The bifunctional protein GlmU is a key factor in biofilm formation induced by alkylating stress in Mycobacterium smegmatis

Insights into the biodegradation of pentachlorobiphenyl by Microbacterium paraoxydans: proteomic and metabolomic studies

Bacterial degradation mechanism for high chlorinated pentachlorobiphenyl (PentaCB) with worse biodegradability has not been fully elucidated, which could limit the full remediation of environments afflicted by the complex pollution of polychlorinated biphenyls (PCBs). In this research, a new PentaCB-degrading bacterium Microbacterium paraoxydans that has not been reported was obtained using enzymatic screening method. The characteristics of its intracellular enzymes, proteome and metabolome variation during PentaCB degradation were investigated systematically compared to non-PentaCB conditions. The findings indicate that the degradation rate of PentaCB (1 mg/L) could reach 23.9% within 4 hours and achieve complete degradation within 12 hours, with the mixture of intracellular enzymes being most effective at a pH of 6.0. During the biodegradation of PentaCB, the 12 up-regulated proteins characterized included ABC transporter PentaCB-binding protein, translocase protein TatA, and signal peptidase I (SPase I), indicating the presence of functional proteins for PentaCB degradation in both the cytoplasm and the outer surface of the cytoplasmic membrane. Furthermore, five differentially enriched metabolites were strongly associated with the aforementioned proteins, especially the up-regulated 1, 2, 4-benzenetriol which feeds into multiple degradation pathways of benzoate, chlorocyclohexane, chlorobenzene and aminobenzoate. These relevant results help to understand and speculate the complex mechanisms regarding PentaCB degradation by M. paraoxydans, which have both theoretical and practical implications for PCB bioremediation.

CRISPR Interference-Mediated Silencing of the mmpL3 Gene in Mycobacterium smegmatis and Its Impact on Antimicrobial Susceptibility

BACKGROUND

The discovery of novel therapeutic agents, especially those targeting mycobacterial membrane protein large 3 (mmpL3), has shown promise. In this study, the CRISPR interference-Streptococcus thermophilus nuclease-deactivated Cas9 (CRISPRi-dCas9Sth1) system was utilized to suppress mmpL3 expression in Mycobacterium smegmatis, and its impacts on susceptibility to antimicrobial agents were evaluated.

METHODS

The repression of the mmpL3 gene was confirmed by RT-qPCR. The essentiality, growth curve, viability, and antimicrobial susceptibility of the mmpL3 knockdown strain were investigated.

RESULTS

mmpL3 silencing was achieved by utilizing 0.5 and 1 ng/mL anhydrotetracycline (ATc), resulting in reductions in the expression of 60.4% and 74.4%, respectively. mmpL3 silencing led to a significant decrease in bacterial viability when combined with one-half of the minimal inhibitory concentrations (MICs) of rifampicin, rifabutin, ceftriaxone, or isoniazid, along with 0.1 or 0.5 ng/mL ATc (p < 0.05). However, no significant difference was observed for clarithromycin or amikacin.

CONCLUSIONS

The downregulation of the mmpL3 gene in mycobacteria was achieved through the use of CRISPRi-dCas9Sth1, resulting in growth deficiencies and resensitization to certain antimicrobial agents. The impact was dependent upon the level of gene expression.

Enhancing effect of natural adjuvant, panduratin A, on antibacterial activity of colistin against multidrug-resistant Acinetobacter baumannii

Colistin- and carbapenem-resistant Acinetobacter baumannii is a serious multidrug resistant (MDR) bacterium in clinical settings. Discovery of new antibacterial drugs against MDR is facing multiple challenges in drug development. Combination of known antibiotics with a robust adjuvant might be an alternative effective strategy for MDR treatment. In the study herein, we report an antibiotic adjuvant activity of a natural compound panduratin A from fingerroot (Boesenbergia rotunda) as a potent adjuvant to colistin. The present study investigated the antibiotic adjuvant effect of panduratin A against 10 colistin- and carbapenem-resistant A. baumannii. Antibacterial activities were tested by broth microdilution method. Biofilm assay was used to determine the efficacy of panduratin A in biofilm formation inhibition on two representative strains Aci46 and Aci44. Genomic and transcriptomic analyses of colistin- and carbapenem-resistant A. baumannii strains were used to identify potential resistance and tolerance mechanism in the bacteria. Panduratin A-colistin combination showed an increased effect on antibacterial in the A. baumannii. However, panduratin A did not improve the antibacterial activity of imipenem. In addition, panduratin A improves anti-biofilm activity of colistin against Aci44 and Aci46, the colistin- and carbapenem-resistant A. baumannii. Panduratin A markedly enhances bactericidal and anti-biofilm activity of colistin against colistin- resistant A. baumannii. Based on genome comparisons, single nucleotide polymorphism (SNP) patterns in six genes encoding biofilm and lipid A biosynthesis were shared in Aci44 and Aci46. In Aci44, we identified a partial sequence of pmrB encoding a polymyxin resistant component PmrB, whereas a full length of pmrB was observed in Aci46. RNA-seq analyses of Aci44 revealed that panduratin A-colistin combination induced expression of ribosomal proteins and oxidative stress response proteins, whereas iron transporter and MFS-type transporter systems were suppressed. Panduratin A-colistin combination could promote intracellular reactive oxygen species (ROS) accumulation could lead to the cidal effect on colistin-resistant A. baumannii. Combination of panduratin A and colistin showed a significant increase in colistin efficacy against colistin- resistant A. baumannii in comparison of colistin alone. Genomic comparison between Aci44 and Aci46 showed mutations and SNPs that might affect different phenotypes. Additionally, based on RNA-Seq, panduratin A-colistin combination could lead to ROS production and accumulation. These findings confirmed the potency of panduratin as colistin adjuvant against multidrug resistant A. baumannii.

