Mechanism of lethal action of 2,450-MHz radiation on microorganisms.

Various bacteria, actinomycetes, fungi, and bacteriophages were exposed to microwaves of 2,450 +/- 20 MHz in the presence and in the absence of water. It was found that microorganisms were inactivated only when in the presence of water and that dry or lyophilized organisms were not affected even by extended exposures. The data presented here prove that microorganisms are killed by "thermal effect" only and that, most likely, there is no "nonthermal effect"; cell constituents other than water do not absorb sufficient energy to kill microbial cells.     

Mechanism of lethal action of 2,450-MHz radiation on microorganisms.

Various bacteria, actinomycetes, fungi, and bacteriophages were exposed to microwaves of 2,450 +/- 20 MHz in the presence and in the absence of water. It was found that microorganisms were inactivated only when in the presence of water and that dry or lyophilized organisms were not affected even by extended exposures. The data presented here prove that microorganisms are killed by "thermal effect" only and that, most likely, there is no "nonthermal effect"; cell constituents other than water do not absorb sufficient energy to kill microbial cells.     

Growth of phenol-mineralizing microorganisms in fresh water.

A method was developed to enumerate the procaryotic and eucaryotic phenol-mineralizing microorganisms present in samples of fresh water. Sixty-five percent or greater mineralization of [U-14C]phenol was considered a positive tube (contained phenol-mineralizing microorganisms) in the most-probable-number technique. Replicate most-probable-number tubes contained no microbial inhibitors, streptomycin and tetracycline, or cyclohexamide and nystatin plus 200 pg to 100 micrograms of phenol per ml. Phenol mineralization rates were obtained by measuring the amount of exogenous phenol that disappeared from solution over time in the presence or absence of the microbial inhibitors. Initially, less than 100 phenol-mineralizing bacteria per ml and 1 phenol-mineralizing fungus per ml were present at both 200 pg and 100 micrograms of phenol per ml. Phenol mineralization rates were 6.3 times greater for the mineralizing bacteria than for the fungi at 200 pg of phenol per ml. Phenol concentrations above 10 micrograms/ml were inhibitory to the microorganisms capable of mineralizing phenol. The phenol mineralizers grew in the water samples in the absence of phenol, indicating that there were sufficient indigenous nutrients in the lake water to support growth. There was no difference in the growth rate of these microorganisms in the presence or absence of 1 ng of phenol per ml, whereas the growth rate was more rapid at 1 microgram of phenol per ml than in its absence. There was a correlation between microbial growth and the amount of phenol mineralized at 1 microgram but not at 1 ng of phenol per ml.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of alternate partial root-zone irrigation on soil microorganism and maize growth

Partial root-zone irrigation creates a dynamic heterogeneous distribution of soil moisture that may affect the numbers and activities of soil microorganisms. In this study, three irrigation methods, i.e. conventional irrigation (CI), alternate partial root-zone irrigation (APRI, alternate watering on both sides of the pot) and fixed partial root-zone irrigation (FPRI, fixed watering on one side of the pot), and three watering levels, i.e. well-watered, mild and severe water deficit, were applied on pot-grown maize. Numbers of soil microorganisms, plant height, stalk diameter, leaf area and biomass accumulation were monitored over the treatment period. A quadratic parabola relationship between the number of soil microorganisms and soil water content was found, indicating the number of soil microorganisms reached a peak at the mild soil water deficit condition, possibly due to better soil aeration. The peak number of soil microorganism was obtained when soil water content was 66, 79 and 75% of field capacity for CI, FPRI and APRI, respectively. Soil microorganisms were evenly distributed in both sides of APRI and their total numbers were always higher than those under other two irrigation methods for the same soil water content. The count of soil microorganisms in the dry root zone of FPRI was reduced by a lack of water. Maximum biomass accumulation was obtained under well watered condition but severe water deficit led to a 50% reduction in the CI treatment. Such reduction was much smaller under APRI and therefore the highest water use efficiency was obtained. Our results suggest that APRI maintained the best aeration and moisture condition in the soil and enhanced the activities of soil microorganisms, which might also have benefited the plant growth.     

