Mechanisms of oxidative stress caused by CuO nanoparticles to membranes of the bacterium Streptomyces coelicolor M145

Novel mechanism of hydrogen peroxide for promoting efficient natamycin synthesis in Streptomyces

The mechanism of regulation of natamycin biosynthesis by Streptomyces in response to oxidative stress is unclear. Here, we first show cholesterol oxidase SgnE, which catalyzes the formation of H2O2 from sterols, triggered a series of redox-dependent interactions to stimulate natamycin production in S. gilvosporeus. In response to reactive oxygen species, residues Cys212 and Cys221 of the H2O2-sensing consensus sequence of OxyR were oxidized, resulting in conformational changes in the protein: OxyR extended its DNA-binding domain to interact with four motifs of promoter p sgnM . This acted as a redox-dependent switch to turn on/off gene transcription of sgnM, which encodes a cluster-situated regulator, by controlling the affinity between OxyR and p sgnM , thus regulating the expression of 12 genes in the natamycin biosynthesis gene cluster. OxyR cooperates with SgnR, another cluster-situated regulator and an upstream regulatory factor of SgnM, synergistically modulated natamycin biosynthesis by masking/unmasking the -35 region of p sgnM depending on the redox state of OxyR in response to the intracellular H2O2 concentration. IMPORTANCE Cholesterol oxidase SgnE is an indispensable factor, with an unclear mechanism, for natamycin biosynthesis in Streptomyces. Oxidative stress has been attributed to the natamycin biosynthesis. Here, we show that SgnE catalyzes the formation of H2O2 from sterols and triggers a series of redox-dependent interactions to stimulate natamycin production in S. gilvosporeus. OxyR, which cooperates with SgnR, acted as a redox-dependent switch to turn on/off gene transcription of sgnM, which encodes a cluster-situated regulator, by masking/unmasking its -35 region, to control the natamycin biosynthesis gene cluster. This work provides a novel perspective on the crosstalk between intracellular ROS homeostasis and natamycin biosynthesis. Application of these findings will improve antibiotic yields via control of the intracellular redox pressure in Streptomyces.

Priestia megaterium Metabolism: Isolation, Identification of Naringenin Analogues and Genes Elevated Associated with Nanoparticle Intervention

The impact of gold nanoparticles (AuNPs) on the biosynthetic manipulation of Priestia megaterium metabolism where an existing gene cluster is enhanced to produce and enrich bioactive secondary metabolites has been studied previously. In this research, we aimed to isolate and elucidate the structure of metabolites of compounds 1 and 2 which have been analyzed previously in P. megaterium crude extract. This was achieved through a PREP-ODS C18 column with an HPLC-UV/visible detector. Then, the compounds were subjected to nuclear magnetic resonance (NMR), electrospray ionization mass spectrometry (ESI-MS), and Fourier-transform infrared spectroscopy (FT-IR) techniques. Furthermore, bioinformatics and transcriptome analysis were used to examine the gene expression for which the secondary metabolites produced in the presence of AuNPs showed significant enhancement in transcriptomic responses. The metabolites of compounds 1 and 2 were identified as daidzein and genistein, respectively. The real-time polymerase chain reaction (RT-PCR) technique was used to assess the expression of three genes (csoR, CHS, and yjiB) from a panel of selected genes known to be involved in the biosynthesis of the identified secondary metabolites. The expression levels of two genes (csoR and yijB) increased in response to AuNP intervention, whereas CHS was unaffected.

Draft genome sequence of potato crop bacterial isolates and nanoparticles-intervention for the induction of secondary metabolites biosynthesis

Introduction

Insights about the effects of gold nanoparticles (AuNPs) on the biosynthetic manipulation of unknown microbe secondary metabolites could be a promising technique for prospective research on nano-biotechnology.

Aim

In this research, we aimed to isolate a fresh, non-domesticated unknown bacterium strain from a common scab of potato crop located in Saudi Arabia and study the metabolic profile.

