New chitosan derivatives inspired on heterocyclic anhydride of potential bioactive for medical applications.

In the present work new chitosan derivatives inspired heterocyclic anhydride were prepared to improve the biological activities of chitosan via imidization reaction of chitosan (CS) and N-(1,3-dioxoisoindolin-2-yl)-1,3-dioxo-1,3-dihydroiso-benzofuran-5-carboxamide (5) to yield amic acid CS-6 at room temperature and imide CS-8 thermally. However, the reaction between (CS) and anhydride (5) in presence of sodium tripolyphosphate (TPP) or Poly (ethylene glycol) diglycidyl ether (PEGDG) at room temperature yielded CS-6 NPs and CS-7 respectively. The structure of new chitosan derivatives was characterized using morphological and spectroscopic analyses. From evaluation of the biological activities, the greatest enzymatic inhibitory for trypsin and α-chymotrypsin revealed by CS-7 at 88.33 ± 2.27 and 79.63 ± 3.16% respectively. Furthermore, the highest inhibition zones, (MIC) and (MBC) against S. aureus and B. subtilis recorded by CS-6 NPs at 21 ± 0.75, 22 ± 0.98 mm, 19.5, 19.5, 38 and 38 ppm respectively. Additionally, CS-8 displayed the best cell growth inhibition against vero cell line at 93.17 ± 0.29%.

Identification of the Anti-Infective Aborycin Biosynthetic Gene Cluster from Deep-Sea-Derived Streptomyces sp. SCSIO ZS0098 Enables Production in a Heterologous Host.

Aborycin is a ribosomally synthesized member of the type I lasso peptide natural products. In the present study, aborycin was isolated and identified from the deep-sea-derived microbe Streptomyces sp. SCSIO ZS0098. The aborycin biosynthetic gene cluster (abo) was identified on the basis of genome sequence analyses and then heterologously expressed in Streptomyces coelicolor M1152 to effectively produce aborycin. Aborycin generated in this fashion exhibited moderate antibacterial activity against 13 Staphylococcus aureus strains from various sources with minimum inhibitory concentrations MICs = 8.0~128 µg/mL, against Enterococcus faecalis ATCC 29212 with an MIC = 8.0 µg/mL, and against Bacillus thuringiensis with MIC = 2.0 µg/mL. Additionally, aborycin displayed potent antibacterial activity (MIC = 0.5 µg/mL) against the poultry pathogen Enterococcus gallinarum 5F52C. The reported abo cluster clearly has the potential to provide a means of expanding the repertoire of anti-infective type I lasso peptides.

Bioengineered silver nanoparticles as potent anti-corrosive inhibitor for mild steel in cooling towers.

Silver nanoparticle-aided enhancement in the anti-corrosion potential and stability of plant extract as ecologically benign alternative for microbially induced corrosion treatment is demonstrated. Bioengineered silver nanoparticles (AgNPs) surface functionalized with plant extract material (proteinacious) was generated in vitro in a test tube by treating ionic AgNO3 with the leaf extract of Azadirachta indica that acted as dual reducing as well as stabilizing agent. Purity and crystallinity of the AgNPs, along with physical and surface characterizations, were evaluated by performing transmission electron microscopy, Fourier transform infrared spectroscopy, energy dispersive x-ray spectra, single-area electron diffractions, zeta potential, and dynamic light scattering measurements. Anti-corrosion studies against mild steel (MS1010) by corrosion-inducive bacterium, Bacillus thuringiensis EN2 isolated from cooling towers, were evaluated by performing electrochemical impedance spectroscopy (EIS), weight loss analysis, and surface analysis by infrared spectroscopy. Our studies revealed that AgNPs profoundly inhibited the biofilm on MS1010 surface and reduced the corrosion rates with the CR of 0.5 mm/y and an inhibition efficiency of 77% when compared to plant extract alone with a CR of 2.2 mm/y and an inhibition efficiency of 52%. Further surface analysis by infrared spectra revealed that AgNPs formed a protective layer of self-assembled film on the surface of MS1010. Additionally, EIS and surface analysis revealed that the AgNPs have inhibited the bacterial biofilm and reduced the pit on MS1010. This is the first report disclosing the application of bioengineered AgNP formulations as potent anti-corrosive inhibitor upon forming a protective layer over mild steel in cooling water towers. Graphical Abstract ᅟ.

