Effect of electrostatic spray parameters on the viability of two bacterial biocontrol agents and their deposition on blueberry flower stigmas

The fungus Monilinia vaccinii-corymbosi infects blueberry flowers via the stigma-style ovary pathway to cause mummy berry disease. Previous laboratory experiments documented considerable activity of stigma-applied biofungicides containing the bacteria Bacillus subtilis and, to a lesser extent, Pseudomonas fluorescens against flower infection by the pathogen. However, adequate and targeted delivery of the biocontrol agents to the stigmatic surfaces of open flowers in the field has remained problematic. Here we consider the application of the biofungicides Serenade AS (containing B. subtilis QST713) and BlightBan A506 (containing P. fluorescens A506) to blueberry flowers by air-assisted electrostatic spraying. In laboratory experiments with typical field-use rates, viability of B. subtilis and P. fluorescens was unaffected by different levels of induction-charging voltage (0–1.2 kV) and atomizing pressure (138–276 kPa) applied to an electrostatic spray-charging nozzle, showing that the bacteria in both formulations readily survived exposure to the intense electrical fields and near-sonic atomizing air shear encountered during electrostatic spraying. Electrostatically charged application significantly (P<0.0001) increased deposition of B. subtilis on the stigmatic surfaces of detached blueberry flower clusters by a factor of 4.5 compared with conventional hydraulic spraying; a similar comparison showed that population densities of P. fluorescens on the stigma were increased by a factor of 2.9, but this effect was not statistically significant (P=0.1487). For Serenade, the increased coverage and/or retention on the flower stigma, along with the excellent bacterial survival, portend well for electrostatic application for mummy berry disease control in the field.     

Relationship between sampling duration and concentration of culturable airborne mould and bacteria on selected culture media

AIMS: This study was designed to evaluate potential effects of sampling duration on observed concentrations of airborne culturable mould and bacteria on selected media. METHODS AND RESULTS: Airborne culturable mould and bacteria from lightly to moderately contaminated environments were collected on selected culture media using two co-located, concurrently operated, Andersen N-6 samplers for five sampling durations in the range of 1-10 min. Differences in mean concentrations, as well as linear relationships between sampling duration and both concentration and variability, were evaluated using nonparametric procedures. For the five sampling durations, there were no significant differences in mean concentrations of mould; for bacteria, there were significant differences, with a trend of decreasing concentrations as sampling duration increased. Data variability decreased with increasing sampling duration for both mould and bacteria. CONCLUSIONS: Airborne culturable mould concentrations were similar for sampling durations in the range of 1-10 min. Airborne bacteria concentrations tended to trend downwards with sampling durations exceeding 3 min. SIGNIFICANCE AND IMPACT OF THE STUDY: This study has shown that sampling durations of 1-10 min are appropriate for collection of airborne culturable mould on malt extract agar (MEA) and dichloran glycerol agar (DG-18); based on the apparent trend of decreasing bacterial sample concentrations associated with increasing sampling duration, sampling durations of 相似文献   

Effect of electrical fields on polar growth of Phycomyces blakesleeanus

Abstract When Phycomyces blakesleeanus spores germinated in an electrical field of 10–20 V · cm⁻¹, the hyphal tips showed a strong tendency to grow towards the cathode in a medium with pH 7. A similar response was found during growth at pH 5 but a maximal response was only obtained at higher field strength. Also the emergence of the germ tubes from the spores could be polarized by such fields but the degree of polarization was much smaller at pH 7 and almost nonexistent at pH 5. Ionic strength of the medium did not play an important role since only minor differences were found in media with 0, 1 or 10 mM KH₂ PO₄ as the only salts. The results suggest that a voltage-dependent rearrangement of (membrane) proteins affects the polar growth of the fungus.     

