Journal of Applied Microbiology最新文献

Aim: As a major efflux pump system in Gram-negative bacteria, AcrAB-TolC plays a key role in the transport of multiple drug substrates and is considered a potential target for the development of novel antimicrobials. Our previous study found that TolC inactivation compromised the resistance to different antimicrobials in porcine extraintestinal pathogenic Escherichia coli (ExPEC) strain PPECC042 (WT). This study was designed to investigate the functional substitution of TolC by other outer membrane proteins (OMPs) with similar β-barrel structures in pumping out different antimicrobials.

Methods and results: In this study, we found that over-expression of several OMPs with similar β-barrel structures, OmpX, OmpC, OmpN, OmpW, and PhoE, in the ΔtolC strain restored the resistance to macrolides, quinolones, or tetracyclines to the level of WT strain. However, the introduction of any one of the five OMPs did not affect the resistance of the strains ΔacrA, ΔacrB, and ΔacrAΔtolC. Further study revealed that the efflux activity was significantly reduced in the ΔtolC strain, but not in the WT strain and the ΔtolC strains over-expressing various OMPs. Additionally, Nile red dye test and ciprofloxacin accumulation test confirmed that the lost efflux activity and drug accumulation in bacterial periplasm by TolC inactivation was restored by the over-expression of each OMP, depending on the presence of genes acrA and acrB.

Conclusion: All five OMPs can replace the TolC protein to play the efflux role in pumping out the drugs from the periplasm to the extracellular space with the help of proteins AcrA and AcrB.

Aims: Carotenoids are a class of hydrophobic substances that are important as food and feed colorants and as antioxidants. The pathway for β-carotene synthesis has been expressed in various yeast species, albeit with rather low yields and titers. The inefficient conversion of phytoene to lycopene is often regarded as a bottleneck in the pathway. In this study, we aimed at the improvement of β-carotene production in Saccharomyces cerevisiae by specifically engineering the enzymatic reactions producing and converting phytoene.

Methods and results: We show that phytoene is stored in intracellular lipid droplets, whereas the enzyme responsible for its conversion, phytoene dehydrogenase, CrtI, is located at the endoplasmic reticulum, like the bifunctional enzyme CrtYB that catalyses the reaction before and after CrtI. To improve the accessibility of phytoene for CrtI and to delay its storage in lipid droplets, we tested the relocation of CrtI and CrtYB to mitochondria. However, only the retargeting of CrtYB resulted in an improvement of the β-carotene content, whereas the mitochondrial variant of CrtI was not functional. Surprisingly, a cytosolic variant of this enzyme, which we obtained through the elimination of its carboxy-terminal membrane anchor, caused an increase in β-carotene accumulation. Overexpression of this CrtI variant in an optimized medium resulted in a strain with a β-carotene content of 79 mg g-1 cell dry weight, corresponding to a 76-fold improvement over the starting strain.

Conclusions: The retargeting of heterologously expressed pathway enzymes improves β-carotene production in S. cerevisiae, implicating extensive inter-organellar transport phenomena of carotenoid precursors. In addition, strong overexpression of carotenoid biosynthetic enzymes and the optimization of cultivation conditions are required for high contents.

Aims: Characterize global genomic features of 86 genomes of Salmonella Gallinarum (SG) and Pullorum (SP), which are important pathogens causing systemic infections in poultry.

Methods and results: All genomes harbored efflux pump encoding gene mdsA and gold tolerance genes golS and golT. Aminoglycoside (aac(6')-Ib, aadA5, aph(6)-Id, aph(3'')-Ib, ant(2'')-Ia), beta-lactam (blaTEM-1, blaTEM-135), efflux pump (mdsB), fosfomycin (fosA3), sulfonamide (sul1, sul2), tetracycline [tet(A)], trimethoprim (dfrA17), acid (asr), and disinfectant (qacEdelta1) resistance genes, gyrA, gyrB, and parC quinolone resistance point mutations, and mercury tolerance genes (mer) were found in different frequencies. Additionally, 310 virulence genes, pathogenicity islands (including SPI-1, 2, 3, 4, 5, 6, 9, 10, 12, 13, and 14), plasmids [IncFII(S), ColpVC, IncX1, IncN, IncX2, and IncC], and prophages (Fels-2, ST104, 500465-1, pro483, Gifsy-2, 103 203_sal5, Fels-1, RE-2010, vB_SenS-Ent2, and L-413C) were detected. MLST showed biovar-specific sequence types, and core genome MLST showed country-specific and global-related clusters.

Conclusion: SG and SP global strains carry many virulence factors and important antimicrobial resistance genes. The diverse plasmids and prophages suggest genetic variability. MLST and cgMLST differentiated biovars and showed profiles occurring locally or worldwide.

Aims: To identify the promising oleaginous Aspergillus oryzae strain and leverage its lipid and biomass production through a mathematical model.