Antimicrobial effects of zero-valent iron nanoparticles on gram-positive Bacillus strains and gram-negative Escherichia coli strains.

BACKGROUND: Zero-valent iron nanoparticles (ZVI NPs) have been used extensively for the remediation of contaminated soil and groundwater. Owing to their large active surface area, they serve as strong and effective reductants. However, the ecotoxicity and bioavailability of ZVI NPs in diverse ecological media have not been evaluated in detail and most studies have focused on non-nano ZVI or Fe0. In addition, the antimicrobial properties of ZVI NPs have rarely been investigated, and the underlying mechanism of their toxicity remains unknown. RESULTS: In the present study, we demonstrate that ZVI NPs exhibited significant toxicity at 1000 ppm against two distinct gram-positive bacterial strains (Bacillus subtilis 3610 and Bacillus thuringiensis 407) but not against two gram-negative strains (Escherichia coli K12 and ATCC11634). Specifically, ZVI NPs caused at least a 4-log and 1-log reductions in cell numbers, respectively, in the two Bacillus strains, whereas no change was detected in the two E. coli strains. X-ray photoelectron spectroscopy, X-ray absorption near-edge, and extended X-ray absorption fine structure spectra confirmed that Bacillus cells exposed to ZVI NPs contained mostly Fe2O3 with some detectable FeS. This finding indicated that Fe0 nanoparticles penetrated the bacterial cells, where they were subsequently oxidized to Fe2O3 and FeS. RedoxSensor analysis and propidium iodide (PI) staining showed decreased reductase activity and increased PI in both Bacillus strains treated with a high (1000 ppm) concentration of ZVI NPs. CONCLUSION: Taken together, these data show that the toxicity of ZVI NPs was derived from their oxidative properties, which may increase the levels of reactive oxygen species and lead to cell death.

An anionic defensin from Plutella xylostella with potential activity against Bacillus thuringiensis.

Insect defensins, are cationic peptides that play an important role in immunity against microbial infection. In the present study, an anionic defensin from Plutella xylostella, (designated as PxDef) was first cloned and characterized. Amino acid sequence analysis showed that the mature peptide owned characteristic six-cysteine motifs with predicted isoelectric point of 5.57, indicating an anionic defensin. Quantitative real-time polymerase chain reaction analysis showed that PxDef was significantly induced in epidermis, fat body, midgut and hemocytes after injection of heat-inactivated Bacillus thuringiensis, while such an induction was delayed by the injection of live B. thuringiensis in the 4th instar larvae of P. xylostella. Knocking down the expression of nuclear transcription factor Dorsal in P. xylostella by RNA interference significantly decreased the mRNA level of PxDef, and increased the sensitivity of P. xylostella larvae to the infection by live B. thuringiensis. The purified recombinant mature peptide (PxDef) showed higher activity against Gram-positive bacteria, with the minimum inhibition concentrations of 1.6 and 2.6 µM against B. thuringiensis and Bacillus subtilis, respectively. To our knowledge, this is the first report about an anionic PxDef, which may play an important role in the immune system of P. xylostella against B. thuringiensis.

Isolation and characterization of Lepidoptera specific Bacillus thuringiensis strains predominantly from north-eastern states of India.

