Exposure to the proton scavenger glycine under alkaline conditions induces Escherichia coli viability loss

Anti-Bacterial Effect of Cannabidiol against the Cariogenic Streptococcus mutans Bacterium: An In Vitro Study

Dental caries is caused by biofilm-forming acidogenic bacteria, especially Streptococcus mutans, and is still one of the most prevalent human bacterial diseases. The potential use of cannabidiol (CBD) in anti-bacterial therapies has recently emerged. Here we have studied the anti-bacterial and anti-biofilm activity of CBD against S. mutans. We measured minimum inhibitory concentration (MIC) and minimum biofilm inhibitory concentration (MBIC). The bacterial growth and changes in pH values were measured in a kinetic study. The biofilm biomass was assessed by Crystal Violet staining and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) metabolic assay. Spinning Disk Confocal Microscopy (SDCM) was used to assess biofilm structure, bacterial viability and extracellular polysaccharide (EPS) production. CBD inhibited S. mutans planktonic growth and biofilm formation in a dose-dependent manner, with similar MIC and MBIC values (5 µg/mL). CBD prevented the bacteria-mediated reduction in pH values that correlated with bacterial growth inhibition. SDCM showed a decrease of 50-fold in live bacteria and EPS production. CBD significantly reduced the viability of preformed biofilms at 7.5 µg/mL with an 80 ± 3.1% reduction of metabolic activity. At concentrations above 20 µg/mL, there was almost no bacterial recovery in the CBD-treated preformed biofilms even 48 h after drug withdrawal. Notably, precoating of the culture plate surfaces with CBD prior to incubation with bacteria inhibited biofilm development. Additionally, CBD was found to induce membrane hyperpolarization in S. mutans. Thus, CBD affects multiple processes in S. mutans including its cariogenic properties. In conclusion, we show that CBD has a strong inhibitory effect against cariogenic bacteria, suggesting that it is a potential drug adjuvant for reducing oral pathogenic bacterial load as well as protecting against dental caries.

Chemically Tuning Resveratrol for the Effective Killing of Gram-Positive Pathogens

In the era of antimicrobial resistance, the identification of new compounds with strong antimicrobial activity and the development of alternative therapies to fight drug-resistant bacteria are urgently needed. Here, we have used resveratrol, a safe and well-known plant-derived stilbene with poor antimicrobial properties, as a scaffold to design several new families of antimicrobials by adding different chemical entities at specific positions. We have characterized the mode of action of the most active compounds prepared and have examined their synergistic antibacterial activity in combination with traditional antibiotics. Some alkyl- and silyl-resveratrol derivatives show bactericidal activity against Gram-positive bacteria in the same low micromolar range of traditional antibiotics, with an original mechanism of action that combines membrane permeability activity with ionophore-related activities. No cross-resistance or antagonistic effect was observed with traditional antibiotics. Synergism was observed for some specific general-use antibiotics, such as aminoglycosides and cationic antimicrobial peptide antibiotics. No hemolytic activity was observed at the active concentrations or above, although some low toxicity against an MRC-5 cell line was noted.

Bacterial Homologs of Progestin and AdipoQ Receptors (PAQRs) Affect Membrane Energetics Homeostasis but Not Fluidity

Membrane potential homeostasis is essential for cell survival. Defects in membrane potential lead to pleiotropic phenotypes, consistent with the central role of membrane energetics in cell physiology. Homologs of the progestin and AdipoQ receptors (PAQRs) are conserved in multiple phyla of Bacteria and Eukarya. In eukaryotes, PAQRs are proposed to modulate membrane fluidity and fatty acid (FA) metabolism. The role of bacterial homologs has not been elucidated. Here, we use Escherichia coli and Bacillus subtilis to show that bacterial PAQR homologs, which we name “TrhA,” have a role in membrane energetics homeostasis. Using transcriptional fusions, we show that E. coli TrhA (encoded by yqfA) is part of the unsaturated fatty acid biosynthesis regulon. Fatty acid analyses and physiological assays show that a lack of TrhA in both E. coli and B. subtilis (encoded by yplQ) provokes subtle but consistent changes in membrane fatty acid profiles that do not translate to control of membrane fluidity. Instead, membrane proteomics in E. coli suggested a disrupted energy metabolism and dysregulated membrane energetics in the mutant, though it grew similarly to its parent. These changes translated into a disturbed membrane potential in the mutant relative to its parent under various growth conditions. Similar dysregulation of membrane energetics was observed in a different E. coli strain and in the distantly related B. subtilis. Together, our findings are consistent with a role for TrhA in membrane energetics homeostasis, through a mechanism that remains to be elucidated.

