<p>Plasmids used in this study.</p>

Bacteria, both individually and as symbionts of other organisms, significantly influence ecosystems by providing nutrients and metabolizing exogenous compounds. Some bacteria polymerize small organic acids such as lactate, pyruvate, and β-or 3-hydroxybutyrate when there is an excess of carbon relative to other elements. One such polymer, poly-β-hydroxybutyrate (PHB) is a biodegradable bioplastic. While the role of PHB as energy/carbon-storage in bacteria is well documented, the effects of PHB on interactions between bacteria and their hosts remain unclear. Here, we discover that PHB-producing bacteria can kill the nematode Caenorhabditis elegans. Death results from a combination of pharyngeal deformation, intestinal distention, disruption of the intestinal barrier, and defecation defects. Remarkably, mutations in C. elegans nuc-1, which encodes DNAse II, partially alleviate PHB-induced lethality. Altogether, our findings illustrate that PHB-producing bacteria can affect host-physiology and survival.