Site-specific community structure and plant growth-promoting properties of cultured actinomycetes associated with Deschampsia antarctica from Galindez Island, Antarctica.

The rhizosphere microbiota plays a crucial role in plant growth and resilience, particularly in extreme environments such as Antarctica. This study explores the diversity and plant growth-promoting properties of actinomycetes associated with the rhizosphere of Deschampsia antarctica on Galindez Island, Maritime Antarctica, under varying microclimatic conditions and human-impacted sites. Using direct inoculation and selective pretreatment methods, a diverse array of actinomycete strains was isolated, representing genera such as Amorphoplanes, Embleya, Kribbella, Lentzea, Micromonospora, Nocardia, Rhodococcoides, Rhodococcus, Saccharopolyspora, Streptomyces, and Winogradskya. Sites influenced by human activity exhibited reduced actinomycete abundance and altered genus ratios compared to less disturbed areas. Among the isolated strains, many demonstrated the ability to produce siderophores for metals such as iron, nickel, copper, zinc, and manganese. Notably, five strains produced siderophores capable of binding all tested metals. Additionally, three strains exhibited the capacity to solubilize insoluble forms of both zinc and phosphorus while producing siderophores for all metals tested. Genomic analysis of one of these strains, namely, Streptomyces sp. Da 82-17, revealed an array of secondary metabolite gene clusters, including those for ectoine, paenibactin, and lidamycin, highlighting its significant biotechnological potential. Functional genomics identified genes encoding phytohormones, such as indole-3-acetic acid (IAA), and siderophores, which are critical for improving plant nutrient uptake and stress tolerance. These findings underscore the high biosynthetic potential of Antarctic actinomycetes for applications in agriculture, medicine, and biotechnology. Further research into microbiota from both human-impacted and pristine regions on Galindez Island will enhance understanding of microbial adaptation and inform strategies to mitigate anthropogenic impacts, preserving the unique Antarctic ecosystem.