Pigmented actinomycetes from coastal areas and their bioactive secondary metabolites

Abstract

Forty soil samples were collected from coastal areas of Chonburi, Rayong, and chanthaburi provinceses. These samples were pretreated at 55ºC for 15 min and 100 ºC for 1 h, respectivrly. They were subsequently made a series of 10-fold-dilutions and inoculated onto starch casein agar and humic acid vitamin agar plates to look for Actinomycetes that having some of bioactive secondary metabolites. Various strains of Actinomycetes grown on both agar plates were selected after 7-14 days of incubation at 32 ºC. The purification of selected grain was made to obtain pure isolates. One hundred and seventy nine isolates were screened for antimicrobial activity and 122 isolates were found to produce active products against gram-positive and/or gram-negative bacteria, including yeasts. Micrococcus luteus TISTR 884, Staphylococcus aureus TISTR 885, and Staphylococcus aureus 815(MRSA 815, the methicillin resistant strain) were used as representative strains of gram-positive bacteria in the antimicrobial activity test. They were inhibited by most Actinomycetes antimicrobial producing strains, while gram-negative bacteria, Pseudomonas aeruginosa TISTR 781, was inhibited by 11 isolates of Actinomycetes. Most antimicrobial producing isolates could inhibit against both bacteria and yeasts, and 29 isolates could inhibit only yeasts. Candida albicans TISTR 5239, Candida tropicalis TISTR 5045, Debaryomyces hansenii TISTR5265, Pichia kluyveri TISTR 5150, and a hospital strain of Candida sp. were used as test strains. Most isolates, both antimicrobial producers and non-antimicrobial producers, were able to produce colorfur colonies as well as soluble pigments in some strains.