# 990: YPS MEDIUM


## Main sol. 990

35	g	Sea Salt (Sigma)	
3.46	g	PIPES	
1	g	Yeast extract	
4	g	Peptone	
5	g	Elemental sulphur	
0.5	g	NH4Cl	
0.35	g	KH2PO4	
0.2	g	CaCl2	
6.7	mg	FeCl3	
2.9	mg	Na2WO4	
0.1	mg	Resazurin	
0.25	g	Na2S x 9 H2O	
1000	ml	Distilled water	

1. Prepare the medium without the yeast extract, peptone and sodium sulphide. Boil the medium and cool under nitrogen. Adjust the pH to 6.8. Dispense into hungate tubes or serum bottles under a nitrogen atmosphere. Sterilise the medium at 100°C for 3 hours on 3 consecutive days. Add the peptone and yeast extract from sterile (10% w/v) stock solutions. The medium is reduced by adding a sterile, neutralised 5% w/v sodium sulphide solution to an end concentration of 0.025%. Final pH should be 6.8