Effects of combined shear and thermal forces on destruction of Microbacterium lacticum.

A twin-screw extruder and a rotational rheometer were used to generate shear forces in concentrated gelatin inoculated with a heat-resistant isolate of a vegetative bacterial species, Microbacterium lacticum. Shear forces in the extruder were mainly controlled by varying the water feed rate. The water content of the extrudates changed between 19 and 45% (wet weight basis). Higher shear forces generated at low water contents and the calculated die wall shear stress correlated strongly with bacterial destruction. No surviving microorganisms could be detected at the highest wall shear stress of 409 kPa, giving log reduction of 5.3 (minimum detection level, 2 x 10(4) CFU/sample). The mean residence time of the microorganism in the extruder was 49 to 58 s, and the maximum temperature measured in the end of the die was 73 degrees C. The D(75 degrees C) of the microorganism in gelatin at 65% water content was 20 min. It is concluded that the physical forces generated in the reverse screw element and the extruder die rather than heat played a major part in cell destruction. In a rotational rheometer, after shearing of a mix of microorganisms with gelatin at 65% (wt/wt) moisture content for 4 min at a shear stress of 2.8 kPa and a temperature of 75 degrees C, the number of surviving microorganisms in the sheared sample was 5.2 x 10(6) CFU/g of sample compared with 1.4 x 10(8) CFU/g of sample in the nonsheared control. The relative effectiveness of physical forces in the killing of bacteria and destruction of starch granules is discussed.     

Reactions of fish to microorganisms in wastewater.

Fish were inoculated with various microorganisms present in wastewater. A threshold concentration was determined over which these microorganisms were recovered from the muscles. The threshold concentrations were different for bacteria, bacteriophages, and polio 1 LSc virus. The threshold values were lower when fish were inoculated than when they were immersed in water containing these organisms. Depuration experiments were efficient when the fish did not contain high concentrations of bacteria in their muscles. As the threshold concentrations are an expression of the capability of the immune system of the fish, these values can be useful for the design and management of fishponds in which treated wastewater is used.     

Clostridium perfringens and somatic coliphages as indicators of the efficiency of drinking water treatment for viruses and protozoan cysts.

To find the most suitable indicator of viral and parasitic contamination of drinking water, large-volume samples were collected and analyzed for the presence of pathogens (cultivable human enteric viruses, Giardia lamblia cysts, and Cryptosporidium oocysts) and potential indicators (somatic and male-specific coliphages, Clostridium perfringens). The samples were obtained from three water treatment plants by using conventional or better treatments (ozonation, biological filtration). All samples of river water contained the microorganisms sought, and only C. perfringens counts were correlated with human enteric viruses, cysts, or oocysts. For settled and filtered water samples, all indicators were statistically correlated with human enteric viruses but not with cysts or oocysts. By using multiple regression, the somatic coliphage counts were the only explanatory variable for the human enteric virus counts in settled water, while in filtered water samples it was C. perfringens counts. Finished water samples of 1,000 liters each were free of all microorganisms, except for a single sample that contained low levels of cysts and oocysts of undetermined viability. Three of nine finished water samples of 20,000 liters each revealed residual levels of somatic coliphages at 0.03, 0.10, and 0.26 per 100 liters. Measured virus removal was more than 4 to 5 log10, and cyst removal was more than 4 log10. Coliphage and C. perfringens counts suggested that the total removal and inactivation was more than 7 log10 viable microorganisms. C. perfringens counts appear to be the most suitable indicator for the inactivation and removal of viruses in drinking water treatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Destruction of coliforms in water and sewage water by dye-sensitized photooxidation.

