Catalase activity as a biomarker for mild-stress-induced robustness in Bacillus weihenstephanensis

Screen-printed biosensor based on electro-polymerization of bio-composite for nitrate detection in aqueous media

Bacillus sp. possessing a periplasmic nitrate reductase was used as a recognition element to develop a nitrate biosensor. The bacteria was embedded within a polyaniline (PANI) electro-conductive matrix via electro-polymerization on miniaturized carbon screen-printed electrodes (SPE) at 100 mV/s and scan rate from -0.35 V to + 1.7 V. Surface medication of SPE was verified via Fourier Transform Infrared spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). The optimal bacterial density was OD600 1.2. To enhance the biosensors performance, Bacillus sp. was (1) grown in riboflavin (RF) inducing media as an endogenous redox mediator and (2) exposed to different gamma radiation doses as a physical method to increase electron transfer. Results show a link between exposing cells to gamma irradiation stress, this was evident by electron spin resonance (ESR) and changes in FTIR spectrum, in addition to the increase in catalase enzyme. The nitrate limit of detection (LOD) was 0.5-25 mg/L for non-irradiated RF induced immobilized cells and LOD was 0.5-75 mg/L nitrate for 2 kGy gamma irradiated cells. The prepared biosensor showed acceptable reproducibility and multiple usages after storage at 4°C over 3 months. Low cost and simple preparation allow the biosensor to be mass-produced as a disposable device. Bacillus sp. and its endogenous redox mediator immobilized within polyaniline are good candidates for the improvement of amperometric biosensors for the quantification of nitrate in aqueous solutions.

Molecular characterization of Paenibacillus antarcticus IPAC21, a bioemulsifier producer isolated from Antarctic soil

Paenibacillus antarcticus IPAC21, an endospore-forming and bioemulsifier-producing strain, was isolated from King George Island, Antarctica. As psychrotolerant/psychrophilic bacteria can be considered promising sources for novel products such as bioactive compounds and other industrially relevant substances/compounds, the IPAC21 genome was sequenced using Illumina Hi-seq, and a search for genes related to the production of bioemulsifiers and other metabolic pathways was performed. The IPAC21 strain has a genome of 5,505,124 bp and a G + C content of 40.5%. Genes related to the biosynthesis of exopolysaccharides, such as the gene that encodes the extracellular enzyme levansucrase responsible for the synthesis of levan, the 2,3-butanediol pathway, PTS sugar transporters, cold-shock proteins, and chaperones were found in its genome. IPAC21 cell-free supernatants obtained after cell growth in trypticase soy broth at different temperatures were evaluated for bioemulsifier production by the emulsification index (EI) using hexadecane, kerosene and diesel. EI values higher than 50% were obtained using the three oil derivatives when IPAC21 was grown at 28°C. The bioemulsifier produced by P. antarcticus IPAC21 was stable at different NaCl concentrations, low temperatures and pH values, suggesting its potential use in lower and moderate temperature processes in the petroleum industry.

Moderate ethanol exposure during early ontogeny of the rat alters respiratory plasticity, ultrasonic distress vocalizations, increases brain catalase activity, and acetaldehyde-mediated ethanol intake