Both, the tobacco caterpillar Spodoptera litura (Fabricius) and the cotton bollworm Helicoverpa armigera (Hibner), are serious polyphagous pests causing considerable loss to crops. Indiscriminate use of chemical pesticides for controlling them has rather resulted in their resistance development. Microbial pesticides, Bacillus thuringiensis in particular, play an important role in pest management. Here, we isolated Bacillus thuringiensis-like bacteria from the soil samples primarily collected from North East region of India along with some states viz., Haryana, Punjab, Maharashtra, West Bengal and Uttarakhand and studied their toxicity against the above two insect pests at 10 gg/g along with standard strain B. thuringiensis subsp. kurstaki HD-I and at 1 pg/g Pseudomonasfluorescens based MVPII expressing CrylAc toxin and AUG-5. Isolates AUG-5 and GTG-7 proved toxic to more than 75% larvae on the 4h as well as 7h day of the treatment of the neonates of H. armigera. The AUG-5 isolate was also effective against S. litura. Ten effective isolates (AUG-5, GTG-4, GTG-7, GTG-9, GTG-42, GTG-64, GTG-70, GTG-3S, GTG-4S and GTG-6S) were characterized using biochemical and 16S rDNA analysis. Nearly, all the isolates tested positive for utilizing monosaccharides. All selected B. thuringiensis isolates showed resistance to ampicillin and co-trimoxazole except AUG-5 to- co-trimoxazole. AUG-5 and GTG-7 were highly toxic to both insects, and possessed cryl, cry1A and cry2 genes. These isolates AUG-5 and GTG-7 also contained high CrylAc (104.8 and 88.32 ng/mg) and Cry2Ab (3792 and 1305.9 ng/mg), respectively in their spore-crystal complex. Both, AUG-5 and GTG-7 isolates, could be considered for further development as bioinsecticides. The present study has established the diversity and richness of B. thuringiensis-like isolates in soils collected from north-eastern region of India.

Antimicrobial activity of Anonna mucosa (Jacq.) grown in vivo and obtained by in vitroculture

Brazilian flora includes numerous species of medicinal importance that can be used to develop new drugs. Plant tissue culture offers strategies for conservation and use of these species allowing continuous production of plants and bioactive substances. Annona mucosa has produced substances such as acetogenins and alkaloids that exhibit antimicrobial activities. The widespread use of antibiotics has led to an increase in multidrug-resistant bacteria, which represents a serious risk of infection. In view of this problem, the aim of this work was to evaluate the antibacterial potential of extracts of A. mucosa obtained by in vitro techniques and also cultured under in vivo conditions. Segments from seedlings were inoculated onto different culture media containing the auxin picloram and the cytokinin kinetin at different concentrations. The calluses obtained were used to produce cell suspension cultures. The materials were subjected to methanol extraction and subsequent fractionation in hexane and dichloromethane. The antimicrobial activity against 20 strains of clinical relevance was evaluated by the macrodilution method at minimum inhibitory and minimum bactericidal concentrations. The extracts showed selective antimicrobial activity, inhibiting the growth of Streptococcus pyogenes and Bacillus thuringiensis at different concentrations. The plant tissue culture methods produced plant materials with antibacterial properties, as well as in vivo grown plants. The antibacterial activity of material obtained through biotechnological procedures of A. mucosa is reported here for the first time.

Developmental regulation and antifungal activity of a growth-blocking peptide from the beet armyworm Spodoptera exigua.

Insect cytokine growth-blocking peptides (GBPs) are involved in growth regulation and the innate immune response. However, the microbial binding and antimicrobial activities of GBPs remain unclear. Here, we investigate the developmental role and antifungal activity of a GBP from the beet armyworm Spodoptera exigua (SeGBP). Sequence analysis predicted that mature SeGBP consists of 24 amino acid residues, including 2 cysteine residues. During S. exigua development, SeGBP is constitutively expressed in the fat body during the larval and adult stages but not in pupae. SeGBP expression is up-regulated by 20-hydroxyecdysone and down-regulated by juvenile hormone analog. Recombinant SeGBP purified from baculovirus-infected insect cells retards the growth of S. exigua larvae. Additionally, SeGBP expression is acutely induced in the fat body after injection with Escherichia coli, Bacillus thuringiensis, or Beauveria bassiana. Recombinant SeGBP can bind to B. bassiana but not to E. coli or B. thuringiensis. Consistent with these findings, SeGBP shows antifungal activity against B. bassiana. Therefore, these results provide insight into the role of SeGBP during the innate immune response following microbial infection, and furthermore, they suggest a novel function for SeGBP as a direct antifungal agent against entomopathogenic fungi, such as B. bassiana.

