A Safe Method of Exposing Microthreads in the Open Air

A safe method for exposing pathogenic organisms held on microthreads to realistic environmental conditions is described. The apparatus consists of an air duct in which the organisms on microthreads are exposed, and contiguous to it a safety cabinet, air from both systems being continuously extracted into high efficiency aerosol filters.     

A Comparison of Various Selective Isolation Media for their Efficiency in the Diagnosis and Enumeration of Soft Rot Coliform Bacteria

The efficiency of various selective isolation media for diagnosis and enumeration of Erwinia carotovora var. atroseptica is described. In both pure culture and mixed population studies the medium of choice is that of Cuppels and Kelman's modified by the addition of manganous sulphate. Difficulties in the preparation of this pectate medium have been overcome by including an antifoam agent.     

Soft Rot Erwinia Bacteria in the Atmospheric Bacterial Aerosol

Using a Casella High Volume Airborne Bacteria Sampler, the soft rot coliform bacteria Erwinia carotovora var. carotovora and E. carotovora var. atroseptica were caught from the open air during rainfall in mid to late summer, autumn and early winter, but not in late winter, spring or early summer. They were not found every time it rained, and never when the weather was dry. The bacteria were caught close to potato crops, but there were several occasions when they were found at sites where there were no such crops or at times of year after potato crops had been harvested. The sources of the organisms are uncertain, but those obtained close to potato crops may have originated there. The results are considered to provide further evidence that airborne spread and subsequent deposition of viable bacteria could cause contamination of Erwinia -free potato stocks, and suggest that rainfall is a major generator of the general atmospheric bacterial aerosol.     

The Survival of Erwinia amylovora in Airborne Particles: Tests in the Laboratory and in the Open Air

The causative organism of fire-blight, Erwinia amylovora , survives well when contained in small airborne particles held in the laboratory at relative humidities between 40 and 90 %. Although greater loss of viability occurred when simulated aerosols were exposed to the open air, there were still significant numbers of organisms viable after 2 h.     

Maintenance of Laboratory Strains of Obligately Anaerobic Rumen Bacteria

Cultures of rumen bacteria can be stored at −20°C for at least 2 years in a liquid medium containing 20% glycerol. Thawing, sampling, and refreezing do not significantly affect viability.     

Relative Humidity and the Killing of Bacteria: The Survival of Damp Serratia marcescens in Air

The viability of washed moist cells of Serratia marcescens after storage has been measured in relation to variations in the prior treatment of the cells and in conditions of storage. The factors considered were: (i) water content during storage; (ii) method of arriving at water content (partial drying in vacuum or freeze-drying and addition of water); (iii) presence or absence of air during storage.

Increasingly rapid decay occurs as the water content at which the cells are stored is diminished from above 90% to 20 or 30% (“critical” water content). It occurs in presence or absence of air and it occurs whether the final water content is approached by removal of water from wet cells or by addition of water to freeze-dried cells.

The rate of decay during storage at 20 to 30% water is somewhat diminished by the presence of air (“protective” effect of air).

As the water content is further reduced to less than 10%, the stability of cells stored in a vacuum approaches that of wet cells. In presence of air the reverse is true: the stability decreases until at less than 1% water, the decay rate is about as great as at the “critical” water content (“toxic” effect of air).

Particularly rapid decay of S. marcescens at the “critical” water content has escaped attention in aerosol studies because accurate control of relative humidity (RH) in this region, RH 94 to 99%, is virtually impossible in such studies. On the other hand, values of decay rates referred to measured water contents are quite unreliable in the 20 to 80% RH zone because the corresponding variation of water content is too small to measure reliably. Thus data of the kind reported in this paper cannot be directly compared to the published results of studies of air-borne bacteria, although they are relevant to the practical question of air-borne infection in humid atmospheres.

     

Assessing Climate Variability Impact on Thermotolerant Coliform Bacteria in Surface Water

This study investigated the impacts of climate variability on thermotolerant coliform bacteria (TCB) transport in the Upper Pearl River watershed (UPRW) in Mississippi. The Soil and Water Assessment Tool (SWAT) was applied using daily observed stream flows and TCB concentration data. The SWAT model was successfully calibrated and validated using both manual and automatic methods from February 2011 to June 2012 (NSE and R² up to 0.79). The Long Ashton Research Station Weather Generator (LARS-WG), a stochastic weather generator, with the global climate model, CCSM3, which was developed by the U.S. National Center for Atmospheric Research (NCAR) was used for future climate variability simulations. The Special Report on Emissions Scenarios (SRES) A1B of the Intergovernmental Panel on Climate Change (IPCC) was simulated for the mid (2046–2065) and late (2080–2099) 21st century. The SWAT model simulated TCB concentrations in surface water and demonstrated reasonable performances (R² up to 0.59 and NSE up to 0.58). During mid-century climate, average monthly TCB levels increase to 175%, while late-century average monthly TCB levels increase to 297% from the watershed. Although late-century climate variability impacts were determined more critical than mid-century climate impacts, appropriate watershed management practices are required to adapt to maintain and improve water quality.     