Effect of magnetic hyperthermia on the structure of biofilm and cellular viability of a food spoilage bacterium

This work evaluated the effect of magnetic hyperthermia (MH) on planktonic cells and biofilms of a major food spoilage bacterium Pseudomonas fluorescens and its performance compared to a conventional direct heating (DH) technique. The results showed that MH had a greater and faster bactericidal effect, promoting a significant reduction in cell viability (≥3 Log CFU) in planktonic and biofilm cells, and leading to a complete eradication of planktonic cells at 55 °C (after only ~8 min). Accordingly, when comparing the same final temperatures, MH was more harmful to the integrity of cell membranes than DH, as observed in confocal laser scanning microscope images. Additionally, scanning electron microscope images revealed that exposure to MH had promoted modifications of the bacterial cell surface as well as of the structure of the biofilm. These results present the possibility of using MH out of the biomedical field as a potential disinfection method in food-related environments.     

Effect of temperature on the viability of Bacillus stearothermophilus

One of the obligate thermophilic bacteria, Bacillus stearothermophilus, was unable to grow at temperatures below 35° C. About 80% of the population in the bacterial culture died at the temperatures, and the same extent of loss in either of the activities of oxygen consumption or synthesis of protein or nucleic acid of the organisms was observed. With the progress of death of the organisms, reduced nicotinamide-adenine dinucleotide came to be oxidized by the organisms, enzymes such as fructose-1,6-diphosphate aldolase, when the organisms were washed with phosphate buffer, were leaked out of the organisms, and an increasing amount of ribonucleoprotein was released into the culture medium. The change of the membrane state was then suggested to be one of the possible causes for the death of the organisms at the temperatures.     

基于菌植互作的植物根际细菌钝化镉作用和机制研究进展

土壤重金属镉(Cd)污染严重危害农产品安全生产,植物根际细菌在钝化土壤Cd和帮助作物抵御Cd胁迫方面发挥重要作用。本文首先概括在修复Cd污染土壤中得到广泛应用的植物根际细菌种类,并从根际细菌直接吸附Cd、调整土壤理化特性、调控土壤微生物群落和其他作用4方面阐述了植物根际细菌对Cd的钝化作用,其次从菌植互作角度阐述植物根系分泌物与根际细菌群落相互影响对土壤Cd的钝化作用。最后展望重金属胁迫下植物根际钝化Cd核心菌群的构建,以在新兴学科与技术的快速发展中探明植物根系-微生物互作体系的分子机制,深入开展植物根际细菌钝化修复重金属污染土壤的理论研究和实践。     

混菌发酵改良棉粕蛋白工艺及协同作用研究

利用筛选到的Aspergillus niger P1和Bacillus subtilis H1混菌发酵改良棉粕蛋白,以提高其利用率。结果表明,混菌发酵的最佳发酵条件为:棉粕 40 g,硫酸铵0.2%,麸皮15%,含水量50%,接种量 15%,同时接菌且两菌接菌比例(A.niger P1 ∶ B.subtilis H1)为2 ∶ 1,发酵温度30 ℃,pH约为6.0,发酵时间 60 h。在此条件下发酵后棉粕小肽含量可提高至18.36%,平均肽链长度可降至4.23,体外消化率可提高至88.59%,显著提高了改良棉粕蛋白的效果。在相同发酵条件下比较单、混菌发酵过程的各营养指标发现:A.niger P1可分泌丰富的酸性蛋白酶,B.subtilis H1可分泌丰富的中、碱性蛋白酶,混菌发酵各种蛋白酶的活性显著提高。混菌发酵将大多数大于10个氨基酸组成的多肽降解为1~3个氨基酸组成的小肽,降解效果明显优于单菌发酵。两菌株具有很好的"协同性",可充分利用棉粕基质,协同改良棉粕蛋白。     

Use of a fluorescent viability stain to assess lethal and sublethal injury in food-borne bacteria exposed to high-intensity pulsed electric fields