IMPORTANCE Eukaryotic homologs of the progestin and AdipoQ receptor family (PAQR) have been shown to regulate membrane fluidity by affecting, through unknown mechanisms, unsaturated fatty acid (FA) metabolism. The bacterial homologs studied here mediate small and consistent changes in unsaturated FA metabolism that do not seem to impact membrane fluidity but, rather, alter membrane energetics homeostasis. Together, the findings here suggest that bacterial and eukaryotic PAQRs share functions in maintaining membrane homeostasis (fluidity in eukaryotes and energetics for bacteria with TrhA homologs).

Functionalized Antimicrobial Nanofibers: Design Criteria and Recent Advances

The rise of antibiotic resistance has become a major threat to human health and it is spreading globally. It can cause common infectious diseases to be difficult to treat and leads to higher medical costs and increased mortality. Hence, multifunctional polymeric nanofibers with distinctive structures and unique physiochemical properties have emerged as a neo-tool to target biofilm and overcome deadly bacterial infections. This review emphasizes electrospun nanofibers' design criteria and properties that can be utilized to enhance their therapeutic activity for antimicrobial therapy. Also, we present recent progress in designing the surface functionalization of antimicrobial nanofibers with non-antibiotic agents for effective antibacterial therapy. Lastly, we discuss the future trends and remaining challenges for polymeric nanofibers.

Sulphate-Reducing Bacteria’s Response to Extreme pH Environments and the Effect of Their Activities on Microbial Corrosion

Sulphate-reducing bacteria (SRB) are dominant species causing corrosion of various types of materials. However, they also play a beneficial role in bioremediation due to their tolerance of extreme pH conditions. The application of sulphate-reducing bacteria (SRB) in bioremediation and control methods for microbiologically influenced corrosion (MIC) in extreme pH environments requires an understanding of the microbial activities in these conditions. Recent studies have found that in order to survive and grow in high alkaline/acidic condition, SRB have developed several strategies to combat the environmental challenges. The strategies mainly include maintaining pH homeostasis in the cytoplasm and adjusting metabolic activities leading to changes in environmental pH. The change in pH of the environment and microbial activities in such conditions can have a significant impact on the microbial corrosion of materials. These bacteria strategies to combat extreme pH environments and their effect on microbial corrosion are presented and discussed.

Antibacterial Synergism of Electrospun Nanofiber Mats Functioned with Silver Nanoparticles and Pulsed Electromagnetic Waves

The over-reliance on antibiotics and their enormous misuse has led to warnings of a future without effective medicines and so, the need for alternatives to antibiotics has become a must. Non-traditional antibacterial treatment was performed by using an aray of nanocomposites synergised with exposure to electromagnetic waves. In this manuscript, electrospun poly(vinyl alcohol) (PVA) nanofiber mats embedded with silver nanoparticles (Ag NPs) were synthesized. The nanocomposites were characterized by Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM), Current-Voltage (I-V) curves, and Thermogravimetric analysis (TGA) along with analysis of antibacterial impact against E. coli and S. aureus bacteria, studied by bacterial growing analysis, growth kinetics, and cellular cytotoxicity. The results indicated a spherical grain shape of silver of average size 20 nm and nanofibers' mean diameter of less than 100 nm. The nanocomposite mats showed good exposure to bacteria and the ability to sustain release of silver for a relatively long time. Moreover, the applied electromagnetic waves (EMWs) were shown to be a synergistic co-factor in killing bacteria even at low concentrations of Ag NPs. This caused pronounced alterations of the bacterial preserved packing of the cell membrane. Thereby, the treatment with nanocomposite mats under EM wave exposure elucidated maximum inhibition for both bacterial strains. It was concluded that the functioning of nanofiber with silver nanoparticles and exposure to electromagnetic waves improved the antibacterial impact compared to each one alone.

