UC San Diego

Bacteria-animal interactions play a widespread role in stimulating the life-cycle transitions of marine invertebrates, this interaction is critical for processes such as coral reef formation, sustaining fisheries stocks and biofouling. However, we know little about the mechanisms mediating this beneficial bacteria-animal communication. Pseudoalteromonas luteoviolacea (P. luteo) release an array of tailocins known as metamorphosis associated contractile structures (MACs) inducing tubeworm metamorphosis. It is currently unknown how these structures induce the cellular response associated with metamorphosis. We have discovered that MACs contain at least two cargo effector proteins, Pne1 and Mif1, which are present in the MAC structure. Pne1 is a nuclease toxin effector which is responsible for MACs ability to kill mouse macrophages and SF9 insect cell lines. Mif1 is an effector loaded within the MACs inner tube complex and is critical for the inductive phenotype of MACs observed in H. elegans larvae. Additionally, we have shown via purified recombinant protein, this cargo is sufficient to induce metamorphosis. Through biochemical analysis we have shown Mif1 shares functionality with a class of secreted effector lipases and exhibits lipase activity. Additionally, we have identified that Mif1 stimulates the upregulation of a lipid second messenger DAG and via pharmacological characterization of metamorphosis we have determined the conserved PKC pathway to be both necessary and sufficient to induce this metamorphosis. This has provided evidence for the bacteria stimulating the PKC signal transduction pathway via lipid second messengers to directly induce animal metamorphosis. These experiments are the first to show a bacterial protein is sufficient to induce the metamorphosis of any marine animal and yields insight into how bacterial stimulate animal development.