Methodology

This was achieved through genomic DNA (gDNA) sequencing using Oxford Nanopore Technology. The genomic data were subjected to several bioinformatics tools, including canu-1.9 software, Prokka, DFAST, Geneious Prime, and AntiSMASH. We exposed the culture of the bacterial isolate with different concentrations of AuNPs and investigated the effects of AuNPs on secondary metabolites biosynthesis using several analytical techniques. Furthermore, Tandem-mass spectrometric (MS/MS) technique was optimized for the characterization of several significant sub-classes.

Results

The genomic draft sequence assembly, alignment, and annotation have verified the bacterial isolate as Priestia megaterium. This bacterium has secondary metabolites related to different biosynthetic gene clusters. AuNPs intervention showed an increase in the production of compounds with the molecular weights of 254 and 270 Da in a direct-dependent manner with the increase of the AuNPs concentrations.

Conclusion

The increase in the yields of compound 1 and 2 concomitantly with the increase in the concentration of the added AuNPs provide evidences about the effects of nanoparticles on the biosynthesis of the secondary metabolites. It contributes to the discovery of genes involved in different biosynthetic gene clusters (BGCs) and prediction of the structures of the natural products.

Cuprous Oxide Nanoparticles Decorated Fabric Materials with Anti-biofilm Properties

Considering the global spread of bacterial infections, the development of anti-biofilm surfaces with high antimicrobial activities is highly desired. This work unraveled a simple, sonochemical method for coating Cu2O nanoparticles (NPs) on three different flexible substrates: polyester (PE), nylon 2 (N2), and polyethylene (PEL). The introduction of Cu2O NPs on these substrates enhanced their surface hydrophobicity, induced ROS generation, and completely inhibited the growth of sensitive (Escherichia coli and Staphyloccocus aureus) and drug-resistant (MDR E. coli and MRSA) planktonic and biofilm. The experimental results confirmed that Cu2O-PE exhibited complete biofilm mass reduction ability for all four strains, whereas Cu2O-N2 showed more than 99% biomass inhibition against both drug-resistant and sensitive pathogens in 6 h. Moreover, Cu2O-PEL also indicated a 99.95, 97.73, 98.00, and 99.20% biomass reduction of MRSA, MDR E. coli, E. coli, and S. aureus, respectively. All substrates were investigated for time-dependent inhibitions, and the associated biofilm mass and log reduction were evaluated. The mechanisms of Cu2O NP action against the mature biofilms include the generation of reactive oxygen species (ROS) as well as electrostatic interaction between Cu2O NPs and bacterial membranes. The current study could pave the way for the commercialization of sonochemically coated Cu2O NP flexible substrates for the prevention of microbial contamination in hospitals and industrial environments.

The combined effects of nanoplastics and dibutyl phthalate on Streptomyces coelicolor M145

The environmental and human health risks posed by nanoplastics have attracted considerable attention; however, research on the combined toxicity of nanoplastics and plasticizers is limited. This study analyzed the combined effects of nanoplastics and dibutyl phthalate (DBP) on Streptomyces coelicolor M145 (herein referred to as M145) and its mechanism. The results demonstrated that when the concentration of both nanoplastics and DBP was 1 mg/L, the co-addition was not toxic to M145. When the DBP concentration increased to 5 mg/L, the combined toxicity of 1 mg/L nanoplastics and 5 mg/L DBP reduced when compared to the 5 mg/L DBP treatment group. Similarly, the combined toxicity of 10 mg/L nanoplastics and 1 mg/L DBP on M145 was also lower than that of only 10 mg/L nanoplastics. The co-addition of 10 mg/L nanoplastics and 5 mg/L DBP resulted in the lowest survival rate (41.3%). The key reason for differences in cytotoxicity were variations in the agglomeration of nanoplastics and the adsorption of DBP on nanoplastics. The combination of 10 mg/L nanoplastics and 5 mg/L DBP maximized the production of antibiotics; actinorhodin and undecylprodigiosin yields were 3.5 and 1.8-fold higher than that of the control, respectively. This indicates that the excessive production of antibiotics may be a protective mechanism for bacteria. This study provides a new perspective for assessing the risk of co-exposure to nanoplastics and organic contaminants on microorganisms in nature.

