DETECTION OF ANTIMICROBIAL COMPOUNDS FROM THERMOPHILIC ACTINOMYCETES USING ONE STRAIN MANY COMPOUNDS (OSMAC) APPROACH

Actinomycetes are a group of filamentous bacteria with high biosynthetic potential that can produce secondary metabolites. Actinomycetes are known to produce secondary metabolites which are potential as antimicrobial, antitumor, and others. Actinomycetes can be found abundantly in diverse environments, including environments with extremely high temperatures such as hot springs, deserts, geothermal areas, and hydrothermal vents. They can survive in high temperatures due to their membrane lipids containing straight-chains and more saturated fatty acids that protect the membrane's fluidity to maintain membrane function. Thermophilic actinomycetes are potential producers of thermostable enzymes and bioactive compounds, which are important in the pharmaceutical, health, and industrial fields. Thermophilic actinomycetes are still less explored for novel metabolites and antimicrobial compounds due to the difficulty in isolation, maintenance, and preservation in pure culture. Novel bioactive compounds produced by actinomycetes are conventionally discovered by isolating potential strains and screening the compound bioactivity through various bioassays. A sequence-independent approach, termed the OSMAC (one strain many compounds), has been widely used in natural product research for activating cryptic biosynthetic gene clusters (BGCs) by modifying the growth conditions of a bacterial culture. This approach aims to optimize the number of secondary metabolites produced by one single microorganism. The application of the OSMAC method has been proven successful in revealing the biosynthetic potential of bacteria.

Ribosome engineering is able to activate "silent" gene clusters by producing mutations in ribosomal components or RNA polymerase (RNAP) using certain antibiotics, resulting in increased production of secondary metabolites (Hosaka et al., 2009). In co-culture techniques, the induction of "silent" gene clusters can result from three modes of interaction such as nutrient supply, competition through the production of antibiotics or signaling molecules, and cellto-cell contact (Okada et al., 2017  Tiwari & Gupta 2012). This is due to the difficulty in isolating and maintaining microorganisms as pure cultures (Kikani et al., 2010). Therefore, this article discusses the isolation of thermophilic actinomycetes in relation to their potential as antimicrobial compound producers using the OSMAC approach to discover antimicrobial compounds.

Potential of Thermophilic Actinomycetes as Antimicrobials Producers
The last 20 th century,  (Chaudhary et al., 2016;Jang et al., 2003).    et al., 2017). Another method that is also considered effective is the one strain many compounds (OSMAC) approach.

Successful OSMAC Approach
The OSMAC is still considered an effective approach that can induce silent  The genome sequence of strain SL3-2-4 T was also analyzed using the antiSMASH and successfully revealed the presence of low and no-similarity BGCs compared with published known clusters which suggested the high potential of strain SL3-2-4 T to produce novel bioactive compounds .
Despite the effectiveness, the OSMAC approach can also be time-consuming and challenging since the alterations of many cultivation parameters were difficult to determine (Okada et al., 2017) (Singh et al., 2017). Previous studies using the OSMAC approach emphasized variation of culture media and cultural conditions (Bode et al., 2002).

CONCLUSION
Actinomycetes can be found abundantly in extreme environments with high temperatures condition.