[Objective] To reveal the composition and functions of endophytic bacterial communities in maize under different patterns of tillage combined with straw returning in the Tumochuan Plain, identify the endophytic bacterial resources that promote maize straw degradation under different patterns, and lay a foundation for the selective isolation, cultivation, and functional verification. [Methods] We employed Illumina MiSeq high-throughput sequencing to compare the diversity and community structure of endophytes during the mature stage of maize under different patterns of tillage combined with straw returning in the continuous positioning experiment in the irrigation area of Tumochuan Plain, Inner Mongolia Autonomous Region. [Results] No tillage and deep tillage demonstrated significant effects on the endophytic bacterial diversity of maize. Tillage methods exerted stronger effects on the composition and structure of endophytic bacterial community than straw returning. The structures of endophytic bacterial communities in maize can be classified into two categories: no tillage combined with straw returning and the other seven patterns. The dominant endophytic bacterial genera shared by the nine patterns of tillage combined with straw returning werePseudomonas, unclassified_f__Enterobacteriaceae,Pantoea,Raoultella, andRahnella1. Straw returning increased the abundance ofRaoultella and unclassified_f__Enterobacteriaceae. [Conclusion] Different tillage practices alter the diversity, composition, and structure of endophytic bacterial community in maize. Straw returning can increase the relative abundance ofRaoultella andLactococcus, which have positive effects on the degradation of maize straw.

[Objective] To alleviate the soil microecological imbalance caused by continuous cropping and improve the quality and yield ofGynostemmapentaphyllum, we studied the effects ofStreptomycesrochei D74 and the newly developed compound microbial agent T3 on the yield, quality, and rhizosphere bacterial community composition ofG.pentaphyllum, aiming to determine the suitable microbial agent for this medicinal plant in continuous cropping and rotational cropping. [Methods] The five-point sampling method was used to determine the yield ofG.pentaphyllum per unit area in the field. The content of main active constituents including flavonoids, polysaccharides, and saponins was determined by UV-VIS spectrophotometry and high performance liquid chromatography. The 16S rRNA gene high-throughput sequencing was employed to reveal the rhizosphere bacterial community structure ofG.pentaphyllum. [Results] In the Z-zone of rotational cropping, the dry weight, total flavonoids, and total polysaccharides of the T3 group increased by 63.44%, 12.50%, and 32.90%, respectively, compared with those in the control group, and T3 outperformed D74 in improving the yield and quality. In the P-zone of continuous cropping, the dry weight, total flavonoids, and total polysaccharides of the D74 group increased by 77.41%, 112.50%, and 23.10%, respectively, compared with those in the control group, and D74 outperformed T3. The differential microorganisms enriched in the T3 group compared with the control group were beneficial microorganisms such asNovosphingobium andRhodanbacter, and those enriched in the D74 group wereBradyrhizobium andNitrospira. [Conclusion] Both T3 and D74 could optimize the microbial community structure in rhizosphere soil and improve the micro-environment for plant growth by recruiting beneficial microorganisms in the soil, thus increasing the content and yield of the active constituents ofG.pentaphyllum. D74 and T3 demonstrate better performance in the fields of continuous cropping and rotational cropping, respectively.

Nattokinase has a variety of physiological functions and serves the treatment of cardiovascular diseases. Menaquinone-7, one of indispensable fat-soluble vitamins in the human body, can prevent diseases such as osteoporosis and Parkinson's disease. [Objective] To enhance the co-production of nattokinase and menaquinone-7 byBacillus subtilis, reveal the co-production mechanism in the recombinant strain, and provide new metabolic engineering strategies for the production of nattokinase and menaquinone-7. [Methods] We constructedB.subtilis 168-ΔbdhA by knocking out the 2,3-butanediol dehydrogenase genebdhA fromB.subtilis 168. RNA-seq was employed to measure the expression changes of key enzyme-coding genes in the nattokinase and menaquinone-7 synthesis pathways. [Results] Compared withB.subtilis 168, the content of 2,3-butanediol inB.subtilis 168-ΔbdhA was 2.76 g/L, which was reduced by 64.0%. The yields of nattokinase and menaquinone-7 were increased by 30.0% and 60.0%, respectively. The expression levels of genes related to central carbon metabolism, oxidative phosphorylation, and the synthesis of nattokinase and menaquinone-7 changed by RNA-seq analysis. The expression level of nattokinase negative regulator genecodY was down-regulated by 2.19-fold in the mutant. The expression ofsecA,tatAD, andtatC involved in protein secretion showed the down-regulation of 0.37-fold, up-regulation of 2.81-fold, and up-regulation of 0.50-fold, respectively. [Conclusion] The knockout ofbdhA blocked the carbon flux of 2,3-butanediol and promoted glycerol uptake, causing more carbon fluxing to the synthesis pathways of nattokinase and menaquinone-7. The down-regulation of the negative regulatorcodY promoted the transcription of nattokinase. The up- and down-regulation of genes involved in protein scretion promoted extracellular secretion of menaquinone-7.

