Primary and secondary oxidative stress in Bacillus

Coping with oxidative stress originating from oxidizing compounds or reactive oxygen species (ROS), associated with the exposure to agents that cause environmental stresses, is one of the prerequisites for an aerobic lifestyle of Bacillus spp. such as B. subtilis, B. cereus and B. anthracis. This minireview highlights novel insights in the primary oxidative stress response caused by oxidizing compounds including hydrogen peroxide and the secondary oxidative stress responses apparent upon exposure to a range of agents and conditions leading to environmental stresses such as antibiotics, heat and acid. Insights in the pathways and damaging radicals involved have been compiled based among others on transcriptome studies, network analyses and fluorescence techniques for detection of ROS at single cell level. Exploitation of the current knowledge for the control of spoilage and pathogenic bacteria is discussed

Bacillus cereus responses to acid stress

Coping with acid environments is one of the prerequisites for the soil saprophytic and human pathogenic lifestyle of Bacillus cereus. This minireview highlights novel insights in the responses displayed by vegetative cells and germinating spores of B. cereus upon exposure to low pH as well as organic acids, including acetic acid, lactic acid and sorbic acid. Insights regarding the possible acid-inflicted damage, physiological responses and protective mechanisms have been compiled based on single cell fluorescence microscopy, flow cytometry and transcriptome analyses

Impact of sorbic acid on germinant receptor-dependent and -independent germination pathways in Bacillus cereus

Amino acid- and inosine-induced germination of Bacillus cereus ATCC 14579 spores was reversibly inhibited in the presence of 3 mM undissociated sorbic acid. Exposure to high hydrostatic pressure, Ca-dipicolinic acid (DPA), and bryostatin, an activator of PrkC kinase, negated this inhibition, pointing to specific blockage of signal transduction in germinant receptor-mediated germination

Comparative analysis of Bacillus weihenstephanensis KBAB4 spores obtained at different temperatures

The impact of Bacillus weihenstephanensis KBAB4 sporulation temperature history was assessed on spore heat resistance, germination and outgrowth capacity at a temperature range from 7 to 30 °C. Sporulation rate and efficiency decreased at low temperature, as cells sporulated at 12, 20 and 30 °C with approximately 99% efficiency, whereas at 7 °C and 10 °C, a maximum 15% of sporulation was reached. Spores formed at 30 °C showed the highest wet heat resistance at 95 °C, with spores formed at 7 and 10 °C displaying only survival of 15 min exposure at 70 °C, indicating their low level heat resistance. RT-PCR analysis revealed expression of sporulation sigma factor sigG, and germinant receptor operons gerI, gerK, gerL, gerR, gerS, and (plasmid-located) gerS2 to be activated in all sporulation conditions tested. Subsequent germination assays revealed a combination of inosine and L-Alanine to be very efficient, triggering over 99% of the spores to germinate, with spores obtained at 30 °C showing the highest germination rates (99%). Notably, spores obtained at 12, 20 and 30 °C, germinated at all tested temperatures, showing > 70% spore germination even at temperatures as low as 5 °C. Less than 5% of spores obtained at 7 and 10 °C showed a germination response. Furthermore, spores produced at 12, 20 and 30 °C showed similar outgrowth effiency at these temperatures, indicating that low temperature sporulation history does not improve low temperature outgrowth performance. Insights obtained in sporulation and germination behaviour of B. weihenstephanensis KBAB4, in combination with the availability of its genome sequence, may contribute to our understanding of the behaviour of psychrotolerant spoilage and pathogenic Bacill

Germinant receptor diversity and germination responses of four strains of the Bacillus cereus group

Four strains of the Bacillus cereus group were compared for their germinant receptor composition and spore germination capacity. Phylogenetic analysis of the germinant receptor encoding operons of the enterotoxic strains B. cereus ATCC 14579 and ATCC 10987, the emetic strain AH187, and the psychrotolerant strain Bacillus weihenstephanensis KBAB4, indicated a core group of five germinant receptor operons to be present in the four strains, with each strain containing one to three additional receptors. Using quantitative PCR, induction of expression during sporulation was confirmed for all identified germinant receptor operons in these strains. Despite the large overlap in receptors, diversity in amino acid-induced germination capacity was observed, with six out of 20 amino acids, serving as germinants for spores of all four strains. Each strain showed unique features: efficient germination of strain KBAB4 spores required non-inducing amounts of inosine as the co-germinant, strain ATCC 10987 spores germinated only efficiently after heat activation. Furthermore, strain ATCC 14579 and AH187 spores germinated without heat activation or inosine, with strain ATCC 14579 spores being triggered by all amino acids except phenylalanine and strain AH187 spores being specifically triggered efficiently only by phenylalanine. Analysis of all germination data did not reveal strict linkages between specific germinants and germinant receptors. Finally, the diversity in nutrient-induced germination capacity was also reflected in the diverse germination responses of heat-activated spores of the four B. cereus strains in food matrices, such as milk, rice water and meat bouillon, indicating that amino acid composition and/or availability of inosine are important germination determinants in foods. Keywords: Ger operon; Food preservation; B. weihenstephanensis; Sporulatio