Potentiating 1-(2-hydroxypropyl)-2-styryl-5-nitroimidazole derivatives against antibacterial agents: design, synthesis and biology analysis.

A series of novel 1-(2-hydroxypropyl)-2-styryl-5-nitroimidazole derivatives had been designed, synthesized, isolated and evaluated as potentiators of antibacterial agents. All these synthesized compounds were determined by elemental analysis, (1)H NMR, and MS. Their biological activities were also evaluated against two Gram-negative bacterial strains: Escherichia coli and Pseudomonas aeruginosa and two Gram-positive bacterial strains: Bacillus thuringiensis and Bacillus subtilis by MTT method as potential FabH inhibitory. The results showed that compound 30 exhibited the most potent E. coli FabH inhibitory activity with IC50 of 4.6 µM. Molecular modeling simulation studies were performed in order to predict the biological activities of the proposed compounds. All compounds have been tested for toxicity by MTT assay on human macrophage.

Antimicrobial and antioxidant activities of Cichorium intybus root extract using orthogonal matrix design.

Solvent, impregnation time, sonication repetitions, and ultrasonic power were important factors in the process of ultrasound-assisted extraction from chicory (Cichorium intybus) root, while there were no studies about optimizing these 4 factors for extract yield, total phenolic content (TPC), antioxidant, antibacterial, and antifungal activity of the extracts using orthogonal matrix design. The present research demonstrated that the solvent composition played a significant role in the improving extract yield, TPC, antioxidant, and antibacterial activities. The other 3 factors had inequable effect on different purposes, ultrasonic power could improve TPC and antioxidant activity, but long time of extraction lowered antioxidant activity. The TPC increased from 22.34 to 27.87 mg GAE (gallic acid equivalents)/100 g (dry extracts) with increasing solvent polarity. The half inhibition concentration (IC(50,) µg/mL) of the radical scavenging activity of the chicory extracts ranged from 281.00 to 983.33 µg/mL. The content of caffeoylquinic acids of root extract, which was extracted by the optimal combination was 0.104%. Several extracts displayed antibacterial activities against Escherichia coli, Staphylococcus aureus, Bacillus thuringiensis, Bacillus subtilis, and Salmonella typhi, while Penicillium sp. and Aspergillus sp. resisted against all the extracts. Combination of 70% ethanol v/v, 24-h impregnation time, 3 sonication rounds, and 300-W ultrasonic input power was found to be the optimal combination for the chicory extract yield, TPC, antioxidant activity, and antibacterial activity.

Halogenated anthraquinones from the marine-derived fungus Aspergillus sp. SCSIO F063.

Metabolomic investigations focusing on the marine-derived fungus Aspergillus sp. SCSIO F063 have unveiled seven new chlorinated anthraquinones (1-7) related to averantin, together with five known analogues (11-15) when the fungus was fermented using sea salt-containing potato dextrose broth. Through the addition of sodium bromide to the broth, two new brominated anthraquinones (8, 9) and one new nonhalogenated anthraquinone (10) were obtained from the fungal mycelia. Their structures were elucidated by extensive spectroscopic analyses including MS and 1D and 2D NMR data. One metabolite, 6-O-methyl-7-chloroaveratin (2), displayed inhibition activity against three human tumor cell lines, SF-268, MCF-7, and NCI-H460, with IC(50) values of 7.11, 6.64, and 7.42 µM, respectively.

Validation of the intact zwittermicin A biosynthetic gene cluster and discovery of a complementary resistance mechanism in Bacillus thuringiensis.

