Patterns of antimicrobial activities from soil actinomycetes isolated under different conditions of pH and salinity A. Basilio, I. Gonza ´ lez, M.F. Vicente, J. Gorrochategui, A. Cabello, A. Gonza ´lez and O. Genilloud Centro de Investigacio´n Ba´sica, Merck Sharp and Dohme de Espan˜a S.A., Madrid, Spain 2002/0420: received 31 October 2002, revised 2 May 2003 and accepted 23 May 2003 ABSTRACT A. BASILIO, I. GONZA ´ LEZ, M.F. VICENTE, J. GORROCHATEGUI, A. CABELLO, A. GONZA ´ LEZ AND O. GENILLOUD. 2003. 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. Keywords: actinomycetes, antibacterial and antifungal compounds, antimicrobial screening, pH and salinity conditions. INTRODUCTION Actinomycetes comprise an extensive and diverse group of Gram-positive, aerobic, mycelial bacteria that play an important ecological role in soil cycles. Many are well known for their economic importance as producers of biologically active substances, such as antibiotics, vitamins and enzymes (McCarthy and Williams 1992; Sanglier et al. 1996; Horan 1999; Lazzarini et al. 2000). In addition, they are one of the major communities of the microbial popu- lation present in soil, and their occurrence is greatly influenced by the environmental conditions of humidity, temperature, pH and vegetation. Soil actinomycetes for the most part show their optimum growth in neutral and slightly alkaline conditions, and isolation procedures have been traditionally based on this neutrophilic character. Previous works showed the existence of a large diversity of acidophilic actinomycetes that differed morphologically and physiologically from neutrophilic spe- cies (Khan and Williams 1975; Williams et al. 1977; Correspondenceto: Angela Basilio, Centro de Investigacio´n Ba´sica, Merck Sharp and Dohme de Espan˜a S.A., Josefa Valca´rcel 38, E-28027 Madrid, Spain (e-mail: basilio_angela@merck.com). ª 2003 Merck & Co., Inc. Journal of Applied Microbiology 2003, 95, 814–823 doi:10.1046/j.1365-2672.2003.02049.x