Early ontogeny of the rat (late gestation and postnatal first week) is a sensitive period to ethanol’s positive reinforcing effects and its detrimental effects on respiratory plasticity. Recent studies show that acetaldehyde, the first ethanol metabolite, plays a key role in the modulation of ethanol motivational effects. Ethanol brain metabolization into acetaldehyde via the catalase system appears critical in modulating ethanol positive reinforcing consequences. Catalase system activity peak levels occur early in the ontogeny. Yet, the role of ethanol-derived acetaldehyde during the late gestational period on respiration response, ultrasonic vocalizations (USVs), and ethanol intake during the first week of the rat remains poorly explored. In the present study, pregnant rats were given a subcutaneous injection of an acetaldehyde-sequestering agent (D-penicillamine, 50 mg/kg) or saline (0.9% NaCl), 30 min prior to an intragastric administration of ethanol (2.0 g/kg) or water (vehicle) on gestational days 17–20. Respiration rates (breaths/min) and apneic episodes in a whole-body plethysmograph were registered on postnatal days (PDs) 2 and 4, while simultaneously pups received milk or ethanol infusions for 40-min in an artificial lactation test. Each intake test was followed by a 5-min long USVs emission record. On PD 8, immediately after pups completed a 15-min ethanol intake test, brain samples were collected and kept frozen for catalase activity determination. Results indicated that a moderate experience with ethanol during the late gestational period disrupted breathing plasticity, increased ethanol intake, as well brain catalase activity. Animals postnatally exposed to ethanol increased their ethanol intake and exerted differential affective reactions on USVs and apneic episodes depending on whether the experience with ethanol occur prenatal or postnatally. Under the present experimental conditions, we failed to observe, a clear role of acetaldehyde mediating ethanol’s effects on respiratory plasticity or affective states, nevertheless gestational acetaldehyde was of crucial importance in determining subsequent ethanol intake affinity. As a whole, results emphasize the importance of considering the participation of acetaldehyde in fetal programming processes derived from a brief moderate ethanol experience early in development, which in turn, argues against “safe or harmless” ethanol levels of exposure.

Model Study for Interaction of Sublethal Doses of Zinc Oxide Nanoparticles with Environmentally Beneficial Bacteria Bacillus thuringiensis and Bacillus megaterium

Zinc oxide nanoparticles (ZnO NPs), due to their antibacterial effects, are commonly used in various branches of the economy and can affect rhizobacteria that promote plant growth. We describe the effect of ZnO NPs on two model bacteria strains, B. thuringiensis and B. megaterium, that play an important role in the environment. The MIC (minimum inhibitory concentration) value determined after 48 h of incubation with ZnO NPs was more than 1.6 mg/mL for both strains tested, while the MBC (minimum bactericidal concentration) was above 1.8 mg/mL. We tested the effect of ZnO NPs at concentrations below the MIC (0.8 mg/mL, 0.4 mg/mL and 0.2 mg/mL (equal to 50%, 25% and 12,5% MIC, respectively) in order to identify the mechanisms activated by Bacillus species in the presence of these nanoparticles. ZnO NPs in sublethal concentrations inhibited planktonic cell growth, stimulated endospore formation and reduced decolorization of Evans blue. The addition of ZnO NPs caused oxidative stress, measured using nitroblue tetrazolium (NBT), and reduced the activity of catalase. It was confirmed that zinc oxide nanoparticles in sublethal concentrations change metabolic processes in Bacillus bacteria that are important for their effects on the environment. B. thuringiensis after treatment with ZnO NPs decreased indole acetic acid (IAA) production and increased biofilm formation, whereas B. megaterium decreased IAA production but, inversely, increased biofilm formation. Comparison of different Bacillus species in a single experiment made it possible to better understand the mechanisms of toxicity of zinc oxide nanoparticles and the individual reactions of closely related bacterial species.

Zinc Oxide Nanoparticles Enhance the Tolerance and Remediation Potential of Bacillus spp. against Heavy Metal Stress

Nanoparticles and bacteria have received a great attention worldwide due to their ability to remove heavy metals (HMs) from wastewater. The current study is aimed at finding the interaction of HMs-resistance strains (Bacillus cereus and Lysinibacillus macroides) with different concentrations (5, 10, 15, 20, and 25 mg/L) of zinc oxide nanoparticles (ZnO NPs) and how they would cope with HM stress (Pb, Cd, Cr, and Cu). The growth rate and tolerance potential of bacteria were increased at lowered concentrations (5 and 10 mg/L) of ZnO NPs against HMs while it was unaffected at higher concentrations of ZnO NPs. These findings were confirmed by minimum inhibition zone and higher zinc solubilization at lower concentrations of ZnO NPs. Scanning electron microscopy (SEM) revealed that higher concentrations of ZnO NP increased HM accumulation in bacteria cells which had a significant impact on bacterial morphology and caused pores in bacterial membrane while in the case of lower concentrations, the cell remained unaffected. These results were further supported by the less production of antioxidant enzymes (SOD, POD, and CAT), thiobarbituric acid reactive substances (TBARS), and hydrogen peroxide (H2O2) contents at lower concentrations of ZnO NPs against heavy metal stress. This study suggested that synergistic treatment of Bacillus spp. with lower concentrations of ZnO NPs enhances the tolerance potential and significantly reduces the HM toxicity.

