Actinomadura sp. 101_SQ a moderate halotolerant isolated from salt lake in east of Algeria: A potential source of antibacterial substances

A NEW Streptomyces STRAIN AHA8 FROM DESERT SOIL: ISOLATION, TAXONOMIC IDENTIFICATION, AND ANTAGONISTIC PROPERTIES

Actinobacteria from extreme environments represent a valuable source of novel bioactive secondary metabolites with potential antimicrobial applications. The aim of this study was to isolate, identify, and evaluate the antimicrobial potential of a newly isolated strain of actinobacteria. AHA8 strain, was isolated from an Algerian desert soil sample in the Ahaggar region (Tamanrasset) by the dilution-agar plating method using a chitin-vitamins B medium supplemented with nalidixic acid and actidione. Morphological characterization indicated that this strain belonged to the genus Streptomyces. Phylogenetic analysis based on the 16S rRNA gene showed that the strain is closely related to Streptomyces djakartensis NBRC 15409T (99.57% sequence similarity). Strain AHA8 showed very strong activity against pathogenic staphylococci, including Staphylococcus aureus (MRSA 639c), as well as against other Gram-positive bacteria: Bacillus subtilis (ATCC 663) and Listeria monocytogenes (ATCC 13932). Additionally, the strain exhibited a moderate activity against mycotoxigenic and phytopathogenic fungi, including Aspergillus carbonarius (M333), A. westerdijkiae (ATCC 3174), Fusarium culmorum (Fc), and Umbelopsis ramanniana (NRRL 1829). Almost the same results were observed for Gram-negative bacteria and the pathogenic yeast Candida albicans (M3). Therefore, four solvents (n-hexane, dichloromethane, ethyl acetate, and n-butanol) were used to extract the bioactive secondary metabolites produced by the AHA8 culture on a synthetic starch medium. The highest antibacterial activity was obtained with the butanolic and ethyl acetate extracts. These findings demonstrate that the desert-derived strain AHA8 represents a promising source of antimicrobial secondary metabolites and supports further studies aimed at the purification and characterization of its bioactive compounds.

Chrysothrix sp., a Lichen from Paposo Fog Oasis: Antibacterial Potential to Combat Multidrug-Resistant ESKAPE-E Pathogens

Lichens are mutualistic symbiosis between a fungus (mycobiont) and an alga or cyanobacteria (photobiont), forming metabolically versatile holobionts capable of producing diverse secondary metabolites that facilitate their survival in extreme environments. Chrysothrix species, commonly known as “gold dust lichens,” are characterized by their vivid yellow thalli and their production of pulvinic acid derivatives, although their bioactive potential remains poorly explored. In this study, using organic chemistry techniques, we characterized the methanolic extract of Chrysothrix sp.—collected from the Paposo Fog Oasis in northern Chile, a unique coastal ecosystem sustained by persistent fog (“camanchacas”) within the Atacama Desert—and identified calycin as its major secondary metabolite through chromatographic purification and single-crystal X-ray diffraction. Antibacterial assays revealed that both the crude methanolic extract and purified calycin exhibited selective inhibitory activity against multidrug-resistant Gram-positive ESKAPE-E pathogens. Minimum Inhibitory Concentrations (MICs) ranged from 125 to 500 μg/mL, with the strongest effects observed against Enterococcus faecium (MDR, VRE) and Staphylococcus aureus (MDR, MRSA). No meaningful activity was detected against Gram-negative bacteria, consistent with the known permeability barrier conferred by the outer membrane. This work provides the first evidence of antibacterial activity for calycin isolated from Chrysothrix sp., highlighting the relevance of pulvinic acid derivatives as promising scaffolds for antimicrobial development. These findings highlight the potential of lichen-derived agents and alternative sources of antibacterial agents to address the global challenge of antimicrobial resistance.

Parasedimentitalea nitratireducens sp. nov., a Novel Nitrate-Reducing Bacterium Isolated from the Yellow Sea

A Gram-stain-negative, rod-shaped, aerobic strain CY06T was isolated from surface marine sediment sample of the Yellow Sea, China. The strain was positive for oxidase and catalase and could reduce nitrate to nitrite but not further to gaseous nitrogen products. Phylogenetic analysis based on 16S rRNA gene sequences and the up-to-date bacterial core gene (UBCG) sequences revealed that strain CY06T formed a distinct clade within the genus Parasedimentitalea. Genomic comparisons, including digital DNA-DNA hybridization (dDDH), average nucleotide identity (ANI) and average amino acid identity (AAI), clearly distinguished strain CY06T from other members of the genus. The morphological, physiological, biochemical and chemotaxonomic data further supported its differentiation from closely related species. Based on the polyphasic evidence, a new species, Parasedimentitalea nitratireducens sp. nov., is proposed, with the type strain CY06T (=MCCC 1K08636T = KCTC 72006T).

Exploring the antibacterial potential of marine pigments from Pseudomonas aeruginosa and Microbacterium hominis isolated from Cox's Bazar, Bangladesh

Abstract The marine environment harbours a rich diversity of microorganisms capable of producing bioactive compounds, including pigments with significant therapeutic potential. However, the exploration of bacterial pigments from marine bacteria, particularly from Cox’s Bazar region in Bangladesh, remains under-researched. This study investigated the antibacterial and cytotoxic properties of two yellow pigment-producing bacteria, Pseudomonas aeruginosa strain BDIFST240011 and Microbacterium hominis strain BDIFST240012, isolated from sediment samples of the Bay of Bengal. The microbial load was assessed, and the isolates were characterized morphologically, molecularly (16S rRNA sequencing), and biochemically to confirm their identities. Pigment production was optimized under various growth conditions, with Luria–Bertani medium supplemented with seawater providing optimal results. The pigments, pyocyanin from P. aeruginosa and pyoverdine from M. hominis, were characterized using UV-visible and Fourier Transform Infrared (FTIR) spectroscopy, confirming their chemical identities. Antibacterial activity was evaluated through agar well diffusion, revealing significant inhibition of Bacillus subtilis and other bacterial strains, with pyocyanin showing stronger efficacy. The cytotoxic effects of both pigments were assessed using the MTT assay, showing a dose-dependent reduction in Vero cell viability, with pyocyanin exhibiting more significant cytotoxicity. This research addresses the gap in marine bacterial pigment studies and highlights their potential for pharmaceutical applications. The findings suggest that marine-derived bacterial pigments can serve as a source of novel antibacterial agents and provide a foundation for future research into their clinical and industrial applications. Future studies should focus on elucidating the mechanisms of action and exploring the broader therapeutic uses of these pigments.

Aquatic-derived Streptomyces cavourensis BA1 as a promising source of antibacterial metabolites against multidrug-resistant gram-negative pathogens

Streptomyces songxianensis sp. nov. SX92T: biocontrol of tobacco black shank and modulation of the rhizosphere microbiome

Strain SX92 T is proposed as the type strain of a novel species, Streptomyces songxianensis, and is established as a promising multifunctional biocontrol agent for sustainable tobacco production.