Interactions in fireblight infections

In the host, Erwinia arnylovora (Burrill) Winslow et al. travels primarily in the inter-cellular spaces of immature cortical tissue; progress in mature tissue is restricted. Only in the later stages of infection are saprophytic bacteria such as Erwinia herbicola (Löhnis) Dye commonly found in association with the pathogen. Their effect on the persistence of the pathogen is still uncertain though commonly assumed (with little supporting evidence) to be inhibitory. Most interaction studies have concentrated on the early stages of infection. The interactants have been inoculated prior to or together with E. amylovora and they have included avirulent E. amylovora, phyto-pathogenic pseudomonads, E. herbicola and other saprophytes or cell components including DNA. Our experience reflects that of other workers in that interactants only inhibit at high doses or at high numbers relative to the pathogen. Prior inoculation is not always necessary for protection. In our preliminary studies of the fate of interactants, the outcome varied. Where infection progressed the interactant disappeared, persisted only at the point of inoculation or progressed alongside the pathogen. Where there was protection, both pathogen and interactant disappeared from the tissues or only the interactant persisted at the site of inoculation. Crown gall apart (possibly a special case), observations with other bacterial plant diseases have been similar to those with fireblight with an added one of stimulation of infection by the interactant. The underlying mechanisms of protection probably vary with different interacting systems and cannot always be attributed to a hypersensitivity reaction or to bacteriophage or bacteriocin activity. If a host response is involved, it seems pertinent to ask whether there are simpler ways of achieving protection of growing tissue other than by using bacteria and their products. With epiphytic bacteria two major problems are the achievement and maintenance of high enough populations at critical sites and the lack of major transmitted or translocated effects beyond the site of interaction.     

Anthraquinones in the biosynthesis of sterigmatocystin by Aspergillus versicolor.

14C-labeled averufin, versiconal hemiacetal acetate, and versicolorin A were efficiently converted to sterigmatocystin by Aspergillus versicolor, thus providing experimental evidence that these anthraquinones are biosynthetic precursors of sterigmatocystin, a xanthone.     

The phospholipid headgroup specificity of an ATP-dependent calcium pump.

We have replaced the lipid associated with a purified calcium transport protein with a series of defined synthetic dioleoyl phospholipids in order to determine the effect of phospholipid headgroup structure on the ATPase activity of the protein. At 37 degrees C the zwitterionic phospholipids (dioleoyl phosphatidylcholine and dioleoyl phosphatidylethanolamine) support the highest activity, while a phospholipid with two negative charges (dioleoyl phosphatidic acid) supports an activity which is at least twenty times lower. Dioleoyl phospholipids with a single net negative charge support at intermediate ATPase activity which is not affected by the precise chemical structure of the phospholipid headgroup. The protocol used to determine the phospholipid headgroup specificity of calcium transport protein is novel because it establishes the composition of the lipid in contact with the protein without the need to isolate defined lipid-protein complexes. This allows the lipid specificity to be determined using only very small quantities of test lipids. We also determined the ability of the same phospholipids to support calcium accumulation in reconstituted membranes. Two requirements had to be met. The phospholipid had to support the ATPase activity of the pump protein and it had to form sealed vesicles as determined by electron microscopy. Since a number of phospholipids met those requirements it is clear that in vitro the lipid specificity of the calcium-accumulating system is rather broad.     

Isolation and characterisation of deletion mutants involving the transfer genes of P-group plasmids in Pseudomonas aeruginosa

Summary The P-group plasmids RP1 and R26 are recovered at low frequency following conjugal transfer to B3-lysogens of P. aeruginosa PAO. The rare carbenicillin-resistant transcipients that do arise are usually transfer-defective (Tra^-) and may show the loss of other plasmid borne functions, namely kanamycin-resistance (Km^r) and reduced plating of phage GlOl (Spp⁺). The four phenotypic classes that occur among the Tra^- derivatives are respectively, Tra^- (69–81%), Tra^- Spp^- (12–30%), Tra^- Km^s and Tra^- Km^s Spp^- (0.2–1%), of which the latter three are due to plasmid deletions. This is seen from the sizes of the plasmids carried by these bacteria and from the transductional analysis of the R26-derivatives. Thus, although R26 (MW=52×10⁶ daltons) is too large to be transduced by phage F116L (MW=40×10⁶), this is possible for its Tra^- Km^s and Tra^- Km^s Spp^- derivatives. The phenotypes and frequencies of the various transcipient classes suggests that the gene order Km..Tra..Spp occurs in both RP1 and R26, and that Spp is more closely linked to Tra than is Km. These conclusions are supported by the sizes of the plasmid mutants since deletions spanning the loci Km Tra Spp, Km Tra, and Tra Spp involve the loss of DNA of MW 8-17×10⁶, 5-13×10⁶ and 1-9×10⁶ daltons respectively.Whilst all the transcipients displayed the incompatibility properties of the parent plasmids (Inc⁺), only some retained plasmid surface exclusion (Sfx⁺). Moreover, a strict correlation existed between the Sfx and Spp phenotypes such that the transcipients were either wild type, Sfx^- Spp^-, or displayed an intermediate phenotype for both characters. This suggests that these phenotypes are controlled by closely linked genes or are different manifestations of the same gene function. The deletion map of these various markers in both RP1 and R26 therefore seems to be Km..Tra..Sfx/Spp..Inc.     

Blood parasites of some birds from Ghana

A total of 135 birds of 26 species in 13 families was examined for blood parasites; 43 birds (31.9%) of 13 species were infected; species of the Ploceidae were the most heavily infected. Species of Haemoproteus occurred most commonly 29 birds) while Leucocytozoon and Plasmodium species were virtually absent. There was no significant difference in the prevalence of hematozoa in birds from the mature rainforest and those in a savannah-urban setting.     

Angiotensin II binding to mammalian brain membranes.

High affinity binding sites for angiotensin II in bovine and rat brain membranes have been identified and characterized using monoiodinated Ile5-angiotensin II of high specific radioactivity. Degradation of labeled and unlabeled peptide by washed brain particulate fractions was prevented by adding glucagon to the final incubation medium and including a proteolytic enzyme inhibitor (phenylmethylsulfonyl fluoride) in preincubation and incubation procedures. 125I-Angiotensin II binding can be studied using either centrifugation or filtration techniques to separate tissue-bound radioactivity. 125I-Angiotensin II binding to calf brain membranes is saturable and reversible, with a dissociation binding constant of 0.2 nM at 37 degrees. A similar binding constant is found in rat brain membranes. Analogues and fragments of angiotensin II compete for these brain binding sites with potencies which correlate with both their in vivo potencies and their binding inhibition protencies at adrenal cortex angiotensin II receptors. Angiotensin I is 1 to 2 orders of magnitude weaker than angiotensin II; the 3-8 hexapeptide and 4-8 pentapeptide are much weaker still. (desAsp1) angiotensin II (angiotensin III) is slightly more potent than angiotensin II, as are several antagonists of angiotensin II with aliphatic amino acids substituted at position 8. In calf brain 125I-angiotensin II binding is restricted almost exclusively to the cerebellum (cortex and deep nuclei). In rat brain, angiotensin II binding is highest in the thalamus-hypothalamus, midbrain, and brainstem, areas which are believed to be involved in mediating angiotensin II-induced central effects. These findings illustrate the presence of high affinity specific binding sites for angiotensin II in rat and bovine brain and suggest a physiological role for angiotensin peptides in the central nervous system.