A new approach to disinfection of water and sewage water, by oxidative destruction of microorganisms by photosensitization, is described. Samples of water and sewage water, to which an inoculum of fecal Escherichia coli had been added, were exposed to solar radiation in the presence of a dye sensitizer, under continuous aeration. The effects of the sensitizer methylene blue at concentrations of 0 to 10 mg/liter, different radiation times from 0 to 2 h, and sunlight intensities of 0, 68, and 2,030 muE/m2 per s were investigated. In laboratory-scale experiments, 1.3 X 10(9) coliforms in 100 ml of oxidation pond municipal sewage water containing 0.5 mg of methylene blue were destroyed in about 30 min. Similar results were obtained with nonchlorinated potable water. These results demonstrate the possibilities available for the disinfection of water and sewage water by this method.     

Modeling of microorganisms transport in a cylindrical pore

A mathematical model accounting for key parameters as microbial propagation, metabolite formation, dispersion, microbial chemotaxis and water flooding has been proposed to simulate the transport of microorganisms and their metabolites in a cylindrical pore with oil adhered to its inside surface. The model focuses on the transport and the concentration distributions of microorganisms and their metabolites in the cylindrical pore, especially the concentrations that on the oil-water interface. Results from the present model indicate that microorganisms and their metabolites assembled on the oil-water interface during the water flooding process, and the concentration gradients of microorganisms and their metabolites from the pore center region up to the oil-water interface in radial direction of the cylindrical pore were consequently formed. Equilibrium concentrations of microorganisms and their metabolites in the cylindrical pore were obtained when water flow rate within a certain scope, and there existed a critical water flow rate at which the maximum equilibrium concentration of microorganisms on the oil-water interface was developed. Investigations carried out in this study may provide better understanding on the transport mechanism of microorganisms in porous media.     

Fountain Flow cytometry, a new technique for the rapid detection and enumeration of microorganisms in aqueous samples.

BACKGROUND: Pathogenic microorganisms are known to cause widespread waterborne disease worldwide. There is an urgent need to develop a technique for the real-time detection of pathogens in environmental samples at low concentrations, <10 microorganisms/ml, in large sample volumes, > or =100 ml. METHODS: A novel method, Fountain Flowtrade mark cytometry, for the rapid and sensitive detection of individual microorganisms in aqueous samples is presented. Each sample is first incubated with a fluorescent label and then passed as a stream in front of a laser, which excites the label. The fluorescence is detected with a CCD imager as the sample flows toward the imager along its optical axis. The feasibility of Fountain Flow cytometry (FFC) is demonstrated by the detection of Escherichia coli labeled with ChemChrome CV6 and SYBR Gold in buffer and natural river water. RESULTS: Detections of labeled E. coli were made in aqueous suspensions with an efficiency of 96% +/- 14% down to a concentration approximately 200 bacteria/ml. CONCLUSIONS: The feasibility of FFC is demonstrated by the detection of E. coli in buffer and natural river water. FFC should apply to the detection of a wide range of pathogenic microorganisms including amoebae.     

Destruction of coliforms in water and sewage water by dye-sensitized photooxidation.

A new approach to disinfection of water and sewage water, by oxidative destruction of microorganisms by photosensitization, is described. Samples of water and sewage water, to which an inoculum of fecal Escherichia coli had been added, were exposed to solar radiation in the presence of a dye sensitizer, under continuous aeration. The effects of the sensitizer methylene blue at concentrations of 0 to 10 mg/liter, different radiation times from 0 to 2 h, and sunlight intensities of 0, 68, and 2,030 muE/m2 per s were investigated. In laboratory-scale experiments, 1.3 X 10(9) coliforms in 100 ml of oxidation pond municipal sewage water containing 0.5 mg of methylene blue were destroyed in about 30 min. Similar results were obtained with nonchlorinated potable water. These results demonstrate the possibilities available for the disinfection of water and sewage water by this method.     

Mechanism of inactivation of enteric viruses in fresh water.

