Elimination of Microcystis aeruginosa through Leuconostoc mesenteroides DH and its underlying mechanism

Microcystis aeruginosa is ubiquitously found in various water bodies and can produce microcystins (MCs), which threaten the health of aquatic animals and human beings. The elimination of excessive M. aeruginosa is beneficial for the protection of the ecosystems and public health. In this regard, algae-lysing bacteria have been extensively studied as an effective measure for their eradication. However, the active substances generated by algae-lysing bacteria are limited. For this study, we reveal that the phenyllactic acid (PLA) produced by Leuconostoc mesenteroides DH exhibits high efficacy for the removal of M. aeruginosa, and explore the elimination mechanism of strain DH on M. aeruginosa. It was found that a cell-free supernatant of strain DH possessed high removal activities against M. aeruginosa. Abundant reactive oxygen species were induced in algal cells following exposure to strain DH supernatant, as well as superoxide dismutase and catalase responses. Furthermore, the integrity of algal cell membranes and photosynthesis was seriously damaged. Interestingly, added exogenous eugenol significantly inhibited the synthesis of active substance produced by strain DH, which further identified that PLA is one of the active substances that contribute to the eradication of M. aeruginosa on the basis of metabolomics analysis. Our finding demonstrated, for the first time, that PLA (as an anti-cyanobacterial compound) can be used for the removal of M. aeruginosa, which provides a theoretical basis for the control of M. aeruginosa.

Formation of adducts during digestion triggered dietary protein for alleviating cytotoxicity of 2-tert-butyl-1,4-benzoquinone

2-tert-butyl-1,4-benzoquinone (TBBQ), a degradation product of lipid antioxidant Tert-Butylhydroquinone (TBHQ), is a new hazardous compound in foods. This study investigated whether co-ingestion of dietary protein and TBBQ can alleviate the toxicity of TBBQ. The results indicated that soy protein isolate, whey protein isolate, and rice protein significantly reduced the residual amount of TBBQ during simulated gastrointestinal digestion. This result was attributed to the excellent elimination capacity of the released amino acids for TBBQ through formation of adducts. Among 20 amino acids, histidine, lysine, glycine, and cysteine showed better elimination capacity for TBBQ; they can eliminate 92.1%, 89.4%, 86.1%, and almost 100%, respectively, in 5 min at pH 8.0. Further study indicated that amino acids with lower ionization constant exhibited greater TBBQ elimination capacity. In addition, incubation of the cells with 50 μM TBBQ for 12 h decreased the cell viability to 28.95 ± 3.25%; while amino acids intervention was involved in the alleviation of TBBQ cytotoxicity via decreasing ROS. Particularly, cysteine showed 100 times more TBBQ detoxifying capacity than other amino acids. This work could provide a theoretical basis for the potential application of amino acids for detoxifying TBBQ in the food industry.

Discerning biodegradation and adsorption of microcystin-LR in a shallow semi-enclosed bay and bacterial community shifts in response to associated process

Hepatotoxic microcystins (MCs) produced by cyanobacteria pose serious risks to aquatic ecosystems and human health, to understand elimination pathways and mechanisms for MCs, especially in a shallow and semi-enclosed eutrophic area, is of great significance. This study succeed in discerning biodegradation and adsorption of microcystin-LR (MCLR) mediated by water and/or sediment in northern part of Meiliang Bay in Lake Taihu, China, and among the first to reveal the shifts of indigenous bacterial community composition in response to MCLR-biodegradation in sediment by Illumina high-throughput sequencing (HTS). Results confirmed that biodegradation predominantly governed MCLR elimination as compared to adsorption in study area. Through faster biodegradation with a rate of 49.21μgL(-1)d(-1), lake water contributed more to overall MCLR removal than sediment. Sediment also played indispensable role in MCLR removal via primarily biodegradation by indigenous community (a rate of 17.27μgL(-1)d(-1)) and secondarily adsorption (<20% of initial concentration). HTS analysis showed that indigenous community composition shifted with decreased phylogenetic diversity in response to sediment-mediated MCLR-biodegradation. Proteobacteria became predominant (39.34-86.78%) in overall composition after biodegradation, which was mostly contributed by sharp proliferation of β-proteobacteria (22.76-74.80%), and might closely link to MCLR-biodegradation in sediment. Moreover, the members of several genera belonging to α-proteobacteria, β-proteobacteria and γ-proteobacteria seemed to be key degraders because of their dominance or increasing population as MCLR degraded. This study expands understanding on natural elimination mechanism for MCs, and provides guidance to reduce MCs' biological risks and guarantee ecosystem safety in aquatic habitats.