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

Domoic acid (DA) is a potent neurotoxin produced by toxigenic Pseudo-nitzschia blooms and quickly transfers to the benthic anaerobic environment by marine snow particles. DA anaerobic biotransformation is driven by microbial interactions, in which trace amounts of DA can cause physiological stress in marine microorganisms. However, the underlying response mechanisms of microbial community to DA stress remain unclear. In this study, we utilized an anaerobic marine DA-degrading consortium GLY (using glycine as co-substrate) to systematically investigate the global response mechanisms of microbial community during DA anaerobic biotransformation.16S rRNA gene sequencing and metatranscriptomic analyses were applied to measure microbial community structure, function and metabolic responses. Results showed that DA stress markedly changed the composition of main species, with increased levels of Firmicutes and decreased levels of Proteobacteria, Cyanobacteria, Bacteroidetes and Actinobacteria. Several genera of tolerated bacteria (Bacillus and Solibacillus) were increased, while, Stenotrophomonas, Sphingomonas and Acinetobacter were decreased. Metatranscriptomic analyses indicated that DA stimulated the expression of quorum sensing, extracellular polymeric substance (EPS) production, sporulation, membrane transporters, bacterial chemotaxis, flagellar assembly and ribosome protection in community, promoting bacterial adaptation ability under DA stress. Moreover, amino acid metabolism, carbohydrate metabolism and lipid metabolism were modulated during DA anaerobic biotransformation to reduce metabolic burden, increase metabolic demands for EPS production and DA degradation. This study provides the new insights into response of microbial community to DA stress and its potential impact on benthic microorganisms in marine environments.

Genomic insights into Pseudoalteromonas sp. JSTW coping with petroleum-heavy metals combined pollution.

Worldwide marine compound contamination by petroleum products and heavy metals is a burgeoning environmental concern. Pseudoalteromonas, prevalently distributed in marine environment, has been proven to degrade petroleum and plays an essential role in the fate of oil pollution under the combined pollution. Nevertheless, the research on the reference genes is still incomplete. Therefore, this study aims to thoroughly investigate the reference genes represented by Pseudoalteromonas sp. JSTW via whole-genome sequencing. Next-generation sequencing technology unfolded a genome of 4,026,258 bp, database including Clusters of Orthologous Groups (COG) and Kyoto Encyclopedia of Genes and Genomes (KEGG) were utilized to annotate the genes and metabolic pathways conferring to petroleum hydrocarbon degradation. The results show that common alkane and aromatic hydrocarbon degradation genes (alkB, ligB, yqhD, and ladA), chemotaxis gene (MCP, cheA, cheB, pcaY, and pcaR), heavy-metal resistance, and biofilm genes (σ54, merC, pcoA, copB, etc.) were observed in whole-genome sequence (WGS) of JSTW, which indicated that strain JSTW could potentially cope with combined pollution. The degradation efficiency of naphthalene in 60 h by JSTW was 99% without Cu2+ and 67% with 400 mg L-1 Cu2+ . Comparative genome analysis revealed that genomes of Pseudoalteromonas lipolytica strain LEMB 39 and Pseudoalteromonas donghaensis strain HJ51 shared similarity with strain JSTW, suggesting they are also the potential degradater of petroleum hydrocarbons under combined pollution. Therefore, this study provides a WGS annotation and reveals the mechanism of response to combined pollution of Pseudoalteromonas sp. JSTW.

Spatial Abundance, Diversity, and Activity of Ammonia-Oxidizing Bacteria in Coastal Sediments of the Liaohe Estuary.