Membrane damage precedes DNA damage in hydroxychavicol treated E. coli cells and facilitates cooperativity with hydrophobic antibiotics

Hydroxychavicol (HC), found abundantly in Piper betle leaves is credited with antimicrobial property. Previously we had shown HC induces reactive oxygen species mediated DNA damage in bacterial cells. HC also resulted in membrane compromise revealing its pleiotropic effects on cellular targets. The kinetics and exact sequence of events leading to inhibition of growth and cell death in E. coli after HC treatment remains poorly understood. We show that sub-lethal concentration (125 μg/mL) of HC causes cellular filamentation within 1 h of treatment, while a higher concentration (750 μg/mL) induces cell breakage. HC-treated cells were found to experience oxidative stress as early as 10 min, while evidence of membrane damage was apparent at 30 min. DNA damage repair genes were found to be activated at 60 min. Interestingly, HC-induced cell permeabilization was inhibited and enhanced by external Mg²⁺ and EDTA, respectively, suggesting that HC damages the outer membrane. Kinetic experiments revealed that HC-treated cells underwent oxidative stress, membrane damage and DNA damage in that order. Because gram negative bacteria such as E. coli are refractory to several antibiotics due to the presence of the outer membrane, we hypothesized that HC pretreatment would sensitize E. coli to hydrophobic antibiotics. Our study reveals for the first time that HC could sensitize bacteria to clinically used antibiotics due to its outer membrane damaging property.

Sterol-Response Pathways Mediate Alkaline Survival in Diverse Fungi

The ability for cells to maintain homeostasis in the presence of extracellular stress is essential for their survival. Stress adaptations are especially important for microbial pathogens to respond to rapidly changing conditions, such as those encountered during the transition from the environment to the infected host. Many fungal pathogens have acquired the ability to quickly adapt to changes in extracellular pH to promote their survival in the various microenvironments encountered during a host infection. For example, the fungus-specific Rim/Pal alkaline response pathway has been well characterized in many fungal pathogens, including Cryptococcus neoformans However, alternative mechanisms for sensing and responding to host pH have yet to be extensively studied. Recent observations from a genetic screen suggest that the C. neoformans sterol homeostasis pathway is required for growth at elevated pH. This work explores interactions among mechanisms of membrane homeostasis, alkaline pH tolerance, and Rim pathway activation. We find that the sterol homeostasis pathway is necessary for growth in an alkaline environment and that an elevated pH is sufficient to induce Sre1 activation. This pH-mediated activation of the Sre1 transcription factor is linked to the biosynthesis of ergosterol but is not dependent on Rim pathway signaling, suggesting that these two pathways are responding to alkaline pH independently. Furthermore, we discover that C. neoformans is more susceptible to membrane-targeting antifungals under alkaline conditions, highlighting the impact of microenvironmental pH on the treatment of invasive fungal infections. Together, these findings further connect membrane integrity and composition with the fungal pH response and pathogenesis.IMPORTANCE The work described here further elucidates how microorganisms sense and adapt to changes in their environment to establish infections in the human host. Specifically, we uncover a novel mechanism by which an opportunistic human fungal pathogen, Cryptococcus neoformans, responds to increases in extracellular pH in order to survive and thrive within the relatively alkaline environment of the human lung. This mechanism, which is intimately linked with fungal membrane sterol homeostasis, is independent of the previously well-studied alkaline response Rim pathway. Furthermore, this ergosterol-dependent alkaline pH response is present in Candida albicans, indicating that this mechanism spans diverse fungal species. These results are also relevant for novel antimicrobial drug development as we show that currently used ergosterol-targeting antifungals are more active in alkaline environments.

Broad-Spectrum Antibacterial Effects of Human Adipose-Derived Stromal Cells

Introduction

Many pathological conditions may benefit from cell therapy using mesenchymal stromal cells, particularly from adipose tissue (ASCs). Cells may be grafted in an environment with a remnant polymicrobial component. The aim is to investigate the behavior of ASCs when brought in contact with a large panel of bacteria.

