The potential of Dictyostelium discoideum for natural product and antimicrobial discovery

Dictyostelium discoideum are single-celled amoebae that grow vegetatively on bacteria. Starvation triggers thousands of cells to aggregate chemotactically and initiate a developmental program culminating in multicellular reproductive structures. Genomic analyses implicate Dictyostelium as a potential source of natural products. Three observations motivate us to explore Dictyostelium’s relationship with bacteria in particular. First, amoebae are susceptible to infection by human pathogens and share conserved genes with humans that mitigate this susceptibility. Second, growth on Gram-positive versus Gram-negative bacteria elicits distinct genetic responses. And third, amoebae extracts display antimicrobial properties. Given the evolutionary distance between Dictyostelium and sources of common antibiotics, amoebae may produce novel antimicrobial molecules. Resources are needed to help interpret Dictyostelium’s responses to environmental cues and isolate relevant genetic elements for further investigation. We have characterized the transcriptional dynamics of vegetative and developing D. discoideum. Future RNA-sequencing with mutants compromised in bacterial growth and development will help reconstruct gene regulatory networks and biosynthetic pathways. One major hurdle in Dictyostelium molecular biology is cloning its notoriously AT-rich genomic DNA. This challenge precludes most attempts to capture and manipulate interesting genomic loci. We report building the first medium-insert D. discoideum genomic library in E. coli using a linear phage derived vector. The inserts are stable over numerous generations and map to the genome with an unbiased distribution. This success dramatically expands our genetic engineering toolkit. Ongoing endeavors include random mutagenesis screens, candidate gene knock-outs and various mass spectroscopy approaches to identify genes and natural products that constitute D. discoideum’s antibacterial armory.