THE IRON-BACTERIA 



By DAVID ELLIS, Ph.D., D.Sc, F.R.S.E. 

 Royal Technical College, Glasgow 



Among the higher bacteria is to be found a certain class of 

 organisms that almost always inhabit ferruginous waters. As 

 a result of their growth and multiplication, their mucilaginous 

 outer membranes become impregnated with ferric hydroxide. 

 This gives them a rusty red appearance, and on this account, 

 and because of their constant presence in iron-laden waters, 

 they have been named Iron-bacteria by Winogradsky. Now 

 part of the iron in these waters is in solution in the ferrous 

 form, and the changes for which the iron-bacteria are respon- 

 sible consist in a transformation of these soluble ferrous com- 

 pounds into the insoluble ferric hydroxide. If a microscopic 

 examination be made of the red deposit which forms the bed of 

 ferruginous streams, or the deposit which rings the mouth of 

 ferruginous springs, in nine cases out of ten the deposit will 

 be seen to consist of a multitudinous number of small hollow 

 tubes such as are figured in Plate I. These tubes are the 

 remains of Iron-bacteria. During their lifetime the enveloping 

 sheath which each individual possesses becomes impregnated 

 with ferric hydroxide, which is an excellent preserving medium, 

 with the result that when the organisms die the sheath which 

 covered them does not disintegrate, and in time their number 

 becomes so great that the bed of the stream is coloured a deep 

 red and in many cases a thick deposit is formed. The majority 

 of these sheaths originally formed a covering to Leptothrix 

 ochracea (syn. Chlamydothrix ochracea), the best known and 

 most widely distributed of the Iron-bacteria ; others, however, 

 may have covered other Iron-bacteria such as Cladothrix 

 dichotoma or Crenothrix polyspora. A more detailed descrip- 

 tion of the sheaths will be given when we come to consider the 

 individual species. It will suffice here to state that in the 

 living organism the sheath is at first a delicate pliable covering 



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