430 Marine Microbiology 



out the bulk of the fluid was taking place (though wall growth 

 was still predominant ) and the organisms were now recognizably 

 vibrios though still elongated and markedly pleomorphic. The 

 strain retained these cultural and moiphological characters for 

 sixteen passages; the culture was pure by the criteria of Postgate 

 ( 14 ) and regained its "ordinary" morphology on transfer back to 

 a fresh water medium. 



The natural salt and fresh water strains, as well as the 

 trained salt water strain were studied from three points of view: 

 ( 1 ) the fragility of their osmotically sensitive bodies resembling 

 spheroplasts; (2) their secretion of a mucin; and (3) their pool 

 of free amino-acid-like material. 



RESULTS 



(I) Preparation and Behaviour of Osmotically Fragile Forms 



Salt water strains of D. desulfuricans do not show the spon- 

 taneous osmotic lysis typical of "strong" halophiles (11). Proto- 

 plasts, spheroplasts or similar osmotically sensitive bodies might 

 be expected to show different osmotic fragilities according to the 

 salinity to which the strain was accustomed. The following section 

 reports the preparation of two morphologically distinct classes of 

 osmotically fragile bodies from these bacteria and an experiment 

 on the relationship of osmotic fragility to saline habit with one 

 class. 



Preparation of Spheroplasts 



Lederberg's (10) penicillin procedure was adopted in the 

 following form. The Hildenborough strain was grown in con- 

 tinuous culture at 30° under H. + 30% v/v CO, (19) in the fol- 

 lowing medium NH.Cl, Ig; (NHO.SO^ 0.3g; KCl, 0.2g; CaCL 

 O.lg; MgSOi: 7H.O, 2g; Na.SO., 12g; yeast extract (Difco dry 4g) 

 distilled water 1 1., pH 7.4±:0.2; cell yield c O.Smg wt./ml. Effluent 

 from the continuous culture was allowed to flow into 1 to 10 vol. 

 of similar medium containing M to 0.05 M sucrose and 10^ to 10^ 

 units penicillin G/ml., with precautions to minimize aeration and 

 temperature shock. After incubation at 30 C under H. + 2()* CO.-, 

 a proportion of spheroplasts appeared. These had the typical 

 "rabbit" or "tadpole" forms obtained with rod-shaped bacteria 