Materials and Methods

Carboxyfluorescein-labelled bacterial interaction with ASCs was followed by confocal time-lapse microscopy. Costaining with LAMP-1 was also analyzed. Viability of 4 gram-negative and 4 gram-positive bacterial strains after 6 h of coculture with ASCs was assessed by agar colony counting and by flow cytometry using SYTO-62®/propidium iodide (PI) for membrane permeabilization and DiOC6 for depolarization. A murine model of periodontitis was used to assess in vivo antibacterial capacities of ASCs.

Results

A significant increase of PI-positive events for all bacterial strains and an increase of the DiOC6 signal were obtained after contact with ASCs. The number of CFU was also significantly decreased for several bacterial strains. 0.4 μm transwell systems illustrated the necessary direct contact to induce maximal bacterial membrane damages. Some bacteria were observed into phagolysosomes, confirming macrophage-like properties of ASCs. In vivo, the bacterial load was significantly lower in the ASC-grafted side compared to the control.

Conclusion

Our results highlight for the first time a broad range of antibacterial actions of ASCs, by phagocytosis, secretion of oxygenated free radicals and antibacterial molecules. These data are in line with the development of new therapeutic strategies based on ASC transplantation, appropriated in immune-dysbiotic tissue context such as periodontitis or chronic wounds.

Flotillin homologue is involved in the swimming behavior of Escherichia coli

Cellular membrane is a key component for maintaining cell shape and integrity. The classical membrane structure and function by Singer and Nicolson groundbreaking model has depicted the membrane as a homogeneous fluid structure. This view has changed by the discovery of discrete domains containing different lipid compositions, called lipid rafts, which play a key role in signal transduction in eukaryotic cells. In the past few years, lipid raft-like structures have been found in bacteria also, constituted by cardiolipin and other modified lipids, perhaps involved in generating a specific site for protein clustering. Here, we report the analysis of a protein termed YqiK from Escherichia coli, a prohibitin homolog that has been implicated in stress sensing by the formation of membrane-associated microdomains. The E. coli yqiK-deficient mutant strain showed an enhanced swimming behavior and was resistant to ampicillin but its response to other stressing conditions was similar to that of the wild-type strain. The abnormal swimming behavior is reversed when the protein is expressed in trans from a plasmid. Also, we demonstrate that YqiK is not redundant with QmcA, another flotillin homolog found in E. coli. Our results, along with the data available in the literature, suggest that YqiK may be involved in the formation of discrete membrane-associated signaling complexes that regulate and agglomerate signaling proteins to generate cell response to chemotaxis.

Flow cytometry, a powerful novel tool to rapidly assess bacterial viability in metal working fluids: Proof-of-principle

Metalworking fluids (MWF) are water- or oil-based liquids to cool and lubricate tools, work pieces and machines, inhibit corrosion and remove swarf. One of the major problems in the MWF industry is bacterial growth as bacterial enzymes can cause MWF degradation. In addition, bacteria can form biofilms which hamper the functioning of machines. Last but not least, some bacterial by-products are toxic (e.g. endotoxins) and present potential health risks for metalworking machine operators via the formation of aerosols. Therefore, a novel fast yet accurate analytical method to evaluate and predict the antibacterial capacity of MWF would be an important asset. As such a tool is currently lacking, the present study aimed to develop a protocol based on flow cytometry (FCM) to assess the antibacterial potential of newly developed MWF independent of bacterial growth. Results of this novel method were compared to a biochallenge test currently used in MWF industry and also to traditional plate counts. Our results represent a proof-of-principle that FCM can reliably predict the antibacterial capacity of MWF already within one day of incubation with Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Proteus mirabilis, being substantially faster than the current growth-based methods.

Antimicrobial potential of endocannabinoid and endocannabinoid-like compounds against methicillin-resistant Staphylococcus aureus