Fresh water obtained from nine sources was shown to cause inactivation of poliovirus. Further testing with four of these water samples showed that enteric viruses from different genera were consistently inactivated in these freshwater samples. Studies on the cause of inactivation were conducted with echovirus type 12 as the model virus. The results revealed that the virucidal agents in the waters tested could not be separated from microorganisms. Any treatment that removed or inactivated microorganisms caused loss of virucidal activity. Microbial growth in a sterilized creek water seeded with a small amount of stream water resulted in concomitant production of virucidal activity. When individual bacterial isolates obtained from a stream were grown in this sterilized creek water, most (22 of 27) produced a large amount of virucidal activity, although the amount varied from one isolate to the next. Active and inactive isolates were represented by both gram-positive and gram-negative organisms. Examination of echoviruses inactivated in stream water revealed that loss of infectivity first correlated with a slight decrease in the sedimentation coefficient of virus particles. The cause appeared to be cleavage of viral proteins, most notably, VP-4 and, to a lesser extent, VP-1. Viral RNA associated with particles was also cleaved but the rate was slower than loss of infectivity. These results suggest that proteolytic bacterial enzymes inactivate echovirus particles in fresh water by cleavage of viral proteins, thus exposing the viral RNA to nuclease digestion.     

Microbial degradation of xenobiotic, aromatic pollutants in humic water.

The microbial degradation of a number of 14C-labeled, recalcitrant, aromatic pollutants, including trichloroguaiacol and di-, tri-, and pentachlorophenol, was investigated in aquatic model systems in the laboratory. Natural, mixed cultures of microorganisms in the water from a brown-water lake with a high content of humic compounds mineralized all of the tested substances to a higher degree than did microorganisms in the water from a clear-water lake. Dichlorophenol was the most rapidly degraded pollutant.     

Microbiologic problems associated with closed process water systems in the paper industry

Summary Process water from the entirely closed water system of a wastepaper reprocessing mill was examined for its content of different groups of microorganisms. Comparison with waste-paper reprocessing mills with nonclosed systems and concomitant higher specific water consumption showed that system closing is associated with a marked increase in the number of anaerobic microorganisms; Bifidobacteria were found to be the most frequently represented bacteria.The development of the microflora in the entirely closed water system was studied after total replacement of the process water with fresh water. Constant levels of anaerobic microorganisms were recorded after a lag period of 15 days. Gas chromatographic analyses showed that the process water from the entirely closed system contains significant amounts of metabolic products of anaerobic microorganisms.     

Unexpected thermal destruction of dried,glass bead-immobilized microorganisms as a function of water activity

To help us understand the factors and mechanisms implicated in the death of microorganisms or their resistance to temperature in a low water activity environment, microorganisms were dried on the surface of glass beads before being subjected to high temperatures for a short period followed by rapid cooling. Two microorganisms were studied: the yeast Saccharomyces cerevisiae and the bacterium Lactobacillus plantarum. Experiments were carried out at 150, 200, and 250 degrees C, with four durations of heat treatment and seven levels of initial water activity between 0.10 and 0.70. We observed an unexpected range of water activity, between 0.30 and 0.50, at which microorganisms were more resistant to the various treatments, with maximal viability at 0.35 for L. plantarum and 0.40 for S. cerevisiae.     

Detection of Legionella species in reclaimed water and air with the EnviroAmp Legionella PCR kit and direct fluorescent antibody staining.

Reclaimed water is an important resource for areas with inadequate water supplies. However, there have been few studies on the variety of microorganisms found in this type of water, since typically reclaimed water is examined only for the presence of coliform bacteria. Many microorganisms, including the legionellae, are known to be more resistant to chlorine than are coliform bacteria. Previously, we detected > 10(3) Legionella cells per ml in primary and secondary sewage effluents and observed no significant reduction in population numbers throughout the treatment process. In this study, we detected Legionella spp. in chlorinated effluent by using an EnviroAmp Legionella PCR kit and direct fluorescent antibody (DFA) staining. However, we were not able to isolate Legionella spp. from either natural or seeded reclaimed water samples. This suggests that the Legionella spp. detected by the PCR and DFA methods may be injured or viable but nonculturable after exposure to the high residual chlorine levels typically found in this type of water source. The numbers of coliform bacteria were low (< 2 cells per 100 ml) in most reclaimed water samples and were not correlated with the presence or absence of Legionella spp. We also collected air samples from above a secondary aeration basin and analyzed them by using the PCR, DFA, and plate culture methods. Legionella spp. were detected in the air obtained from above the secondary basin with all three methods. We concluded that the PCR was superior to the culture and DFA methods for detecting Legionella spp. in environmental water samples.     