AIMS: To apply scanning electron microscopy, image analysis and a fluorescent viability stain to assess lethal and sublethal in food-borne bacteria exposed to high-intensity pulsed electric fields (PEF). METHODS AND RESULTS: A rapid cellular staining method using the fluorescent redox probes 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) and 4',6-diamidino-2-phylindole was used for enumerating actively respiring cells of Listeria mononcytogenes, Bacillus cereus and Escherichia coli. This respiratory staining (RS) approach provided good agreement with the conventional plate count agar method for enumerating untreated and high-intensity PEF-treated bacteria suspended in 0.1% (w/v) peptone water. However, test organisms subjected to similar levels of lethality by heating at 56 degrees C resulted in ca 3-log-unit difference in surviving cell numbers ml(-1) when enumerated by these different viability indicators. PEF-treated bacteria were markedly altered at the cellular level when examined by scanning electron microscopy. CONCLUSIONS: While PEF-treatment did not produce sublethally injured cells (P < 0.05), substantial subpopulations of test bacteria rendered incapable of forming colonies by heating may remain metabolically active. SIGNIFICANCE AND IMPACT OF THE STUDY: The fluorescent staining method offers interesting perspectives on assessing established and novel microbial inactivation methods. Use of this approach may also provide a better understanding of the mechanisms involved in microbial inactivation induced by PEF.     

Effect of cell density and attachment on resuscitation in soil of starved Pseudomonas fluorescens MON787

The effect of cell density and attachment on starvation survival and recovery was determined using luminometry to measure activity of a lux -marked strain of Pseudomonas fluorescens MON787. Bioluminescence was found to be a sensitive indicator of in situ activity of P. fluorescens MON787 in soil. The activity of a bacterial inoculum could be monitored during growth in soil, and was found to correlate with an increase in cell numbers. Luminescence could detect decreasing activity of P. fluorescens during starvation in soil, and recovery of activity and cell numbers following exposure to starvation and matric potential stress. The effect of localised cell density and attachment in soil on recovery from lag phase after nutrient addition was investigated and compared to recovery of starved liquid cultures. Nutrient addition to starved P. fluorescens in soil or liquid medium resulted in an immediate recovery of activity, followed by a second increase in luminescence after 5 h. Cells exposed to both starvation and matric potential stress in soil did not show a detectable immediate increase of activity, but required a 5-h lag phase before recovery of both activity and cell growth. The lag phase values were not significantly different over a range of localised cell densities. This suggests that cell density of P. fluorescens in the range tested is not a factor which affects recovery of soil bacteria from starvation.     

Magnetic fields alter electrical properties of solutions and their physiological effects

Calcium chloride and snail physiological salt solutions were exposed to static magnetic fields (2.3–350 mT), and the physical properties of the solutions as well as their biologic effects were studied. Our preliminary observations show that these fields alter physicochemical properties of CaCl₂ solutions and the functional effects of physiological solutions. Experiments on CaCl₂ solutions demonstrated field-dependent changes of electrical conductivity, with the magnitude and the direction of conductivity change being a function of both concentration and field intensity. The changes in conductivity were maintained for periods in excess of 1 h after exposure. Conductivity changes were not found after exposure of physiological solutions to static magnetic fields, but changes of biological consequence did occur. Other experiments showed that there were several changes in cellular function observed in ganglia and isolated neurons of Helix pomatia when the perfusing medium was changed from the normal physiologic solution to the same solution after exposure to magnetic fields. These changes include membrane depolarization and increased action potential discharge, reduced uptake of Ca into cells, altered content of cyclic nucleotides in ganglia, and increased volume of isolated cell bodies. A change in hydration of calcium ions may be one of the consequences of magnetic-field exposure, and in physiological solutions this change may have functional consequences. © 1994 Wiley-Liss, Inc.     

Effect of incubation in natural and autoclaved soil upon potency and viability of Bacillus thuringiensis

Spores and parasporal crystals of a Bacillus thuringiensis var. aizawai H-serotype 7, strain HD137, streptomycin-resistant mutant, were added to normal and autoclaved aliquots of pH 5 soil incubated at 25°C and ?0.10 MPa water availability. Viable B. thuringiensis in soil samples were estimated by dilution-plating on a streptomycin-based medium, and combined spore and crystal insecticidal activity was bioassayed with larvae of Galleria mellonella. Populations of B. thuringiensis in both soil treatments suffered exponential rates of mortality, which were represented by segmented linear regression. Mortality was far greater in natural than autoclaved soil. Potency also fell in both soil treatments. This loss of potency was greater in natural soil, although the rates of potency loss in either soil treatment correlated poorly with the respective mortality rates of the B. thuringiensis populations, as potency losses were not exponential functions. The results suggest that the presence of indigenous microorganisms in natural soil accelerated the rate of mortality and loss of potency of B. thuringiensis.     

