GRB 090423 at a redshift of z approximately 8.1.

Gamma-ray bursts (GRBs) are produced by rare types of massive stellar explosion. Their rapidly fading afterglows are often bright enough at optical wavelengths that they are detectable at cosmological distances. Hitherto, the highest known redshift for a GRB was z = 6.7 (ref. 1), for GRB 080913, and for a galaxy was z = 6.96 (ref. 2). Here we report observations of GRB 090423 and the near-infrared spectroscopic measurement of its redshift, z = 8.1(-0.3)(+0.1). This burst happened when the Universe was only about 4 per cent of its current age. Its properties are similar to those of GRBs observed at low/intermediate redshifts, suggesting that the mechanisms and progenitors that gave rise to this burst about 600,000,000 years after the Big Bang are not markedly different from those producing GRBs about 10,000,000,000 years later.

Rapid oxidase method for testing oxidase-variable Aeromonas hydrophila strains.

A rapid, same-day oxidase test procedure which obviates the problem of false-negative oxidase reactions of Aeromonas hydrophila removed from the surface of differential media such as MacConkey agar is described. This method allows oxidase testing to be performed within 3 h, rather than delaying the oxidase test for an additional 18 to 24 h. This procedure is applicable to any rapidly growing gram-negative rod.

Role of pH in oxidase variability of Aeromonas hydrophila.

Some strains of Aeromonas hydrophila may be oxidase negative or only weakly oxidase positive by the Kovacs method taken from the surface of a differential medium, such as MacConkey agar. Six strains of A. hydrophila, two oxidase variable, one oxidase constant, and three weakly oxidase positive on MacConkey agar, were studied to determine the cause of oxidase variability. The bacteriostatic dyes in MacConkey agar were considered possible inhibitors of the oxidase reaction. The concentration of these dyes was varied from twice the normal concentration in zero. No change in the oxidase reaction of any of the six strains was noted. Carbohydrate utilization was also studied. When lactose was deleted from the MacConkey agar formula, the oxidase-variable and weakly oxidase-positive stains become strongly oxidase positive. When glucose was substituted for lactose in the MacConkey agar formula, all strains became oxidase negative. Substitution of nonfermentable carbohydrates, such as dulcitol or raffinose, returned all strains to the oxidase-positive state. When trehalose, which is utilized by all of the strains, was substituted for lactose, the oxidase-variable strains and two of the three weakly oxidase-positive strains became oxidase negative. The other weakly oxidase-positive strain remained weakly positive and the oxidase-constant strain remained strongly oxidase positive when trehalose was substituted for lactose. Oxidase reactions were found to be negative when the pH of the medium was 5.1 or lower. Negative oxidase reactions could be reversed by raising the pH above 5.2, and positive oxidase reactions could be reversed by lowering the pH to 5.1. Therefore, the fermentation of lactose in MacConkey agar results in the inhibition of the oxidase reaction. The acid end products of the fermentation of lactose include acetic, formic, lactic, oxaloacetic, pyruvic, and succinic acids.

Stressed mirror polishing. 2: Fabrication of an off-axis section of a paraboloid.

A mirror has been fabricated with the shape of an off-axis section of a paraboloid by grinding and polishing a sphere into a prestressed blank. The applied stresses were then removed allowing the mirror to spring into the desired paraboloidal shape. The 36-cm diam off-axis section deviated 9.9-microm rms from the polished sphere. The final surface deviated 0.03-microm rms from the desired off-axis section.