Bacterial infection has become one of the major problems threatening public health, and the abuse of antibiotics has accelerated the development of bacterial resistance. Antimicrobial peptides have attracted extensive attention due to their broad-spectrum antibacterial activity, rapid bactericidal effect, low toxicity, and low risk of drug resistance. However, the natural structures of antimicrobial peptides indicate some limitations, such as easy degradation, instability, low permeability, and high costs, in their application. How to improve antimicrobial peptides is still a problem to be solved. From the sources and structural characteristics of antimicrobial peptides, we analyzed the spatial structures related to the antibacterial activity and corresponding antibacterial mechanisms. In addition, we summarize the existing improvement strategies of antimicrobial peptides to lay a foundation for seeking new improvement schemes. This review provides new ideas and directions for the modification and clinical application of antimicrobial peptides in the future.

[Objective] Soft rot is the main disease ofAmorphophallus konjac K. Koch in konjac production areas. Crop failure can be caused by the wide spreading of soft rot, because the serious destructiveness of the disease can not be effectively prevented and controlled at present. The occurrence and explosive spreading of soft rot are closely related to the microflora and pathogenic bacteria in konjac. This study explored the main pathogenic bacteria and dominant microbial species in rotten corms and rhizosphere soil, and analyzed the structural characteristics of microflora in the samples infected by soft rot in two main konjac production areas of Yunnan, aiming to provide theoretical support for the prevention and control of soft rot in konjac production. [Methods] The konjac samples infected by soft rot were collected from Fuyuan and Yongping in Yunnan. The Illumina NovaSeq 6000 platform was used for metagenomic sequencing, and the sequencing data were analyzed. Meanwhile, the pathogenic bacteria and dominant microorganisms in the rotten corms were isolated by multistage purification using selective medium, and observed by an electron microscop. [Results] Large quantities of microorganisms were detected in the rotten corms of diseased konjac from the two main production areas, including 15 721 species that belonging to 2 502 genera of 107 phyla.Pectobacteriumcarotovorum was the main pathogen in all of the diseased samples infected by soft rot. The main characteristic feature of microflora in rotten corms was that the abundances of pathogen andStenotrophomonas maltophilia were higher than all the other microorganisms. The composition of microflora present great differences between diseased tissue samples and soil samples, in the same production area, whereas, the microflora composition in the diseased tissue samples or soil samples had slight differences between the two production areas. [Conclusion] The microflora composition showed low correlations between the diseased corm and rhizosphere soil, in the two production areas. The regional difference of microflora in soil was larger than that in the diseased tissue. The results showed that the dominant pathogens and saprophytes played a key role in forming the microflora structure by breaking through the regional impact, and resulted in the microbial ecosystems in the konjac corms infected by soft rot were highly similar in two main production areas.

Bacterial cellulose, a natural biopolymer with higher purity and better mechanical properties than plant cellulose, is expected to be widely used as a new green polymer material. A variety of bacteria have now been proven to have the ability to produce cellulose, in which bacterial cellulose synthase plays a crucial role. Therefore, understanding the catalysis mechanism of bacterial cellulose synthase is a key to the mass production and broad utilization of bacterial cellulose. This paper reviews the basic properties of bacterial cellulose synthase, including the screening of strains, the enhancement of yield, and the cellular localization of the synthase, aiming to promote the research on the catalysis mechanism of cellulose synthase. Further, based on the mechanism of cellulose synthase, this paper detail the influencing factors ofin vitro synthesis and review the research progress in the roles of each subunit of this synthesis method. We explore the catalysis mechanism of bacterial cellulose synthase, point out the problems in the current research, and envision the future research directions in this field, with a view to providing a theoretical basis for the large-scale application of bacterial cellulose by deciphering the synthesis mechanism.

[Objective] Environmental fungi emerge as the principal agents causing microbial deterioration of museum collections. The varying materials and origins of collections and the different storeroom environments in a museum contribute to high diversity of environmental fungi. Additionally, the air conditioning system within a museum may instigate fungal dispersion among storerooms. Recognizing the compositional differences and seasonal variations of fungal communities in the air across varied storerooms underpins the early warning and prevention against microbial hazards in museum settings. [Methods] Sampling was carried out every two months by the impacting method in the iron and silk storerooms of a museum for one year. Fungal species and community composition were examined by ITS rDNA sequencing. [Results] The amplicon sequencing yielded a broad spectrum of fungal data, encompassing five phyla, 20 classes, and 184 families, over half of which displayed notable seasonal changes. Distinct and comparatively consistent fundamental fungal populations existed in both iron and silk storerooms, exhibiting minimal seasonal variations. However, during summer when it was humid, substantial proliferation of the fungi capable of degrading proteinaceous and cellulosic materials was observed in both storerooms, which presented a latent hazard to the collections. Furthermore, it was noted that certain fungi produced acidic by-products during growth, which could compromise the integrity of the collections. [Conclusion] This investigation provides groundwork for the mitigation and management of environmentally derived fungal threats in museum contexts, underscoring importance for the preventive conservation of museum collections.

