Heavy metals bring long-term hazardous consequences and pose a serious threat to all life forms. Being non-biodegradable, they can remain in the food webs for a long period of time. Metal ions are ...essential for life and indispensable for almost all aspects of metabolism but can be toxic beyond threshold level to all living beings including microbes. Heavy metals are generally present in the environment, but many geogenic and anthropogenic activities has led to excess metal ion accumulation in the environment. To survive in harsh metal contaminated environments, bacteria have certain resistance mechanisms to metabolize and transform heavy metals into less hazardous forms. This also gives rise to different species of heavy metal resistant bacteria. Herein, we have tried to incorporate the different aspects of heavy metal toxicity in bacteria and provide an up-to-date and across-the-board review. The various aspects of heavy metal biology of bacteria encompassed in this review includes the biological notion of heavy metals, toxic effect of heavy metals on bacteria, the factors regulating bacterial heavy metal resistance, the diverse mechanisms governing bacterial heavy metal resistance, bacterial responses to heavy metal stress, and a brief overview of gene regulation under heavy metal stress.
Biofilms are structured microbial communities attached to surfaces, which play a significant role in the persistence of biofoulings in both medical and industrial settings. Bacteria in biofilms are ...mostly embedded in a complex matrix comprised of extracellular polymeric substances that provide mechanical stability and protection against environmental adversities. Once the biofilm is matured, it becomes extremely difficult to kill bacteria or mechanically remove biofilms from solid surfaces. Therefore, interrupting the bacterial surface sensing mechanism and subsequent initial binding process of bacteria to surfaces is essential to effectively prevent biofilm-associated problems. Noting that the process of bacterial adhesion is influenced by many factors, including material surface properties, this review summarizes recent works dedicated to understanding the influences of surface charge, surface wettability, roughness, topography, stiffness, and combination of properties on bacterial adhesion. This review also highlights other factors that are often neglected in bacterial adhesion studies such as bacterial motility and the effect of hydrodynamic flow. Lastly, the present review features recent innovations in nanotechnology-based antifouling systems to engineer new concepts of antibiofilm surfaces.
The quorum-sensing (QS) system is an intercellular cell-cell communication mechanism that controls the expression of genes involved in a variety of cellular processes and that plays critical roles in ...the adaption and survival of bacteria in their environment. The LuxS/AI-2 QS system, which uses AI-2 (autoinducer-2) as a signal molecule, has been identified in both Gram-negative and Gram-positive bacteria. As one of the important global regulatory networks in bacteria, it responds to fluctuations in the numbers of bacteria and regulates the expression of a number of genes, thus affecting cell behavior. We summarize here the known relationships between the LuxS/AI-2 system and drug resistance, discuss the inhibition of LuxS/AI-2 system as an approach to prevent bacterial resistance, and present new strategies for the treatment of drug-resistant pathogens.
Geobacter sulfurreducens biofilms have promising applications in renewable energy, pollutant bioremediation, and bioelectronic applications. Genetically manipulating G. sulfurreducens biofilms is an ...effective strategy to improve the capacity of extracellular electron transfer (EET). Extracellular polysaccharide, a sticky component surrounding microbes, plays an important role in EET. Herein, we constructed a mutant of G. sulfurreducens strain PCA overexpressing the gene GSU1501 (part of the ATP-dependent exporter of the polysaccharide biosynthesis gene operon), designated strain PCA-1501, to increase EET capacity. Experimental results showed that the overexpression of GSU1501 increased extracellular polysaccharide secretion by 25.5%, which promoted the formation of biofilm with higher thickness and viability, as well as the content of extracellular c-type cytochromes. Compared with the control strain, the mutant showed a higher capacity of Fe(III) oxide reduction and current generation (increased by 20.4% and 22.2%, respectively). Interestingly, the overexpression of GSU1501 hindered the pili formation by reducing the transcription level of pilA; a compensatory relationship between extracellular polysaccharide and pili in promoting biofilm formation deserves further investigation. This study provides a feasible method to promote the EET capacity of G. sulfurreducens biofilms, which benefit their bioelectrochemical applications.
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•Constructed a mutant Geobacter sulfurreducens overexpressing the gene GSU1501•The mutant strain increased extracellular polysaccharide and EET capacity.•Increased extracellular polysaccharide promoted biofilm formation.•Increased extracellular polysaccharides anchored more cytochromes.
