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.

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.