UV-aging of microplastics increases proximal ARG donor-recipient adsorption and leaching of chemicals that synergistically enhance antibiotic resistance propagation

Despite growing attention to environmental pollution by microplastics (MP), the effects of MP aging on bacterial horizontal gene transfer (HGT) have not been systematically investigated. Here, we used UV-aged polystyrene microplastics (PS-MPs) to investigate how aging affects antibiotic resistance genes (ARGs) transfer efficiency from various ARG vectors to recipient bacteria. The adsorption capacity of MP₂₀ (20-day UV-aged PS-MPs) towards E. coli (harboring plasmid-borne bla_TEM-1), plasmid pET29 (harboring bla_NDM-1) and phage lambda (carrying the aphA1 ARG) increased by 6.6-, 5.2- and 8.3-fold, respectively, relative to pristine PS-MPs (MP₀), due to increased specific surface area and affinity for these ARG vectors. Moreover, MP₂₀ released more organic compounds (TOC 1.6 mg/g-MP₂₀, versus 0.2 mg/g-MP₀ in 4 h) -possibly depolymerization byproducts (verified by GC-MS), which induced intracellular ROS generation, increased cell permeability and upregulated HGT associated genes. Accordingly, MP₂₀ enhanced ARG transfer frequency from E. coli, plasmid pET29 and phage lambda (relative to MP₀) by 1.3-, 4.7- and 3.5-fold, respectively. The Bliss independence model infers that higher bacterial adsorption and exposure to chemicals released during MP aging synergistically enhanced ARG transfer. This underscores the need to assess the significance of this overlooked phenomenon to the environmental dissemination of antibiotic resistance and other HGT processes.

Single and combined toxicity effects of nanoplastics and bisphenol F on submerged the macrophyte Hydrilla verticillata

Nano- and microplastics pose severe risks to the ecological environment. Nanoplastics (NPs) not only directly affect aquatic organisms, but also adsorb to other pollutants, resulting in compound pollution. Bisphenol F (BPF), an endocrine-disrupting chemical, is increasingly replacing bisphenol A (BPA) and is therefore widely distributed in the environment. In this study, the toxic effects of polystyrene nanoplastics (PS-NPs) and BPF and their combined exposure on the submerged macrophytes Hydrilla verticillata (H. verticillata) and leaf biofilms, were investigated. Results showed that 10 mg/L PS-NPs and combined exposure to 10 mg/L PS-NPs and 10 mg/L BPF significantly decreased the relative growth rate and chlorophyll content of H. verticillata, whereas BPF exposure alone had no impact on the growth and the contents of photosynthetic pigments in H. verticillata. Individual and combined exposure to PS-NPs and BPF can trigger antioxidant responses such as increased activities of superoxide dismutase, peroxidase, and malondialdehyde, as well as higher levels of glutathione S-transferase and glutathione and decreased catalase activity. The results of the scanning electron microscopy (SEM) showed that the nanoplastics particles were adsorbed on the surface of plant leaves, explaining their toxic effects, whereas BPF increases the sorption of PS-NPs on the surface of H. verticillata, potentially leading to PS-NPs enrichment in the food chain. The diversity and richness of the microbial community were altered by exposure to PS-NPs and BPF individually and in combination. The current study is the first to assess the effects of PS-NPs and BPF exposure on the growth, physiological characteristics, and leaf biofilm properties of submerged macrophytes.

