Background Saccharomyces cerevisiae is well known in the baking and brewing industry and is also used as a probiotic in humans. However, it is a very uncommon cause of infection in humans. Methods ...During the period of 15–30 April 2003, we found 3 patients with S. cerevisiae fungemia in an intensive care unit (ICU). An epidemiological study was performed, and the medical records for all patients who were in the unit during the second half of April were assessed. Results The only identified risk factor for S. cerevisiae infection was treatment with a probiotic containing Saccharomyces boulardii (Ultralevura; Bristol-Myers Squibb). This probiotic is used in Europe for the treatment and prevention of Clostridium difficile-associated diarrhea. The 3 patients received the product via nasograstric tube for a mean duration of 8.5 days before the culture result was positive, whereas only 2 of 41 control subjects had received it. Surveillance cultures for the control patients admitted at the same time did not reveal any carriers of the yeast. Strains from the probiotic capsules and the clinical isolates were identified as S. cerevisiae, with identical DNA fingerprinting. Discontinuation of use of the product in the unit stopped the outbreak of infection. A review of the literature identified another 57 cases of S. cerevisiae fungemia. Overall, 60% of these patients were in the ICU, and 71% were receiving enteral or parenteral nutrition. Use of probiotics was detected in 26 patients, and 17 patients died. Conclusions Use of S. cerevisiae probiotics should be carefully reassessed, particularly in immunosuppressed or critically ill patients.
Bacillus thuringiensis subsp. israelensis is the most widely used microbial control agent against mosquitoes and blackflies. Its insecticidal success is based on an arsenal of toxins, such as Cry4A, ...Cry4B, Cry11A, and Cyt1A, harbored in the parasporal crystal of the bacterium. A fifth toxin, Cry10Aa, is synthesized at very low levels; previous attempts to clone and express Cry10Aa were limited, and no parasporal body was formed. By using a new strategy, the whole Cry10A operon was cloned in the pSTAB vector, where both open reading frames ORF1 and ORF2 (and the gap between the two) were located, under the control of the cyt1A operon and the STAB-SD stabilizer sequence characteristic of this vector. Once the acrystalliferous mutant 4Q7 of B. thuringiensis subsp. israelensis was transformed with this construct, parasporal bodies were observed by phase-contrast microscopy and transmission electron microscopy. Discrete, ca. 0.9-μm amorphous parasporal bodies were observed in the mature sporangia, which were readily purified by gradient centrifugation once autolysis had occurred. Pure parasporal bodies showed two major bands of ca. 68 and 56 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. These bands were further characterized by N-terminal sequencing of tryptic fragments using matrix-assisted laser desorption ionization-time of flight mass spectrometry analysis, which identified both bands as the products of ORF1 and ORF2, respectively. Bioassays against fourth-instar larvae of Aedes aegypti of spore-crystal complex and pure crystals of Cry10Aa gave estimated 50% lethal concentrations of 2,061 ng/ml and 239 ng/ml, respectively. Additionally, synergism was clearly detected between Cry10A and Cyt1A, as the synergistic levels (potentiation rates) were estimated at 13.3 for the mixture of Cyt1A crystals and Cry10Aa spore-crystal complex and 12.6 for the combination of Cyt1A and Cry10Aa pure crystals.
The characterization of selected Bacillus thuringiensis strains isolated from different Latin America countries is presented. Characterization was based on their insecticidal activity against Aedes ...aegypti, Culex quinquefasciatus, and Anopheles albimanus larvae, scanning electron microscopy, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and plasmid profiles as well as PCR analysis using novel general and specific primers for cry and cyt genes encoding proteins active against mosquitoes (cyt1, cyt2, cry2, cry4A, cry4B, cry10, cry11, cry17, cry19, cry24, cry25, cry27, cry29, cry30, cry32, cry39, and cry40). Strains LBIT315, LBIT348, and IB604 showed threefold higher mosquitocidal activity against A. aegypti and C. quinquefasciatus larvae than B. thuringiensis subsp. israelensis and displayed high similarities with the B. thuringiensis subsp. israelensis used in this study with regard to protein and plasmid profiles and the presence of cry genes. Strain 147-8906 has activity against A. aegypti similar to that of B. thuringiensis subsp. israelensis but has different protein and plasmid profiles. This strain, harboring cry11, cry30, cyt1, and cyt2 genes, could be relevant for future resistance management interventions. Finally, the PCR screening strategy presented here led us to identify a putative novel cry11B gene.
Interfacial tension of some hydrocarbon/water systems, including a mixture of aliphatic and aromatic hydrocarbons, has been estimated on the basis of molecular dynamics simulations. The dependence of ...the interfacial properties on the salinity of the aqueous phase and the temperature has been simulated. Different concentrations in NaCl and CaCl
2
up to 2 M have been used. It is found that, in all considered cases, interfacial tension increases with salt concentration. This effect depends on the preference of the salt ions for the bulk of the aqueous phase that, in turn, results in an increased difficulty for the water molecules to be at the interface. The influence of salinity is fundamentally electrostatic in origin and does not depend on the chemical nature of the salt cation. Finally, the impact of temperature on the dodecane/brine interfacial tension has also been inspected. A decreasing of the values of the interfacial tension is found in agreement, both in trend and magnitude, with experimental available data.
