WLN Agar Medium

A New Selective Media Agar
Wallerstein Laboratory Nutrient (WLN) is a medium which is prepared already and sold by various lab companies. I used WLN from the Oxiod company with an additional 1% (1 g/l) of agar added to help further solidify the media for better streaking ability without gouging into the media. Here is a link to the properties of WLN agar medium. The Bromocresol Green present in the medium acts as a dye which Saccharomyces yeast take up and don’t normally metabolize (strain dependent). The agar medium which starts off green becomes clear/opaque as the Bromocresol Green is taken up by the developing yeast colonies. Brettanomyces spp. will take up the Bromocresol Green but have been observed to metabolize the dye leaving the Brettanomyces yeast colonies an often cyan, or yellowish off white color. This medium is therefore good as a differentiation medium for observing mixed yeast cultures.
*Some warning: Not all Saccharomyces spp. take up the Bromocresol Green the same way so there are different shades of green and it is reported that some Saccharomyces spp. (Wit ale strains!) can also metabolize the Bromocresol Green so care must be taken if this medium is to be used for identification and it should be one of a few tests done in differentiating. Also it is possible that Brettanmyces spp. (B. claussenii!) only metabolize varying amounts of the Bromocresol Green so astute observations should be made when trying to decide if only a single strain is present on a plate and plating should be done out in serial dilutions so cell counts are low enough to allow ample growth of all possible organisms present.

Wallerstein Laboratory Nutrient agar – 1,000 ml
WLN 75 g
Agar (additional 1%) 10 g
*Autoclaved at 121°C for 15 minutes at 15 psi

Wallerstein Laboratory Nutrient+cycloheximide (WLD) agar – 1,000 ml
WLN 75 g
Agar (additional 1%) 10 g
*Autoclaved at 121°C for 15 minutes at 15 psi
*Add Cycloheximide after autoclaving media – 10 mg (10 ppm=10 mg/l)

WLN agar with green medium
and Brettanomyces sp. colonies
just starting to form

After the Brettanomyces sp.
colonies have grown and all
the Bromocresol Green is
taken up

Mixed Brettanomyces spp.
colonies? Observed color change
after a few days in the fridge,
possible strain dependent
phenomenon of not fully
metabolizing the Br. Green

Mixed Saccharomyces spp.
M-strain distillers yeast used
to inoculate plate


~ by Chad on March 6, 2009.

One Response to “WLN Agar Medium”

  1. Stunning… very awesome topic. I am going to blog about it too!!

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