Evaluation of copper uptake in individual spores of Streptomyces coelicolor and endogenic nanoparticles formation to modulate the secondary metabolism

Copper modulates secondary metabolism in Streptomyces. Although the cytosolic copper concentration is controlled by several chaperones and transporters, the formation of copper nanoparticles and its relation to the antibiotic production has never been established in the model Streptomyces coelicolor. In this work, state-of-the-art analytical tools are used to evaluate the incorporation of copper in individual spores of Streptomyces coelicolor at different exposure concentrations (40, 80 and 160 µM Cu). Among them, the use of single cell-inductively coupled plasma-mass spectrometry (SC-ICP-MS) revealed incorporation levels in the range of 2 to 2.5 fg/spore (median) increasing up to 4.75 fg/spore at the upper exposure concentrations. The copper storage within the spores in the form of nanoparticles was evaluated using a combination of single particle-ICP-MS (sp-ICP-MS) and transmission electron microscopy (TEM). The obtained data confirmed the presence of nanoparticles in the range of 8 to 40 (mean size 21 nm) inside S. coelicolor spores. The presence of the nanoparticles was correlated with the actinorhodin production in liquid non-sporulating cultures amended with up to 80 µM Cu. However, further increase to 160 µM Cu, yielded to a significant decrease in antibiotic production. Secondary metabolism is activated under stressful conditions and cytosolic copper seems to be one of the signals triggering antibiotic production. Particularly, nanoparticle formation might contribute to modulate the secondary metabolism and prevent for copper toxicity. This work describes, for first time, the formation of endogenous copper nanoparticles in S. coelicolor and reveals their correlation with the secondary metabolism.

Evaluating the Antibacterial Activity and Mode of Action of Thymol-Loaded Chitosan Nanoparticles Against Plant Bacterial Pathogen Xanthomonas campestris pv. campestris

The bacterium Xanthomonas campestris pv. campestris (Xcc) causes black rot disease in cruciferous crops, resulting in severe yield loss worldwide. The excessive use of chemical pesticides in agriculture to control diseases has raised significant concern about the impact on the environment and human health. Nanoparticles have recently gained significant attention in agriculture owing to their promising application in plant disease control, increasing soil fertility and nutrient availability. In the current study, we synthesized thymol-loaded chitosan nanoparticles (TCNPs) and assessed their antibacterial activity against Xcc. The synthesis of TCNPs was confirmed by using ultraviolet–visible spectroscopy. Fourier-transform infrared spectroscopy, transmission electron microscopy, and scanning electron microscopy analysis revealed the functional groups, size, and shape of TCNPs, with sizes ranging from 54 to 250 nm, respectively. The antibacterial activity of TCNPs against Xcc was investigated in vitro by liquid broth, cell viability, and live dead staining assay, and all of them demonstrated the antibacterial activity of TCNPs. Furthermore, TCNPs were found to directly inhibit the growth of Xcc by suppressing the growth of biofilm formation and the production of exopolysaccharides and xanthomonadin. The ultrastructure studies revealed membrane damage in TCNP-treated Xcc cells, causing a release of intracellular contents. Headspace/gas chromatography (GC)–mass spectrometry (MS) analysis showed changes in the volatile profile of Xcc cells treated with TCNPs. Increased amounts of carbonyl components (mainly ketones) and production of new volatile metabolites were observed in Xcc cells incubated with TCNPs. Overall, this study reveals TCNPs as a promising antibacterial candidate against Xcc.

Use of elicitors to enhance or activate the antibiotic production in streptomyces

Streptomyces is the largest and most significant genus of Actinobacteria, comprising 961 species. These Gram-positive bacteria produce many versatile and important bioactive compounds; of these, antibiotics, specifically the enhancement or activation of their production, have received extensive research attention. Recently, various biotic and abiotic elicitors have been reported to modify the antibiotic metabolism of Streptomyces, which promotes the production of new antibiotics and bioactive metabolites for improvement in the yields of endogenous products. However, some elicitors that obviously contribute to secondary metabolite production have not yet received sufficient attention. In this study, we have reviewed the functions and mechanisms of chemicals, novel microbial metabolic elicitors, microbial interactions, enzymes, enzyme inhibitors, environmental factors, and novel combination methods regarding antibiotic production in Streptomyces. This review has aimed to identify potentially valuable elicitors for stimulating the production of latent antibiotics or enhancing the synthesis of subsistent antibiotics in Streptomyces. Future applications and challenges in the discovery of new antibiotics and enhancement of existing antibiotic production using elicitors are discussed.