Infections caused by antibiotic-resistant strains of Staphylococcus aureus have reached epidemic proportions globally. Staphylococcal biofilms are associated with increased antimicrobial resistance and are generally less affected by host immune factors. Therefore, there is an urgent need for novel agents that not only aim at multidrug-resistant pathogens, but also ones that will act as anti biofilms. In the present study, we investigated the antimicrobial activity of the endocannabinoid (EC) anandamide (AEA) and the endocannabinoid-like (EC-like), arachidonoyl serine (AraS) against methicillin resistant S. aureus strains (MRSA). We observed a strong inhibition of biofilm formation of all tested MRSA strains as well as a notable reduction of metabolic activity of pre-formed MRSA biofilms by both agents. Moreover, staphylococcal biofilm-associated virulence determinants such as hydrophobicity, cell aggregation and spreading ability were altered by AEA and AraS. In addition, the agents were able to modify bacterial membrane potential. Importantly, both compounds prevent biofilm formation by altering the surface of the cell without killing the bacteria. Therefore, we propose that EC and EC-like compounds may act as a natural line of defence against MRSA or other antibiotic resistant bacteria. Due to their anti biofilm action these agents could also be a promising alternative to antibiotic therapeutics against biofilm-associated MRSA infections.

Bicarbonate Inhibits Bacterial Growth and Biofilm Formation of Prevalent Cystic Fibrosis Pathogens

We investigated the effects of bicarbonate on the growth of several different bacteria as well as its effects on biofilm formation and intracellular cAMP concentration in Pseudomonas aeruginosa. Biofilm formation was examined in 96-well plates, with or without bicarbonate. The cAMP production of bacteria was measured by a commercial assay kit. We found that NaHCO₃ (100 mmol l^-1) significantly inhibited, whereas NaCl (100 mmol l^-1) did not influence the growth of planktonic bacteria. MIC and MBC measurements indicated that the effect of HCO3− is bacteriostatic rather than bactericidal. Moreover, NaHCO₃ prevented biofilm formation as a function of concentration. Bicarbonate and alkalinization of external pH induced a significant increase in intracellular cAMP levels. In conclusion, HCO3− impedes the planktonic growth of different bacteria and impedes biofilm formation by P. aeruginosa that is associated with increased intracellular cAMP production. These findings suggest that aerosol inhalation therapy with HCO3− solutions may help improve respiratory hygiene in patients with cystic fibrosis and possibly other chronically infected lung diseases.

Antimicrobial Properties and Mechanism of Action of Some Plant Extracts Against Food Pathogens and Spoilage Microorganisms

This work aims to evaluate the antimicrobial potential of ethanolic and water extracts of roselle (Hibiscus sabdariffa), rosemary (Rosmarinus officinalis), clove (Syzygium aromaticum), and thyme (Thymus vulgaris) on some food pathogens and spoilage microorganisms. Agar well diffusion method has been used to determine the antimicrobial activities and minimum inhibitory concentrations (MIC) of different plant extracts against Gram-positive bacteria (Bacillus cereus, Staphylococcus aureus), Gram-negative bacteria (Escherichia coli, Salmonella enteritidis, Vibrio parahaemolyticus, and Pseudomonas aeruginosa), and one fungus (Candida albicans). The extracts exhibited both antibacterial and antifungal activities against tested microorganisms. Ethanolic roselle extract showed significant antibacterial activity (P < 0.05) against all tested bacterial strains, while no inhibitory effect on Candida albicans (CA) was observed. Only the ethanolic extracts of clove and thyme showed antifungal effects against CA with inhibition zones ranging from 25.2 ± 1.4 to 15.8 ± 1.2 mm, respectively. Bacillus cereus (BC) appears to be the most sensitive strain to the aqueous extract of clove with a MIC of 0.315%. To enhance our understanding of antimicrobial activity mechanism of plant extracts, the changes in internal pH (pHint), and membrane potential were measured in Staphylococcus aureus (SA) and Escherichia coli (EC) cells after exposure to the plant extracts. The results indicated that the plant extracts significantly affected the cell membrane of Gram-positive and Gram-negative bacteria, as demonstrated by the decline in pHint as well as cell membrane hyperpolarization. In conclusion, plant extracts are of great value as natural antimicrobials and can use safely as food preservatives.

