Cold-adapted microorganisms as a source of new antimicrobials

Abstract

Thirty out of 8,000 different colony morphotypes isolated from soil samples of Isla de los Estados were selected based on their ability to produce antimicrobials. The significant influence of culture media and incubation temperature on antimicrobial production was proved, being LB medium and 8C the conditions of choice. Most of the psychrotolerant isolates were phylogenetically related to Serratia proteamaculans (96.4?97.9%) while the psychrophilic isolated 8H1 was closely related to Pseudomonas sp. (90?94% similarity). Produced antimicrobials showed a promising wide spectrum of activity both against grampositive and gram-negative pathogenic bacteria. They were suspected to be microcin-like compounds (Mw\2,000 Da) and showed a marked tolerance to heat (1 h in boiling water bath) and pH-treatments (1?12). Antimicrobial compounds also showed to partially keep their activity even after overnight freezing at -20 and -80C and displayed a negative net charge at pH 8.0, a common feature of class II microcins.