The bacterial phylum Planctomycetes as novel source for bioactive small molecules.

Abstract Extensive knowledge and methodological expertise on the bacterial cell biology have been accumulated over the last decades and bacterial cells have now become an integral part of several (bio-)technological processes. While it appears reasonable to focus on a relatively small number of fast-growing and genetically easily manipulable model bacteria as biotechnological workhorses, the for the most part untapped diversity of bacteria needs to be explored when it comes to bioprospecting for natural product discovery. Members of the underexplored and evolutionarily deep-branching phylum Planctomycetes have only recently gained increased attention with respect to the production of small molecules with biomedical activities, e.g. as a natural source of novel antibiotics. Next-generation sequencing and metagenomics can provide access to the genomes of uncultivated bacteria from sparsely studied phyla, this, however, should be regarded as an addition rather than a substitute for classical strain isolation approaches. Ten years ago, a large sampling campaign was initiated to isolate planctomycetes from their varied natural habitats and protocols were developed to address complications during cultivation of representative species in the laboratory. The characterisation of approximately 90 novel strains by several research groups in the recent years opened a detailed in silico look into the coding potential of individual members of this phylum. Here, we review the current state of planctomycetal research, focusing on diversity, small molecule production and potential future applications. Although the field developed promising, the time frame of 10 years illustrates that the study of additional promising bacterial phyla as sources for novel small molecules needs to start rather today than tomorrow.