Soya bean tempe extracts show antibacterial activity against Bacillus cereus cells and spores

Aims: Tempe, a Rhizopus ssp.-fermented soya bean food product, was investigated for bacteriostatic and/or bactericidal effects against cells and spores of the food-borne pathogen Bacillus cereus. Methods and results: Tempe extract showed a high antibacterial activity against B. cereus ATCC 14579 based on optical density and viable count measurements. This growth inhibition was manifested by a 4 log CFU ml-1 reduction, within the first 15 min of exposure. Tempe extracts also rapidly inactivated B. cereus spores upon germination. Viability and membrane permeability assessments using fluorescence probes showed rapid inactivation and permeabilization of the cytoplasmic membrane confirming the bactericidal mode of action. Cooked beans and Rhizopus grown on different media did not show antibacterial activity, indicating the unique association of the antibacterial activity with tempe. Subsequent characterization of the antibacterial activity revealed that heat treatment and protease addition nullified the bactericidal effect, indicating the proteinaceous nature of the bioactive compound. Conclusions: During fermentation of soya beans with Rhizopus, compounds are released with extensive antibacterial activity against B. cereus cells and spores. Significance and Impact of Study: The results show the potential of producing natural antibacterial compounds that could be used as ingredients in food preservation and pathogen contro

The quest for the elusive causative SNP

El Kares et al. present evidence that fetal genetic variation in the 3′ end of ALDH1A2 may influence nephrogenesis and blood retinoic acid levels. This may be correct, but only replication of this association, ideally accounting for both the fetal and the maternal genotypes, will provide a better understanding of the biology that underlies the association

The impact of smartphone use on student learning experience in higher education in South Africa

Background: The use of mobile devices for learning has been on the increase due to the availability of affordable data and free WiFi networks across institutions of higher learning. However, very few studies seek to understand if there is any impact that these devices have on a student's overall learning experience particularly from a developing country's perspective. Objectives: This research study determines the positive and negative impacts smartphone use has on a student's learning experience and whether this leads to overall satisfaction with mobile learning. Methods/Approach: Quantitative and qualitative data were collected through an online survey that was distributed via email to a student body from the sample. Statistica software was used to analyse the quantitative data while Nvivo software was used to analyse the qualitative data. Results: With over 400 responses, we found evidence for some, but not all hypothesized positive and negative impacts. Additionally, there was very strong support for how these impacts contribute to the overall satisfaction of using a smartphone for learning, explaining more than 60% of the variance. Conclusions: We found that the overall positive satisfaction leads to differentiated, continued uses of the smartphone for learning

Analysis of acid-stressed Bacillus cereus reveals a major oxidative response and inactivation-associated radical formation

Acid stress resistance of the food-borne human pathogen Bacillus cereus may contribute to its survival in acidic environments, such as encountered in soil, food and the human gastrointestinal tract. The acid stress responses of B. cereus strains ATCC 14579 and ATCC 10987 were analysed in aerobically grown cultures acidified to pH values ranging from pH 5.4 to pH 4.4 with HCI. Comparative phenotype and transcriptome analyses revealed three acid stressinduced responses in this pH range: growth rate reduction, growth arrest and loss of viability. These physiological responses showed to be associated with metabolic shifts and the induction of general stress response mechanisms with a major oxidative component, including upregulation of catalases and superoxide dismutases. Flow cytometry analysis in combination with the hydroxyl (OH center dot) and peroxynitrite (ONOO-)-specific fluorescent probe 3'-(phydroxyphenyl) fluorescein (HPF) showed excessive radicals to be formed in both B. cereus strains in bactericidal conditions only. Our study shows that radicals can indicate acid-induced malfunctioning of cellular processes that lead to cell death