Influences and mechanisms of nanoparticles on pentachloronitrobenzene accumulation by earthworms

Pesticides and nanoparticles may coexist in soil; however, influences of nanoparticles on accumulation of pesticides in terrestrial organisms are still unclear. This study aims to investigate the influences and mechanisms of metal oxide nanoparticles (nano ZnO and nano CuO) on accumulation of pentachloronitrobenzene (PCNB) in earthworms and their combined toxicity. The earthworms were cultivated in the soil spiked with nanoparticles (10, 50, 250 mg/kg) and PCNB (100 μg/kg) for 21 days. The concentrations of PCNB in earthworms in binary exposure treatments (PCNB + ZnO and PCNB + CuO) reached 2.47 and 3.13 times of that in individual PCNB exposure treatment, indicating that nanoparticles facilitated the accumulation of PCNB in earthworms. The contents of reactive oxygen species (ROS) in earthworms in treatments PCNB + ZnO 250 and PCNB + CuO 250 reached 379 and 316 fluorescence intensity/mg Protein, respectively, which were significantly higher than that in control group (183 fluorescence intensity/mg protein), indicating that nanoparticles would cause oxidative stress to earthworms. Earthworm coelomocytes were extracted from healthy earthworms and cultivated in culture media in cytotoxicity tests. Changes of intracellular ROS contents and cell viability suggested that PCNB and nanoparticles caused serious oxidative damage to earthworm coelomocytes, thus leading to the damage of cell membrane and cell death. In in vivo tests, changes of biomarkers (ROS and malondialdehyde) demonstrated that these pollutants injured the earthworms. Increased accumulation of PCNB in binary exposure treatments was due to the damage of body cavity caused by nanoparticles. This study provides a novel hypothesis for nanoparticles facilitating organic pollutants entering terrestrial organisms and determines whether nanoparticles would bring about greater environmental risks of other pollutants.

Joint effects of carbon nanotubes and copper oxide nanoparticles on fermentation metabolism towards Saccharofermentans acetigenes: Enhancing environmental adaptability and transcriptional expression

In this study, the joint effects of widely used copper oxide nanoparticles (CuO NPs) and multi-walled carbon nanotubes (MWCNTs) on the fermentation metabolism of a model acetogenic bacterium Saccharofermentans acetigenes were investigated and the underlying mechanisms were further explored. The presence of sole CuO NPs or MWCNTs severely inhibited the acetate generation, while their co-existences did not further decrease the acetate yield as expected. Further analysis indicated the joint effects facilitated the enhancement of bacterial stimulus response to the environment and interspecies communication, which improved adaptive capacity to the adverse environment involved in nanomaterials. Meanwhile, the co-existence reduced inhibitory effects of sole nanomaterial on the gene expressions and catalytic activities of key enzymes involved in glycolysis and pyruvate metabolism. Therefore, the joint effects could enhance environmental adaptation of S. acetigenes and transcriptional expressions of key enzymes for acetic acid production-related processes, alleviating the inhibition of CuO NPs to acetate production.

