Currently, less favorable C=O hydrogenation and weak concerted acid catalysis cause unsatisfactory catalytic performance in the upgrading of biomass‐derived furfurals (i.e., furfural, 5‐methyl ...furfural, and 5‐hydroxymethyl furfural) to ketones (i.e., cyclopentanone, 2,5‐hexanedione, and 1‐hydroxyl‐2,5‐hexanedione). A series of partially oxidized MAX phase (i.e., Ti3AlC2, Ti2AlC, Ti3SiC2) supporting Pd catalysts were fabricated, which showed high catalytic activity; Pd/Ti3AlC2 in particular displayed high performance for conversion of furfurals into targeted ketones. Detailed studies of the catalytic mechanism confirm that in situ hydrogen spillover generates Frustrated Lewis H+−H− pairs, which not only act as the hydrogenation sites for selective C=O hydrogenation but also provide acid sites for ring opening. The close intimate hydrogenation and acid sites promote bifunctional catalytic reactions, substantially reducing the reported minimum reaction temperature of various furfurals by at least 30–60 °C.
Frustrated Lewis H+−H− pairs, generated in situ by hydrogen spillover on partially oxidized MAX phases, act as the hydrogenation sites for C=O hydrogenation and provide acid sites for ring opening. The close intimate hydrogenation and acid sites demonstrate unprecedented bifunctional catalytic performance for the conversion of furfurals.
The existence of quorum sensing (QS) and quorum quenching (QQ) plays important roles in biofilm formation. However, direct detection of QS ability is difficult due to the low concentrations of signal ...molecules inside the biofilm. Therefore, QQ activity is typically used to indicate the attribution of QS/QQ to the biofilm. Nevertheless, current detection methods of QQ activity based on biosensors present undesirable operability and accuracy. In this study, the 96-well plate assay based on a specific biosensor, Agrobacterium tumefaciens A136, and a colorimetric substance, X-gal was established. The reliable fitting results were obtained by standardizing the composition of the A136 X-gal assay solution and optimizing the operating conditions. This method improved the accuracy of QQ activity detection and reduced time and cost consumption. Finally, the 96-well plate assay was successfully applied to detect the QQ activities of biofilm samples and explore possible environmental influencing factors. In general, this study provided a new strategy for understanding the QQ effect in biofilm systems.
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•A rapid and quantitative detection method for quorum quenching (QQ) activity is established.•Microorganisms in various biofilm systems showed different QQ activities.•Artificial biofilm systems present higher QQ activities than natural environment.•Several environmental factors affect the QQ activities in biofilm systems.
•Three distinct developmental phases during biofilter operation were observed.•Trade-offs in biofilm community and function was studied at different phases.•QS related genera active a fast biofilm ...accumulation at startup phase.•Odorants degradation dominated biofilm community evolution at stable operation phase.•QQ behaviors and competition between species play important role in clogging phase.
Biofilters inoculated with activated sludge are widely used for odor control in WWTP. In this process, biofilm community evolution plays an important role in the function of reactor and is closely related to reactor performance. However, the trade-offs in biofilm community and bioreactor function during the operation are still unclear. Herein, an artificially constructed biofilter for odorous gas treatment was operated for 105 days to study the trade-offs in the biofilm community and function. Biofilm colonization was found to drive community evolution during the start-up phase (phase 1, days 0–25). Although the removal efficiency of the biofilter was unsatisfactory at this phase, the microbial genera related to quorum sensing and extracellular polymeric substance secretion led to the rapid accumulation of the biofilm (2.3 kg biomass/m3 filter bed /day). During the stable operation phase (phase 2, days 26–80), genera related to target-pollutant degradation showed increases in relative abundance, which accompanied a high removal efficiency and a stable accumulation of biofilm (1.1 kg biomass/m3 filter bed/day). At the clogging phase (phase 3, days 81–105), a sharp decline in the biofilm accumulation rate (0.5 kg biomass/m3 filter bed /day) and fluctuating removal efficiency were observed. The quorum quenching-related genera and quenching genes of signal molecules increased, and competition for resources among species drove the evolution of the community in this phase. The results of this study highlight the trade-offs in biofilm community and functions during the operation of bioreactors, which could help improve bioreactor performance from a biofilm community perspective.
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Abstract
Background
Controlling excess biomass accumulation and clogging is important for maintaining the performance of gas biofilters and reducing energy consumption. Interruption of bacterial ...communication (quorum quenching) can modulate gene expression and alter biofilm properties. However, whether the problem of excess biomass accumulation in gas biofilters can be addressed by interrupting bacterial communication remains unknown.
