Response mechanism of microbial community during anaerobic biotransformation of marine toxin domoic acid

Biogenic ROS mediated degradation mechanism of marine toxin domoic acid

Domoic acid (DA) is a compound generated as a secondary metabolite during harmful algal blooms, has historically received attention as the potent neurotoxicity in marine environment. However, the aerobic degradation mechanism of DA and the DA-degrader remain largely unknown. Here, we revealed the mechanism of aerobic degradation of DA by a ubiquitous marine Pseudoalteromonas sp., and more importantly, we confirmed that the degradation of DA is mediated by biogenic reactive oxygen species (ROS), rather than direct enzyme-mediated as traditionally conceived. Results indicated that DA degradation was caused by biogenic O2- and OH, where DA underwent reactions of decarboxylation, hydroxylation, and oxidation to yield the detoxification terminal product. Besides, whole genome sequencing and RT-qPCR analysis revealed that the genes conferring to encoding leucine dehydrogenase (ldh) and Na+-translocated NADH-quinone oxidoreductase (nqrA, nqrF) are responsible for biogenic ROS production. Finally, we found through comparative proteomic analysis that biogenic ROS mediated the DA degradation may be prevalent in the environment. Overall, this work not only reveals aerobic biotransformation mechanism of DA, but also identifies a novel mechanism of DA degradation, which provides new perspective into the environmental fate of DA and the artificial bioremediation of DA.

Applying metabolic modeling and multi-omics to elucidate the biotransformation mechanisms of marine algal toxin domoic acid (DA) in sediments

Domoic acid (DA)-producing algal blooms are a global marine environmental issue. However, there has been no previous research addressing the question regarding the fate of DA in marine benthic environments. In this work, we investigated the DA fate in the water-sediment microcosm via the integrative analysis of a top-down metabolic model, metagenome, and metabolome. Results demonstrated that biodegradation is the leading mechanism for the nonconservative attenuation of DA. Specifically, DA degradation was prominently completed by the sediment aerobic community, with a degradation rate of 0.0681 ± 0.00954 d-1. The DA degradation pathway included hydration, dehydrogenation, hydrolysis, decarboxylation, automatic ring opening of hydration, and β oxidation reactions. Moreover, the reverse ecological analysis demonstrated that the microbial community transitioned from nutrient competition to metabolic cross-feeding during DA degradation, further enhancing the cooperation between DA degraders and other taxa. Finally, we reconstructed the metabolic process of microbial communities during DA degradation and confirmed that the metabolism of amino acid and organic acid drove the degradation of DA. Overall, our work not only elucidated the fate of DA in marine environments but also provided crucial insights for applying metabolic models and multi-omics to investigate the biotransformation of other contaminants.

Deep insights into the biofilm formation mechanism and nitrogen-transformation network in a nitrate-dependent anaerobic methane oxidation biofilm

Nitrate/nitrite-dependent anaerobic methane oxidation (n-DAMO) process offers a promising solution for simultaneously achieving methane emissions reduction and efficient nitrogen removal in wastewater treatment. Although nitrogen removal at a practical rate has been achieved by n-DAMO biofilm process, the mechanisms of biofilm formation and nitrogen transformation remain to be elucidated. In this study, n-DAMO biofilms were successfully developed in the membrane aerated moving bed biofilm reactor (MAMBBR) and removed nitrate at a rate of 159 mg NO3--N L-1 d-1. The obvious increase in the content of extracellular polymeric substances (EPS) indicated that EPS production was important for biofilm development. n-DAMO microorganisms dominated the microbial community, and n-DAMO bacteria were the most abundant microorganisms. However, the expression of biosynthesis genes for proteins and polysaccharides encoded by n-DAMO archaea was significantly more active compared to other microorganisms, suggesting the central role of n-DAMO archaea in EPS production and biofilm formation. In addition to nitrate reduction, n-DAMO archaea were revealed to actively express dissimilatory nitrate reduction to ammonium and nitrogen fixation. The produced ammonium was putatively converted to dinitrogen gas through the joint function of n-DAMO archaea and n-DAMO bacteria. This study revealed the biofilm formation mechanism and nitrogen-transformation network in n-DAMO biofilm systems, shedding new light on promoting the application of n-DAMO process.