ON THE DIFFERENTIATION AND CLASSIFICATION OF WATER BACTERIA

Bacteriology of fresh water: III. The types of bacteria present in lakes and streams and their relationship to the bacterial flora of soil

1. Approximately 800 cultures of bacteria have been isolated from samples of water taken from lakes and from some of their inflowing waters. The morphology and Gram-staining reaction of the cultures have been determined together with the reactions in nutrient gelatin, dextrose broth, nitrate broth, and litmus milk.

2. Many organisms grew poorly on artificial media, and were unable to grow in either dextrose or nitrate broth. In general the cultures showed weak physiological activity, particularly in litmus milk and in dextrose, though gelatin liquefaction was fairly common. Colonies produced on solid media were frequently pigmented, shades of yellow being particularly common. A significant feature was that most of the bacteria (95%) were rod-shaped, and though many cultures showed considerable variation in cell length and were consequently difficult to classify, short rods were in general more prevalent than long. Coccus forms made up less than 1 % of the toal number considered.

3. When the cultures were grouped according to their biochemical activities no consistent differences were observed between the types from near the surface and from near the bottom of a lake, nor between the lake and the inflow, but differences were observed in samples taken from the same lake on different occasions. Some types were common to both the lake and the inflows, while others occurred in only one of those habitats. Some types were found both near the surface of the lake and near the bottom, whilst others were confined to one depth.

4. A comparison of the types of bacteria isolated from waters with those found by other workers in soils shows that the main difference in the bacterial flora is the absence in water of the Gram-positive pleomorphic forms of the generaMycobacteriumandCorynebacteriumand ofBact. globiformeConn.;, all of which are common in soils of very widely different agricultural types.

5. In the discussion it is pointed out that, in common with soil types bacteria isolated from water cannot be adequately classified by the usual tests in carbohydrates; in dextrose broth, for instance, the reaction is often only a slight change inpH value.