Combination of sequencing batch reactor activated sludge process with sludge lysis using thermophilic bacterial community for minimizing excess sludge.

Sludge reduction is a major challenge in biological wastewater treatment. Hydrolytic enzymes secreted by thermophilic bacteria can lyse sludge and thus achieve sludge reduction, and the indigenous thermophilic community in sludge can lyse sludge more effectively. In this study, the feasibility of combining a sludge lysis reactor based on thermophilic bacteria community (LTBC reactor, 75 °C) with a conventional sequencing batch activated sludge reactor (SBR) for sludge reduction (i.e., LTBC-SBR process) was systematically investigated first time. The effect of lysed sludge returning to the biochemical tank on pollutant removal efficiency, sludge flocculation, sludge settling, and microbial community and function of the LTBC-SBR process was studied. In the LTBC1-SBR process, a sludge growth rate of 0.71 g TSS/day was observed when the lysed sludge reflux ratio (LRR) was 1, and the sludge generation was reduced by 81.5% compared to the conventional SBR reactor. In the LTBC1-SBR process, the removal efficiencies of chemical oxygen demand and total nitrogen were 94.0% and 80.5%, respectively. There was no significant difference in the sludge volume index from the SBR to the LTBC1-SBR stage, however, the effluent suspended solids concentration increased from 35.2 ± 2.1 mg/L to 80.1 ± 5.3 mg/L. This was attributed to the reflux of sludge lysate. In addition, the changes in extracellular polymers content and composition resulted in poor sludge flocculation performance. Heterotrophic bacteria associated with Actinobacteria and Patescibacteria enriched in LTBC1-SBR with relative abundance of 28.51 ± 1.25% and 20.01 ± 1.21%, respectively, which decomposed the macromolecules in the refluxed lysed sludge and contributed to the sludge reduction. Furthermore, due to the inhibition of nitrite-oxidizing bacteria, the nitrite concentration in the effluent of the LTBC1-SBR system reached 4.7 ± 1.1 mg/L, and part of the denitrification process was achieved by short-cut nitrification and simultaneous denitrification. These results indicate that in-situ sludge reduction technology based on lyse sludge lysing by thermophilic community has considerable potential to be widely used in wastewater treatment.

Vip3Aa domain IV and V mutants confer higher insecticidal activity against Spodoptera frugiperda and Helicoverpa armigera.

BACKGROUND: The fall armyworm Spodoptera frugiperda and cotton bollworm Helicoverpa armigera are major insect pests of corn and cotton worldwide. Genetically engineered crops producing Vip3Aa, a potent endotoxin, from the bacterium Bacillus thuringiensis (Bt) are effective in controlling these two harmful pests. However, Vip3Aa efficacy is relatively weak compared to that of other Bt proteins such as Cry1A and Cry1F. This study sought to modify Vip3Aa for increased insecticidal activity and determine the cause of elevated activity. RESULTS: The two triple Vip3Aa mutants in domains IV and V (Vip3Aa-S543N/I544L/E627A and Vip3Aa-S543N/I544L/S686R) exhibited 7.3-fold and 2.8-fold increased toxicity against S. frugiperda, respectively, compared with the wild type while the toxicity of Vip3Aa-S543N/I544L/S686R was 3.2 times that of wild-type protein in H. armigera. The mutants had enhanced stability in midgut juice and 2.6-5.1 times higher binding affinity against S. frugiperda and H. armigera compared with wild type protein. CONCLUSIONS: The enhanced toxicity of Vip3Aa mutants was due to increased stability and binding affinity during infection. The amino acids S543 and I544 combined with E627 or S686 in domains IV and V of Vip3Aa are important for maintaining structural stability and receptor binding. The results match insecticidal activity (LC50 ) with binding activity (Kd ), which provides novel clues for the rational design of Bt insecticidal proteins. © 2022 Society of Chemical Industry.

In Silico Structure-Based Identification and Validation of Key Residues of Vip3Aa Involving in Lepidopteran Brush Border Receptor Binding.

The vegetative insecticidal proteins (VIPs) of Bacillus thuringiensis (Bt) have a broad-spectrum insecticidal activity against Lepidopteran pests and no cross-resistance with the insecticidal crystal protein Cry protein. So there are great potentials for the control of agricultural pests and the resolution of resistance problems. The structural information of Vip3Aa protein and the predicted key amino acid sites on the C-terminal domain of Vip3Aa were analyzed with the methods of bioinformatics such as homology modeling and molecular docking. Site-directed mutagenesis was used to replace these amino acids with alanine, and there was difference in the activities of the mutant protein and Vip3Aa protein. Y619A had improved insecticidal activity against Helicoverpa armigera, but the toxicity of W552A and E627A to Helicoverpa armigera was significantly reduced. The mutants of W552A and E627A had reduced insecticidal activity against Spodoptera exigua. This study demonstrated that the C-terminal domain played an important role in the function of Vip3Aa protein toxin, and the deletion of the side chain of key residues had a significant effect on the activity of the insecticidal protein. This study provides the theoretical basis for revealing the relationship between the structure and function of Vip3Aa protein.

Correction to: In Silico Structure-Based Identification and Validation of Key Residues of Vip3Aa Involving in Lepidopteran Brush Border Receptor Binding.

The original version of this article unfortunately contained a mistake. The missing acknowledgement is provided below.