Zwittermicin A (ZmA) is a hybrid polyketide-nonribosomal peptide produced by certain Bacillus cereus group strains. It displays broad-spectrum antimicrobial activity. Its biosynthetic pathway in B. cereus has been proposed through analysis of the nonribosomal peptide synthetase (NRPS) and polyketide synthase (PKS) modules involved in ZmA biosynthesis. In this study, we constructed a bacterial artificial chromosome (BAC) library from Bacillus thuringiensis subsp. kurstaki strain YBT-1520 genomic DNA. The presence of known genes involved in the biosynthesis of ZmA in this BAC library was investigated by PCR techniques. Nine positive clones were identified, two of which (covering an approximately 60-kb region) could confer ZmA biosynthesis ability upon B. thuringiensis BMB171 after simultaneous transfer into this host by two compatible shuttle BAC vectors. Another previously unidentified gene cluster, named zmaWXY, was found to improve the yield of ZmA and was experimentally defined to function as a ZmA resistance transporter which expels ZmA from the cells. Putative transposase genes were detected on the flanking regions of the two gene clusters (the ZmA synthetic cluster and zmaWXY), which suggests a mobile nature of these two gene clusters. The intact ZmA gene cluster was validated, and a resistance mechanism complementary to that for zmaR (the previously identified ZmA self-resistance gene) was revealed. This study also provided a straightforward strategy to isolate and identify a huge gene cluster from Bacillus.

Transcriptional responses of Bacillus subtillis and thuringiensis to antibiotics and anti-tumour drugs.

DNA supercoiling is a major regulator of transcription in all organisms. This process is regulated by type I and type II DNA topoisomerases that are targets for microbial antibiotics and/or anti-tumour drugs. Despite extensive studies in this field, no information is available on the response of Bacillus (B) species to eukaryotic DNA topoisomerase inhibitors. Here we found that B. thuringiensis BMG1.7 and HD9 strains are sensitive to DNA gyrase inhibitors (e.g. ciprofloxacin, novobiocin) and to etoposide VP16, a specific inhibitor of eukaryotic type II DNA topoisomerase. Inhibitory or sub-inhibitory concentrations of VP16 induced a drug-tolerant response: an immediate inhibition of growth, followed by a prolonged (10-12 h) lag in growth, and then resumption of normal growth subsequent to overnight culture. Inhibition of the DNA gyrase ATPase activity in B. subtillis 168 by novobiocin activated 80 genes and repressed 89 genes at 20 min after drug addition (P<0.05). The altered genes belonged to various functional categories dominated by those whose products maintained DNA integrity, mediated transport of low molecular-weight compounds, and SOS response genes. Quantitative RT-PCR revealed comparable effects of novobiocin in B. subtillis and thuringiensis on gene expression. In contrast to novobiocin, VP16 treatment resulted in a moderate effect on gyrA, gyrB, and topA gene expression. However, dinB and lexA genes, involved in SOS response, displayed relatively high transcriptional levels compared to those seen in untreated cells. Furthermore, a small DNA plasmid isolated from novobicin-treated B. thuringiensis BMG 1.7 contained a ladder of partially relaxed topoisomers, while the electrophoretic mobility of its counterpart isolated from VP16-treated cells was unchanged. Collectively, the present study would assist in defining common and/or different pathways affected by eubacterial and eukaryotic type DNA topoisomerase inhibitors in the same living organism.

A fundamental regulatory role of formate on thuringiensin production by resting cell of Bacillus thuringiensis YBT-032.

In this work, a fundamental regulatory role of formate on thuringiensin production by resting cell of Bacillus thuringiensis YBT-032 was investigated. Nicotinamide adenine dinucleotide (NADH) production and formate dehydrogenase activity increased with formate addition from 0.5 to 2.0 g/L, respectively. However, with the formate addition of 1.5 g/L, the activities of pyruvate kinase and glucose 6-phosphate dehydrogenase reached a peak and increased by 316 and 150% relative to those of the control, respectively. In addition, intracellular production of pyruvate, aspartate, citrate and adenine were significantly enhanced by 75, 66, 32 and 78% as well. An improvement (90%) of thuringiensin production was also successfully obtained. Interestingly to point out, thuringiensin yield was closely correlative with adenine production, and the linear relationship was also observed. The results suggest that appropriate formate addition did act as a modulator and facilitate carbon flux in glycolysis and pentose phosphate pathway to synthesize adenine and thuringiensin via intracellular NADH availability.

