ABSTRACT
Naturally-occurring antibiotics, which is to say most of clinically-used antibacterial drugs, are old molecules. While the actual “role’’ these molecules play in microbial physiology and ecology is still controversial (see section 1.1.2), antibiotic biosynthetic pathways are millions of years old (unless, of course, The Earth is actually only 6,000 years old). J. Davies even propose that some antibiotics can be prebiotic molecules, which would then be billions of years old. However, antibiotic production is not a very common feature amongst microbes: nearly 50% of known antibiotics are produced by a single bacterial genus, Streptomyces, a tiny fraction of all bacterial diversity. Furthermore, although about 1% of soil actinomycetes produce streptomycin, which seems to be pretty common, the number of strains that synthesize other antibiotics is much smaller – in the 0.000001% order (Laskaris et al., 2012). Of course, the key word in the two previous sentences is “known’’: there could be many more antibiotics unknown to us, produced by as many unknown bacteria (or even known antibiotics produced by other, unknown bacteria – at risk of sounding Rumsfeld-ish). This was very elegantly demonstrated with the discovery of teixobactin: by growing previously uncultured soil bacteria in an ingenious device (iChip), an unknown species named Eleftheria terrae, related toAquabacteria, not previously known to produce antibiotics, was discovered, along with a new peptidoglycan-synthesis inhibitor (Ling et al., 2015). (This important discovery was however announced with the preposterous claim that resistance was unlikely to arise; while some immediately disagreed, providing evidence (Hochberg and Jansen, 2015), a simple movie quotation perhaps should suffice: “life finds a way’’). A relevant question remains: how much and how many naturallyproduced antibiotics exist in the environment?