Methods and results: Comparative profiling of the cell growth and total fatty acid (TFA) content among 13 strains of A. oryzae was performed to explore the discrimination in their lipid productions. The oleaginicity of A. oryzae was found to be strain dependent, where the fungal strain BCC7051 exhibited superior performance in producing lipid-rich biomass by submerged fermentation. The TFA contents of the strain BCC7051 were comparable when cultivated at a range of pH values (pH 3.5-6.5) and temperatures (24-42°C). The mathematical model was generated, well describing and predicting the fungal growth and lipid phenotypic traits at various temperatures and carbon substrates.

Conclusion: The A. oryzae strain BCC7051 was a robust cell factory, acquiring economically feasible options for producing valuable lipid-based products.

Public sector data associated with health are a highly valuable resource with multiple potential end-users, from health practitioners, researchers, public bodies, policy makers, and industry. Data for infectious disease agents are used for epidemiological investigations, disease tracking and assessing emerging biological threats. Yet, there are challenges in collating and re-using it. Data may be derived from multiple sources, generated and collected for different purposes. While public sector data should be open access, providers from public health settings or from agriculture, food, or environment sources have sensitivity criteria to meet with ethical restrictions in how the data can be reused. Yet, sharable datasets need to describe the pathogens with sufficient contextual metadata for maximal utility, e.g. associated disease or disease potential and the pathogen source. As data comprise the physical resources of pathogen collections and potentially associated sequences, there is an added emerging technical issue of integration of omics 'big data'. Thus, there is a need to identify suitable means to integrate and safely access diverse data for pathogens. Established genomics alliances and platforms interpret and meet the challenges in different ways depending on their own context. Nonetheless, their templates and frameworks provide a solution for adaption to pathogen datasets.

Aims: Enteric viruses are recognized as a major concern in health care and in the food sector in Canada. Novel clean-label strategies for controlling enteric viruses are sought in the food industry. In this study, we examined the antiviral potential of plant extracts and essential oils on murine norovirus 1 (MNV-1), hepatitis A virus (HAV), and herpes simplex virus 1 (HSV-1).

Methods and results: Inactivation of the viruses by grape seed, blueberry, green tea, and cranberry extracts and by rosemary and thyme essential oils was measured using plaque formation assay. Concentrations ranging from 50 to 200 000 ppm with a contact time of 90 min were tested. Grape seed extract at 10 000 ppm was the most effective (P < 0.05) at reducing MNV-1 and HAV infectious titers, respectively, by 2.85 ± 0.44 log10 and 1.94 ± 0.17 log10. HSV-1 titer was reduced by 3.81 ± 0.40 log10 at 1000 ppm grape seed extract.

Conclusions: Among the plant products tested, grape seed extract was found the most effective at reducing the infectious titers of MNV-1, HAV, and HSV.

Aims: In Tunisia, limited research has focused on characterizing clinical vancomycin-resistant Enterococcus faecium (VREfm). This study aimed to bridge this knowledge gap by molecular characterization of antimicrobial resistance, determining the genetic elements mediating vancomycin-resistance, and whole-genome sequencing of one representative VREfm isolate.

Methods and results: Over 6 years (2011-2016), a total of eighty VREfm isolates responsible for infection or colonization were identified from hospitalized patients, with the incidence rate increasing from 2% in 2011 to 27% in 2016. All of these strains harbored the vanA gene. The screening for antimicrobial resistance genes revealed the predominance of ermB, tetM, and aac(6')-Ie-aph(2'')-Ia genes and 81.2% of strains harbored the Tn1545. Pulsed-field gel electrophoresis identified seven clusters, with two major clusters (belonging to ST117 and ST80) persisting throughout the study period. Seven Tn1546 types were detected, with type VI (truncated transposon) being the most prevalent (57.5%). Whole-genome sequencing revealed a 3 028 373 bp chromosome and five plasmids. Mobile genetic elements and a type I CRISPR-cas locus were identified. Notably, the vanA gene was carried by the classic Tn1546 transposon with ISL3 insertion on a rep17pRUM plasmid.

Conclusion: A concerning trend in the prevalence of VREfm essentially attributed to CC17 persistence and to horizontal transfer of multiple genetic variants of truncated vanA-Tn1546.

Aims: This study explores the plant growth-promoting effect (PGPE) and potential mechanisms of the arsenic (As)-resistant bacterium Flavobacterium sp. A9 (A9 hereafter).

Methods and results: The influences of A9 on the growth of Arabidopsis thaliana, lettuce, and Brassica napus under As(V) stress were investigated. Additionally, a metabolome analysis was conducted to unravel the underlying mechanisms that facilitate PGPE. Results revealed that A9 significantly enhanced the fresh weight of Arabidopsis seedlings by 62.6%-135.4% under As(V) stress. A9 significantly increased root length (19.4%), phosphorus (25.28%), chlorophyll content (59%), pod number (24.42%), and weight (18.88%), while decreasing As content (48.33%, P ≤ .05) and oxidative stress of Arabidopsis. It also significantly promoted the growth of lettuce and B. napus under As(V) stress. A9 demonstrated the capability to produce ≥31 beneficial substances contributing to plant growth promotion (e.g. gibberellic acid), stress tolerance (e.g. thiamine), and reduced As accumulation (e.g. siderophores).

Conclusions: A9 significantly promoted the plant growth under As stress and decreased As accumulation by decreasing oxidative stress and releasing beneficial compounds.