Dissimilatory Iodate Reduction by Marine Pseudomonas sp. Strain SCT

ABSTRACT Bacterial iodate (IO3 −) reduction is poorly understood largely due to the limited number of available isolates as well as the paucity of information about key enzymes involved in the reaction. In this study, an iodate-reducing bacterium, designated strain SCT, was newly isolated from marine sediment slurry. SCT is phylogenetically closely related to the denitrifying bacterium Pseudomonas stutzeri and reduced 200 μM iodate to iodide (I−) within 12 h in an anaerobic culture containing 10 mM nitrate. The strain did not reduce iodate under the aerobic conditions. An anaerobic washed cell suspension of SCT reduced iodate when the cells were pregrown anaerobically with 10 mM nitrate and 200 μM iodate. However, cells pregrown without iodate did not reduce it. The cells in the former category showed methyl viologen-dependent iodate reductase activity (0.31 U mg−1), which was located predominantly in the periplasmic space. Furthermore, SCT was capable of anaerobic growth with 3 mM iodate as the sole electron acceptor, and the cells showed enhanced activity with respect to iodate reductase (2.46 U mg−1). These results suggest that SCT is a dissimilatory iodate-reducing bacterium and that its iodate reductase is induced by iodate under anaerobic growth conditions.

Postharvest Biological Control of Rhizopus Rot of Nectarine Fruits by Pichia membranefaciens

A new yeast antagonist, Pichia membranefaciens, isolated from wounds of peach fruit, was evaluated for its biocontrol capability against Rhizopus stolonifer on nectarine fruits at different temperatures and with other treatments. P. membranefaciens at 5 × 108 CFU/ml of washed-cell suspension completely inhibited Rhizopus rot in nectarine wounds artificially inoculated with 5 × 104 spores per ml at 25, 15, and 3°C. A culture filtrate of the yeast antagonist failed to provide any protection against Rhizopus rot in nectarine fruits. The yeast mixed with iprodione at 100 μg a.i./ml gave better control of R. stolonifer than either yeast or iprodione alone. A solution of 20 g CaCl2 per liter enhanced the efficacy of P. membranefaciens (107 to 108 CFU/ml) as an aqueous suspension. Rapid colonization of the yeast in wounds was observed during the first 48 h at 25 and 15°C. P. membranefaciens at 5 × 108 CFU/ml was effective when applied 0 to 72 h before the pathogen, while at 1 × 108 CFU/ml, its efficacy was best when applied 24 to 48 h prior to inoculation with R. stolonifer. However, its efficacy was significantly reduced when the yeast was applied simultaneously with the pathogen, with disease incidence of 60% and lesion diameter of 37 mm.

Spiroplasma cells utilize carbohydrates via the phosphoenolpyruvate-dependent sugar phosphotransferase system

Ten Spiroplasma species tested were found capable of fermenting glucose, mannose, fructose, and sucrose, but not ribose, maltose, 2-deoxyglucose, xylose, sorbitol, glactose, lactose, and arabinose. Sugar utilization was measured by a direct measurement of the changes in pH of a washed cell suspension upon the addition of the various sugars. Sulfhydryl reagents, uncouplers, and glycolysis inhibitors prevented the sugar-induced pH shifts. The spiroplasmas were capable of phosporylating α-methylgucoside in a reaction that required phosphoenolypyruvate, but not ATP, as a phosphate donor, suggesting that Spiroplasma species possess a phosphoenolpyruvate-dependent sugar phosphotransferase system. Key words: Spiroplasma, carbohydrate utilization, pH changes, phosphenolpyruvate-dependent sugar phosphotransferase system.

Cobalt and sodium requirements for methanogenesis in washed cells of Methanosaeta concilii

Methanosaeta concilii GP6 lost methanogenic activity upon thorough washing of the cells with an anaerobic buffer. Methane production from acetate could be restored by supplementing the washed cell suspension with spent growth medium, and to a lesser degree (65–70% of the rate obtained with spent medium) by the coaddition of NaCl and CoCl2. The latter reactivation had an apparent Km for CoCl2 of 5.6 μM in the presence of 40 mM NaCl, and an apparent Km for NaCl of 2.5 mM in the presence of 5 μM CoCl2. The requirement for NaCl could be met by LiCl but only partially by MgCl2, CaCl2, or NiCl2. Methylcobalamin could substitute for CoCl2. Severe inhibition of methanogenesis in unwashed GP6 cells caused by 5 μM propyl iodide and the role of methylcobalamin in regeneration of methane production in washed cells suggest the involvement of corrinoids in the methane pathway of the aceticlastic Methanosaeta concilii. This represents the first documentation for cobalt/methylcobalamin and sodium requirements for methanogenesis in Methanosaeta concilii. Key words: cobalt, sodium, methylcobalamin, methanogenesis, Methanosaeta concilii.

Isoepoxydon, a new metabolite of the patulin pathway in Penicillium urticae

A patulin-negative mutant (J1) of Penicillium urticae (N.R.R.L. 2159A) was known to accumulate about 100mg per litre quantities of the 5,6-epoxygentisyl quinone, (−)-phyllostine and another metabolite (UIII). Both were derived from acetate and hence were polyketides. Purified UIII (m.p. 53°C, [α]32D+206°, λmethanolmax. 240nm; ε 3806 litre·mol−1·cm−1) was characterized as a partially reduced derivative of (−)-phyllostine and was found to be a diastereoisomer of the known phytotoxin, (+)-epoxydon. Hence its designation as (+)-iso- or epi-epoxydon. From 1H n.m.r. and c.d. data the stereochemistry of the epoxide ring in (+)-isoepoxydon was determined to be identical with that in (+)-epoxydon (i.e. R,R) but the configuration of the secondary alcohol at C-4 was S rather than R as in (+)-epoxydon. Isoepoxydon (compound UIII) is therefore (4S,5R,6R)-5,6-epoxy-4-hydroxy-2-hydroxymethylcyclohex-2-en-1-one. The boat conformation in which the C-4 hydroxy group is axial is preferred. In the range of 1mm to 5mm, the antibiotic activity of (+)-isoepoxydon against Bacillus subtilis sp. was 56% of that obtained with patulin. Over a period of 1 to 3h, [14C]isoepoxydon was efficiently converted into patulin by a shake culture of the parent strain of P. urticae. The precursor relationship of isoepoxydon to patulin was confirmed by feeding unlabelled isoepoxydon (1mm) to a washed-cell suspension of a mutant (J2) in which, over a period of 3 to 5h, a better than 60% conversion into patulin was attained. The enzymic relationship between isoepoxydon and phyllostine and their positions in the late portion of the patulin biosynthetic pathway are discussed.