Genome-wide experimental determination of barriers to horizontal gene transfer

Horizontal gene transfer, in which genetic material is transferred from the genome of one organism to that of another, has been investigated in microbial species mainly through computational sequence analyses. To address the lack of experimental data, we studied the attempted movement of 246,045 genes from 79 prokaryotic genomes into Escherichia coli and identified genes that consistently fail to transfer. We studied the mechanisms underlying transfer inhibition by placing coding regions from different species under the control of inducible promoters. Our data suggest that toxicity to the host inhibited transfer regardless of the species of origin and that increased gene dosage and associated increased expression may be a predominant cause for transfer failure. Although these experimental studies examined transfer solely into E. coli, a computational analysis of gene-transfer rates across available bacterial and archaeal genomes supports that the barriers observed in our study are general across the tree of life.     

Design and use of an automatic humidity chamber in phytopathological research

Inexpensive humidity chambers, equipped with spore traps, were designed for the study of various ecological phenomena. The basic apparatus enables cycling conditions of any desired humidity with a period of high humidity with or without leaf wetness; and two conditions of air movement through the chamber, each of them chosen in the range of 0 to 14 1/min. The chamber’s performance was tested withUromyces phaseoli on beans in relation to (a) the duration of leaf wetness needed for infection, (b) the effect of relative humidity on the appearance of sori. and (c) the amount of sori and the number of uredospores produced. Iiberated and trapped under various conditions of relative humidity.     

Effect of wetting duration,and of other environmental factors,on the development ofStemphylium botryosum f. sp.lycopersici in tomatoes

In experiments on artificial inoculation of tomato leaves byStemphylium botryosum f. sp.lycopersici, infection was found to be relatively insensitive to temperature between 15° and the 25°C optimum. Wetting duration had a greater effect on infection than either temperature or spore load, and also influenced the extent of the effect of the two latter factors. The optimum temperature for leaf colonization was found to be 25°C; it was more sharply defined under constant temperature than when alternating with a night temperature of 10°C. At 39°C, colonization was inhibited only by exposure longer than 12 h. The results are used to explain the seasonal pattern of the blight in Israel.     

Effect of light on sporulation ofalternaria porri f. sp.solani and ofstemphylium botr yosum f. sp.lycopersici in vivo

The highest spore production ofStemphylium botryosum f. sp.lycopersici on tomato leaves during a 24-h wetting period occurred in continuous darkness, and ofAlternaria porri f. sp.solani on potato leaves in a 12-h dark period which had been preceded by a 12-h light period. Sporulation of both pathogens was inhibited by illumination during the entire wetting period or during the last 12 h of it. In inhibitory conditions spore yield increased with a decrease in the incubation temperature and as tested withA. porri f. sp. solani, also with lowered light intensity.     

Inhibition of shedding of pepper leaves infected with powdery mildew (Leveillula taurica) by application of auxins

In greenhouse and field experiments, shedding of pepper leaves infected withLeveillula taurica was inhibited by treatments with indole acetic acid or butyric acid. Spraying with MnSO₄ increased shedding in greenhouse trials.     

In vitro study of the ilial anatomic landmarks for safe implant insertion in the first sacral vertebra of the intact canine sacroiliac joint

OBJECTIVE: To define landmarks on the canine ilial wing for accurate, consistent insertion of implants into the 1st sacral (S1) vertebral body when the sacroiliac joint is intact. STUDY DESIGN: Anatomic study. ANIMALS: Intact, cadaveric canine pelves and sacra (n=25). METHODS: Median sections (5 specimens) were drilled from the center of S1 in a lateral direction, exiting on the ilial wing. Landmarks on the ilial wing and shaft used to define this exit point were then used to locate this point on both wings of 20 articulated specimens, positioned and rigidly held so that the dorsal plane of the pelvis was aligned with a plumb line and the median plane of the pelvis was horizontal. A 2 mm hole was drilled from the marked point, parallel to the plumb line, until it exited the contralateral ilial wing. Distance of drill hole position from the geometric center (GC) of S1 was located on median and paramedian plane images derived from plane, computed tomographic (CT) scans. RESULTS: The entire drill hole was located within S1 in 18 specimens. Mean deviation of the hole from GC (ratio of the distance of GC from the closest S1 body border) in median section was 0.40 +/- 0.29 (craniocaudal direction) and 0.29 +/- 0.23 (dorsoventral). CONCLUSIONS: Use of ilial wing landmarks and drilling perpendicular to the median plane will improve accuracy for insertion of implants into S1 when the sacroiliac joint is intact. CLINICAL RELEVANCE: Ilial wing landmarks should be used to improve accuracy of implant insertion into S1.     

Scale-dependent correlates of reptile communities in natural patches within a fragmented agroecosystem

Landscape Ecology - Studying biodiversity in light of increased fragmentation in agroecosystems requires the understanding of scale-dependent and multi-scale determinants of various community...     

Epidemiological limitations to the forecasting of downy mildews and late blight in Israel

Agricultural practices such as irrigation and year-round cultivation of crops, render semi-arid areas much more suitable for development of downy mildews and late blight than might be supposed by weather criteria alone. These diseases can develop even under not very favorable humidity conditions, owing to a favorable microclimate and to abundant pathogen reproduction. However, the complex interrelations and shifting significance to be attributed to factors affecting disease development, make their regional forecasting in semi-arid areas impracticable. This is due to the absence of a clear-cut “zero-time” for the beginning of the disease development, the limited significance of the temperature factor, the unpredictable occurrence of hot and dry spells, the characteristics of short, intense subtropical rainfall, and the dominance of microclimatic factors. On the other hand, timing of control operations can be aided by regional determination of disease-free periods in crops sown in different seasons and by prediction of the length of such periods in individual fields according to their age and density, irrigation regime, and proximity to sources of inoculum.     

Overwintering of alternaria macrospora in Cotton Debris

An epidemic ofAlternaria macrospore in cotton started 1 month earlier, and developed faster in plots contaminated withA. macrospora-infected cotton debris than in debris-free plots. Overwintering of the pathogen in debris was associated with survival of the debris itself. With the exception of debris in dry soil, overwintering was better in debris located on the soil surface than in that buried beneath the surface. Under all conditions it was better in dry than in wet soil and in sterilized than in unsterilized soil. Survival was associated with micTobial activity in the soil, was highest in pure sand and decreased progressively in sandy loam, heavy soil and peat. The survival in debris was highest in soil kept at 10°C and decreased progressively at 20, 30 and 40°C. Increasing the soil moisture content reduced survival. Overwintering was better in a cotton field that was not cropped during the winter than in a field sown with wheat between the cotton seasons. The rate of transfer of disease to seedlings from debris buried in soil was low except when debris was in contact with the seed. The main means of disease transfer was by airborne spores produced on debris located on the soil surface. These spores had low infectivity and caused few lesions, but the second generation of spores formed on these lesions was highly infectious.