Redox imbalance induced by docetaxel in the neuroblastoma SH-SY5Y cells: a study of docetaxel-induced neuronal damage

Objectives

In cancer survivors, chemotherapy-associated adverse neurological effects are described as side effects in non-targeted tissue. We investigated the role of redox-imbalance in neuronal damage by a relative low dose of Docetaxel (DTX).

Methods

The neuroblastoma cells (SH-SY5Y cells) were exposed to DTX at a dose of 1.25 nM for 6 h. Antioxidant defenses (i.e. ascorbic acid, glutathione, and catalase) and lipid oxidation products (i.e. F₂-isoprostanes) were evaluated. To investigate cell ultrastructure and tubulin localisation, transmission electron microscopy (TEM) and immunofluorescence techniques were applied.

Results

In the SH-SY5Y cells, DTX induced a significant reduction of total glutathione (P < 0.001) and ascorbic acid (P < 0.05), and an increase in both total F₂-Isoprostanes (P < 0.05) and catalase activity (P < 0.05), as compared to untreated cells. Additionally, TEM showed a significant increase in cells with apoptotic characteristics. Immunolocalisation of tubulin showed a compromised cytoskeletal organisation.

Discussion

The investigated sublethal dose of DTX, to which non-targeted cells may be exposed throughout the duration of chemotherapy treatment, induces a redox imbalance resulting in a specific modulation of the antioxidant response. This study provides new insights into DTX-induced cellular mechanisms useful for evaluating whether the concomitant use of antioxidants associated with chemotherapy mitigates chemotherapy side effects in cancer survivors.

Modified semi-continuous fermentation for resuscitating nongrowing cells during high-temperature gluconic acid production by Acetobacter senegalensis

AIMS

The formation of metabolically inactive and nongrowing cells is an inevitable by-product of intensive fermentation. This study investigated whether co-feeding can be used to resuscitate nongrowing Acetobacter senegalensis cells to enable them to produce gluconic acid in successive fermentation runs at 38°C.

METHODS AND RESULTS

In the first fermentation cycle, 75 g l^-1 of glucose were converted to gluconic acid. Subsequently, however, stationary-phase cells were unable to initiate a new fermentation cycle. The majority of stationary-phase cells (97%) were nonculturable on glucose at 38°C. In addition, 54 and 41% of cells contained non-active cellular dehydrogenases and a compromised cell envelope respectively. Co-feeding stationary-phase cells with a mixture of ethanol, glucose and acetic acid for 7 h enabled these cells to grow on 75 g l^-1 of glucose and produce gluconic acid. Additionally, 74% of cells contained active forms of cellular dehydrogenases after 7 h of co-feeding. However, co-feeding did not improve cell envelope integrity. Quantification of cellular NAD content showed that stationary-phase cells contained moderately reduced levels of total NAD (NADt) as compared with exponential-phase cells. Interestingly, the analysis of stationary-phase cells showed that co-feeding resulted in higher levels of NADt and NADH, suggesting that the regeneration of NADH is one of the limiting factors of glucose consumption. Expression of catalase and superoxide dismutase was increased in stationary-phase cells, but analysis of protein carbonylation and lipid peroxidation did not confirm an extensive oxidative stress.

CONCLUSIONS

Co-feeding with favourable nutrients may enable resuscitation of cells and utilization of less-favourable carbon sources in successive cycles.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study proposed a unique method for resuscitation of nongrowing cells during high-temperature fermentation. By applying this method, cells can be used for consecutive fermentation cycles.

