Pseudomonas tolaasii is a species of Gram-negative

Gram-negative

Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...

 soil

Soil

Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...

 bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 that is the causal agent of bacterial blotch on cultivated mushrooms (Agaricus bisporus). It is known to produce a toxin

Toxin

A toxin is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded...

, called tolaasin

Tolaasin

Tolaasin is a toxin produced by the soil bacterium Pseudomonas tolaasii. It has been shown to have hemolytic properties....

, which is responsible for the brown blotches associated with the disease

Disease

A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...

. It also demonstrates hemolytic activity, causing lysis

Lysis

Lysis refers to the breaking down of a cell, often by viral, enzymic, or osmotic mechanisms that compromise its integrity. A fluid containing the contents of lysed cells is called a "lysate"....

 of erythrocytes. Based on 16S rRNA analysis, P. tolaasii has been placed in the P. fluorescens

Pseudomonas fluorescens

Pseudomonas fluorescens is a common Gram-negative, rod-shaped bacterium. It belongs to the Pseudomonas genus; 16S rRNA analysis has placed P. fluorescens in the P. fluorescens group within the genus, to which it lends its name....

group.