Hydrophobic residues are critical for the helix-forming, hemolytic and bactericidal activities of amphipathic antimicrobial peptide TP4

Antimicrobial peptides are important components of the host innate defense mechanism against invading pathogens, especially for drug-resistant bacteria. In addition to bactericidal activity, the 25 residue peptide TP4 isolated from Nile tilapia also stimulates cell proliferation and regulates the innate immune system in mice. In this report, TP4 hyperpolarized and depolarized the membrane potential of Pseudomonas aeruginosa at sub-lethal and lethal concentrations. It also inhibited and eradicated biofilm formation. The in vitro binding of TP4 to bacterial outer membrane target protein, OprI, was markedly enhanced by a membrane-like surfactant sarkosyl and lipopolysaccharide, which converted TP4 into an α-helix. The solution structure of TP4 in dodecylphosphocholine was solved by NMR analyses. It contained a typical α-helix at residues Phe10-Arg22 and a distorted helical segment at Ile6-Phe10, as well as a hydrophobic core at the N-terminus and a cationic patch at the C-terminus. Residues Ile16, Leu19 and Ile20 in the hydrophobic face of the main helix were critical for the integrity of amphipathic structure, other hydrophobic residues played important roles in hemolytic and bactericidal activities. A model for the assembly of helical TP4 embedded in sarkosyl vesicle is proposed. This study may provide valuable insight for engineering AMPs to have potent bactericidal activity but low hemolytic activity.

Sarkosyl-Induced Helical Structure of an Antimicrobial Peptide GW-Q6 Plays an Essential Role in the Binding of Surface Receptor OprI in Pseudomonas aeruginosa

The emergence of antibiotic-resistant microbial strains has become a public health issue and there is an urgent need to develop new anti-infective molecules. Although natural antimicrobial peptides (AMPs) can exert bactericidal activities, they have not shown clinical efficacy. The limitations of native peptides may be overcome with rational design and synthesis. Here, we provide evidence that the bactericidal activity of a synthetic peptide, GW-Q6, against Pseudomonas aeruginosa is mediated through outer membrane protein OprI. Hyperpolarization/depolarization of membrane potential and increase of membrane permeability were observed after GW-Q6 treatment. Helical structure as well as hydrophobicity was induced by an amphipathic surfactant, sarkosyl, for binding to OprI and possible to membrane. NMR studies demonstrated GW-Q6 is an amphipathic α-helical structure in DPC micelles. The paramagnetic relaxation enhancement (PRE) approach revealed that GW-Q6 orients its α-helix segment (K7-K17) into DPC micelles. Additionally, this α-helix segment is critical for membrane permeabilization and antimicrobial activity. Moreover, residues K3, K7, and K14 could be critical for helical formation and membrane binding while residues Y19 and W20 for directing the C-terminus of the peptide to the surface of micelle. Taken together, our study provides mechanistic insights into the mode of action of the GW-Q6 peptide and suggests its applicability in modifying and developing potent AMPs as therapeutic agents.

Antimicrobial Properties of an Immunomodulator - 15 kDa Human Granulysin

Granulysin, a cationic protein expressed by human natural killer cells and cytotoxic T lymphocytes, is a mediator for drug-induced Stevens-Johnson syndrome and graft-versus-host disease. Some 15 kDa granulysin are processed into 9 kDa forms and sequestered in cytolytic granules, while others are constitutively secreted into body fluids. Both 9 and 15 kDa granulysin have been shown to be a serum marker for cell-mediated immunity. Furthermore, 15 kDa is able to activate monocyte differentiation. However, its antimicrobial properties have not been clearly addressed. Here, we report a novel method to prepare both the soluble 9 and 15 kDa granulysin and show that the 15 kDa form is more effective than the 9 kDa form in exerting specific antimicrobial activity against Pseudomonas aeruginosa within a range of few micromolars. We also show that the 15 kDa granulysin is able to hyperpolarize the membrane potential and increase membrane permeability of treated bacteria. Interestingly, the bactericidal activity and membrane permeability of the granulysins were markedly reduced at lower pH (pH 5.4) as a result of probable increase in hydrophobicity of the granulysins. Additionally, we’ve also shown the granulysin to inhibit biofilm formation by P. aeruginosa. These results suggest that the 15 kDa granulysin exhibits a novel mechanism in bacteria killing in a way that’s different from most antimicrobial peptides. Our novel granulysin preparation methodology will be useful for further study of action mechanisms of other antimicrobial, cytotoxic and immunomodulating properties in granulysin-mediated diseases.

