Isolation of bacteria that synthesize polyunsaturated fatty acids under mesophilic conditions from environments with high oxidative stress

Polyunsaturated fatty acids (PUFAs) are fatty acids with more than one double bond in their acyl chain. They function as components of membranes as well as precursors of signaling molecules. Some are essential nutrients in the human diet. Given the diminishing availability of classical marine sources such as fish oil, more sustainable sources such as single-cell oils from eukaryotic microorganisms have been identified, but they are not yet economically competitive as food additives. Bacteria have been proposed as a less expensive platform to manufacture single-cell oils, but many bacterial species only produce PUFAs in response to cold temperatures and are, thus, unsuitable for commercial fermentation. We, therefore, initiated a bioprospecting campaign to identify PUFA-producing bacteria from intertidal sediments at warmer temperatures, reasoning that such isolates may produce PUFAs as a defense against oxidative stress rather than the cold. The sediments were collected from various ecosystems along the German North Sea coast. Following the comprehensive screening of more than 2,000 isolates from sediments and other sources, we identified 54 PUFA producers, 18 of which from habitats with high concentrations of reactive oxygen species. The latter bacteria were shown to produce PUFAs at higher temperatures than cold-adapted strains. This finding will facilitate the utilization of bacterial systems for the production of PUFAs at temperatures commonly used for laboratory and industrial fermentation.IMPORTANCEPolyunsaturated fatty acids (PUFAs) are essential nutrients in the human diet. They are traditionally obtained from fish oil, but global fisheries are declining, while the demand for PUFAs is increasing due to the growing global population. Sustainable alternatives exist in the form of oils from single-celled eukaryotes, but production is not yet economically competitive. Therefore, unsustainable sources such as wild fish continue to be used. Many bacteria produce PUFAs but mostly as a low-temperature adaptation to improve membrane fluidity, which is incompatible with biotechnological processes. The identification of habitats containing bacteria that produce PUFAs at elevated temperatures could help to circumvent this limitation by allowing large-scale production based on conventional biotechnology.