Bacillus licheniformis is one of the major spore-forming bacteria with great genotypic diversity in raw milk, dairy ingredients, final dairy products, and is found throughout the dairy processing ...continuum. Though being widely used as a probiotic strain, this species also serves as a potential risk in the dairy industry based on its roles in foodborne illness and dairy spoilage. Biofilm formation of B. licheniformis in combined with the heat resistance of its spores, make it impossible to prevent the presence of B. licheniformis in final dairy products by traditional cleaning and disinfection procedures. Despite the extensive efforts on the identification of B. licheniformis from various dairy samples, no reviews have been reported on both hazard and benefits of this spore-former. This review discusses the prevalence of B. licheniformis from raw milk to commercial dairy products, biofilm formation and spoilage potential of B. licheniformis, and its potential prevention methods. In addition, the potential benefits of B. licheniformis in the dairy industry were also summarized.
Chlorpyrifos, a common organophosphorus pesticide, is widely used for agricultural pest control and can inhibit nitrogen-fixing bacteria biomass in paddy. In this study, the additions of chlorpyrifos ...(1 and 8 mg kg
) to soil, with or without Pseudomonas stutzeri A1501, resulted in a significant decrease in nitrogen fixation, despite insignificant effects on the abundances of P. stutzeri A1501 and bacteria in soil. Toxic effect of chlorpyrifos on P. stutzeri A1501 nitrogenase activity in medium was also observed, accompanied by a significant reduction in the expression of nitrogen-fixing related genes (nifA and nifH). Furthermore, rhizosphere colonization and biofilm formation by P. stutzeri A1501 were repressed by chlorpyrifos, leading to decreased nitrogenase activity in the rhizosphere. Biofilm formation in medium was inhibited by bacterial hyperkinesis and reduction of extracellular polymeric substance, including exopolysaccharides and proteins. Together, these findings showed that chlorpyrifos-induced production of reactive oxygen species (ROS) which was directly responsible for reduced nitrogenase activity in the medium, soil, and rhizosphere by inhibiting the expressions of nitrogen-fixing related genes. Furthermore, the inhibition of biofilm formation by chlorpyrifos or ROS likely aggravated the reduction in rhizospherere nitrogenase activity. These findings provide potentially valuable insights into the toxicity of chlorpyrifos on nitrogen-fixing bacteria and its mechanisms. Furthermore, for sustainable rice production, it is necessary to evaluate whether other pesticides affect nitrogen fixation and select pesticides that do not inhibit nitrogen fixation.
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•DsbA and PepP affected C. sakazakii resistance to environmental stresses.•DsbA and PepP affected biofilm formation and motility capacity of C. sakazakii.•DsbA and PepP deletion ...attenuated C.sakazakii invasion on host cells.•DsbA and PepP regulated the mRNA expression of virulence genes in C. sakazakii.
Cronobacter sakazakii, an opportunity foodborne pathogen, could contaminate a broad range of food materials and cause life-threatening symptoms in infants. The bacterial envelope structure contribute to bacterial environment tolerance, biofilm formation and virulence in various in Gram-negative bacteria. DsbA and PepP are two important genes related to the biogenesis and stability of bacterial envelope. In this study, the DsbA and PepP were deleted in C. sakazakii to evaluate their contribution to stress tolerance and virulence of the pathogen. The bacterial environment resistance assays showed DsbA and PepP are essential in controlling C. sakazakii resistance to heat and desiccation in different mediums, as well as acid, osmotic, oxidation and bile salt stresses. DsbA and PepP also played an important role in regulating biofilm formation and motility. Furthermore, DsbA and PepP deletion weaken C. sakazakii adhesion and invasion in Caco-2, intracellular survival and replication in RAW 264.7. qRT-PCR results showed that DsbA and PepP of C. sakazakii played roles in regulating the expression of several genes associated with environment stress tolerance, biofilm formation, bacterial motility and cellular invasion. These findings indicate that DsbA and PepP played an important regulatory role in the environment resisitance, biofilm formation and virulence of C. sakazakii, which enrich understanding of genetic determinants of adaptability and virulence of the pathogen.