The toxicity effects of nano/microplastics on an antibiotic producing strain - Streptomyces coelicolor M145

The toxic effects of nano/microplastics on microorganisms are still unclear. In this study, Streptomyces coelicolor (S. coelicolor) M145 was selected to study the toxicity and mechanism of nano/microplastics (20 nm, 100 nm, 1 μm and 1 mm) at concentration of 0.1, 1 and 10 mg/L on microorganisms. Results showed that the cytotoxicity, reactive oxygen species (ROS) level, permeability, and antibiotic production of M145 cells changed significantly after the addition of nano/microplastics, and the trends were size and concentration dependent. After M145 was exposed to 10 mg/L of 20 nm nanoplastics, its fatality rate was 64.8%, which was the highest among the particle size of 20 nm to 1 mm at a concentration of 0.1-10 mg/L. And the ROS level and cell permeability also reached their highest values, which was about 2.7 folds and 2.2 folds of control, respectively. After this treatment, the maximum yields of actinorhodin and undecylprodigiosin were 6.7 and 5.3 mg/L, respectively. Transcriptome analysis indicated that nanoplastics could inhibit the transport capacity, primary metabolism, and oxidative phosphorylation of M145, and that the inhibition extend was negatively related to the particle size. Moreover, the toxicity of microplastics to M145 was significantly less than that of nanoplastics. This study provides a new perspective for understanding the toxicity of nano/microplastics on microorganisms in nature.

Cytotoxicological evaluation of copper oxide nanoparticles on green algae, bacteria and crustacean systems

PURPOSE

Copper oxide (CuO) nanoparticles (NPs) have been utilized in several industries including textile, consumer products, medical, automobiles etc. The discharge of industrial effluents in environment increased the probability of CuO NPs contamination in the ecosystem.

METHODS

The present investigation used CuO NPs to determine the toxic effect on Lyngbya species, fresh water algae isolated from natural pond, bacterial species Pseudomonas aeruginosa and Staphylococcus aureus and a crustacean species Daphnia magna.

RESULTS

The NPs average diameter and zeta potential was estimated to be 45 ± 3 nm and 29 ± 1.78 mV respectively. The results showed that 0.1 µg/mL CuO NPs showed the growth inhibition of 47 ± 2% on Lyngbya sp. after 5 days of incubation. The CuO NPs also showed toxic effect to bacterial systems such as P. aeruginosa and S. aureus and crustacean system D. magna. Further, there was an increased lipid peroxidation and generation of reactive oxygen species (ROS) in algal cells observed up on NPs exposure. The exposure of NPs suppressed the antioxidant defense system. The amount of glutathione was reduced after the exposure of NPs.

CONCLUSION

The study suggested the role of ROS in toxicity of algal and bacterial systems. The present study pointed out the potent toxicity of CuO NPs to the organisms present in the aquatic environment.

A novel assessment system of toxicity and stability of CuO nanoparticles via copper super sensitive Saccharomyces cerevisiae mutants

CuO nanoparticles (CuO-NPs) toxicity in organisms is contributed mainly through the copper uptake by both the ionic and nanoparticle form. However, the relative uptake ratio and bioavailability of the two different forms is not well known due to a lack of sensitive and effective assessment systems. We developed a series of both copper resistant and hyper sensitive Saccharomyces cerevisiae mutants to investigate and compare the effects of CuO-NPs and dissolved copper (CuCl₂), on the eukaryote with the purpose of quantitating the relative contributions of nanoparticles and dissolved species for Cu uptake. We observed the toxicity of 10 mM CuO-NPs for copper sensitive strains is equal to that of 0.5 mM CuCl₂ and the main toxic effect is most likely generated from oxidative stress through reactive oxygen species (ROS) production. About 95% CuO-NPs exist in nanoparticle form under neutral environmental conditions. Assessing the cellular metal content of wild type and copper transporter 1(CTR1) knock out cells showed that endocytosis is the major absorption style for CuO-NPs. This study also found a similar toxicity of Ag for both 10 mM Ag-NPs and 0.2 mM AgNO₃ in the copper super sensitive strains. Our study revealed the absorption mechanism of soluble metal based nanomaterials CuO-NPs and Ag-NPs as well as provided a sensitive and delicate system to precisely evaluate the toxicity and stability of nanoparticles.

