Isolating microorganisms from marine and marine-associated samples
a targeted search for novel natural antibiotics
AntibioticsNatural productsMarine microorganismsIsolation methodsActinomycetesRare actinomycetesWhole-cell screeningAntimicrobialsAntibiotic resistance
The search for antibiotic compounds from the natural environment has been going on for seven decades, ever since penicillin entered the market and antibiotic treatments became routine. The evolutionary pressure put on the pathogenic microorganisms induced a rapid spreading of naturally occurring resistance genes, leaving only the option of finding new antibiotics to treat the resistant pathogens. Microorganisms have been extensively mined for their biosynthetic abilities to produce biologically active compounds. To date, more than 23 000 microbial natural products have been discovered. The Actinomycetales are ubiquitous bacteria that have been used for antibiotic discovery for more than half a century, and over 10 000 natural products have been identified from the order. The genus of Streptomyces is acknowledged as the most prolific producer of natural products, but lately, non-Streptomyces species have been on the rise in novel drug research. Mainly terrestrial species have been studied, but the marine environment offer just as much, if not more, biodiversity to mine for new natural products. In this study, five marine and marine-associated samples were collected from south Shetland archipelago and southern Sweden coastal areas. The samples were subjected to seven selective treatments of varying chemical or physical nature. The samples were subsequently incubated on one general and six selective agar media of varying compositions of nutrients to enrich mainly for bacteria of more advanced metabolic capacity. Bacterial isolates (340 and counting) were recovered from the cultures, and the 16S rDNA of 96 strains was sequenced. A phylogenetic tree analysis of 91 sequences identified to the genus or species level was carried out. Biological assays were carried out on a few selected isolates, and their antibiotic potential was assessed. One strain analyzed by HPLC was found to produce the known antibiotic compound oxydifficidin.