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Abstract Aims: To evaluate the patterns of the production of antimicrobial compounds by diverse collection of actinomycetes isolated from different geographies under alternative conditions of pH and salinity in the media. Methods and Results: Actinomycetes were grouped based on their method of isolation and their phenotype diversity was determined by total fatty acid analysis. A total of 335 representative isolates, including 235 Streptomyces species and 100 actinomycetes from other taxa, were screened for the production of antimicrobial activities against a panel of bacteria, filamentous fungi and yeasts, including some of clinical relevance. Production of antimicrobial activities was detected in 230 strains. In the case of the genus Streptomyces , 181 antimicrobial activities (77% of the tested isolates) were recorded. The activities observed among the other actinomycetes taxa were lower (49% of the tested isolates). Conclusions: The results of this study support the idea that species of actinomycetes isolated in alternative selective conditions of pH and salinity present a significant capacity to produce compounds with antibacterial or antifungal activity. The best group of isolates in terms of production of active secondary metabolites was the one isolated in saline conditions. Significance and Impact of the Study: The results demonstrate that these actinomycetes strains isolated in alternative selective conditions of pH and salinity and collected from diverse geographical locations present a significant capacity to produce compounds with antibacterial or antifungal activity. [ABSTRACT FROM AUTHOR]