Ion transporters play an important role in maintaining intracellular pH homeostasis and ionic equilibrium. Sodium ion transporters and potassium ion transporters exist widely in halophilic and halotolerant microorganisms, and their function of retaining potassium and excreting sodium is one of the two major strategies for microbial tolerance to salt stress. In recent years, new sodium and potassium ion transporters, such as RDD, UPF0118, DUF, and KimA, have been discovered in halophilic and halotolerant microorganisms. The transporters of other metal ions, such as Fe³⁺ and Mg²⁺, have been proved to play a role in microbial osmoregulation by participating in the synthesis of intracellular compatible solutes. This paper reviews the ion transporters associated with salt stress tolerance in halophilic and halotolerant microorganisms, analyzes their molecular structures and working mechanisms, and prospects for their applications in agriculture. Discovering new ion transporters, revealing the structures and mechanisms of ion transporters associated with salt stress tolerance, and analyzing the synergistic effect of coexisting transporter systems and their regulation mechanisms will deepen the understanding of the regulatory mechanisms of salt stress tolerance of halophilic and halotolerant microorganisms and provide new ideas for the improvement of crops in saline-alkali land.

[Objective] This study explored the proliferation dynamics and persistent spread characteristics ofCnaphalocrocis medinalis granulovirus (CnmeGV) inCnaphalocrocis medinalis, aiming to enrich the epidemiological knowledge about baculovirus and provide theoretical support for the efficient application of CnmeGV formulations. [Methods] Transcriptome sequencing was employed to determine the transcriptional levels of viral genes in the larvae infected with CnmeGV for 96 h and in the emerged adults. A quantitative detection marker based on the specific geneCmorf123 of CnmeGV was established to measure the proliferation dynamics and persistent spread characteristics of CnmeGV inC.medinalis. [Results] All the genes of CnmeGV were transcribed in the infected larvae, with the acetyltransferase gene showing the highest transcription level. However, no transcription of viral gene was detected in the transcriptome of adults. The measurement with the quantitative detection marker of CnmeGV showed that the replication level of viral gene remained stable within 48 h post infection. The copies of viral genes significantly increased 2 and 4 days post infection, and each nanogram of DNA contained 83 copies of viral genes 4 days post infection. After infection, no viral transcription was detected in the adults or eggs, while a few transcripts were detected in the pupae. Viral DNA was detected in more than 86.7% of pupa and pupal slough samples and while 13.3% of adults. Viral DNA was detected in both the eggs and the second-generation larvae after infection, while no viral DNA was detected on the egg after the surface treatment. [Conclusion] The proliferation level of CnmeGV inC.medinalis gradually increased and then remained stable within 4 days post infection. CnmeGV particles can be spread for two generations by the egg surface. The eclosion ofC.medinalis is the main pathway for clearing CnmeGV.

[Objective] To construct the γ-aminobutyrate-producing recombinant strains ofEscherichia coli and investigate their fermentation characteristics.[Methods] We constructed two recombinant plasmids pTrc99a-gadB and pTrc99a-gadB-SNO1-SNZ1 and then respectively transformed them into the gene-knockout strainE.coli K12/ΔgabTΔgabPΔpuuE. We investigated and optimized the fermentation process of the recombinant strains for producing γ-aminobutyrate.[Results] The target proteins were highly expressed in the recombinant strains harboring the constructed plasmids. The highest concentration of γ-aminobutyrate was 4.6 g/L in the fermentation broth ofE.coli K12ΔgabTΔgabPΔpuuE/pTrc99a-gadB cultured in the medium containing 10 g/L l-monosodium glutamate and was 21.9 times higher than that in the fermentation broth of the wild type strain. At the l-monosodium glutamate concentration of 20 g/L, the conversion rate of substrate was the highest and the concentration of γ-aminobutyrate reached 8.4 g/L. The concentration of γ-aminobutyrate was slightly lower in the fermentation broth of the recombinant strainE.coli K12ΔgabTΔgabPΔpuuE/pTrc99a-gadB-SNO1-SNZ1, probably due to the excessive consumption of energy. The highest concentration of γ-aminobutyrate was 9.4 g/L whenE.coli K12ΔgabTΔgabPΔpuuE/ pTrc99a-gadB was cultured in 1 L fermentation medium containing 20 g/L l-monosodium glutamate.[Conclusion] We obviously increased the yield of γ-aminobutyrate produced by the recombinant strain. This finding lays a foundation for the industrial production of γ-aminobutyrate.