A fundamental dual regulatory role of citrate on the biosyntheses of thuringiensin and poly-beta-hydroxybutyrate in Bacillus thuringiensis YBT-032.

The production of alpha-ketoglutarate, adenine, thuringiensin production rate and thuringiensin yield on glucose consumed increased by 22%, 36%, 40% and 40%, respectively, in presence of 2 g citrate/l. However, citrate decreased pyruvate production, poly-beta-hydroxybutyrate (PHB) production rate and PHB yield by 62%, 31% and 45%, respectively. The activities of pyruvate kinase and glucose-6-phosphate dehydrogenase were 36%-45% lower and 50%-120% higher than those of the control, respectively. The results suggest that citrate regulated the carbon flux to synthesis of adenine present in thuringiensin with a higher efficiency of utilization of glucose by decreasing PHB synthesis.

Evaluation of chlorine, chlorine dioxide, and a peroxyacetic acid-based sanitizer for effectiveness in killing Bacillus cereus and Bacillus thuringiensis spores in suspensions, on the surface of stainless steel, and on apples.

Chlorine (10 to 200 microg/ml), chlorine dioxide (10 to 200 microg/ml), and a peroxyacetic acid-based sanitizer (40 and 80 microg/ ml) were evaluated for effectiveness in killing spores of Bacillus cereus and Bacillus thuringiensis in suspensions and on the surface of stainless steel and apples. Water and 5% horse serum were used as carriers for spore inoculum applied to the surface of stainless steel coupons, and 5% horse serum was used as a carrier for inoculum applied to apples. Inocula were dried on stainless steel for 5 h and on apples for 22 to 24 h before treating with sanitizers. At the concentrations of sanitizers tested, sensitivities of planktonic B. cereus and B. thuringiensis spores were similar. A portion of the spores surviving treatment with chlorine and, more markedly, chlorine dioxide had decreased tolerance to heat. Planktonic spores of both species were more sensitive to sanitizers than were spores on the surface of stainless steel or apples. At the same concentrations, chlorine was more effective than chlorine dioxide in killing spores in suspension and on stainless steel. The lethality of chlorine dioxide was markedly reduced when inoculum on stainless steel coupons was suspended in 5% horse serum as a carrier rather than water. Chlorine and chlorine dioxide at concentrations of 10 to 100 microg/ml were equally effective in killing spores on apples. Significant reductions of > or = 3.8 to 4.5 log CFU per apple were achieved by treatment with 100 microg/ml of either of the two sanitizers. The peroxyacetic acid sanitizer (40 and 80 microg/ml) was ineffective in killing Bacillus spores in the test systems investigated. Results provide information on the effectiveness of sanitizers commonly used in the food processing industry in killing Bacillus spores in suspension, on a food-contact surface, and on a ready-to-eat food.

Decontamination of Bacillus thuringiensis spores on selected surfaces by chlorine dioxide gas.

This work examined the efficacy of chlorine dioxide (ClO2) gas for the decontamination of Bacillus thuringiensis spores on paper, wood, epoxy, and plastic surfaces. Spores representing an inoculation level of approximately 6 log colony-forming units (CFU) per surface were treated with 5, 10, 15, 20, 25, or 30 milligrams per liter (mg/L) ClO2 gas for 12 hours under 85-92 percent relative humidity and at 22 +/- 1 degrees C. Under the tested treatment conditions, the highest population of surviving spores was found on the paper surface and the lowest was found on the plastic surface (p < .05). The 5 mg/L ClO2 gas treatment inactivated 2.5, 3.6, 4.0, and 4.9 log spores per surface on paper, wood, epoxy, and plastic surfaces, respectively. A greater than 5-log reduction of spores was achieved on each surface after the 15 mg/L ClO2 gas treatment. The minimum ClO2 gas concentration needed to completely inactivate the inoculated spores was 30 mg/L for paper and wood surfaces, 25 mg/L for epoxy surfaces, and 20 mg/L for plastic surfaces. The results of this study may provide insight into the parameters of effective decontamination procedures for Bacillus spores.