Bacillus cereus cshA Is Expressed during the Lag Phase of Growth and Serves as a Potential Marker of Early Adaptation to Low Temperature and pH

The spore-forming bacterium B. cereus is a major cause of foodborne outbreaks in Europe. Some B. cereus strains can grow at low temperatures and low pH in many processed foods. Modeling of the bacterial lag time is hampered by a lack of knowledge of the timing of events occurring during this phase. In this context, the identification of lag phase markers, not currently available, could be a real advance for the better prediction of lag time duration. Currently, no molecular markers of this phase are available. By determining that cshA was always expressed early during the lag phase, we provide a molecular marker of the early adaptation process of B. cereus cells when exposed to low temperature and pH.

Bacterial adaptation is characterized by a lag phase during which cells do not multiply or modify their physiology to cope with the constraints of their environment. Our aim was to determine a sequence of events during the lag phase of growth at low temperature and pH for three Bacillus cereus strains. The onsets of expression of two genes, one of which is essential for stress adaptation (cshA, coding for a RNA helicase) and one of which is involved in the transition between lag phase and exponential phase (abrB, coding for a transition regulator), were determined using fluorescent transcriptional reporter systems. Regardless of the stressing conditions and the tested strains, the cshA promoter was active very early, while the biomass increased and always did so before the first cell division. At 12°C and pH 7.0, the onset of cshA promoter activity occurred at between 3 h and 7 h, while the bacterial counts started to increase at between 12 h and 13 h. At pH 5.0 and at 20°C or 30°C, the onset of cshA promoter activity occurred before 1 h and earlier than at pH 7.0. In contrast, the onset of abrB promoter activity depended on the strain and the stressing conditions. In the ATCC 14579 strain, the onset of abrB promoter activity always started at between 30 min and 3 h, before biomass increased and cell division occurred. For the other strains, it took place along with the first cell division at 12°C but did so much later during growth under the other tested conditions.

IMPORTANCE The spore-forming bacterium B. cereus is a major cause of foodborne outbreaks in Europe. Some B. cereus strains can grow at low temperatures and low pH in many processed foods. Modeling of the bacterial lag time is hampered by a lack of knowledge of the timing of events occurring during this phase. In this context, the identification of lag phase markers, not currently available, could be a real advance for the better prediction of lag time duration. Currently, no molecular markers of this phase are available. By determining that cshA was always expressed early during the lag phase, we provide a molecular marker of the early adaptation process of B. cereus cells when exposed to low temperature and pH.

Enhancing the Adaptability of the Deep-Sea Bacterium Shewanella piezotolerans WP3 to High Pressure and Low Temperature by Experimental Evolution under H2O2 Stress

Oxidative stresses commonly exist in natural environments, and microbes have developed a variety of defensive systems to counteract such events. Although increasing evidence has shown that high hydrostatic pressure (HHP) and low temperature (LT) induce antioxidant defense responses in cells, there is no direct evidence to prove the connection between antioxidant defense mechanisms and the adaptation of bacteria to HHP and LT. In this study, using the wild-type (WT) strain of a deep-sea bacterium, Shewanella piezotolerans WP3, as an ancestor, we obtained a mutant, OE100, with an enhanced antioxidant defense capacity by experimental evolution under H₂O₂ stress. Notably, OE100 exhibited better tolerance not only to H₂O₂ stress but also to HHP and LT (20 MPa and 4°C, respectively). Whole-genome sequencing identified a deletion mutation in the oxyR gene, which encodes the transcription factor that controls the oxidative stress response. Comparative transcriptome analysis showed that the genes associated with oxidative stress defense, anaerobic respiration, DNA repair, and the synthesis of flagella and bacteriophage were differentially expressed in OE100 compared with the WT at 20 MPa and 4°C. Genetic analysis of oxyR and ccpA2 indicated that the OxyR-regulated cytochrome c peroxidase CcpA2 significantly contributed to the adaptation of WP3 to HHP and LT. Taken together, these results confirmed the inherent relationship between antioxidant defense mechanisms and the adaptation of a benthic microorganism to HHP and LT.IMPORTANCE Oxidative stress exists in various niches, including the deep-sea ecosystem, which is an extreme environment with conditions of HHP and predominantly LT. Although previous studies have shown that HHP and LT induce antioxidant defense responses in cells, direct evidence to prove the connection between antioxidant defense mechanisms and the adaptation of bacteria to HHP and LT is lacking. In this work, using the deep-sea bacterium Shewanella piezotolerans WP3 as a model, we proved that enhancement of the adaptability of WP3 to HHP and LT can benefit from its antioxidant defense mechanism, which provided useful insight into the ecological roles of antioxidant genes in a benthic microorganism and contributed to an improved understanding of microbial adaptation strategies in deep-sea environments.

