Effect of propionate-cultured sludge augmentation on methane production from upflow anaerobic sludge blanket systems treating fresh landfill leachate.

This research investigates the effect of propionate-cultured sludge augmentation on methane (CH4) production from upflow anaerobic sludge blanket systems (UASB) treating fresh landfill leachate. In the study, both UASB reactors (UASB 1 and UASB 2) contained acclimatized seed sludge, and UASB 2 was augmented with propionate-cultured sludge. The organic loading rate (OLR) was varied between 120.6, 84.4, 48.2, and 12.0 gCOD/L·d. The experimental results indicated that the optimal OLR of UASB 1 (non-augmentation) was 48.2 gCOD/L·d, achieving the CH4 production of 4019 mL/d. Meanwhile, the optimal OLR of UASB 2 was 12.0 gCOD/L·d, achieving the CH4 yield of 6299 mL/d. The dominant bacterial community in the propionate-cultured sludge included the genera Methanothrix, Methanosaeta, Methanoculleus, Syntrophobacter, Smithella, Pelotomamulum, which are the VFA-degrading bacteria and methanogens responsible for unblocking the CH4 pathway bottleneck. Essentially, the novelty of this research lies in the use of propionate-cultured sludge to augment the UASB reactor in order to enhance CH4 production from fresh landfill leachate.

A defect in BRI1-EMS-SUPPRESSOR 1 (bes1)-mediated brassinosteroid signaling increases photoinhibition and photo-oxidative stress during heat stress in Arabidopsis.

Heat stress has negative effects on plant performance, especially in photosynthesis and photoprotection. To withstand heat stress, plants modulate steroid phytohormones, brassinosteroids (BRs). However, their regulation and functions in heat stress acclimation are still poorly understood. Plant growth, photoinhibition, photo-oxidative stress and endogenous contents of hormones (including not only BRs but also abscisic acid, salicylic acid and jasmonic acid) were evaluated during heat stress in Arabidopsis thaliana wild type plants and loss-of-function mutations in either BR biosynthetic or signaling genes. It was found that a defect in BRI1-EMS-SUPPRESSOR 1 (bes1)-mediated BR signaling showed the most sensitive characteristics to heat stress compared to wild type and other BR mutants. Sensitivity was associated with declined PSII photochemistry efficiency (Fv/Fm) together with increased carotenoid, tocopherol and lipid hydroperoxide contents, which evidences higher photoinhibition and photo-oxidative stress in the bes1 mutant under heat stress. Furthermore, the bes1 mutant showed greater contents of abscisic acid (ABA) after one day of exposure to heat stress. However, all heat stress symptoms in the bes1 mutant could be mitigated by the application of 24-epibrassinolide. Therefore, it is concluded that BES1 transcription factor plays a role in plants responses to heat stress, relieving photoinhibition and photo-oxidative stress, but that alternative BR signaling pathways to BES1 may also be effective in heat stress acclimation. Furthermore, this study emphasizes the complex interplay between BR and ABA in the heat acclimation process.

Exogenous 24-epibrassinolide enhanced benzene detoxification in Chlorophytum comosum via overexpression and conjugation by glutathione.

Benzene, a hydrophobic xenobiotic, induces cell damage in both humans and plants. Due to its volatilization, benzene is an airborne environmental problem. The potential of an exogenous bioactive brassinosteroid phytohormone to enhance benzene removal for phytoremediation was investigated. Chlorophytum comosum had higher brassinosteroids content under benzene stress. Plant treated with 24-epibrassinolide (EBR) removed significantly more gaseous benzene than untreated plants under both light and dark conditions at an initial benzene of 12.75 µmol in the systematic chambers (P < 0.05). Although benzene increased malondialdehyde in plant tissue, EBR-treated plants lowered this lipid peroxidation by enhancing their antioxidant content and increasing benzene detoxification-related genes expression, including ascorbic acid (AsA), homogentisate phytyltransferase (HPT), and glutathione synthethase (GS). This contributed to maintaining higher photosynthetic performances. Moreover, EBR-treated plants had higher gene expression of ferredoxin-NADP reductase (FNR) and glucose-6-phosphate 1-dehydrogenase (G6PDH), thus promoting NADPH biosynthesis to cope with benzene under light and dark conditions, respectively. Further, higher glutathione biosynthesis promoted more glutathione conjugate of benzene products including S-phenylcysteine (SPC) in EBR-treated plants. Hence, application of exogenous EBR as foliar spray provided for enhanced benzene detoxification via antioxidant content, benzene detoxification-related genes and benzene conjugation products with glutathione (GSH) and consequently greater gaseous benzene removal.

