D-Alanine substitution of teichoic acids as a modulator of protein folding and stability at the cytoplasmic membrane/cell wall interface of Bacillus subtilis

The extracytoplasmic folding of secreted proteins in Gram-positive bacteria is influenced by the microenvironment of the compartment into which they are translocated, namely the negatively charged matrix of the cell wall polymers. In this compartment, the PrsA lipoprotein facilitates correct post-translocational folding or prevents misfolding of secreted proteins. In this study, a secretion mutant of B. subtilis (prsA3) encoding a defective PrsA protein was mutagenized and screened for restored secretion of the AmyQ alpha-amylase. One mini-Tn10 insertion, which partially suppressed the secretion deficiency, was found to interrupt dlt, the operon involved in the d-alanylation of teichoic acids. The inactivation of dlt rescued the mutant PrsA3 protein from degradation, and the increased amount of PrsA3 was shown to enhance the secretion of PrsA-dependent proteins. Heterologous or abnormal secreted proteins, which are prone to degradation after translocation, were also stabilized and secreted in increased quantities from a dlt prsA(+) strain. Furthermore, the dlt mutation partially suppressed the lethal effect of PrsA depletion, suggesting that the dlt deficiency also leads to stabilization of an essential cell wall protein(s). Our results suggest that main influence of the increased net negative charge of the wall caused by the absence of d-alanine is to increase the rate of post-translocational folding of exported proteins.     

Arthropod abundance in an Australian apple orchard under mating disruption and supplementary insecticide treatments for codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae)

The impacts of three codling moth management strategies (i, mating disruption alone; ii, mating disruption plus azinphos-methyl; iii, mating disruption plus fenoxycarb) on some secondary pests and their natural enemies in an apple orchard were compared over two growing seasons: 1993/1994 and 1994/1995. In the absence of azinphos-methyl (strategies i and iii), two-spotted mite ( Tetranychus urticae ) was controlled by Typhlodromus occidentalis and populations of generalist predators (e.g. ladybirds, lacewings and earwigs) increased. The populations of a parasitoid of woolly aphid ( Eriosoma lanigerum ), Aphelinus mali, also increased but not enough to provide adequate control of the aphid. Combined damage caused by lightbrown apple moth ( Epiphyas postvittana ), budworms ( Helicoverpa spp.) and San José scale ( Quadraspidiotus perniciosus ) was significantly higher in the absence of azinphos-methyl in 1994/1995. Beneficial insect populations were not suppressed by fenoxycarb. In 1994/1995, mating disruption plus fenoxycarb produced better control of E. postvittana than mating disruption alone. During transition to an apple integrated pest management program based on codling moth mating disruption, fenoxycarb was shown to be less disruptive to any natural control of secondary pests than azinphos-methyl.     

Tebufenpyrad: compatibility with integrated mite control on apples

Successful integrated mite control (IMC) depends on the availability of acaricides which act selectively on pest mites with minimal effects on predators. Laboratory bioassays of tebufenpyrad against adult female Panonychus ulmi (Koch) provided baseline toxicity data and showed it to be highly active. Bioassays also showed tebufenpyrad was toxic to the predatory mite Typhlodromus pyri Scheuten but it was approximately 70 times less toxic to the predators than to P. ulmi at the lc ₅₀. Field trials using four concentrations of tebufenpyrad (10, 7.5, 5 and 2.5 g a.i./100 l) confirmed it was selectively more toxic to the pest mites than to predators and showed that it is compatible with IMC. It is suggested that a concentration of 5 g a.i./100 l would be suitable for IMC. A resistance management strategy for tebufenpyrad is proposed.     

The auration of 2-hydroxy-pyridine (2-pyridone): preparative and structural studies and a comparison with reactions of related aliphatic O,N-donors

In a study of the isolobal analogy between the proton H⁺ and the ligand-backed gold(I) cations [(R₃P)Au]⁺, the reaction of the mixture of 2-pyridone/2-hydroxy-pyridine tautomers with [(Ph₃P)Au]BF₄ has been investigated. It affords the 1:1 complex with the gold atom N-bonded to the 2-hydroxy-pyridine tautomer: {(Ph₃P)Au[NC₅H₄-(OH-2)]}⁺BF₄ ⁻, which is related to known salts with the 2-hydroxy-pyridinium cation such as [HNC₅H₄(OH-2)]⁺Cl⁻. The structure was derived from analytical and spectroscopic data and from a comparison with the salt [(Ph₃P)Au(pyr)]BF₄, prepared and investigated structurally as a reference compound. An analogue was also prepared with 2-dimethylamino-ethanol as a substrate, which also affords the N-bonded complex [(Ph₃P)Au([Me₂NCH₂CH₂OH)]⁺BF₄ ⁻, the structure of which has been determined. The OH group is not attached to the gold atom but engaged in hydrogen bonding with the counterion. By contrast, in the complex [(Ph₃P)Au(Me₂NCH₂CH₂NMe₂)]⁺BF₄ ⁻ synthesized similarly with tmeda and crystallized as the dichloromethane solvate, one nitrogen atom is bonded firmly to the metal atom, but the second nitrogen atom is also weakly engaged in coordinative bonding. The compound is fluxional in solution, where a site exchange is observed which is rapid on the NMR time scale. The reaction of two equivalents of [(Ph₃P)Au]BF₄ with an alkali 2-pyridinolate, prepared from the above tautomeric mixture and sodium metal or a potassium alkoxide, yields the diaurated product {N,O-[(Ph₃P)Au]₂(NC₅H₄-O-2)}BF₄. In the crystal structure determination of a sesqui-solvate with dichloromethane it has been shown that one gold atom is attached solely to the nitrogen atom and the other solely to the oxygen atom. The dinuclear cations are associated into cyclic dimers through head-to-tail aurophilic bonding. From the geometrical characteristics of the core unit of the cations the ligand can be assigned a 2-pyridinolate form featuring pyridine and phenolate donor sites.     

Resistance to clofentezine and hexythiazox inPanonychus ulmi from apples in Australia

The ovicides clofentezine and hexythiazox have been used in Australia againstPanonychus ulmi (Koch) since 1984 and 1987, respectively. Failure of clofentezine in the field againstP. ulmi was first reported in early 1988. In 1988–89, laboratory bioassays were carried out against susceptible reference strains, and discriminating doses for clofentezine and hexythiazox established. Suspected resistant strains were tested, as were randomly collected strains.Panonychus ulmi from 23 apple orchards in eastern Australia were found to be resistant to clofentezine, and 19 of these strains were also resistant to hexythiazox. In all cases, a total of four or more ovicide sprays had been used. Of 15 samples ofP. ulmi from blocks where less than four ovicides had been used, none were resistant to either clofentezine or hexythiazox. A survey of orchards in the Orange district of New South Wales found that 30% had received four or more ovicide sprays and were likely to experience resistance problems. The control problems with clofentezine and hexythiazox means the few remaining acaricides will be subject to extreme selection pressure.