Survival of Bacillus spp. SUBB01 at high temperatures and a preliminary assessment of its ability to protect heat-stressed Escherichia coli cells

Background

The bacterial stressed state upon temperature raise has widely been observed especially in Escherichia coli cells. The current study extended such physiological investigation on Bacillus spp. SUBB01 under aeration at 100 rpm on different culture media along with the high temperature exposure at 48, 50, 52, 53 and 54 °C. Bacterial growth was determined through the enumeration of the viable and culturable cells; i.e., cells capable of producing the colony forming units on Luria–Bertani and nutrient agar plates up to 24 h. Microscopic experiments were conducted to scrutinize the successive physiological changes. Suppression of bacterial growth due to the elevated heat was further confirmed by the observation of non-viability through spot tests.

Results

As expected, a quick drop in both cell turbidity and colony forming units (~10⁴) along with spores were observed after 12–24 h of incubation period, when cells were grown at 54 °C in both Luria–Bertani and nutrient broth and agar. The critical temperature (the temperature above which it is no longer possible to survive) of Bacillus spp. SUBB01 was estimated to be 53 °C. Furthermore, a positive impact was observed on the inhibited E. coli SUBE01 growth at 45 and 47 °C, upon the supplementation of the extracellular fractions of Bacillus species into the growing culture.

Conclusions

Overall the present analysis revealed the conversion of the culturable cells into the viable and nonculturable (VBNC) state as a result of heat shock response in Bacillus spp. SUBB01 and the cellular adaptation at extremely high temperature.

Identification of oxidoreductases from the petroleum Bacillus safensis strain

A gram-positive bacterium, denominated CFA-06, was isolated from Brazilian petroleum in the Campos Basin and is responsible for the degradation of aromatic compounds and petroleum aromatic fractions. The CFA-06 strain was identified as Bacillus safensis using the 16S rRNA and gyrase B sequence. Enzymatic assays revealed the presence of two oxidoreductases: a catalase and a new oxidoreductase. The oxidoreductases were enzymatically digested and analyzed via ESI-LTQ-Orbitrap mass spectrometry. The mass data revealed a novel oxidoreductase (named BsPMO) containing 224 amino acids and 89% homology with a hypothetic protein from B. safensis (CFA-06) and a catalase (named BsCat) with 491 amino acids and 60% similarity with the catalase from Bacillus pumilus (SAFR-032). The new protein BsPMO contains iron atom(s) and shows catalytic activity toward a monooxygenase fluorogenic probe in the presence of cofactors (NADH, NADPH and NAD). This study enhances our knowledge of the biodegradation process of petroleum by B. safensis.

Mechanisms of food processing and storage-related stress tolerance in Clostridium botulinum

Vegetative cultures of Clostridium botulinum produce the extremely potent botulinum neurotoxin, and may jeopardize the safety of foods unless sufficient measures to prevent growth are applied. Minimal food processing relies on combinations of mild treatments, primarily to avoid deterioration of the sensory qualities of the food. Tolerance of C. botulinum to minimal food processing is well characterized. However, data on effects of successive treatments on robustness towards further processing is lacking. Developments in genetic manipulation tools and the availability of annotated genomes have allowed identification of genetic mechanisms involved in stress tolerance of C. botulinum. Most studies focused on low temperature, and the importance of various regulatory mechanisms in cold tolerance of C. botulinum has been demonstrated. Furthermore, novel roles in cold tolerance were shown for metabolic pathways under the control of these regulators. A role for secondary oxidative stress in tolerance to extreme temperatures has been proposed. Additionally, genetic mechanisms related to tolerance to heat, low pH, and high salinity have been characterized. Data on genetic stress-related mechanisms of psychrotrophic Group II C. botulinum strains are scarce; these mechanisms are of interest for food safety research and should thus be investigated. This minireview encompasses the importance of C. botulinum as a food safety hazard and its central physiological characteristics related to food-processing and storage-related stress. Special attention is given to recent findings considering genetic mechanisms C. botulinum utilizes in detecting and countering these adverse conditions.