In this report, physical and chemical properties, and total arsenic (As) concentrations were analyzed in agricultural (MASE) and mining soils (SMI) in the State of Guanajuato, México. Additionally, a ...metagenomic analysis of both types of soils was the bases for the identification and selection of bacteria and fungi resistant to As. The SMI soil showed higher concentration of As (39 mg kg
−1
) as compared to MASE soil (15 mg kg
−1
). The metagenome showed a total of 175,240 reads from both soils. MASE soil showed higher diversity of bacteria, while the SMI soil showed higher diversity of fungi. 16S rRNA analysis showed that the phylum Proteobacteria showed the highest proportion (39.6% in MASE and 36.4% in SMI) and Acidobacteria was the second most representative (24.2% in SMI and 11.6% in MASE). 18S rRNA analysis, showed that the phylum Glomeromycota was found only in the SMI soils (11.6%), while Ascomycota was the most abundant, followed by Basidiomycota, and Zygomycota, in both soils. Genera
Bacillus
and
Penicillium
were able to grow in As concentrations as high as 5 and 10 mM, reduced As (V) to As (III), and removed As at 9.8% and 12.1% rates, respectively. When
aoxB
,
arsB, ACR3(1), ACR3(2,)
and
arrA
genes were explored, only the
arsB
gene was identified in
Bacillus
sp.,
B. simplex
, and
B. megaterium
. In general, SMI soils showed more microorganisms resistant to As than MASE soils. Bacteria and fungi selected in this work may show potential to be used as bioremediation agents in As contaminated soils.
The understanding of the relationships between the planktonic communities in a reservoir allows us to infer possible changes in the redistribution of matter and energy flows in these systems. This ...work proposes a dynamic model for the trophic network of the Riogrande II tropical reservoir, which integrates the planktonic trophic chains of detritus and grazing, limiting the prey-predator interactions by introducing the prey meeting factor (pmf). We built a dynamic model of mass balance supported by an extensive bibliographic search. The limitations of consumers and resources were represented simultaneously by means of the pmf. The data used to validate the model were compiled from previous investigations carried out in this reservoir from 2010 to 2013. The values of pmf that we found in each simulation suggest that the top predator can access its main prey in certain concentrations of total phosphorus, with a probability of encounter ranging from 9.3 % to 17.7 %. Our simulations indicate that most of the primary production is poorly used by the primary consumers in the photic zone, however, it enters in the flows of the detrital chain and supports the production of zooplankton almost entirely. According to this finding, the biomass densities obtained in the previous studies can be better explained by the causal relationships assumed in this model.
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•Cry1Ac39 is from 4 to 10 times more toxic than Cry1Ac1 against M. sexta and T. ni.•They differ only in two amino acids located in the toxic region of the molecules.•Single and double ...mutants of Cry1Ac1 exchanged these two amino acids.•Mutated Cry1Ac1 toxins restored Cry1Ac39’s toxic levels against the same pests.•The major effect was observed in the N547Y mutant.
The LBIT-1200 strain of Bacillus thuringiensis was recently isolated from soil, and showed high biochemical and genetic similarities with the HD-73 standard strain, besides expressing only a Cry1Ac protein: Cry1Ac39. However, LBIT-1200 was 6.4 and 9.5 times more toxic against Manduca sexta and Trichoplusia ni larvae, respectively, than HD-73, which expresses the Cry1Ac1 protein. Sequencing of Cry1Ac1 and Cry1Ac39 proteins showed only four amino acid differences, including two amino acid replacements in domain III, as compared to the rest of Cry1Ac proteins reported to date: N547Y and R602G. These two amino acid substitutions in domain III were introduced in the Cry1Ac1 protein from HD-73 through site directed mutagenesis. Three mutants were obtained: two single and one double mutant, which were expressed in an acrystaliferous B. thuringiensis strain, as well as the native Cry1Ac1 and Cry1Ac39 toxins. Bipyramidal crystals produced by the single mutant strains were larger than the original Cry1Ac1 protein; however, the high toxicity levels previously observed in the strain LBIT-1200 were restored in the three mutants, when tested against M. sexta and T. ni. The substitution N547Y seems to have a higher contribution to LBIT-1200 toxicity.
The chitinase ChiA74 is synthesized by Bacillus thuringiensis and possesses a modular organization composed of four domains. In the C-terminal of the enzyme is located the chitin-binding domain ...(CBD), which has not been isolated as a single unit or characterized. Here, we aimed to isolate the ChiA74's CBD as a single unit, determine the binding properties, and evaluate its antimicrobial and hemolytic activities. We cloned the ChiA74's CBD and expressed it in Escherichia coli BL21. The single domain was purified, analyzed by SDS-PAGE, and characterized. The recombinant CBD (rCBD) showed a molecular mass of ∼14 kDa and binds strongly to α-chitin, with Kd and Bmax of ∼4.7 ± 0.9 μM and 1.5 ± 0.1 μmoles/g chitin, respectively. Besides, the binding potential (Bmax/Kd) was stronger for α-chitin (∼0.31) than microcrystalline cellulose (∼0.19). It was also shown that the purified rCBD inhibited the growth of the clinically relevant Gram-negative bacteria (GNB) Vibrio cholerae, and V. parahemolyticus CVP2 with minimum inhibitory concentrations (MICs) of 121 ± 9.9 and 138 ± 3.2 μg/mL, respectively, and of one of the most common GNB plant pathogens, Pseudomonas syringae with a MIC of 230 ± 13.8 μg/mL. In addition, the rCBD possessed antifungal activity inhibiting the conidia germination of Fusarium oxysporum (MIC = 192 ± 37.5 μg/mL) and lacked hemolytic and agglutination activities against human erythrocytes. The significance of this work lies in the fact that data provided here show for the first time that ChiA74's CBD from B. thuringiensis has antimicrobial activity, suggesting its potential use against significant pathogenic microorganisms. Future works will be focused on testing the inhibitory effect against other pathogenic microorganisms and elucidating the mechanism of action.
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