotaxis, spore production and pilus assembly in all representatives of the family. A rich carbon metabolism including four different CO2 fixation pathways and a battery of enzymes able to degrade complex carbohydrates were also identified in Blastococcus genomes.

Blastococcus tunisiensis sp. nov., isolated from limestone collected in Tunisia

A new actinobacterium strain, designated BMG 823T, was isolated from a limestone sample collected in Tunisia. Its taxonomic position was scrutinized using a polyphasic approach. Colonies of strain BMG 823T were pink orange-coloured, regular and had a moist surface. Cells are Gram-stain-positive, catalase-negative and oxidase-negative. The strain grew at pH 5.5–9, 10–40 °C and in presence of up to 4 % NaCl (w/v). Chemotaxonomically, strain BMG 823T was characterized by cell-wall type III containing meso-diaminopimelic acid as diamino acid, glucose, ribose and rhamnose as whole-cell sugars, MK-9(H4) as predominant menaquinone, and phosphatidylcholine, diphosphadidylglycerol, phosphatidethanolamine, phosphatidylcholine, phosphatidylinositol, unidentified glycolipid, unidentified aminophospholipids and unidentified glycophospholipid as major polar lipids. The fatty acid profile consisted of iso-C16 : 0 and iso-C17 : 1  ω9. Phylogenetic trees based on 16S rRNA gene and genome sequences placed strain BMG 823T within the genus Blastococcus and separated it from all type strains of validly published species. Comparison of 16S rRNA gene sequence similarity, digital DNA–DNA hybridization and average nucleotide identity indicated that strain BMG 823T was most closely related to Blastococcus litoris DSM 106127T and Blastococcus colisei BMG 822T with pairwise values well below the species differentiation thresholds. The distinct phenotypic and genotypic features of strain BMG 823T (=DSM 46838T=CECT 8881T) within the genus Blastococcus warrant its recognition as the type strain for the new species for which we propose the name Blastococcus tunisiensis sp. nov.

Culturable bacteria from two Portuguese salterns: diversity and bioactive potential

Salterns are extreme environments, where the high salt concentration is the main limitation to microbial growth, along with solar radiation, temperature and pH. These selective pressures might lead to the acquisition of unique genetic adaptations that can manifest in the production of interesting natural products. The present study aimed at obtaining the culturable microbial diversity from two Portuguese salterns located in different geographic regions. A total of 190 isolates were retrieved and identified as belonging to 30 genera distributed among 4 phyla-Firmicutes, Proteobacteria, Actinobacteria and Bacteroidetes. Specifically, members of the genus Bacillus were the most frequently isolated from both salterns and all actinobacterial isolates belong to the rare members of this group. The molecular screening of NRPS and PKS-I genes allowed the detection of 38 isolates presenting PKS-I, 25 isolates presenting NRPS and 23 isolates presenting both types of biosynthetic genes. Sequencing of randomly selected amplicons revealed similarity with known PKS-I and NRPS genes or non-annotated hypothetical proteins. This study is the first contribution on the culturable bacterial diversity of Portuguese salterns and on their bioactive potential. Ultimately, these findings provide a novel contribution to improve the understanding on the microbial diversity of salterns.

Blastococcus deserti sp. nov., isolated from a desert sample

A Gram-positive and aerobic actinobacterium, strain SYSU D8006^T, was isolated from a desert sand sample collected from Gurbantunggut desert, China. Phenotypically, the strain was found to grow at 14-50 °C, pH 6.0-9.0 and in the presence of up to 4% (w/v) NaCl. The chemotaxonomic features of strain SYSU D8006^T included menaquinone MK-9(H₄) as the respiratory quinone, diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol and phosphatidylinositol mannoside as known polar lipids, iso-C_15:0, iso-C_16:0, C_17:1ω8c and C_18:1ω9c as the predominant fatty acids, and arabinose, galactose and glucose as the whole cell sugars. Strain SYSU D8006^T shared the highest 16S rRNA gene sequence identity with Blastococcus jejuensis DSM 19597^T (98.2%). Based on the analyses of the phenotypic, genotypic and phylogenetic characteristics, strain SYSU D8006^T is characterized to represent a novel species of the genus Blastococcus, for which the name Blastococcus deserti sp. nov. is proposed. The type strain is SYSU D8006^T (= CGMCC 1.15935^T = KCTC 49026^T = CPCC 204618^T).

