Biodegradation and antimicrobial capability-induced heavy metal resistance of the marine-derived actinomycetes Nocardia harenae JJB5 and Amycolatopsis marina JJB11.

Currently, heavy metal-resistant (HMR) marine actinomycetes have attracted much attention worldwide due to their unique capabilities. In this study, 27 marine-derived actinomycetes were isolated from coastal beaches in the Arabian Gulf of Al-Jubail in Saudi Arabia and screened for resistance to 100 mg/L of the heavy metals Cd2+, Cr6+, Cu2+, Fe2+, Pb2+, and Ni2+ using different assay techniques. Six isolates were selected as HMRs, of which two isolates, JJB5 and JJB11, exhibited the highest maximum tolerance concentrations (200- > 300 mg/L). Both isolates were the highest among six-HMR screened for their biodegradation potential of plastics low-density polyethylene, polystyrene, and polyvinyl chloride, recording the highest weight loss (15 ± 1.22 - 65 ± 1.2%) in their thin films. They also showed the highest biodegradability of the pesticides acetamiprid, chlordane, hexachlorocyclohexane, indoxacarb and lindane, indicating promising removal capacities (95.70-100%) for acetamiprid and indoxacarb using HPLC analysis. Additionally, the cell-free filtrate (CFF) of both isolates displayed the highest antimicrobial activity among the six-HMR screened against a variety of microbial test strains, recording the highest inhibition zone diameters (13.76 ± 0.66 - 26.0 ± 1.13 mm). GC‒MS analyses of the ethyl acetate extract of their CFFs revealed the presence of diverse chemical compounds with a multitude of remarkable biological activities. Based on their spore morphology and wall-chemotype, they were assigned to the nocardioform-actinomycetes. Furthermore, their phenotypic characteristics, together with 16S rRNA gene sequencing (OR121525-OR121526), revealed them as Nocardia harenae JJB5 and Amycolatopsis marina JJB11. Our results suggest that marine HMR actinomycetes are promising candidates for various biotechnological applications.

Rhizospheric-Derived Nocardiopsis alba BH35 as an Effective Biocontrol Agent Actinobacterium with Antifungal and Plant Growth-Promoting Effects: In Vitro Studies.

The biocontrol approach using beneficial microorganisms to control crop diseases is becoming an essential alternative to chemical fungicides. Therefore, new and efficient biocontrol agents (BCA) are needed. In this study, a rhizospheric actinomycete isolate showed unique and promising antagonistic activity against three of the most common phytopathogenic fungi, Fusarium oxysporum MH105, Rhizoctonia solani To18, and Alternaria brassicicola CBS107. Identification of the antagonistic strain, which was performed according to spore morphology and cell wall chemotype, suggested that it belongs to the Nocardiopsaceae. Furthermore, cultural, physiological, and biochemical characteristics, together with phylogenetic analysis of the 16S rRNA gene (OP869859.1), indicated the identity of this strain to Nocardiopsis alba. The cell-free filtrate (CFF) of the strain was evaluated for its antifungal potency, and the resultant inhibition zone diameters ranged from 17.0 ± 0.92 to 19.5 ± 0.28 mm for the tested fungal species. Additionally, the CFF was evaluated in vitro to control Fusarium wilt disease in Vicia faba using the spraying method under greenhouse conditions, and the results showed marked differences in virulence between the control and treatment plants, indicating the biocontrol efficacy of this actinomycete. A promising plant-growth promoting (PGP) ability in seed germination and seedling growth of V. faba was also recorded in vitro for the CFF, which displayed PGP traits of phosphate solubilization (48 mg/100 ml) as well as production of indole acetic acid (34 µg/ml) and ammonia (20 µg/ml). This study provided scientific validation that the new rhizobacterium Nocardiopsis alba strain BH35 could be further utilized in bioformulation and possesses biocontrol and plant growth-promoting capabilities.