Effects of electroconductive heat treatment and electrical pretreatment on thermal death kinetics of selected microorganisms

Suspensions of yeast cell (zygo Saccharomyces bailii) in a phosphate buffer solution were subjected to conventional (hot water) and ohmic (electric current) heating under identical temperature histories. Experiments were also conducted with cells of Escherichia coli to compare the lethal effect of combination of sublethal electrical preteatment and conventional heating with conventional heating. The kinetic parameters (D,Z,K and E(a)) were determined for both organisms during different treatments. There was no significant difference in the death rate of yeast cells during conventional and ohmic heating at the voltage range used in this study. Results of electrical pretreatment and conventional heating on E. coli indicated differences under certain conditions when compared with pure conventional heating. Thus it is concluded that microbial death during ohmic heating was due primarily to thermal effects with no significant effect of electric current per se. Sublethal electrical pretreatment appears to offer potential for increased bacterial inactivation in certain cases.     

Effect of ammonia on the growth of Bacillus species and some other bacteria

The tolerance of 26 Bacillus species isolated from alkaline fermented foods, five other bacilli and nine non spore-forming bacteria to alkaline pH and ammonia was determined. All grew at pH 7, 8 and 9 in the presence of 930 mmol l-1 NH4 + at pH 7.0, and in the presence of NH3 concentrations up to 5 mmol l-1 at pH 7.0 and 8.0. At higher NH3 concentrations, growth of some of the bacteria was inhibited and at 500 mmol l-1 only B. pasteurii and B. pumilus grew. Bacteria from alkaline food fermentations included strains relatively sensitive to NH3 (inhibited by 50 mmol l-1) and relatively tolerant strains (grew in the presence of 300 mmol l-1) and there was no evidence that they were more tolerant to NH3 than bacteria not associated with these fermentations.     

Effect of electrical fields and external ionic currents on pollen-tube orientation

Summary Agapanthus umbelatus pollen tubes (PTs) display a number of different growth patterns when germinated in an electric field of 750 mV· mm^–1. When pollen is germinated near the cathode (82.44% of orientation to the cathode side) or near the anode (55.35% of orientation to the anode), growth is oriented parallel to the applied field but when germinated at an intermediate position, there is random growth. An increase and decrease in the orientation rates as well as reversion of the polarized growth were observed when the growth conditions were systematically altered. These findings reflect the influence of different ionic currents present in the germination medium. These ionic currents induce the formation of ionic gradients, which were monitored by ion-HPLC. The individual omission of Ca²⁺, K⁺, Mg²⁺ and Cl^– suppresses or alters the oriented growth pattern. The presence of ionic gradients is not by itself suficient to trigger the polarization of tube growth as the presence of an electric field which drives the ionic currents is essential for this to occur.Abbreviations PT Pollen tube - DNS 3,5-dinitro salycilic acid; - TP transient polarization - HPLC high precision liquid chroma tography - DC direct current     

Quantitative Analysis of Polymyxin B Released from Polymyxin B-Treated Dormant Spores of Bacillus subtilis and Relationship between Its Permeability and Inhibitory Effect on Outgrowth

Polymyxin B, one of the cyclic polypeptide antibiotics, binds to the coat of Bacillus subtilis dormant spores and inhibits them from growing after germination. When about 2.8 × 10⁸ cells/ml of polymyxin B-treated dormant spores were incubated in heart infusion broth, 3.6 μg/ml of polymyxin B were released into the liquid medium during germination. Incubation of the same concentration of polymyxin B-treated ones in 100 mM CaCl₂ solution released 4.0 μg/ml of the antibiotic. The effect of various concentrations of polymyxin B on germination, outgrowth and vegetative growth of the dormant spores was investigated; the results showed that concentrations of 4.0 μg/ml and higher of the antibiotic inhibited their outgrowth and vegetative growth after germination. Young vegetative cells were less sensitive to the antibiotic than germinated spores. In addition to these results, immunoelectron microscopy with colloidal gold particles indicated that polymyxin B permeated into the core of the germinated spores and inhibited them from outgrowing.     

