ZoBell — 58 — Marine Microbiology 



mental data which permitted the calculation of the numbers to be ex- 

 pected from the attachment count, if the plate counts were known." 



Smith and ZoBell (1937) used the submerged slide technic to demon- 

 strate the occurrence and growth of bacteria and allied microorganisms in 

 Great Salt Lake. Controlled experiments proved that neither dead nor 

 senescent bacteria adhere to submerged slides. The development of 

 micro-colonies on slides submerged in the lake indicated that the bacteria 

 were multiplying. 



While it is unquestionably a useful and practical method for making 

 qualitative and quantitative studies on microorganisms in relatively 

 shallow water, the submerged slide technic has its limitations. Henrici 

 (1936) emphasized that it selects only those bacteria in water which are 

 capable of growing attached to a submerged surface. ZoBell (19436) 

 carefully examined the attachment propensities of 96 different species of 

 marine bacteria, finding that only 29 of them attached in appreciable 

 numbers to glass slides submerged in sea water, 47 of them showed some 

 tendency to attach, and 20 of them failed to attach to glass slides. More- 

 over, not all individual cells of the attachment species attached them- 

 selves to glass slides. ZoBell (1943&) discusses several factors including 

 the attachment propensity of the species, the growth phase (bacteria 

 attaching more readily during the logarithmic phase of growth than later) , 

 interfacial tension, organic content of the water, the associative or syner- 

 gistic ellects of other sessile organisms, and other factors which influence 

 the attachment of bacteria to solid surfaces. 



Slides must be submerged in sea water for a few hours to several days 

 before appreciable numbers of bacteria appear. If they are not left sub- 

 merged long enough, there will be too few bacteria to give significant 

 counts and if they are left too long, the bacterial film may be too dense to 

 make an attachment count, or the bacteria may be obliterated by the 

 attachment of larger sedentary plants and animals. Therefore the sub- 

 merged slide technic is most useful at places where continuous observa- 

 tions can be made rather than in the open ocean or in deep water where it 

 is difficult to anchor boats or buoys. 



Aged sea water: — In order to obtain reproducible results, it is recom- 

 mended that "aged" or "rotted" sea water be employed in the prepara- 

 tion of dilution water blanks or nutrient media for marine bacteria. Such 

 water is prepared by storing raw sea water in glass bottles in the dark for 

 a few weeks or longer. The water should be collected from places that are 

 reasonably free of fresh-water or terrigenous pollution. Because contact 

 with certain heavy metals renders sea water bacteriostatic, glass recepta- 

 cles should be used for the collection and storage of the water. Passing 

 the water through a sintered glass filter of medium porosity serves to 

 remove particulate material, thereby providing for greater uniformity in 

 composition. If germ-proof filters are used for this purpose, the water 

 should be inoculated with a little raw sea water to insure the presence of a 

 bacterial flora which will decompose the organic matter in the water. 

 During storage or incubation in the laboratory at room temperature for a 

 few weeks the organic content of the water may be reduced from an initial 

 4 or 5 mgm./L. to one-tenth this amount. Of greater importance than the 

 reduction or stabilization of the organic content of the water, the slightly 

 bacteriostatic principle referred to on pages 44, 47, and 81 gradually dis- 

 appears with prolonged storage. The water must be stored in the dark to 

 prevent the growth of photosynthetic organisms. 