Ammonia-oxidizing bacteria (AOB) play an important role in nitrification in estuaries. The aim of this study was to examine the spatial abundance, diversity, and activity of AOB in coastal sediments of the Liaohe Estuary using quantitative PCR, high-throughput sequencing of the amoA gene coding the ammonia monooxygenase enzyme active subunit, and sediment slurry incubation experiments. AOB abundance ranged from 8.54 × 104 to 5.85 × 106 copies g-1 of wet sediment weight and exhibited an increasing trend from the Liaohe Estuary to the open coastal zone. Potential nitrification rates (PNRs) ranged from 0.1 to 336.8 nmol N g-1 day-1 along the estuary to the coastal zone. Log AOB abundance and PNRs were significantly positively correlated. AOB richness decreased from the estuary to the coastal zone. High-throughput sequencing analysis indicated that the majority of amoA gene sequences fell within the Nitrosomonas and Nitrosomonas-like clade, and only a few sequences were clustered within the Nitrosospira clade. This finding indicates that the Nitrosomonas-related lineage may be more adaptable to the specific conditions in this estuary than the Nitrosospira lineage. Sites with high nitrification rates were located in the southern open region and were dominated by the Nitrosomonas-like lineage, whereas the Nitrosospira lineage was found primarily in the northern estuary mouth sites with low nitrification rates. Thus, nitrification potentials in Liaohe estuarine sediments in the southern open region were greater than those in the northern estuary mouth, and the Nitrosomonas-related lineage might play a more important role than the Nitrosospira lineage in nitrification in this estuary.

Spatial distribution characteristics and interaction effects of DOM and microbial communities in kelp cultivation areas.

The influence of macroalgae cultivation on aquaculture carbon sinks is significant, with microbial carbon (C) pumps contributing to a stable inert dissolved carbon pool in this context. Concurrently, dissolved organic matter (DOM) exchange at the marine sediment-water interface profoundly affects global ecosystem element cycling. However, the interactions between DOM and bacterial communities at the sediment-water interface in kelp cultivation areas, especially regarding microbial function prediction, have not been fully explored. This study analyzed the DOM characteristics, environmental factors, and bacterial community structure in the Tahewan kelp--Saccharina japonica cultivated area and compared them with those in non-cultivated areas. The results indicated significantly higher dissolved organic carbon (DOC) concentrations in the kelp culture area, particularly in surface seawater and overlying water. The dominant bacterial phyla in both regions included Pseudomonadota, Actinomycetota, and Bacteroidota in both regions, while Desulfobacterota was more prevalent in the sediment environment of the cultivated region. Parallel factor analysis (EEM-PARAFAC) was used to identify DOM components, among which component C2 (a microbial humic-like substance DOM) was highly resistant to microbial degradation. We infer that C2 has similar properties to recalcitrant dissolved organic matter (RDOM). Analysis of the predicted functional genes based on 16S rRNA gene data showed that methanol oxidation, methylotrophy, and methanotrophy were significant in the bottom seawater of the cultivation area. The carbon (C), nitrogen (N), and sulfur (S) cycle functional genes in the sediment environment of the kelp cultivation area were more active than those in other areas, especially in which sulfate reduction and denitrification were the two main processes. Furthermore, a DOM priming effect was identified in the cultivated sediment environment, where kelp-released labile dissolved organic matter (LDOM) stimulates rapid degradation of the original RDOM, potentially enhancing C sequestration.

Cyclohexanecarboxylic acid degradation with simultaneous nitrate removal by Marinobacter sp. SJ18.

Naphthenic acid (NA) is a toxic pollutant with potential threat to human health. However, NA transformations in marine environments are still unclear. In this study, the characteristics and pathways of cyclohexanecarboxylic acid (CHCA) biodegradation were explored in the presence of nitrate. The results showed that CHCA was completely degraded with pseudo-first-order kinetic reaction under aerobic and anaerobic conditions, accompanied by nitrate removal rates exceeding 70%, which was positively correlated with CHCA degradation (P < 0.05). In the proposed CHCA degradation pathways, cyclohexane is dehydrogenated to form cyclohexene, followed by ring-opening by dioxygenase to generate fatty acid under aerobic conditions or cleavage of cyclohexene through ß-oxidation under anaerobic conditions. Whole genome analysis indicated that nitrate was removed via assimilation and dissimilation pathways under aerobic conditions and via denitrification pathway under anaerobic conditions. These results provide a basis for alleviating combined pollution of NA and nitrate in marine environments with frequent anthropogenic activities.

A new pathway for anaerobic biotransformation of marine toxin domoic acid.