Conjugal transfer of plasmid pAMβ1 from Streptococcus lactis and Bacillus subtilis to Clostridium acetobutylicum

Abstract A filter mating procedure has been used to transfer the plasmid pAMβ;1 from Streptococcus lactis to Clostridium acetobutylicum at high efficiency. Once established in this latter host the plasmid can be transferred, with lower efficiency to other strains of C. acetobutylicum or back to S. lactis . A procedure has also been developed for the co-cultivation of Bacillus subtilis and C. acetobutylicum and the transfer of pAMβ;1 between these organisms has been demonstrated.     

肠道共生细菌预发酵鸡粪对黑水虻生长发育的影响

以利用黑水虻Hermetia illucens L.肠道共生细菌不同菌株培养液预发酵的鸡粪为培养料,研究了添加不同菌株的发酵鸡粪对黑水虻幼虫生长发育的影响。结果表明,添加不同菌株的预发酵鸡粪能显著增加预蛹和蛹的重量,显著提高化蛹率并增加雌、雄成虫体长,缩短预蛹所需时间,但对幼虫存活率、成虫羽化率、成虫寿命没有显著影响。同时,不同菌株的作用效果有所不同。     

The effects of human tear electrolytes on the viability and hydrogel colonization of Pseudomonas aeruginosa and Staphylococcus aureus

This study was designed to evaluate the effects of the inorganic electrolytes present in human tear film on the viability and colonization of bacteria to hydrogels. Pseudomonas aeruginosa and Staphylococcus aureus were used in these experiments. A D-value test was performed to investigate any bacteriostatic effect by measuring the reduction of viable test microorganisms over time when exposed to the inorganic electrolyte solution. No D-value was calculable for S. aureus in electrolyte solution whereas a D-value of 8.1 h was obtained for P. aeruginosa in electrolyte solution. The D-value data indicate that staphylococci have a greater survivability potential in a hypertonic environment than do pseudomonads. Bacterial adhesion to high water, ionic hydrogels was studied using the Modified Robbins Device (MRD). The data for P. aeruginosa recovered from the lenses showed an 82% decrease in bacterial counts in electrolyte solution as compared to bacteria incubated in control solution. In contrast there were slight increases in S. aureus counts recovered from the lenses. Journal of Industrial Microbiology & Biotechnology (2000) 25, 17–19. Received 12 August 1999/ Accepted in revised form 05 January 2000     

Effect of hypophysectomy on estrogen conjugation and on plasma and tissue concentrations of tritium after administration of 3H-estradiol-17beta.

Estradiol-17beta-6,7-3H was injected into ovariectomized (control) and ovariectomized, hypophysectomized (hypox) rats in order to study the binding of estradiol in the brain. Hypophysectomy resulted in a significant increase in the concentration of tritium in the hypothalamus, and preoptic area, as well as cortex, muscle, plasma and liver. However, since the liver was lighter in hypox rats, the total tritium content in the liver was unchanged from controls. Part of the weight reduction in the liver was due to a loss of stainable glycogen, which took place within 24 hours of hypox. The increase in circulating tritiated estradiol after hypox led us to investigate hepatic metabolism of estradiol. In vitro studies on liver slices from control and hypox rats demonstrated a significant reduction in the formation of conjugates of estrogen. Specifically, estradiol glucuronide and estrone sulfate formation were reduced in hypox rats and conversely the unmetabolized estradiol concentration was higher. Hypophysectomy for 24 hours results in a significant decrease in hepatic metabolism of estradiol-17beta.