Nature's original bioplastic may have fed animals for hundreds of millions of years

A groundbreaking study reveals that animals, not just microorganisms, can break down microbial bioplastics known as polyhydroxyalkanoates (PHAs). These bioplastics, produced by many bacteria and archaea, were long believed to be degradable solely by microorganisms. However, researchers at the Max Planck Institute for Marine Microbiology in Bremen, Germany, have demonstrated that a variety of animals, from marine worms and starfish to terrestrial species such as earthworms, possess enzymes capable of degrading PHAs. The findings, published in Nature Ecology & Evolution, highlight a previously unrecognized pathway through which microbial carbon enters animal food webs. The discovery originated with a unique marine worm named Olavius algarvensis. This gutless creature, measuring only about two centimeters in length, relies entirely on symbiotic bacteria living beneath its skin for sustenance and waste processing. These bacteria store large quantities of PHA within their cells. Scientists hypothesized that the worm might have developed a mechanism to access this energy-rich resource. Their investigation confirmed this hypothesis, revealing an enzyme in the worm that effectively breaks down PHA into smaller molecules usable by the animal. Researchers collected samples of Olavius algarvensis from the seafloor near Elba, Italy, where the worm resides under Mediterranean seagrass meadows. By analyzing the worm’s biology, they identified the specific location where the enzyme responsible for breaking down PHA is produced, precisely where the worm digests its bacterial partners. This finding indicates that the worm can directly utilize the PHA stored by its symbiotic bacteria. Expanding beyond the initial discovery, the team examined genetic data from over 66 animal species spanning nine different phyla. They found similar enzymes in a wide range of organisms, including sponges, earthworms, and springtails. Laboratory tests confirmed that these diverse species could indeed degrade PHAs. According to Caroline Zeidler, the study’s first author, this result was unexpected. What initially appeared to be a unique adaptation in one marine worm turned out to be a widespread trait across multiple branches of the animal kingdom. Microbial PHAs are prevalent in natural environments, existing in soils, sediments, and aquatic ecosystems globally. These bioplastics are formed when microorganisms store surplus carbon for future use. As interest grows in using PHAs as sustainable alternatives to traditional plastics, understanding their degradation processes becomes crucial. The new research suggests that animals play a role in breaking down these materials alongside microorganisms, contributing to the overall cycle of carbon utilization in ecosystems. The implications of this study extend beyond ecological understanding. It challenges previous assumptions about the accessibility of microbial carbon reserves and highlights the intricate relationships between animals and microorganisms. For instance, the ability of animals to harness PHA from their symbiotic bacteria opens up new perspectives on nutrient cycling and energy transfer within complex biological networks. Further research will focus on exploring the extent of this phenomenon across various ecosystems and species. Scientists aim to investigate how this capability influences food web dynamics and whether it affects the broader environmental impact of PHAs. Understanding these interactions could provide valuable insights into developing more effective strategies for managing biodegradable plastics in both natural and human-made environments.