[Objective] The cell wall structure characteristics make it a challenge to obtain the whole proteins ofPaenibacillus sp. as a Gram-positive bacterium. We employed three representative lysis methods: lysozyme combined with ultrasonic treatment (method 1), lysozyme combined with SDS heat treatment (method 2), and liquid nitrogen combined with ultrasonic treatment (method 3), to obtain the samples for mass spectrometry-based proteomics research onPaenibacillus sp.[Methods] We compared the protein extraction efficiency of the three methods based on protein yield and SDS-PAGE. Furthermore, we analyzed the obtained protein samples by mass spectrometry.[Results] The protein extraction efficiency of the three methods was similar. The number of proteins identified in the sample prepared with method 3 was the highest (2 638 proteins), followed by that with method 1 (2 452 proteins), and that with method 2 was the lowest (2 003 proteins). The Venn diagram was established to compare the protein identification flux of the samples prepared with different methods. Considering the protein extraction efficiency and the shortcomings of method 3, we finally chose method 1 as the most suitable method to extract the proteins for mass spectrometry-based proteomic analysis. Finally, the basic properties of proteins identified by mass spectrometry, including molecular weight, isoelectric point, and hydrophobicity, were analyzed. The proportion of each component of the proteins obtained by the three methods was the same as that of the predicted proteins of the model strainPaenibacillus polymyxa.[Conclusion] For the proteomics research on Gram-positivePaenibacillus sp. by mass spectrometry, lysozyme combined with ultrasonic treatment is the most suitable method for sample preparation.

Guanosine tetraphosphate (ppGpp)/guanosine pentaphosphate (pppGpp) is a signaling molecule in the bacterial stringent response, whose synthesis and hydrolysis are controlled by the synthesis and hydrolysis activities of proteins in the RelA/SpoT homologue (RSH) family. The (p)ppGpp-mediated stringent response enhanced bacterial adaptation to nutrient deprivation and antibiotic resistance. In recent years, (p)ppGpp has been found to associate with bacterial growth, cell division, and antibiotic synthesis, which was an important global regulator in the bacteria. (p)ppGpp has many target sites in the cell, which allow it to regulate DNA replication, transcription, cell cycle, ribosome biosynthesis, and the expression of antibiotic synthesis gene clusters. However, how (p)ppGpp controls transcription and other metabolic processes depends on the bacterial species, and (p)ppGpp regulates the same processes in different bacteria species through different mechanisms. Therefore, this manuscript reviewed the types of (p)ppGpp synthetic and hydrolytic enzymes, the mechanisms of (p)ppGpp regulation on microbial metabolism and the cell cycle, as well as the regulation mechanisms of antibiotic synthesis and tolerance, which lays the foundation for bacterial resistance and cell physiology researches.

Terpenoids, a group of natural products possessing diverse chemical structures and biological activities, have been widely used in the production of food additives, medicines, and cosmetics. Terpenoids are mainly produced by plants. With the rapid development of synthetic biology, heterologous production of terpenoids by engineered microbial strains is more economical and environmentally friendly compared with the conventional methods of extraction from plants and chemical synthesis. The catalytic activities of terpene synthases and the structural specificity of their products are pivotal for the heterologous biosynthesis of terpenoids. Directed evolution and rational design can be adopted to optimize the catalytic properties and product profile of target terpene synthases. However, this requires a feasible high-throughput method to screen mutant libraries. In recent years, various high-throughput screening methods have been developed to boost the sensitivity and efficiency in screening terpene synthases. We review recently established high-throughput screening methods for terpene synthases and briefly outline the principles and advantages and disadvantages of each method. Eventually, we envision the future directions of the application of high-throughput screening in the engineering of terpene synthases.

Salinization is a global soil problem. Plant growth-promoting rhizobacteria (PGPR) have unique advantages in remediating saline-alkali soils and promoting plant growth. Screening the rhizosphere microorganisms ofTamarix chinensis, a typical halophyte, and revealing the growth-promoting effect and mechanism of these microorganisms are of great significance for developing microbial fertilizers. [Objective] To screen out the microorganisms from the rhizosphere soil of saline-alkaline tolerantT.chinensis and measure their basic characteristics, salt and alkali tolerance, and plant growth-promoting effects.[Methods] A saline-alkali tolerant strain Bachu 26 was screened out from the rhizosphere soil of wildT.chinensis in Bachu, Xinjiang and identified based on the morphological, physiological, and biochemical characteristics and 16S rRNA gene sequence. We cultured the strain Bachu 26 in the media with different salt concentrations (0%–20%) and pH values (7.0–13.0) to evaluate its salt and alkali tolerance. We then used multiple functional media to examine the growth-promoting function of Bachu 26 and measured the production of indole-3-acetic acid (IAA). The petri dishes with two compartments were used to verify the ability of Bachu 26 to produce acidic volatile substances.Arabidopsis thaliana seedlings were co-cultured with strain Bachu 26 in common culture dishes, based on which the growth-promoting effect of Bachu 26 onA.thaliana seedlings was analyzed. Furthermore,A.thaliana seedlings and Bachu 26 were cultured dividually in the petri dishes with two compartments, based on which the growth-promoting effect of volatile acidic substances produced by Bachu 26 on the seedlings was analyzed. The growth-promoting effect of Bachu 26 on maize seedlings was analyzed by pot experiments.[Results] Strain Bachu 26 was identified as a species ofHalomonas and namedHalomonas sp. Bachu 26, with the maximum tolerance to 20% salt and pH 11.0.Halomonas sp. Bachu 26 could solubilize organic phosphorus, fix nitrogen, and produce ACC deaminase, IAA, and volatile acidic substances, with the IAA yield reaching 45.885 6 mg/L.Halomonas sp. Bachu 26 significantly increased the fresh weight, lateral roots, taproot length, and leaves ofA.thaliana seedlings under saline-alkali stress. In pot experiments,Halomonas sp. Bachu 26 significantly increased the fresh weight of aboveground part, fresh weight of underground part, and plant height of maize under saline-alkali stress.[Conclusion] The newly isolated PGPR strain Bachu 26 has a significant plant growth-promoting effect. The findings provide material and theoretical support for the remediation of saline-alkali soil and development of saline-alkali tolerant plant growth-promoting microbial fertilizers. Furthermore, the results will promote the applied and basic research onHalomonas.