Dermatophytes are saprophytic fungi which invade the skin and contribute to the pathogenesis of Tinea corporis. Dermatophytes are resistant to conventional antifungal agents due to biofilm formation, ...that's why effective therapy is still urgently needed. The edible aromatic plant, Pelargonium graveolens, is known for antimicrobial efficacies, and is extensively colonized by endophytic fungi with potent bio-efficacies. Aspergillus caespitosus AUMC 14405 was isolated from P. graveolens leaves and subjected to GC/MS analysis which led to the tentative identification of 27 metabolites, as well as phytochemical investigation which led to the isolation of 8 compounds. The in silico-based antifungal investigation highlighted 6-methoxymellein as a potent inhibitor of Trichophyton rubrum (a tinea corporis clinical isolate) growth with a MIC of 6.25 µg/ml, compared to fluconazole with a MIC of 25 µg/ml. Interestingly, 6 methoxy mellein exhibited 16.54 % inhibition of biofilm formation compared to fluconazole (0.36 %) at 1.56 µg/ml (P < 0.001) as well as 68.38 % inhibition compared to fluconazole (39.70 %) at 200 µg/ml (p ≤ 0.005). Our results revealed that 6-methoxymellein inhibits the fungal growth of T. rubrum isolates and inhibits their biofilm formation via hyphal disintegration. This may be attributed to targeting 1,3-β-glucan synthase and Δ-14-sterol reductase responsible for maintaining cell wall integrity and ergosterol biosynthesis, which was further confirmed via docking analysis. The study highlights 6-methoxymellein, the vital crop biocide, as a promising antifungal candidate to eradicate therapy-resistant cases of biofilm forming dermatophytes, with the need for further processing for mechanistic analysis, animal testing and clinical trials.
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•Dermatophytes are saprophytic fungi which cause superficial tinea infections.•Aspergillus caespitosus endophytes grow on surfaces of the economic plant, Pelargonium graveolens.•Pelargonium graveolens contains essential oil with bioactive secondary metabolites.•Metabolites detected in A. caespitosus exhibits antidermatophyte efficacy against clinical isolates of dermatophytes.•6‑methoxy mellein effectively inhibits growth and biofilm formation by Trichophyton rubrum.
The antibacterial effect and mechanism of eugenol from Syzygium aromaticum (L.) Merr. & L. M. Perry (clove) leaf essential oil (CLEO) against oral anaerobe Porphyromonas gingivalis were investigated. ...The results showed that eugenol, with content of 90.84% in CLEO, exhibited antibacterial activity against P. gingivalis at a concentration of 31.25 μM. Cell shrink and lysis caused by eugenol were observed with Scanning Electron Microscopy (SEM). The release of macromolecules and uptake of fluorescent dye indicated that the antibacterial activity was due to the ability of eugenol to permeabilize the cell membrane and destroy the integrity of plasmatic membrane irreversibly. In addition, eugenol inhibited biofilm formation and reduced preformed biofilm of P. gingivalis at different concentrations. The down-regulation of virulence factor genes related to biofilm (fimA, hagA, hagB, rgpA, rgpB, kgp) explained that eugenol suppressed biofilm formation at the initial stage. These findings suggest that eugenol and CLEO may be potential additives in food and personal healthcare products as a prophylactic approach to periodontitis.
•Eugenol exhibited a strong antibacterial activity against planktonic P. gingivalis.•Eugenol damaged the cell membrane of P. gingivalis.•Eugenol suppressed biofilm formation of P. gingivalis at the initial stage.•Eugenol down-regulated the expressions of virulence factor genes related to biofilm of P. gingivalis.•Eugenol is a potential and effective antibacterial additive for peridontitis prevention.
The potential effects of engineered metal oxide nanoparticles (MONPs) on bacterial nitrogen fixation are of great concern. Herein, the impact and mechanism of the increasing-used MONPs, including ...TiO2, Al2O3, and ZnO nanoparticles (TiO2NP, Al2O3NP, and ZnONP, respectively), on nitrogenase activity was studied at the concentrations ranging from 0 to 10 mg L−1 using associative rhizosphere nitrogen-fixing bacteria Pseudomonas stutzeri A1501. Nitrogen fixation capacity was inhibited by MONPs in an increasing degree of TiO2NP < Al2O3NP < ZnONP. Realtime qPCR analysis showed that the expressions of nitrogenase synthesis-related genes, including nifA and nifH, were inhibited significantly when MONPs were added. MONPs could cause the explosion of intracellular ROS, and ROS not only changed the permeability of the membrane but also inhibited the expression of nifA and biofilm formation on the root surface. The repressed nifA gene could inhibit transcriptional activation of nif-specific genes, and ROS reduced the biofilm formation on the root surface which had a negative effect on resisting environmental stress. This study demonstrated that MONPs, including TiO2NP, Al2O3NP, and ZnONP, inhibited bacterial biofilm formation and nitrogen fixation in the rice rhizosphere, which might have a negative effect on the nitrogen cycle in bacteria-rice system.
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•MONPs inhibited nitrogenase activity of P. stutzeri A1501 both in medium and on rice root surface.•ROS induced by MONPs repressed nifA expression and enhanced membrane permeability.•Abundance and biofilm formation of P. stutzeri A1501 on root surface decrease when MONPs were added.•Nitrogen fixation and biofilm were inhibited in an increasing degree of TiO2NP < Al2O3NP < ZnONP.
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