Chlorophytum comosum-bacteria interactions for airborne benzene remediation: Effect of native endophytic Enterobacter sp. EN2 inoculation and blue-red LED light.

This study was performed to determine the effect of plant-endophytic Enterobacter sp. EN2 interactions and blue-red LED light conditions on gaseous benzene removal by plants. It was found that under consecutive benzene fumigation for three cycles (18 days), inoculation of the strain EN2 into sterilized and non-sterilized native C. comosum resulted in significantly increased gaseous benzene removal compared to that in non-inoculated groups under the same light conditions (P < 0.05). Remarkably, EN2 colonization in inoculated plants under LED conditions was higher than under fluorescence conditions as the EN2 could grow better under LED conditions. Strain EN2 possesses NADPH that is used to facilitate benzene degradation and modulate plant growth under benzene stress by bacterial IAA production and ACC deaminase activity; higher IAA and lower ethylene levels were found in inoculated plants compared to non-inoculated ones. These contributed to better benzene removal efficiency. Interestingly, under fumigation for 16 cycles (67 days), there was no difference in gaseous benzene removal between inoculated plants and non-inoculated plants under the same light conditions at initial benzene concentrations of 5 ppm. This is probably due to EN2 reaching maximum growth under all treatments. However, C. comosum exhibited better benzene removal under LED conditions than under fluorescence conditions during 16 cycles, possibly due to better photosynthetic performance and plant growth, leading to more NADPH, and eventually enhanced benzene removal efficiency. Hence, the most efficient acceleration of benzene removal was provided by inoculation of strain EN2 onto C. comosum under blue-red LED light conditions.

The influence of different light quality and benzene on gene expression and benzene degradation of Chlorophytum comosum.

Benzene, a carcinogenic compound, has been reported as a major indoor air pollutant. Chlorophytum comosum (C. comosum) was reported to be the highest efficient benzene removal plant among other screened plants. Our previous studies found that plants under light conditions could remove gaseous benzene higher than under dark conditions. Therefore, C. comosum exposure to airborne benzene was studied under different light quality at the same light intensity. C. comosum could remove 500 ppm gaseous benzene with the highest efficiency of 68.77% under Blue:Red = 1:1 LED treatments and the lowest one appeared 57.41% under white fluorescent treatment within 8 days. After benzene was uptaken by C. comosum, benzene was oxidized to be phenol in the plant cells by cytochrome P450 monooxygenase system. Then, phenol was catalyzed to be catechol that was confirmed by the up-regulation of phenol 2-monooxygenase (PMO) gene expression. After that, catechol was changed to cic, cis-muconic acid. Interestingly, cis,cis-muconic acid production was found in the plant tissues higher than phenol and catechol. The result confirmed that NADPH-cytochrome P450 reductase (CPR), cytochrome b5 (cyt b5), phenol 2-monooxygenase (PMO) and cytochrome P450 90B1 (CYP90B1) in plant cells were involved in benzene degradation or detoxification. In addition, phenol, catechol, and cis,cis-muconic acid production were found under the Blue-Red LED light conditions higher than under white fluorescent light conditions due to under LED light conditions gave higher NADPH contents. Hence, C. comosum under the Blue-Red LED light conditions had a high potential to remove benzene in a contaminated site.