Transcriptomic analysis of (group I) Clostridium botulinum ATCC 3502 cold shock response

Profound understanding of the mechanisms foodborne pathogenic bacteria utilize in adaptation to the environmental stress they encounter during food processing and storage is of paramount importance in design of control measures. Chill temperature is a central control measure applied in minimally processed foods; however, data on the mechanisms the foodborne pathogen Clostridium botulinum activates upon cold stress are scarce. Transcriptomic analysis on the C. botulinum ATCC 3502 strain upon temperature downshift from 37°C to 15°C was performed to identify the cold-responsive gene set of this organism. Significant up- or down-regulation of 16 and 11 genes, respectively, was observed 1 h after the cold shock. At 5 h after the temperature downshift, 199 and 210 genes were up- or down-regulated, respectively. Thus, the relatively small gene set affected initially indicated a targeted acute response to cold shock, whereas extensive metabolic remodeling appeared to take place after prolonged exposure to cold. Genes related to fatty acid biosynthesis, oxidative stress response, and iron uptake and storage were induced, in addition to mechanisms previously characterized as cold-tolerance related in bacteria. Furthermore, several uncharacterized DNA-binding transcriptional regulator-encoding genes were induced, suggesting involvement of novel regulatory mechanisms in the cold shock response of C. botulinum. The role of such regulators, CBO0477 and CBO0558A, in cold tolerance of C. botulinum ATCC 3502 was demonstrated by deteriorated growth of related mutants at 17°C.

Bacillus cereus cell response upon exposure to acid environment: toward the identification of potential biomarkers

Microorganisms are able to adapt to different environments and evolve rapidly, allowing them to cope with their new environments. Such adaptive response and associated protections toward other lethal stresses, is a crucial survival strategy for a wide spectrum of microorganisms, including food spoilage bacteria, pathogens, and organisms used in functional food applications. The growing demand for minimal processed food yields to an increasing use of combination of hurdles or mild preservation factors in the food industry. A commonly used hurdle is low pH which allows the decrease in bacterial growth rate but also the inactivation of pathogens or spoilage microorganisms. Bacillus cereus is a well-known food-borne pathogen leading to economical and safety issues in food industry. Because survival mechanisms implemented will allow bacteria to cope with environmental changes, it is important to provide understanding of B. cereus stress response. Thus this review deals with the adaptive traits of B. cereus cells facing to acid stress conditions. The acid stress response of B. cereus could be divided into four groups (i) general stress response (ii) pH homeostasis, (iii) metabolic modifications and alkali production and (iv) secondary oxidative stress response. This current knowledge may be useful to understand how B. cereus cells may cope to acid environment such as encountered in food products and thus to find some molecular biomarkers of the bacterial behavior. These biomarkers could be furthermore used to develop new microbial behavior prediction tools which can provide insights into underlying molecular physiological states which govern the behavior of microorganisms and thus opening the avenue toward the detection of stress adaptive behavior at an early stage and the control of stress-induced resistance throughout the food chain.

A method for molecular analysis of catalase gene diversity in seawater

Catalase plays an important role in the metabolism of marine bacteria and has potential impact on the marine environment. Four PCR primers were designed to amplify the catalase gene fragments in marine bacteria by applying metagenomic DNA from Yellow Sea surface water as the template. Of the four reproducible target PCR products, the longest one with 900 bp were chosen for catalase gene library construction by the T-vector and the white Escherichia coli colonies in the library was screened through restriction-digesting the reamplified insert fragments by the selected restriction endonuclease MboI, and then the bands of the resulting products were displayed in the agarose gel by electrophoresis. The unique restriction fragment length polymorphism (RFLP) pattern was selected and the corresponding catalase gene fragments were sequenced, which verified that every unique RFLP pattern represented one type of catalase. This PCR-RFLP method above was established to investigate the bacterial catalase diversity in seawater.