Effect of toluene on Pseudomonas stutzeri ST-9 morphology - plasmolysis, cell size, and formation of outer membrane vesicles

Isolated toluene-degrading Pseudomonas stutzeri ST-9 bacteria were grown in a minimal medium containing toluene (100 mg·L(-1)) (MMT) or glucose (MMG) as the sole carbon source, with specific growth rates of 0.019 h(-1) and 0.042 h(-1), respectively. Scanning (SEM) as well as transmission (TEM) electron microscope analyses showed that the bacterial cells grown to mid-log phase in the presence of toluene possess a plasmolysis space. TEM analysis revealed that bacterial cells that were grown in MMT were surrounded by an additional "material" with small vesicles in between. Membrane integrity was analyzed by leakage of 260 nm absorbing material and demonstrated only 7% and 8% leakage from cultures grown in MMT compared with MMG. X-ray microanalysis showed a 4.3-fold increase in Mg and a 3-fold increase in P in cells grown in MMT compared with cells grown in MMG. Fluorescence-activated cell sorting (FACS) analysis indicated that the permeability of the membrane to propidium iodide was 12.6% and 19.6% when the cultures were grown in MMG and MMT, respectively. The bacterial cell length increased by 8.5% ± 0.1% and 17% ± 2%, as measured using SEM images and FACS analysis, respectively. The results obtained in this research show that the presence of toluene led to morphology changes, such as plasmolysis, cell size, and formation of outer membrane vesicles. However, it does not cause significant damage to membrane integrity.

The metabolism and biotechnological application of betaine in microorganism

Glycine betaine (betaine) is widely distributed in nature and can be found in many microorganisms, including bacteria, archaea, and fungi. Due to its particular functions, many microorganisms utilize betaine as a functional chemical and have evolved different metabolic pathways for the biosynthesis and catabolism of betaine. As in animals and plants, the principle role of betaine is to protect microbial cells against drought, osmotic stress, and temperature stress. In addition, the role of betaine in methyl group metabolism has been observed in a variety of microorganisms. Recent studies have shown that betaine supplementation can improve the performance of microbial strains used for the fermentation of lactate, ethanol, lysine, pyruvate, and vitamin B12, during which betaine can act as stress protectant or methyl donor for the biosynthesis of structurally complex compounds. In this review, we summarize the transport, synthesis, catabolism, and functions of betaine in microorganisms and discuss potential engineering strategies that employ betaine as a methyl donor for the biosynthesis of complex secondary metabolites such as a variety of vitamins, coenzymes, and antibiotics. In conclusion, the biocompatibility, C/N ratio, abundance, and comprehensive metabolic information of betaine collectively indicate that this molecule has great potential for broad applications in microbial biotechnology.

Effect of extremely low frequency electromagnetic fields on bacterial membrane

PURPOSE

The effect of extremely low frequency electromagnetic fields (ELF-EMF) on bacteria has attracted attention due to its potential for beneficial uses. This research aimed to determine the effect of ELF-EMF on bacterial membrane namely the membrane potential, surface potential, hydrophobicity, respiratory activity and growth.

MATERIALS AND METHODS

Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli were subjected to ELF-EMF, 50 Hz, 1 mT for 2 h. Membrane potential was determined by fluorescence spectroscopy with or without EDTA (Ethylenediaminetetraacetic acid) with DisC3(5) (3,3-dipropylthiacarbocyanine iodide), zeta potential measurements were performed by electrophoretic mobility, hydrophobicity of the membrane was measured with MATH (Microbial Adhesion to Hydrocarbons) test, respiratory activity was determined with CTC (5-Cyano-2,3-ditolyl tetrazolium chloride), colony forming unit (CFU) and DAPI (4',6-diamidino-2-phenylindole, dihydrochloride) was used for growth determinations.

RESULTS

ELF-EMF caused changes in physicochemical properties of both Gram-positive and Gram-negative bacteria. Hyperpolarization was seen in S. aureus and EDTA-treated E. coli. Surface potential showed a positive shift in S. aureus contrariwise to the negative shift seen in EDTA-untreated E. coli. Respiratory activity increased in both bacteria. A slight decrease in growth was observed.

CONCLUSION

These results show that ELF-EMF affects the crucial physicochemical processes in both Gram-positive and Gram-negative bacteria which need further research.