High-Yield Synthesis of Lacto-N-Neotetraose from Glycerol and Glucose in Engineered Escherichia coli

Lacto-N-neotetraose (LNnT) is a neutral human milk oligosaccharide with important biological functions. However, the low LNnT productivity and the incomplete conversion of the intermediate lacto-N-tetraose II (LNT II) currently limited the sustainable biosynthesis of LNnT. First, the LNnT biosynthetic module was integrated in Escherichia coli. Next, the LNnT export system was optimized to alleviate the inhibition of intracellular LNnT synthesis. Furthermore, by utilizing rate-limiting enzyme diagnosis, the expressions of LNnT synthesis pathway genes were finely regulated to further enhance the production yield of LNnT. Subsequently, a strategy of cofermentation using a glucose/glycerol (4:6, g/g) mixed feed was employed to regulate carbon flux distribution. Finally, by overexpressing key transferases, LNnT and LNT II titers reached 112.47 and 7.42 g/L, respectively, in a 5 L fermenter, and 107.4 and 2.08 g/L, respectively, in a 1000 L fermenter. These are the highest reported titers of LNnT to date, indicating its significant potential for industrial production.

Insights into the central role of N-acetyl-glucosamine-1-phosphate uridyltransferase (GlmU) in peptidoglycan metabolism and its potential as a therapeutic target

Several decades after the discovery of the first antibiotic (penicillin) microbes have evolved novel mechanisms of resistance; endangering not only our abilities to combat future bacterial pandemics but many other clinical challenges such as acquired infections during surgeries. Antimicrobial resistance (AMR) is attributed to the mismanagement and overuse of these medications and is complicated by a slower rate of the discovery of novel drugs and targets. Bacterial peptidoglycan (PG), a three-dimensional mesh of glycan units, is the foundation of the cell wall that protects bacteria against environmental insults. A significant percentage of drugs target PG, however, these have been rendered ineffective due to growing drug resistance. Identifying novel druggable targets is, therefore, imperative. Uridine diphosphate N-acetylglucosamine (UDP-GlcNAc) is one of the key building blocks in PG production, biosynthesized by the bifunctional enzyme N-acetyl-glucosamine-1-phosphate uridyltransferase (GlmU). UDP-GlcNAc metabolism has been studied in many organisms, but it holds some distinctive features in bacteria, especially regarding the bacterial GlmU enzyme. In this review, we provide an overview of different steps in PG biogenesis, discuss the biochemistry of GlmU, and summarize the characteristic structural elements of bacterial GlmU vital to its catalytic function. Finally, we will discuss various studies on the development of GlmU inhibitors and their significance in aiding future drug discoveries.

GlmU inhibitor from the roots of Euphorbia ebracteolata as an anti-tuberculosis agent

Ebractenoid F was identified to be a GlmU inhibitor from Euphorbia ebracteolata, which could inhibit the cell wall biosynthesis of M. tb H37Ra, along with the biofilm formation.

Integrated meta-analysis and machine learning approach identifies acyl-CoA thioesterase with other novel genes responsible for biofilm development in Staphylococcus aureus

Biofilm forming Staphylococcus aureus is a major threat to the health-care industry. It is important to understand the differences between planktonic and biofilm growth forms in the pathogen since conventional treatments targeting the planktonic forms are not effective against biofilms. The current study conducts a meta-analysis of three public transcriptomic profiles to examine the differences in gene expression between the planktonic and biofilm states of S. aureus using random-effects modeling. Mean effect sizes were calculated for 2847 genes among which 726 differentially expressed genes were taken for further analysis. Major genes that are discriminatory between the two conditions were mined using supervised learning techniques and validated by high-accuracy classifiers. Ten different feature selection algorithms were applied and used to rank the most important genes in S. aureus biofilms. Finally, an optimal set of 36 genes are presented as candidate genes in biofilm formation or development while throwing light on the novel roles of an acyl-CoA thioesterase enzyme and 10 hypothetical proteins in biofilms. The relevance of the identified gene set was further validated by building five different classification models using SVM, RF, kNN, NB and DT algorithms that were compared with models built from other relevant gene sets and by reviewing the functional role of 25 previously known genes in biofilm development. The study combines meta-analysis of differential expression with supervised machine learning strategies and feature selection for the first time to identify and validate a discriminatory set of genes important in biofilms of S. aureus. The functional roles of the identified genes predicted to be important in biofilms are further scrutinized and can be considered as a signature target list to develop anti-biofilm therapeutics in S. aureus.