[Objective] Riemerella anatipestifer (RA) is a Gram-negative pathogen that can cause duck serositis. The type Ⅸ secretion system (T9SS) of this bacterium is involved in sliding and pathogenic processes. The previous study showed that the expression ofB739_0093 inR.anatipestifer CH-1 was significantly up-regulated under the iron-limited condition. The sequence analysis showed that the protein encoded byB739_0093 contained a conserved C-terminal domain of the proteins secreted by T9SS, while its function remained unknown. This study aims to identify whether the protein encoded byB739_0093 is secreted by T9SS and the role of this protein in the pathogenesis of this bacterium. [Methods] qPCR was conducted to determine whether the transcription ofB739_0093 was regulated by iron and the ferric uptake regulator (Fur). The recombinant truncated B739_0093 protein was expressed inEscherichia coli, and the polyclonal antibody was prepared. Western blotting was employed to detect whether the protein was secreted by T9SS. Furthermore, we deletedB739_0093 from RA CH-1 and identified the role ofB739_0093 in the pathogenicity ofR.anatipestifer by virulence and colonization tests in ducklings. [Results] The expression ofB739_0093 was significantly up-regulated in the iron-restricted medium, which was mediated by Fur. Western blotting results showed that the protein encoded byB739_0093 was localized in the secretion of the parent strain RA CH-1, while it was localized in the bacterial lysate and not detected in the secretion of the T9SS-deleted strain. Compared with the parent strain RA CH-1, RA CH-1ΔB739_0093 demonstrated attenuated pathogenicity and reduced colonization ability in various tissues and organs of ducklings. [Conclusion] The protein encoded byB739_0093 is secreted by T9SS and involved in the pathogenicity ofR.anatipestifer, and its expression is regulated by iron and Fur.

L-asparaginase, a key enzyme in amino acid metabolism, is widely used in the food and pharmaceutical industries. The gut microbiota and its product L-asparaginase are closely associated with host health and diseases. [Objective] This study aims to acquire a novel L-asparaginase gene from gut microbiota and explore its enzymatic characteristics and potential applications. [Methods] An L-asparaginase gene was cloned from the metagenome of the fecal microbiota ofNomascus concolor and heterologously expressed inEscherichia coli BL21(DE3). The enzymatic properties of the expressed protein were determined. Furthermore, the potential applications of this protein were explored, including processing potato chips and treating cancer cells. [Results] The cloned L-asparaginase gene,NCasn5, was 996 bp. It encoded the recombinant enzyme NCasn5 with a molecular weight of 37.296 kDa, optimal activity at pH 8.0 and 60 ℃,K_m of (3.33±0.21) mmol/L,V_max of (836.30±13.91) µmol/(min·mg), and a serum half-life of about 69 hin vitro at 37 ℃. NCasn5 reduced the acrylamide content in potato chips by 69.35% and inhibited the growth of human liver cancer cells (QGY-7703) and human melanoma cells (A-375). [Conclusion] We obtained a novel L-asparaginase demonstrating good thermal stability and a prolonged serum half-life. This enzyme lacks the glutaminase activity and reduces acrylamide levels in potato chips. Moreover, it can induce apoptosis in the cancer cell lines QGY-7703 and A-375. These findings suggest the potential applicability of L-asparaginase in both food processing and pharmaceutical industries.

[Objective] A genetically engineered virus strainrGS15-∆2 with deletion of the residues at the positions 519–565 and 628–747 of the non-structural protein 2 (NSP2) had been rescued based on the PRRSV/GSWW/2015 infectious clone. This study aims to construct and rescue an engineered virus strain with the deletion of three sites in NSP2 based onrGS15-∆2. [Methods] Based on the infectious clones ofrGS15-∆2, two recombinant plasmids with the deletion of three sites were constructed by fusion PCR. Specifically, the dominant epitope at the amino acid site 323–364 or 372–433 of NSP2 was further deleted on the basis ofrGS15-∆2. The recombinant plasmids were linearized and mixed with liposome, which were transfected into Marc-145 cells for virus rescue. The growth characteristics of the engineered virus strains were analyzed by electron microscopy, immunofluorescence assay (IFA), virus titer determination, and growth curve establishment. [Results] The engineered virus strainsrGS15-∆3-1 andrGS15-∆3-2 were rescued successfully. Virions with the diameter from 50 nm to 80 nm can be observed under an electron microscope. The results of IFA confirmed the expression of PRRSV N protein by the rescued virus strains and the parent strain GS15. Furthermore, the rescued viruses were cultured with Marc-145 cells for 40 passages, and the deletion regions were confirmed to be stable by RT-PCR and sequencing. The titers ofrGS15-∆3-1 andrGS15-∆3-2 were 2.00×10^6.0 TCID₅₀/mL and 2.25×10^5.8 TCID₅₀/mL, respectively, which had differences from that of the parent strain (P < 0.05). The growth curves showed that the rescued viruses had lower replication levels than the parent strain, and they reached the peak titers 24 h later than the parent strain. [Conclusion] We characterized the growth of the viruses with the deletion of multiple sites in NSP2 of PRRSV. The findings laid a foundation for the development of novel PRRSV-labeled vaccines and provided a new strategy for the prevention and control of porcine reproductive and respiratory syndrome.