Fabrication of monodispersed copper oxide nanoparticles with potential application as antimicrobial agents

Cuprous oxide nanoparticles (Cu2O NPs) were fabricated in reverse micellar templates by using lipopeptidal biosurfactant as a stabilizing agent. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive x-ray spectrum (EDX) and UV-Vis analysis were carried out to investigate the morphology, size, composition and stability of the nanoparticles synthesized. The antibacterial activity of the as-synthesized Cu2O NPs was evaluated against Gram-positive B. subtilis CN2 and Gram-negative P. aeruginosa CB1 strains, based on cell viability, zone of inhibition and minimal inhibitory concentration (MIC) indices. The lipopeptide stabilized Cu2O NPs with an ultra-small size of 30 ± 2 nm diameter exhibited potent antimicrobial activity against both Gram-positive and Gram-negative bacteria with a minimum inhibitory concentration of 62.5 µg/mL at pH5. MTT cell viability assay displayed a median inhibition concentration (IC50) of 21.21 μg/L and 18.65 μg/mL for P. aeruginosa and B. subtilis strains respectively. Flow cytometric quantification of intracellular reactive oxygen species (ROS) using 2,7-dichlorodihydrofluorescein diacetate staining revealed a significant ROS generation up to 2.6 to 3.2-fold increase in the cells treated with 62.5 µg/mL Cu2O NPs compared to the untreated controls, demonstrating robust antibacterial activity. The results suggest that lipopeptide biosurfactant stabilized Cu2O NPs could have promising potential for biocompatible bactericidal and therapeutic applications.

Synergistic toxic effects of ball-milled biochar and copper oxide nanoparticles on Streptomyces coelicolor M145

The toxic effects of multi-nanomaterial systems are receiving increasing attention owing to their inevitable release of various nanomaterials. Knowledge of the bioavailability of the new carbon material ball-milled biochar (BMB) and its synergistic toxicity with metal oxide nanoparticles in bacteria is currently limited. In this study, the interactions of BMB with copper oxide nanoparticles (CuO NPs) and their synergistic toxicity towards Streptomyces coelicolor M145 were analyzed. Results showed that the cytotoxicity, ROS level and permeability of cells changed greatly with the pyrolysis temperatures of biochar and the concentrations of CuO NPs. The greatest cytotoxicity (up to 63.1%) was achieved by adding 20 mg/L CuO NPs to BMB700. The ROS level and cell permeability of this treatment was also the highest, about 4.2 folds and 2.9 folds greater than that of control, respectively. The combination of 10 mg/L BMB700 with 10 mg/L CuO NPs can maximize production of antibiotics, with the yield of undecylprodigiosin (RED) and actinorhodin (ACT) 3.0 times and 4.2 times higher than that in the control, respectively, and the change trend of related genes was consistent with that of antibiotics production. Mechanism analysis showed that the different adsorption capacity of BMB of different pyrolysis temperatures on copper ions played a vital role in the synergistic toxicity, and the increase in cell membrane permeability caused by cell collisions with particles was also an important reason for cytotoxicity. Overall, the synergistic toxicity of BMB with other NPs varies the pyrolysis temperatures, when considering the synergistic toxicity of these materials, the preparation conditions need to be taken into account so as to assess their environmental risks more accurately. On the other hand, this research may provide a new approach for the antibiotic industry to increase its output.

Mechanism of CuO nano-particles on stimulating production of actinorhodin in Streptomyces coelicolor by transcriptional analysis