Biofilm formation and extracellular microvesicles-The way of foodborne pathogens toward resistance

Almost all known foodborne pathogens are able to form biofilms as one of the strategies for survival under harsh living conditions, to ward off the inhibition and the disinfection during food production, transport and storage, as well as during cleaning and sanitation of corresponding facilities. Biofilms are communities where microbial cells live under constant intracellular interaction and communication. Members of the biofilm community are embedded into extracellular matrix that contains polysaccharides, DNA, lipids, proteins, and small molecules that protect microorganisms and enable their intercellular communication under stress conditions. Membrane vesicles (MVs) are produced by both Gram positive and Gram negative bacteria. These lipid membrane-enveloped nanoparticles play an important role in biofilm genesis and in communication between different biofilm members. Furthermore, MVs are involved in other important steps of bacterial life like cell wall modeling, cellular division, and intercellular communication. They also carry toxins and virulence factors, as well as nucleic acids and different metabolites, and play a key role in host infections. After entering host cells, MVs can start many pathologic processes and cause serious harm and cell death. Prevention and inhibition of both biofilm formation and shedding of MVs by foodborne pathogens has a very important role in food production, storage, and food safety in general. Better knowledge of biofilm formation and maintaining, as well as the role of microbial vesicles in this process and in the process of host cells' infection is essential for food safety and prevention of both food spoilage and host infection.

Enhancement of Production of D-Glucosamine in Escherichia coli by Blocking Three Pathways Involved in the Consumption of GlcN and GlcNAc

D-Glucosamine is a commonly used dietary supplement that promotes cartilage health in humans. Metabolic flux analysis showed that D-glucosamine production could be increased by blocking three pathways involved in the consumption of glucosamine-6-phosphate and acetylglucosamine-6-phosphate. By homologous single-exchange, two key genes (nanE and murQ) of Escherichia coli BL21 were knocked out, respectively. The D-glucosamine yields of the engineered strains E. coli BL21ΔmurQ and E. coli BL21ΔnanE represented increases by factors of 2.14 and 1.79, respectively. Meanwhile, for bifunctional gene glmU, we only knocked out its glucosamine-1-phosphate acetyltransferase domain by 3D structural analysis to keep the engineered strain E. coli BL21glmU-Δgpa survival, which resulted in an increase in the production of D-glucosamine by a factor of 2.16. Moreover, for further increasing D-glucosamine production, two genes encoding rate-limiting enzymes, named glmS and gna1, were coexpressed by an RBS sequence in those engineered strains. The total concentrations of D-glucosamine in E. coli BL21 glmU-Δgpa', E. coli BL21ΔmurQ', and E. coli BL21ΔnanE' were 2.65 g/L, 1.73 g/L, and 1.38 g/L, which represented increases by factors of 8.83, 5.76, and 3.3, respectively.

Computational Identification of the Proteins Associated With Quorum Sensing and Biofilm Formation in Mycobacterium tuberculosis

With prolonged therapy and increased instances of drug resistance, tuberculosis is viewed as a serious infectious disease causing high mortality. Emerging concepts in Mycobacterium tuberculosis pathogenicity include biofilm formation, which endows bacterial survival in the host for a long time. To tackle chronic tuberculosis infection, a detailed understanding of the bacterial survival mechanisms is crucial. Using comparative genomics and literature mining, 115 M. tuberculosis proteins were shortlisted for their likely association with biofilm formation or quorum sensing. These include essential genes such as secA2, lpqY-sugABC, Rv1176c, and Rv0195, many of which are also known virulence factors. Furthermore, the functional relationship among these proteins was established by considering known protein-protein interactions, regulatory interactions, and gene expression correlation data/information. Graph centrality and motif analyses predicted the importance of proteins, such as Rv0081, DevR, RegX3, Rv0097, and Rv1996 in M. tuberculosis biofilm formation. Analysis of conservation across other biofilm-forming bacteria suggests that most of these genes are conserved in mycobacteria. As the processes, such as quorum sensing, leading to biofilm formation involve diverse pathways and interactions between proteins, these system-wide studies provide a novel perspective toward understanding mycobacterial persistence.

Toward a structome of Acinetobacter baumannii drug targets

Acinetobacter baumannii is well known for causing hospital-associated infections due in part to its intrinsic antibiotic resistance as well as its ability to remain viable on surfaces and resist cleaning agents. In a previous publication, A. baumannii strain AB5075 was studied by transposon mutagenesis and 438 essential gene candidates for growth on rich-medium were identified. The Seattle Structural Genomics Center for Infectious Disease entered 342 of these candidate essential genes into our pipeline for structure determination, in which 306 were successfully cloned into expression vectors, 192 were detectably expressed, 165 screened as soluble, 121 were purified, 52 crystalized, 30 provided diffraction data, and 29 structures were deposited in the Protein Data Bank. Here, we report these structures, compare them with human orthologs where applicable, and discuss their potential as drug targets for antibiotic development against A. baumannii.