Thirty-four
Sphaerotilus and
Leptothrix strains were isolated from sewage, activated sludge and iron-containing ditch- and well-water, and their morphological and physiological characters studied. The organisms were grown under different conditions, e.g. on peptoneglucose agar and yeast-extract-manganous-carbonate agar, and in running ditch-water containing ferrous iron. Growth of these bacteria in synthetic media, with glucose as carbon source and aspartic and glutamic acids or inorganic nitrogen compounds as nitrogen source, required added vitamin B
12 unless nitrogen was supplied as hydrolyzed casein or as a mixture of
l-amino acids. Methionine was found to be responsible for this replacement of vitamin B
12.Five different types of sheath-forming bacteria were distinguished in the present study. Type I is the typical sewage organism
Sphaerotilus natans. It has large cells, grows well with relatively high concentrations of organic substrates, but cannot oxidize manganous compounds. In running ditch-water containing ferrous iron, ferric hydroxide may be deposited in and on its sheaths. Although
S. natans under such conditions may resemble the iron bacterium
Leptothrix ochracea, it has relatively long sheaths, partly filled with cells in contrast with the short and mostly empty sheaths of the latter.
S. natans could be readily reisolated from its iron-bacterium cultures but very seldom from crude cultures of
L. ochracea; thus the two organisms are clearly different. Types II and III have relatively large cells, respond poorly to organic nutrients, but are able to oxidize manganous compounds. Type II forms fungus-like flocks in liquid media and resembles microscopically
L. lopholea, with which it may be identical. Type III resembles
L. ochracea more closely than does any other type, but is probably not identical with it; the name
L. pseudo-ochracea sp.n. is proposed for this type. Type IV is intermediate between types I and V. In media with relatively high concentrations of organic nutrients it behaves like a sewage organism, but in poor media containing ferrous and manganous compounds, it behaves like an iron bacterium, depositing large amounts of ferric and manganic oxides in and on its sheaths; for this type the name
L. cholodnii sp.n. is proposed. Type V has small cells, grows poorly in all media tested, but actively oxidizes manganous compounds; the name
Leptothrix discophora is reserved for this type.The globular inclusions in the cells of
S. natans and other members of the
Sphaerotilus-Leptothrix group consist of poly-
-hydroxybutyrate.
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