Using ultrafiltration to concentrate and detect Bacillus anthracis, Bacillus atrophaeus subspecies globigii, and Cryptosporidium parvum in 100-liter water samples

A strategy that uses ultrafiltration (UF) to concentrate microorganisms from water samples has been developed and tested. This strategy was tested using 100-liter water samples with volume reduction achieved through ultrafiltration and recycling the microorganisms of interest through a retentate vessel, rather than returning them to the sample container, where they might pose an incremental hazard to sample takers or the environment. Three protocols based on this strategy were tested. The first protocol entailed sample volume reduction and collection of the final reduced sample. The second and third protocols both incorporated pretreatment of the filter and fluid lines with a solution to prevent microorganisms from adhering. In the second protocol, the filter was back flushed with a surfactant solution to recover microorganisms. The third protocol used recirculation of a surfactant solution to recover microorganisms. Tests were undertaken using 100-liter water samples spiked with approximately 100 or 1000 microorganisms (1 or 10 per liter). Test microorganisms included Bacillus anthracis Sterne strain, Bacillus atrophaeus subsp. globigii, and Cryptosporidium parvum. The first protocol had significantly lower recovery than the other two. Back flushing resulted in higher recovery than forward flushing, but the difference was not statistically significant.     

Allomonas--a new group of microorganisms of the Vibrionaceae family. Allomonas enterica in seawater and various hydrobiotas

Bacteriological investigations made in the Black Sea, the Sea of Azov and the Sea of Japan have revealed that Allomonas enterica are widely spread in sea water and hydrobionts. The prevalence of these microorganisms in biotopes with unfavorable sanitary characteristics and their high correlation with the main indicator microorganisms suggest their importance as indicators, and a high percentage of seafood contaminated with Allomonas necessitates their study as possible causative agents of toxinfections.     

Hydrocarbon-oxidizing microorganisms in the waters of certain regions of the Western and Central Atlantic

The incidence of hydrocarbon-oxidizing microorganisms in water was determined by the method of plating on solid media. Vertical distribution of hydrocarbon-oxidizing microflora was different near the shore and in the open ocean; the incidence of the microorganisms was low in the surface water layer but increased at depths of 25 and 75 m in the open ocean in contrast to regions near the shore. Pure bacterial and fungal cultures were isolated and their properties were described. The cultures were grown in a liquid mineral medium with diesel fuel and 50 cultures out of 66 were found to be true hydrocarbon-oxidizing microorganisms surviving under the laboratory conditions. It was shown that bacteria and fungi have grown on tarballs collected from the surface of the ocean during their incubation at 30 degrees C.     

塔克拉玛干沙漠腹地人工绿地土壤中微生物的生态分布及其与土壤因子间的关系

对咸水灌溉条件下的塔克拉玛干沙漠腹地人工绿地土壤微生物的分布规律和环境因子对土壤微生物分布的影响进行了研究．结果表明,人工绿地建成后,土壤结构和养分状况得到改善,土壤微生物在时间和地域分布上呈现明显的规律性．土壤微生物区系组成中,细菌占绝对优势,放线菌次之,真菌最少;表层微生物数量远多于下层土壤;林地外围距林缘近的土壤微生物数量较多,3m以外微生物数量已接近流沙微生物量;3类土壤微生物分布具有不同的季节性规律,且不同立地类型土壤微生物分布差异显著．土壤速效磷、速效氮、全N对微生物的分布有较大的直接作用,通径系数为1．01～2．58．速效磷-速效钾、有机质-速效钾、速效氮-速效钾、速效氮-效磷速、有机质-速效磷、速效磷-速效氮、全N-速效钾、速效钾-速效磷、全N-速效磷和含水量．速效氮之间的间接作用对微生物影响较明显,作用系数为1．37～2．58。其余因素的作用相对不显著．