我国马铃薯软腐病防治的研究进展

马铃薯软腐病是马铃薯细菌性病害中最严重的一种,简要介绍了我国马铃薯软腐病的病原菌、病害性状以及对病害的防治方法。利用现代生物技术手段人为地操纵细菌群体感应系统,将会成为提高植物抗病性的新方法、新途径。     

Pectinase Activity of Anaerobic and Facultatively Anaerobic Bacteria Associated with Soft Rot of Yam (Diascorea rotundata)

[This corrects the article on p. 564 in vol. 41.].     

Application of Amplified Fragment Length Polymorphism Fingerprinting for Taxonomy and Identification of the Soft Rot Bacteria Erwinia carotovora and Erwinia chrysanthemi

The soft rot bacteria Erwinia carotovora and Erwinia chrysanthemi are important pathogens of potato and other crops. However, the taxonomy of these pathogens, particularly at subspecies level, is unclear. An investigation using amplified fragment length polymorphism (AFLP) fingerprinting was undertaken to determine the taxonomic relationships within this group based on their genetic relatedness. Following cluster analysis on the similarity matrices derived from the AFLP gels, four clusters (clusters 1 to 4) resulted. Cluster 1 contained Erwinia carotovora subsp. carotovora (subclusters 1a and 1b) and Erwinia carotovora subsp. odorifera (subcluster 1c) strains, while cluster 2 contained Erwinia carotovora subsp. atroseptica (subcluster 2a) and Erwinia carotovora subsp. betavasculorum (subcluster 2b) strains. Clusters 3 and 4 contained Erwinia carotovora subsp. wasabiae and E. chrysanthemi strains, respectively. While E. carotovora subsp. carotovora and E. chrysanthemi showed a high level of molecular diversity (23 to 38% mean similarity), E. carotovora subsp. odorifera, E. carotovora subsp. betavasculorum, E. carotovora subsp. atroseptica, and E. carotovora subsp. wasabiae showed considerably less (56 to 76% mean similarity), which may reflect their limited geographical distributions and/or host ranges. The species- and subspecies-specific banding profiles generated from the AFLPs allowed rapid identification of unknown isolates and the potential for future development of diagnostics. AFLP fingerprinting was also found to be more differentiating than other techniques for typing the soft rot erwinias and was applicable to all strain types, including different serogroups.     

Pectinase Activity of Anaerobic and Facultatively Anaerobic Bacteria Associated with Soft Rot of Yam (Diascorea rotundata)

Anaerobic and facultatively anaerobic bacteria associated with soft rot of yam (Diascorea rotundata) were isolated by the looping-out method and found to consist of Clostridium (three isolates), Corynebacterium (three isolates), Vibrio (one isolate), and Bacillus lentus (one isolate). Enzyme assay for hydrolase, lyase, and pectinesterase activities by the cup-plate method showed that except for Vibrio sp., B. lentus, and two isolates of Corynebacterium no pectinase activity could be detected for organisms cultured on pectin medium. Most of the cultures on yam tissue, however, showed activities for the three enzymes. The viscometric assay for hydrolase and lyase enzymes indicated a significant level of hydrolase activity (a 40.90% decrease in viscosity for Vibrio sp. and Corynebacterium spp.), but no lyase activity for most of the isolates. Two isolates of Corynebacterium and B. lentus caused changes in fresh yams suggestive of soft rot.     

Regulation of the Biosynthesis of Amino Acids of the Aspartate Family in Coliform Bacteria and Pseudomonads

The control of aspartokinase and homoserine dehydrogenase activities was compared in aerobic and fermentative pseudomonads (genera Pseudomonas and Aeromonas), and in coliform bacteria representative of the principal genera of the Enterobacteriaceae. Isofunctional aspartokinases subject to independent end-product control occur in the Enterobacteriaceae and in Aeromonas. In Pseudomonas, there appears to be a single aspartokinase, subject to concerted feedback inhibition by lysine and threonine. Within this genus, the sensitivity of aspartokinase to the single allosteric inhibitors varies considerably: the aspartokinase of the acidovorans group is little affected by the single inhibitors, whereas that of the fluorescent group is severely inhibited by either amino acid at high concentration. In all bacteria examined, homoserine dehydrogenase activity is inhibited by threonine; inhibition is more severe in aerobic pseudomonads than in the other groups. In most of the bacteria examined, either nicotinamide adenine dinucleotide (NAD) or nicotinamide adenine dinucleotide phosphate can serve as a cofactor for this enzyme, though the relative activity with the two pyridine nucleotides varies widely. Aerobic pseudomonads of the acidovorans group contain a homoserine dehydrogenase that is absolutely specific for NAD. The taxonomic implications of these findings are discussed.