Discovery of a Microbial Carrier with High Adsorption Affinity for Syntrophic Long-Chain Fatty Acid-Degrading Microorganisms

Long-chain fatty acid (LCFA) degradation primarily involves several species of Syntrophomonas and hydrogenotrophic methanogens, constituting the rate-limiting step in anaerobic digestion. It is crucial to augment their abundance to enhance LCFA degradation. Utilizing microbial carriers presents an effective strategy to maintain the microorganisms on the surface and prevent their washout from the digester. In this study, we aimed to identify a suitable microbial carrier with a superior adsorption capacity for LCFA-degrading microorganisms. We tested various polymers, poly­(vinyl alcohol) (PVA), polypropylene (PP), polyethylene glycol (PEG), and polyvinylidene chloride (PVDC), adding them to the sludge at the concentration of 28.25 g L–1 and incubating with olive oil. The amplicon sequencing analysis revealed that PVDC retained Syntrophomonas more abundantly than the other polymers. Remarkably, PVDC predominantly adsorbed LCFA-degrading S. sapovorans and S. zehnderi, whereas medium- to short-chain fatty acid-degrading S. wolfei was abundant in the sludge. Moreover, hydrogenotrophic Methanospirillum hungatei was detected at 2.3–9.5 times higher abundance on PVDC compared to the sludge. Further analysis indicated that not only these LCFA-degrading syntrophic microbial communities but also Propionispira and Anaerosinus, which are capable of lipid hydrolysis and glycerol degradation, became dominant on PVDC. Actually, chemical analysis confirmed that adding PVDC promoted the olive oil degradation. These results underscore the potential of PVDC in promoting anaerobic LCFA degradation.