Host-Specific Phytotoxic Polysaccharide from Apple Tissue Infected by Erwinia amylovora.

A toxin isolated from apple fruit tissue infected by Erwinia amylovora is 98 percent galactose in polymeric form, 0.375 percent protein, and has an average molecular weight of approximately 165,000. Young shoots of rosaceous, but not nonrosaceous, species wilt in a manner characteristic of the disease when placed in toxin solutions with concentrations as low as 10 micrograms per milliliter. Varieties of apple and pear susceptible to Erwinia amylovora wilt in 1 to 3 hours, whereas resistant varieties display symptoms 12 to 24 hours after treatment.

Conversion of DDT to DDD by pathogenic and saprophytic bacteria associated with plants.

Of 27 microorganisms examined, 23 plant pathogenic and saprophytic bacterial species were found to convert p,p' DDT to p,p' DDD under anaerobic conditions. The range of conversion of DDT (10 micrograms per milliliter) during an incubation of 14 days was from a trace to over 5 micrograms per milliliter, with the majority of the bacteria showing the greatest activity during the final 7-day period. There is evidence that metabolites of DDT other than DDD are also produced.

T-DNA genes responsible for inducing a necrotic response on grape vines.

Agrobacterium tumefaciens supervirulent strain A281 induces a progressive necrotic response, rather than tumor formation, when inoculated on stems of several grape cultivars. The Ti plasmid, and specifically its T-DNA, is required for the process. In the present study, 40 T-DNA insertion mutants of A281 were generated via transposon mutagenesis and tested for their necrosis-inducing ability on grape stems in vitro. Ten mutants were attenuated in inducing necrogenesis. Restriction mapping and DNA sequencing revealed that at least two genes, tms1 and 6b, whose gene products are involved in the synthesis and activity modulation of auxin, are responsible for inducing necrogenesis. Double mutants of tms1 and 6b were totally non-necrogenic. The orientation of grapevine stem explants showed strong effects on the occurrence and progress of necrogenesis. Inoculation of Agrobacterium on physiological basal ends resulted in the greatest degree of necrogenesis. In addition, gene 5 of T-DNA, which modulates auxin responses in plants by the autoregulated synthesis of an auxin antagonist, was found to be separated from other TL-DNA genes by a novel insertion sequence, IS1312. Since a T-DNA borderlike sequence occurs in IS1312, gene 5 might not always be transferred into plants. Based on the accumulated data, we propose that the necrogenesis induced by Agrobacterium results from the sensitivity of grapevine cells to elevated levels of auxin or a precursor of auxin.

Interhemispheric commissurotomy for congenital hemiplegics with intractable epilepsy.

Five patients with congenital hemiplegia and intractable epilepsy had interhemispheric commissurotomy (the split-brain operation). After intervals of 2 to 12 years, the response has been excellent in four cases. One patient had moderate benefit. There were no late complications. Commissurotomy seems to be substantially better than hemispherectomy for this syndrome.

Fine Structure of Extracellular Polysaccharide of Erwinia amylovora.

Virulent E(9) and avirulent E(8) strains of Erwinia amylovora were shown by means of light, transmission, and scanning microscopy to be, respectively, encapsulated and unencapsulated. Difficulty was encountered in stabilizing the fibrillar-appearing capsular extracellular polysaccharide. We suggest that the ephemeral nature of extracellular polysaccharide is due to the collapse of its extended structure upon dehydration. This occurs when bacteria are prepared for either transmission or scanning electron microscopy. The electron micrographs support our previous biochemical and immunological studies contending that the capsule is composed of tightly bound and loosely held components. The preparation of bacteria in freeze-dried colonies has permitted us to observe and explain the fluidity of the encapsulated strain. We suggest that this fluidity is a reflection of the loosely held extracellular polysaccharide or slime.

Attachment of agrobacteria to grape cells.

The presence of the Ti plasmid favorably influences the attachment of agrobacteria to grape callus cells, especially during the early stages of a 2-h incubation. Agrobacterium strains attached to a similar extent to both the crown gall-resistant cultivar (Catawba), Vitis labruscana, and the crown gall-susceptible cultivar (Chancellor), Vitis sp. Attachment of the virulent strain to grape callus cells is blocked by the avirulent strain HLB-2 in both the tissue culture cell suspension and the seedling root systems.

Morphology and ultrastructure of normal rod-shaped and filamentous forms of Erwinia amylovora.

Filamentous cells of Erwinia amylovora were usually 3 to 35 times longer than the normal rod-shaped ones, and only the former produced minicells.

Ultrastructure of the cell wall of Erwinia amylovora.

Thin sectioned cells of Erwinia amylovora revealed two electron-dense layers in their walls when fixed at 24 to 27 C and three when fixed at 4 C.

Extracellular Polysaccharide of Erwinia amylovora: a Correlation with Virulence.

The extracellular polysaccharides produced as slime or capsule layers by bacterial pathogens of animals and plants have been often implicated as factors essential to pathogenesis. In the present study, virulence of the plant pathogen Erwinia amylovora was correlated with the ability to produce extracellular polysaccharide (EPS). EPS production by a series of field isolates and bacterio-phage-resistant mutants differing in the extent to which they cause symptoms in host tissues was examined by quantitation with a modified Laurell rocket immunoelectrophoresis assay. The amount of EPS produced as an easily removed capsular layer or slime on solid nutrient agar approximated the capacity to exhibit symptoms in host inoculation tests. Features common to the virulent isolates are mucoid colony morphology, sensitivity to EPS-specific bacteriophages [Sphi3 and PEal(h)], and ability to produce a characteristic EPS. Mutants selected for resistance to Sphi3 or nonmucoid colony morphology are deficient in EPS production and have lost the ability to multiply in host tissue and cause symptoms. We conclude that EPS may be directly involved in symptom expression and provide a function essential to the growth of the pathogen in host tissues.

Ultrastructure of soybean nodules. I: release of rhizobia from the infection thread.

Root nodules on soybeans (var. Clark 63) were examined by transmission electron microscopy 10-12 days after seed inoculation and planting. The cell infection process appeared identical in both effective nodules, induced by Rhizobium japonicum strain 138 (USDA) and in ineffective nodules, induced by strain 8-0 (Iowa). Electron micrographs are presented which suggest that rhizobia are freed from the infection thread by disintegration of the thread wall and compartmentalization of the distintegrated wall material in membrane-bound vesicles derived from the membrane surrounding the thread. As the thread wall is removed in this manner, the bacteria are released into the host cytoplasm by a process which encloses each in an envelope also dervide from the thread membrane. Any thread wall material remaining around a bacterium after it has dissociated from the thread is removed from the envelope space by vesiculation of the membrane envelope. thus, it appears that endocytosis of both the bacteria and the material composing the infection thread wall occurs during release of rhizobia into the host cell.