In this research, antibiotic-producing bacteria, Streptomyces coelicolor (S. coelicolor) M145, was exposed to copper oxide (CuO) particles to investigate the effects of nano-particles (NPs) on antibiotic production. Results showed that a higher yield of antibiotics was obtained with smaller particle sizes of CuO NPs. When exposed to 10 mg/L of 40 nm CuO NPs, the maximum amount of actinorhodin (ACT) obtained was 2.6 mg/L after 144 h, which was 2.0-fold greater than that of control. However, the process was inhibited when the concentration of CuO NPs was increased to higher than 20 mg/L. Transcriptome analysis showed that all the genes involved in the ACT cluster were significantly up-regulated after exposure to 10 mg/L NPs, which could be the direct cause of the increase of ACT production. Additionally, some genes related to the generation of acetyl-coA were up-regulated. In this way, CuO NPs led to an increase of secondary metabolites. The mechanism related to these changes indicated that nano-particle‒induced ROS and Cu²⁺ played synergetic roles in promoting ACT biosynthesis. This is a first report suggesting that CuO NPs had a significant effect on antibiotic production, which will be helpful in understanding the mechanism of antibiotic production in nature.

A comparative analysis of ball-milled biochar, graphene oxide, and multi-walled carbon nanotubes with respect to toxicity induction in Streptomyces

Ball-milled biochar has recently attracted a lot of attention due to the simplicity of its preparation and low cost. However, it is unknown if the biochar is environmentally safe. Here, the toxic effect of ball-milled biochar on Streptomyces was compared to that of pristine biochar and two other carbon nanomaterials of different shapes-graphene oxide and multi-walled carbon nanotubes. The effect of these different materials on antibiotic production was characterized. The results showed that even at concentrations of up to 10 mg/L, pristine biochar had a negligible effect on toxicity and antibiotic production in Streptomyces. However, after ball milling, the physical and chemical properties of biochar changed dramatically. Cells were severely damaged, and there was a significant increase in antibiotic production after the addition of ball-milled biochar. Exposure to 10 mg/L of ball-milled biochar caused massive cell disruption; the survival rate of Streptomyces coelicolor M145 cells was only 68.2% as compared to 90% after treatment with 10 mg/L graphene oxide and multi-walled carbon nanotubes. The secretion of the antibiotics- the red intracellular pigment undecylprodigiosin (RED) and blue diffusible pigment actinorhodin (ACT) was enhanced with the highest level in treatment with ball milled biochar, as compared to that with the other two carbon nanomaterials. This effect can be attributed to increased expression of pathway-specific regulatory genes redD, redZ and actⅡ-ORF4. Ball-milled biochar can be developed as an effective additive to increase antibiotic yield. However, we should restrict the large-scale use of ball-milled biochar before fully understanding its impact on the environment and human health.

Al2O3 nanoparticles promote secretion of antibiotics in Streptomyces coelicolor by regulating gene expression through the nano effect

Toxic effects of nanoparticles (NPs) on microorganisms have attracted substantial attention; however, there are few reports on whether NPs can affect the secondary metabolism of microbes. To investigate the toxic effects of Al₂O₃ NPs on cell growth and antibiotic secretion, Streptomyces coelicolor M145 was exposed to Al₂O₃ NPs with diameters of 30 and 80 nm and bulk Al₂O₃ at concentrations up to 1000 mg/L. The results indicated that differences in the toxicity of Al₂O₃ NPs were related to the particle size. In treatment with Al₂O₃ NPs, the maximum yields of undecylprodigiosin (RED) and actinorhodin (ACT) were 3.7- and 4.6-fold greater than that of the control, respectively, and the initial time of antibiotic production was much shorter. ROS quenching experiment by N-acetylcysteine (NAC) confirmed that ROS were responsible for the increased RED production. From 0 to 72 h, ROS had a significant impact on ACT production; however, after 72 h, the ROS content began to decrease until it disappeared. During ongoing exposure (0-144 h), ACT production continued to increase, indicating that in addition to ROS, nano effect of Al₂O₃ NPs also played roles in this process. Transcriptional analysis demonstrated that Al₂O₃ NPs could increase the expression levels of antibiotic biosynthetic genes and two-component systems (TCSs) and inhibit the expression levels of primary metabolic pathways. This study provides a new perspective for understanding the mechanisms of antibiotic production in nature and reveals important implications for exploring other uses of NPs in biomedical applications or regulation of antibiotics in nature.