Lignin Degradation Potential of Novel Streptomyces Isolates from the Juniperus turcomanica Rhizosphere via Broad-Spectrum Enzymatic Activities

This study provides a comprehensive characterization of Streptomyces isolates associated with the rhizosphere of the centenarian Juniperus turcomanica. Screening for ligninolytic activity revealed that isolates—ATM9, ATM14, ATM15, ATM16, ATM18, and ATM19 synthesize enzymes capable of decolorizing methylene blue and modifying lignosulfonates. Isolates ATM16 and ATM18 demonstrated the highest efficiency in lignosulfonate decomposition, with lignosulfonate becoming undetectable in their culture broth. In the straw lignin degradation process, isolates ATM15 and ATM16 showed the most significant reductions in lignin content (44.2% and 54.8%, respectively), demonstrating promising biodegradation potential. Majority of isolates demonstrated antagonistic activity against fungal strains, while ATM19 completely inhibited the growth of all phytopathogenic fungi tested. Taxonomic identification based on 16S rRNA gene sequencing confirmed that all isolates belong to the genus Streptomyces, with species including S. shaanxiensis (ATM9), S. chryseus (ATM14), S. narbonensis (ATM15), S. venezuelae (ATM16), S. spiroverticillatus (ATM18), S. longhuiensis (ATM19), and Streptomyces sp. (ATM24). Considering our data, S. venezuelae ATM16 and S. spiroverticillatus ATM18 stand out as the most promising strains for biotechnological applications due to their ligninolytic and antagonistic activity against fungal phytopathogens. Furthermore, this study provides the first report on enzymatic and antifungal activities for the recently proposed species S. longhuiensis (ATM19) and S. shaanxiensis (ATM9).