Using genomic data and bioinformatics methods has become an important approach to rapidly identify the genes and predict the phenotypes of bacterial antibiotic resistance. Dozens of antibiotic resistance databases have been established, providing information and auxiliary tools for the identification and prediction of bacterial antibiotic resistance. As the bacterial genome data and antibiotic resistance phenotype data are increasing, the correlation between them can be establishedvia big data and machine learning. Therefore, establishing efficient models predicting antibiotic resistance phenotypes has become a research hot topic. Focusing on the gene identification and phenotype prediction of bacterial antibiotic resistance, this review discusses the related databases, the theories and methods, the machine learning algorithms, and the prediction models. In addition, we made an outlook on the future prospects in this field, aiming to provide new ideas for the related studies.

[Objective] Pseudomonas aeruginosa is a major Gram-negative pathogen that can exacerbate lung infections in the patients with cystic fibrosis, which can ultimately lead to death. The emerging multi-drug resistant and pan-drug resistant strains pose challenges to the prevention and control ofP.aeruginosa infection.[Methods] A phage capable of lysing multi-drug resistantP.aeruginosa was isolated from farm sewage. The morphological characteristics, biological characteristics, host range, genomic features, andin vitro inhibitory ability of the isolate were studied. The biofilm inhibition test was conducted with both the phage and antibiotics.[Results] The phage PH826 was identified to be a member of the genus Nankokuvirus and it can keep stability within a wide temperature range from 4 ℃ to 60 ℃ and pH range (pH 3.0–11.0). The host range test showed that PH826 could lyse 13P.aeruginosa strains from human and animals. The antibacterial testin vitro showed that PH826 was strongly lytic againstP.aeruginosa at multiplicity of infection (MOI) of 10, 1, and 0.1. The genome of PH826 was 87 956 bp in length, with the G+C content of 54.70%, encoding 165 open reading frames (ORFs) including an endolysin gene. The combination of PH826 at 1×MIC (minimum inhibitory concentration, MIC), 2×MIC, or 4×MIC and ciprofloxacin reduced biofilm formation by more than 80% at the time points of 24 h and 48 h. The combination of PH826 at 2×MIC or 4×MIC and meropenem reduced biofilm formation by more than 80% at the time points of 24 h and 48 h.[Conclusion] PH826 may be a potential disinfectant and therapeutic agent that can be used alone or in combination with antibiotics for the prevention and treatment of pathogenicP.aeruginosa.

[Objective] To explore the roles of phytochrome genesPaPhy1 andPaPhy2 in the sexual reproduction and asexual development ofPodospora anserina and decipher the regulatory mechanisms.[Methods] The homologous recombination method was employed to knock out the two phytochrome genes, and the resulting mutants, ΔPaPhy1 and ΔPaPhy2, were obtained. A double mutant, ΔPaPhy1ΔPaPhy2, was constructedvia genetic cross. We compared the sexual production, asexual development, growth rate, and reactive oxygen metabolism between the mutants and wild-type strains under different light conditions to reveal the main roles of the phytochrome genes inP.anserina.[Results] Blue light and white light induced the formation ofP.anserina ascospore shells. ΔPaPhy produced fewer ascospores in the light and showed prolonged life cycle.[Conclusion] Phytochrome genes are associated with the sexual reproduction ofP.anserina. The aging delay of ΔPaPhy is related to reactive oxygen metabolism. The results of this study provide new ideas for further exploring the mechanism of light in regulating the reproduction of filamentous fungi as well as anti-aging studies.