Marine Agar

Marine Agar is the most widely used medium for growing samples taken from marine or estuarine habitats. It offers a rich medium for marine bacteria to grow, but it is not recommended for further analysis of bacteria (purification, identification, etc.) due to the high concentration of ions.

It is available from commercial sources (Difco Marine agar 2216), but a simple and effective medium can be prepared in the lab from commonly available ingredients, as recommended by Jannasch and Jones (1959 Limnol Oceanogr 4(2):128-139).

Ingredients

• Bacteriological agar: 15.0 g
• Bactopeptone or polypeptone: 5.0 g
• Yeast extract: 1.0 g
• Ferric chloride (FeCl2 1.2 g/l H2O): 1.0 ml
• Distilled water: 250 ml
• Aged sea water: 750 ml

Preparation

Adjust the pH to 7.5 ± 0.1 before adding the agar. Autoclave at 121 °C for 20 minutes. Do not add the agar if you want a broth. After autoclaving, some precipitation can be observed. Note. FeCl2 can be replaced with 0.01 g of FePO4.