688 Marine Microbiology 



terial (21). This was regarded as being less selective than con- 

 ventional rich laboratory media likely to encourage disproportion- 

 ate growth of zymogenous organisms. Preliminary trials by the 

 author in developing a medium of similar properties suitable for 

 marine materials indicated that sea water extracts of marine 

 muds when enriched with phosphate and iron would support 

 good growth of many marine bacteria. Extracts have been pre- 

 pared* from freshly collected mud obtained locally in Wellington 

 Harbour by dredging surface sediments. In contrast to the rapid 

 effusive growth frequently encountered when plating marine sam- 

 ples on yeast extract peptone sea water agar, bacterial colonies de- 

 veloping on mud extract agar are small, discrete, and show little 

 tendency for surface spreading. Antagonistic effects on primary 

 isolation plates, possibly leading to the suppression of some fonns, 

 are thereby minimised using the latter medium, which moreover 

 permits a relatively long incubation period ( 14-20 days at 18- 

 20 C) during which time many pin-point colonies arise that could 

 otherwise be difficult to isolate. 



MATERIALS AND METHODS 



Sampling 



Two oceanographic stations were worked on 24/25 June, 

 1960, one, B 294, (41° 34'S, 175°02'E) 3 miles offshore in 

 50 fms, and the second, B 293 (41°55'S, 174°57'E) 30 miles 

 offshore in 1200 fms. Using ZoBell samplers, water samples were 

 taken from 25 m at both stations and from 1500 m at the second. 

 Sediments were sampled using gravity corers. 



On ship, 100 ml - 200 ml volumes of the water samples, de- 

 pending upon the expected abundance of bacteria present, were 

 concentrated by membrane filtration ( pore size 0.45/i ) in a sterile 

 apparatus until 1-2 ml water remained in the well of a rubber 

 gasket above the filter. To reduce carryover of any factors in the 

 raw samples inhibitory to bacterial growth, this concentrate was 

 diluted twice in succession by adding aseptically 50 ml filter- 



Current procedure is to autoclave for one hour at 115 CI 1 kg wet mud with 

 1100 ml aged sea water diluted to a salinity of Ca. 6%^- After filtering, the 

 volume of the extract is adjusted to 1 litre with distilled water, 1 mg Fe 

 (as FeCl3-6H;0) and 15 g agar arc added, and after sterilization, 0.1 g 

 K2HPO4 is added. 