Domoic acid (DA) is a harmful algal toxin produced by marine diatom Pseudo-nitzschia and seriously threatens ecosystem and human health. However, the current knowledge on its biotransformation behavior in coastal anaerobic environment is lacking. This study investigated the anaerobic biotransformation of DA by a new marine consortium GH1. The results demonstrated that 90% of DA (1 mg L-1) was cometabolically biotransformed under sulfate-reducing condition. A new anaerobic biotransformation pathway involving DA hydration, dehydrogenation, and C-C bond cleavage was proposed, where the conjugated double-bond of DA was interrupted, resulting in the corresponding alcohols and ketones, subsequently cleaved hydrolytically, and yielding the lower molecular weight products. Desulfovibrio and Clostridiales were markedly enriched in the anaerobic biotransformation of DA, which might jointly contribute to the elevated bacterial consortium resistance and degradation to DA. This study could deepen understanding of behavior and fate for DA in marine environments.

Enhanced bioremediation of cyclohexaneacetic acid in offshore sediments with green synthetic iron oxide and Pseudoalteromonas sp.

Naphthenic acids (NAs) have been found to exert serious threats on offshore sediment ecosystems and human health in recent years, which entails us the urgent need for NAs remediation. Bioremediation is considered an ideal method for sediment remediation due to ecological sustainability and economic feasibility. However, current bioremediation efficiency of offshore sediments suffers from relatively slow and there has never any attempts to bioremediate offshore sediment NAs contamination hitherto. In this study, the green synthetic iron oxides (gFeOx) based on Laminaria extracts was employed to enhance the biodegradation of NAs (Cyclohexylacetic acid, CHAA) in offshore sediments by Pseudoalteromonas sp. JSTW (an indigenous microorganism). The results showed that CHAA (20 mg·kg-1) in offshore sediments was removed almost 100% within 7 days at 30 mg·kg-1 gFeOx and 0.6 mg·kg-1 Strain JSTW. High-throughput sequencing results revealed that the structure and function of sediment microbial community were essentially restored to uncontaminated levels after bioremediation, highlighting the joint remediation approach is an efficient and eco-friendly method. Overall, this work has firstly provided insights into the application for NAs in situ bioremediation in offshore sediments.

Anaerobic biotransformation mechanism of marine toxin domoic acid.

Domoic acid (DA) is a major marine neurotoxin, occurs frequently in most of the world's coastlines and seriously threatens ecosystem and public health. However, information on its biotransformation process in coastal anaerobic environments remains unclear. In this study, the underlying mechanism of anaerobic biotransformation of DA by marine consortium GLY was investigated using the combination of liquid chromatography-high-resolution Orbitrap mass spectrometry and comparative metatranscriptomics analysis. The results demonstrated that DA could be cometabolically biotransformed under anaerobic conditions with pseudo-first-order reaction. Anaerobic biotransformation pathway of DA was clarified, including decarboxylation, dehydrogenation, carboxylation activation with CoA and multiple ß-oxidation steps occurring at aliphatic side chain, which facilitated DA detoxification. Furthermore, anaerobic cometabolic biotransformation mechanism of glycine-DA by consortium GLY was established for the first time, a number of genes related to the metabolic pathways of glycine fermentation, fatty acid synthesis and ß-oxidation were responded in the consortium GLY transcriptome and involved in the anaerobic biotransformation of DA. This study could deepen understanding of interaction mechanism between toxin DA and marine microorganisms, which provides a new insight into the DA fate and its effects on benthic microbial community in marine environments.

A novel degradation mechanism of naphthenic acids by marine Pseudoalteromonas sp.

Naphthenic acids (NAs) are a persistent toxic organic pollutant that occur in different environment worldwide and cause serious threat to the ecosystem and public health. However, knowledge on the behavior and fate of NAs in marine environments still remains unknown. In this study, the degradation mechanism of NAs (cyclohexylacetic acid, CHAA) was investigated using an common indigenous marine Pseudoalteromonas sp. The results showed that CHAA could be degraded completely under aerobic condition, but could not be utilized directly under anaerobic condition. Interestingly, transcriptome and key enzyme activity results showed the CHAA degradation pathway induced under aerobic condition could still work in anaerobic condition. The degradation was activated by acetyl-CoA transferase and sequentially formed the corresponding cyclohexene, alcohol, and ketone with the assistance of related enzymes, and finally cleaved by hydroxymethylglutarate-CoA lyase. Besides, there was a positive correlation between chemotaxis and aerobic degradation genes (r = 0.976, P < 0.05), the chemotaxis would enhance bacterium movement and NAs biodegradation. It is proposed that bacterium could translocate to NAs and accomplish biodegradation from aerobic to anaerobic environments, which was a new anaerobic degradation pathway of NAs. This study provides new insights into the fate of NAs and other organic contaminants in marine environment.

