Most antibiotics in use today are molecules which are made by bacteria, particularly in soil. The problem is, it is not possible to grow all soil bacteria in the lab, and even if they can be grown in the lab the antibiotic (or another molecule you are looking for) may not be produced under these artificial conditions. Therefore, in this study the authors used an approach which did not involve growing bacteria from soil - instead, they targeted specific DNA fragments in environmental samples. DNA contains all the information necessary to build a living organism, and the authors looked for a cluster which had elements needed to make antibiotic-like molecules.
Specifically, they looked for clusters which would lead to molecules which contain calcium-binding motifs. Antibiotics like daptomycin are small proteins which need to bind to calcium before they can kill bacteria. This group of antibiotics all have different ways which leads to the killing of bacteria, therefore authors chose to focus on these calcium-binding molecules. Once fragments of DNA containing the cluster of interest, the authors transferred the fragment into a bacteria which can be grown in the lab - Streptomyces albus.
When the bacteria with the transferred DNA fragment was grown, it was found that it produced a compound capable of killing Staphylococcus aureus (MRSA). From there, the authors identified the malacidins - these molecules are "lipopeptides", or small proteins (peptides) connected to a fat (lipid). Experiments showed that malacidins need calcium in order to be able to kill bacteria, but it was noted that the calcium-binding motif is different to the motif frequently seen in calcium-binding molecules. Importantly, the authors did not see resistance to malacidins under their lab testing.
So, what does this mean? Well, with the technologies available today it is not necessary to grow bacteria in the lab in order to study them. This in turn means that we can look for more molecules produces by soil bacteria and identify any which may have a therapeutic potential. Of course, this is just the beginning and it is unclear whether malacidins will be safe to treat infections in humans. Only time will tell...
But it is encouraging that we are finding new antibiotics - we need a good strategy to ensure that we can maintain the ability to control infections, and finding new antibiotics is a vital part of this!
I hope you enjoyed my attempt at science writing - let me know what you think! Also, if you would like to read the article I based this post on, or see a diagrams of the process, follow the link: "Culture-independent discovery of the malacidins as calcium-dependent antibiotics with activity against multidrug-resistant Gram-positive pathogens" (Hover et al., Nature Microbiology (2018) doi:10.1038/s41564-018-0110-1)
Cheers,
Maho