Results
In this study, parallel laboratory-scale gas biofilters were operated with
Rhodococcus
sp. BH4 (QQBF) and without
Rhodococcus
sp. BH4 (BF) to explore the effects of quorum quenching (QQ) bacteria on biomass accumulation and clogging. QQBF showed lower biomass accumulation (109 kg/m
3
) and superior operational stability (85–96%) than BF (170 kg/m
3
; 63–92%) at the end of the operation. Compared to BF, the QQBF biofilm had lower adhesion strength and decreased extracellular polymeric substance production, leading to easier detachment of biomass from filler surface into the leachate. Meanwhile, the relative abundance of quorum sensing (QS)-related species was found to decrease from 67 (BF) to 56% (QQBF). The QS function genes were also found a lower relative abundance in QQBF, compared with BF. Moreover, although both biofilters presented aromatic compounds removal performance, the keystone species in QQBF played an important role in maintaining biofilm stability, while the keystone species in BF exhibited great potential for biofilm formation. Finally, the possible influencing mechanism of
Rhodococcus
sp. BH4 on biofilm adhesion was demonstrated. Overall, the results of this study achieved excess biomass control while maintaining stable biofiltration performance (without interrupting operation) and greatly promoted the use of QQ technology in bioreactors.
Graphical Abstract
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•The acclimation leads to the deterministic process in community assembly.•Rare taxa have a high degree of interpretation for the stochastic assembly process.•Rare taxa dominated the ...construction of microbial communities as keystone species.•Top 20 taxa of feature importance are all rare taxa.
Stochastic and deterministic processes are the major themes governing microbial community assembly; however, their roles in bioreactors are poorly understood. Herein, the mechanisms underlying microbial assembly and the effect of rare taxa were studied in biofilters. Phylogenetic tree analysis revealed differences in microbial communities at various stages. Null model analysis showed that stochastic processes shaped the community assembly, and deterministic processes emerged only in the inoculated activated sludge after domestication. This finding indicates the dominant role of stochastic factors (biofilm formation, accumulation, and aging). The Sloan neutral model corroborated the advantages of stochastic processes and mainly attributed these advantages to rare taxa. Cooccurrence networks revealed the importance of rare taxa, which accounted for more than 85% of the keystones. Overall, these results provide good foundations for understanding community assembly, especially the role of rare taxa, and offer theoretical support for future community design and reactor regulation.
Aeromonas veronii has a serious impact on the aquaculture industry and human public health. The type VI secretory system (T6SS) is the virulence regulation system of gram-negative bacteria, of which ...hcp is the core component. In this study, we constructed the mutant (Δ hcp1) and complemented (C-hcp1) strains of A. veronii TH0426 were using homologous recombination to study the effect of hcp1 gene on the virulence of TH0426. We found that deletion of the hcp1 gene caused fracture of the flagella of TH0426 and significantly affected basic biological characteristics, including motility, biofilm formation, bacterial competition, and flagellate-related gene expression., In terms of pathogenicity, compared with wild-type strain, LD50 of Δ hcp1 decreased 17.5-fold (P < 0.001), adhesion and invasion of EPC ability of the Δ hcp1 significantly decreased 1.5-fold (P < 0.001), and both the bacterial load at 12 h and 24 h and the cytotoxicity of Δ hcp1 decreased significantly. In conclusion, the hcp1 gene can affect the basic biological characteristics and animal pathogenicity of TH0426 cells by regulating flagella assembly. This study is helpful to explaining the gene function of hcp1 in the T6SS and its mechanism of action in animal pathogenesis.
•hcp1 gene affects the motility, biofilm formation ability and bacterial competition of A. veronii TH0426.•hcp1 gene is involved in regulating the formation of flagella in A. veronii TH0426.•hcp1 gene negatively regulates flagellar component-related genes in A. veronii TH0426.•hcp1 gene can regulate the virulence of A. veronii TH0426.
