Understanding polymicrobial interactions on structured surfaces

Soil organisms, including bacteria and amoebae, often engage in a wide range of interspecific and intraspecific interactions. Social amoebae, among other bacterivores, play a crucial role in regulating microbial communities and are often used as a non-mammalian model system to understand several metazoan processes. This thesis explores the spatiotemporal dynamics of predator–prey interactions and intercellular communication in social amoebae. By examining the interactions between Dictyostelium disoideum, a social amoeba, and Pseudomonas fluorescens HKI0770, a toxin-producing bacterium, we identified the circumstances under which amoebae can consume bacteria that were otherwise considered extracellular pathogens. Alterations in nutrient availability coupled with changes in microbial cell density generated a strong Allee effect leading to diminished production of the amoebicidal natural product pyreudione A. This pleiotropic regulation of bacterially derived natural products alters amoebal feeding behavior, turning inedible bacteria into edible ones and vice versa. These findings highlight the importance of non-genetic regulation in shaping not only predator–prey interactions but the whole spectrum of symbiosis in natural environments. In addition, we uncovered a previously uncharacterized mode of intraspecific communication in social amoebae. We report, for the first time, the formation of tunneling nanotubes (TNTs) in social amoebae. Our findings demonstrate that these actin-rich protrusions establish membrane continuity and enable the transport of various cargoes, including mitochondria. TNT formation offers a new perspective on the emergence of multicellularity in amoebae beyond classical aggregation-mediated multicellular development. Taken together, our findings highlight the intricate ecological roles of microbial interactions, with broader applications in microbiome engineering and evolutionary biology.