Blastococcus litoris sp. nov., isolated from sea-tidal flat sediment

A novel Gram-strain-positive, non-spore-forming bacterial strain, designated GP-S2-8^T, was isolated from a sea-tidal flat sediment sample from Gopado, Republic of Korea. Cells were aerobic, catalase-negative, oxidase-positive, non-motile and cocci, occurring singly, in pairs or in tetrads, and often tending to form aggregates. The strain grew at 4-45 °C (optimum, 28-37 °C), at pH 4.0-11.0 (pH 7.0-9.0) and in the presence of 0-11 % (w/v) NaCl (0-3 %). Phylogenetic analyses based on 16S rRNA gene sequences represented that the isolate belongs to the genus Blastococcus. The diagnostic diamino acid in the cell-wall peptidoglycan was meso-diaminopimelic acid. Whole-cell sugar analysis of strain GP-S2-8^T revealed rhamnose, glucose and mannose as characteristic sugars. The predominant respiratory quinone was MK-9(H4) and the major fatty acids were iso-C16 : 0, iso-C16 : 1 H, summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c), iso-C15 : 0 and iso-C14 : 0. The polar lipid profile included diphosphadidylglycerol, phosphatidylethanolamine, phosphatidylcholine, phosphatidylinositol, one unidentified glycophospholipid, two unidentified phospholipids and five unidentified lipids. The DNA G+C content was 74.2 mol%. DNA-DNA relatedness values between strain GP-S2-8^T and type strains of the genus Blastococcus ranged from 14.6 to 48.6 %. On the basis of the phenotypic differences and DNA-DNA relatedness data, the isolate represents a new species of the genus Blastococcus, for which the name Blastococcuslitoris sp. nov. is proposed. The type strain is GP-S2-8^T (=KCCM 43275^T=JCM 32354^T=DSM 106127^T=KCTC 49078^T).

Blastococcus atacamensis sp. nov., a novel strain adapted to life in the Yungay core region of the Atacama Desert

A polyphasic study was undertaken to establish the taxonomic status of a Blastococcus strain isolated from an extreme hyper-arid Atacama Desert soil. The isolate, strain P6^T, was found to have chemotaxonomic and morphological properties consistent with its classification in the genus Blastococcus. It was shown to form a well-supported branch in the Blastococcus 16S rRNA gene tree together with the type strains of Blastococcus capsensis and Blastococcus saxobsidens and was distinguished from the latter, its close phylogenetic neighbour, by a broad range of phenotypic properties. The draft genome sequence of isolate P6^T showed 84.6 % average nucleotide identity, 83.0 % average amino acid identity and a digital DNA-DNA hybridisation value of 27.8 % in comparison with the genome sequence of B. saxobsidens DSM 44509^T, values consistent with its assignment to a separate species. Based on these data it is proposed that isolate P6^T (NCIMB 15090^T=NRRL B-65468^T) be assigned to the genus Blastococcus as Blastococcus atacamensis sp. nov. Analysis of the whole genome sequence of B. atacamensis P6^T, with 3778 open reading frames and a genome size of 3.9 Mb showed the presence of genes and gene clusters that encode for properties that reflect its adaptation to the extreme environmental conditions that prevail in Atacama Desert soils.

Blastococcus xanthinilyticus sp. nov., isolated from monument

A novel, non-motile, coccoid, Gram-stain-positive actinobacterium, designated BMG 862^T, was isolated from a marble sample collected from the Bulla Regia monument, Northern Tunisia. Its taxonomic position was determined using a polyphasic approach. Results from chemotaxonomic analyses showed MK-9(H4), MK-8(H4) and MK-9(H2) as the predominant menaquinones. The major polar lipids comprised diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, glycophosphatidylinositol, hydroxy-phosphatidylethanolamine and three unidentified phospholipids. The fatty acids consisted of significant amounts (≥10 %) of iso-C16 : 0, C17 : 1ω8c, iso-C15 : 0 and C16 : 1ω7c. Phylogenetic analysis on the basis of 16S rRNA gene sequence comparisons showed that strain BMG 862^T belongs to the genus Blastococcus, being most closely related to Blastococcus saxobsidens (=DSM 44509^T) (99.5 %) and Blastococcus capsensis (=DSM 46835^T=CECT 8876^T) (99.3 %). The genomic DNA G+C content of the organism was 74.7 mol%. Results of DNA-DNA hybridization and physiological tests allowed differentiation of strain BMG 862^T from related species. The strain was also characterized by its ability to hydrolyse xanthine. On the basis of phenotypic and molecular characteristics, strain BMG 862^T (=DSM 46842^T=CECT 8884^T) represents the type strain of a novel species of the genus Blastococcus, for which the name Blastococcus xanthinilyticus sp. nov. is proposed.