Risk assessment of etofenprox (Vectron) on non-target aquatic fauna compared with other pesticides used as Simulium larvicide in a tropical environment.

Within the rotational scheme developed by the Programme to fight the resistance of Simulium damnosum to chemical larvicides, there was an operational gap at discharges between 5 and 70 m3 s(-1) for the treatment of rivers where resistance to organophosphates was present. The use of permethrin and carbosulfan was precluded because of risk of environmental impact and, Bacillus thuringiensis ser. H-14 treatments were not envisageable due to cost and logistics constraints. Among the possible complementary groups of larvicides tested, the pseudo-pyrethroids, held promise, because of a mode of action similar to that of pyrethroids, but along with a usually lower toxicity for fish. Etofenprox, one of the pseudo-pyrethroids tested, shows a global detachment of non-target insects in 24 h close to that of pyraclofos, an organo-phosphorus compound (27 against 23%). In laboratory conditions, six times the operational dose which is 0.03 mg l(-1) 10 min, is needed to cause 50% mortality of Caridina sp. (a small shrimps species) and 30 times this same dose for 95% mortality. For fish species, a safety margin of 400-800 times the operational dose is observed for Oreochromis niloticus and 200-400 times for Tilapia zillii.

Cadmium biosorption by a cadmium resistant strain of Bacillus thuringiensis: regulation and optimization of cell surface affinity for metal cations.

A marine bacterial strain putatively identified as Bacillus thuringiensis strain DM55, showed multiple heavy metal resistance and biosorption phenotypes. Electron microscopic studies revealed that DM55 cells are encased in anionic cell wall polymers that can immobilize discrete aggregates of cations. Factors affecting cell surface affinity for metal cations, monitored by means of Cd2+ binding capability, are investigated. The mechanisms of cadmium resistance and Cd2+ biosorption by the bacterium appeared to be inducible and coincident. Medium components affecting metal removal under cadmium-stressed growth conditions were explored based on the application of two sequential multi-factorial statistical designs. Concentrations of potassium phosphates and peptone were the most significant variables. Optimized culture conditions allowed DM55 cells grown in the presence of 0.25 mM CdCl2 to remove about 79% of the metal ions within 24 h with a specific biosorption capacity of 21.57 mg g(-1) of biomass. Both fresh and dry cells of DM55 prepared under cadmium-free optimal nutrient condition were also able to biosorb Cd2+. In addition to the concentration of phosphate in the medium, KinA, a major phosphate provider in the phosphorelay of Bacillus cells, was also demonstrated to regulate the magnitude of cell surface affinity for cadmium ions.

[Effect of pesticides on Bacillus thuringiensis strains under controlled conditions]. / Efecto de pesticidas sobre cepas de Bacillus thuringiensis bajo condiciones controladas.

Little is known about native populations of Bacillus thuringiensis (Bt) isolated from soils of Argentina. We undertook this study to determine the resistance to different pesticides of two commercial and fourteen native strains of Bt under in vitro conditions. An agar plate bioassay test conducted with ten pesticides and sixteen strains of Bt showed that Basagran, Scepter, Fungoxan and Decis were not toxic for the bioinsecticide bacteria at recommended application rates (RAR). In contrast, low concentrations (3.2% RAR) of Agil, Select and Isomero showed a deleterious effect on the bacteria investigated. Simultaneously, four of the pesticides were able to produce phenotypical changes on the Bt colonies grown on nutrient agar. Moreover, in a greenhouse experiment, seven pesticides applied at 1.6%, 12.5% and 100% RAR on soybean leaves were not as inhibitory as under in vitro conditions for two Bt strains (HD-1 and A61). However, survival of these strains in the phyllosphere of soybean differed significantly between untreated leaves and leaves treated with pesticides after 20 days of study (P < 0.05). Finally, and from an ecological point of view, these findings suggest that the addition of some pesticides to soybean leaves in lower concentrations than those recommended could be favourable for the persistence of Bt in this environment.