Biofilms are widely used and play important roles in biological processes. Low temperature of wastewater inhibits the development of biofilms derived from wastewater activated sludge. However, the ...specific mechanism of temperature on biofilm development is still unclear. This study explored the mechanism of temperature on biofilm development and found a feasible method to enhance biofilm development at low temperature. The amount of biofilm development decreased by approximately 66 % and 55 % at 4 °C and 15 °C, respectively, as compared to 28 °C. The cyclic dimeric guanosine monophosphate (c-di-GMP) concentration also decreased at low temperature and was positively correlated with extracellular polymeric substance (EPS) content, formation, and adhesion strength. Microbial community results showed that low temperature inhibited the normal survival of most microorganisms, but promoted the growth of some psychrophile bacteria like Sporosarcina, Caldilineaceae, Gemmataceae, Anaerolineaceae and Acidobacteriota. Further analysis of functional genes demonstrated that the abundance of functional genes related to the synthesis of c-di-GMP (K18968, K18967 and K13590) decreased at low temperature. Subsequently, the addition of exogenous spermidine increased the level of intracellular c-di-GMP and alleviated the inhibition effect of low temperature on biofilm development. Therefore, the possible mechanism of low temperature on biofilm development could be the inhibition of the microorganism activity and reduction of the communication level between cells, which is the closely related to the EPS content, formation, and adhesion strength. The enhancement of c-di-GMP level through the exogenous addition of spermidine provides an alternative strategy to enhance biofilm development at low temperatures. The results of this study enhance the understanding of the influence of temperature on biofilm development and provide possible strategies for enhancing biofilm development at low temperatures.
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•Biofilms are widely used in environmental engineering and play roles in biological processes.•Inhibition of biofilm development at low temperatures.•The increase of c-di-GMP alleviated the inhibition effect of low temperature on biofilm development.•The mechanism is to inhibit the activity of microorganisms and reduce the communication level.
•An engineered QQ bacteria was successfully constructed using Pseudomonas putida.•The engineered bacteria achieved both biofilm formation control and benzene series degradation.•The environmental ...risk of this engineered bacteria was controllable in actual activated sludge.
Bacterial communication interruption based on quorum quenching (QQ) has been proven its potential in biofilm formation inhibition and biofouling control. However, it would be more satisfying if QQ could be combined with the efficient degradation of contaminants in environmental engineering. In this study, we engineered a biofilm of Pseudomonas putida through introducing a QQ synthetic gene, which achieved both biofilm formation inhibition and efficient degradation of benzene series in wastewater. The aiiO gene introduced into the P. putida by heat shock method was highly expressed to produce QQ enzyme to degrade AHL-based signal molecules. The addition of this engineered P. putida reduced the AHLs concentration, quorum sensing gene expression, and connections of the microbial community network in activated sludge and therefore inhibited the biofilm formation. Meanwhile, the sodium benzoate degradation assay indicated an enhanced benzene series removal ability of the engineering bacteria on activated sludge. Besides, we also demonstrated a controllable environmental risk of this engineered bacteria through monitoring its abundance and horizontal gene transfer test. Overall, the results of this study suggest an alternative strategy to solve multiple environmental problems through genetic engineering means and provide support for the application of engineered bacteria in environmental biotechnology.
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Traditionally partial sulfur-poisoned Pd is used to enhance selectivity in hydrogenation reactions. Herein, we report that this type of catalyst can also display ultraselective hydrodehydroxylation ...of the C–OH group, which is important in synthesizing biomass-based fine chemicals. A series of thiol (i.e., 4-fluorobenzenethiol, 2,3,4,5,6-pentafluorobenzenethiol, and 1-hexanethiol)-modified Pd catalysts were fabricated and showed a high yield of 5-methyl furfural product formed from 5-hydroxymethyl furfural in H2/H2O at 100 °C. Furthermore, the catalysts also exhibit excellent catalytic performance in hydrogenative ring-opening reactions of furan alcohols (i.e., 5-methylfuran alcohol and furan alcohol) to the corresponding ketones (i.e., 2,5-hexanedione and cyclopentanone, respectively). Elucidation of the catalytic mechanism indicates that H2 is heterolytically activated on Pd–S as a frustrated Lewis pair to form H––Pd–S–H3O+ via a water-mediated pathway, which can selectively dehydroxylate the C–OH group and substantially promote these bifunctional catalytic reactions at the lowest reaction temperature compared to the literature. This study presents exciting bifunctional catalysis for challenging substrates by generating a transient H+–H– pair using thiol-modified metal catalysts in water.
The job shop scheduling problem (JSP) is one of the most notoriously intractable NP-complete optimization problems. Over the last 10–15 years, tabu search (TS) has emerged as an effective algorithmic ...approach for the JSP. However, the quality of solutions found by tabu search approach depends on the initial solution. To overcome this problem and provide a robust and efficient methodology for the JSP, the heuristics search approach combining simulated annealing (SA) and TS strategy is developed. The main principle of this approach is that SA is used to find the elite solutions inside big valley (BV) so that TS can re-intensify search from the promising solutions. This hybrid algorithm is tested on the standard benchmark sets and compared with the other approaches. The computational results show that the proposed algorithm could obtain the high-quality solutions within reasonable computing times. For example, 17 new upper bounds among the unsolved problems are found in a short time.
