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Pseudomonas tolaasii is a bacterium endemic to the compost beds where common mushroom (Agaricus bisporus) is cultivated. Under some environmental conditions still not well-determined, but influenced by temperature and relative humidity, the bacterium can become pathogenic and provoke the brown blotch disease. This review describes the interaction between P. tolaasii and A. bisporus that results in the appearance of brown spots on the mushroom caps, typical symptoms of the disease. Firstly, P. tolaasii is studied, the changes in pathogenicity are explained, the compounds that provoke the damage are enumerated as well as various experimental methods to identify the pathogenic form of the bacteria. Secondly, mechanisms involved in the formation of the brown colour on the A. bisporus caps upon infection are briefly mentioned, taking into account the enzymes that catalyse the reaction, their mechanism, substrates and reaction products. Afterwards, a detailed description of the infection process is presented step by step, starting by the chemotactical attraction, fixation, secretion of the toxins, membrane breakdown, effect of the toxin on mushroom polyphenol oxidases and on the discolouration reaction. A possible mechanism of infection is hypothesised at the molecular level. Finally, the strategies tested until now to control the disease are discussed.

Agaritine [( -N-(γ-L(+)-glutamyl)-4-hydroxymethylphenylhydrazine] was isolated and purified from mushrooms (Agaricus bisporus). This paper reports for the first time the inhibition of the monophenolase and diphenolase activities of mushroom polyphenol oxidase by this abundant and characteristic compound from the Agaricus genus. Agaritine showed uncompetitive inhibition (K I ) 2.3 mM) and partial competitive inhibition (K I ) 0.13 mM; R ) 2.5) when L-DOPA and L-tyrosine were assayed, respectively. In addition to the ability of agaritine to inhibit the enzyme per se, this compound was capable of removing the enzymatically generated o-quinones in the assay. To solve this problem, the inhibition was characterized by using 3-methyl-2-benzothiazolinone hydrazone as nucleophile reagent to form a stable nucleophile-quinone adduct that could not be attacked by agaritine. The inhibition of mushroom polyphenol oxidase by other inhibitors is compared to the inhibition by agaritine. Moreover, a possible role for agaritine in the browning of mushrooms is discussed.

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