Promoting anaerobic digestion by algae-based hydrochars in a continuous reactor.

The microalgae and macroalgae-based hydrochars produced by hydrothermal carbonization were mainly used as biofuels, however, their application in anaerobic digestion (AD) was little known. This study investigated the effects of microalgae Chlorella-based hydrochar (HC-C) and macroalgae Laminaria-based hydrochar (HC-L) on a continuous AD reactor under different organic loading rates (OLR). The AD process stability of hydrochars supplemented reactors were performed well under the increase of OLR from 2.6 to 6.5 g COD/L/d, and HC-C and HC-L addition could significantly enhance the daily methane yield by 36.0% and 31.4%, respectively. Interestingly, the possible mechanisms of HC-C and HC-L on the enhanced AD were similar, namely increasing sludge granulation, promoting the Methanothrix relative abundance and key enzyme activities, and further facilitating potential direct interspecies electron transfer between methanogens and organic-degrading bacteria. This study provided an implication on the potential application of algae-based hydrochars in wastewater treatment and energy recovery.

Effects of process water recirculation on solid and liquid products from hydrothermal carbonization of Laminaria.

Hydrothermal carbonization (HTC) is a promising thermo-chemical technology to treat wet biomasses for production of hydrochars but produces excessive process water. In this study, recirculation of process water from HTC of macroalgae Laminaria was investigated for 12 rounds. Recycling process water increased the hydrochar yield, carbon recovery rate and high heating value from 13.3% to 17.1%, from 22.9% to 32.6%, and from 18.4 MJ/kg to 20.5 MJ/kg after 12 rounds, respectively. The process water recirculation could partly alleviate the toxicity of process water through seed germination test. Volatile fatty acids (VFAs) predominantly accumulate with process water recirculation. The increased proportion of VFAs on chemical oxygen demand could promote methane production of diluted process waters, a 12.3% increase was observed in the round 10, compared with initial process water. These results showed that recycling the process water could reduce water consumption significantly and enhance energy recovery efficiency.

Variation and distribution of naphthenic acids in Dalian Bay sediment.

Previous studies that have investigated marine oil pollution have predominantly focused on petroleum hydrocarbons. Naphthenic acids (NAs), in contrast, are toxins that are less well studied. Following the Dalian oil spill accident, monitoring surveys were carried out to investigate NAs in Dalian Bay sediments. Concentrations of NAs were between 14.826 and 34.279 mg kg-1, with acyclic and motorcycle carboxylic acids (43.28% and 35.12%, respectively) being the dominant components. NAs were 10-30 times more abundant than polycyclic aromatic hydrocarbons (PAHs) in the sediment. Further correlation analysis showed the abundance of NAs was highly correlated with total PAH levels (0.705, p < 0.01, n = 24) and total oil (0.485, p < 0.05, n = 24), indicating that NAs may be a potential marker for oil pollution in coastal sediments. The present study may help to expand the scope of marine environmental monitoring and provide guidance for the remediation of marine pollutants.

Aerobic cometabolism of tetrabromobisphenol A by marine bacterial consortia.

The coastal environments worldwide are subjected to increasing TBBPA contamination, but current knowledge on aerobic biodegradability of this compound by marine microbes is lacking. The aerobic removal of TBBPA using marine consortia under eight different cometabolic conditions was investigated here. Results showed that the composition and diversity of the TBBPA-degrading consortia had diverged after 120-day incubation. Pseudoalteromonas, Alteromonas, Glaciecola, Thalassomonas, and Limnobacter were the dominant genera in enrichment cultures. Furthermore, a combination of beef extract- and peptone-enriched marine consortia exhibited higher TBBPA removal efficiency (approximately 60%) than the other substrate amendments. Additionally, Alteromonas macleodii strain GCW was isolated from a culture of TBBPA-degrading consortium. This strain exhibited about 90% of degradation efficiency toward TBBPA (10 mg L-1) after 10 days of incubation under aerobic cometabolic conditions. The intermediates in the degradation of TBBPA by A. macleodii strain GCW were analyzed and the degradation pathways were proposed, involving ß-scission, debromination, and nitration routes.