Variability of Bacteria in North Atlantic Sediments 529 



Comparison of Fluorescence Microscopy Counts 

 with Membrane Filter Counts 



The fluorescence technique of Strugger (6) difi^ers from other 

 direct counting methods in distinguishing between living and 

 dead bacteria on the basis of diff^erential absorption of acridine 

 orange. Direct counts of living bacteria in 77 marine sediment 

 samples were made by this method. In order that they might be 

 compared vdth colony counts on the filters, the two methods were 

 applied concurrently to duplicate samples from the three coastal 

 regions. 



In general, the direct counts exceeded filter counts by a fac- 

 tor of 10*. The means of direct counts were subject to the same 

 or smaller enors than corresponding filter counts, but the former 

 did not follow a Poisson series. While it is possible to distinguish 

 between the three coastal regions on basis of the fluorescence 

 counts, it may be seen from Table 2 that the regions are ranked 

 differently by the two methods, and it will be even more apparent 

 from Figure 3 that no simple ratio exists between the two counts. 



TABLE 2 

 A Comparison of Regional Variability in Bacterial Numbers as Observed 

 BY Two Methods of Counting: Membrane Filter and Fluorescence Micro- 

 scopy. Fluorescence Counts were Higher than Filter Counts by a 



Factor of 10* 



Relative Numbers of Bacteria in 



Sediments, Calling Highest Count 



for Each Method 100 



The working time required to obtain a trip average is about 

 the same for these two tecliniques. Tlie membrane filter method 

 is readily earned out at sea, but it is doubtful that such is the case 

 for fluorescence microscopy. Eye fatigue undoubtedly involves 

 error that might be avoided by introducing photometric measure- 

 ments in place of the visual counts of fluorescing particles. 



