ZoBell — 104 — Marine Microbiology 



producing oxygen, algae and diatoms may cause the precipitation of ferric 

 iron. Starkey and Halvorson question the widespread occurrence and 

 activity of autotrophic iron bacteria. 



Thiel (1928) is also of the opinion that the importance of true auto- 

 trophic iron bacteria as geological agents has been overemphasized, while 

 the effects of heterotrophs on the deposition and transformation of iron 

 have been neglected. He reports that manganese as well as iron com- 

 pounds are precipitated by heterotrophic bacteria and by certain fungi 

 found in peat. 



Hardman and Henrici (1939) believe that Siderocapsa treubii, which 

 has been regarded as an autotroph, probably is a heterotrophic organism, 

 utilizing the organic radicle of organic iron compounds and merely depos- 

 iting the iron as a waste product upon the cell capsules. This organism, 

 together with the closely related Siderocapsa major, was found abun- 

 dantly in alkaline, hard- water lakes of the drainage type and in certain 

 rapidly flowing streams. Species of Siderocapsa were not found in neutral 

 or acidic soft-water lakes of the seepage type. Leptothrix crassa and related 

 iron-depositing bacteria were found in certain lakes having a high content 

 of iron. 



Microbiological deposition of manganese is believed to occur in about 

 the same way as iron deposition (Dorff, 1935; Baier, 19376; Zapffe, 

 1 93 1 ) . In many environments iron and manganese are deposited together, 

 and most of the bacteria which precipitate iron likewise precipitate man- 

 ganese. According to Jackson (1902), Crenothrix polyspora, Cr. man- 

 ganifera, and Cr. ochracea are able to precipitate either iron, manganese, 

 or aluminum from water. 



The precipitation of copper (as sulfide) in mud by bacterial activity has 

 been reported by Lovering (1927). Copper precipitation is due not to 

 specific bacteria but rather to the action of reducing substances produced 

 during bacterial metabolism. Lovering believed that the precipitation 

 of vanadium as vanadite and cornotite may be accounted for upon a basis 

 of bacterial activity. In discussing the role of bacteria in halloysite for- 

 mation, Bucher (1921) stated that sulfate-reducing bacteria promote 

 the precipitation of aluminum silicate. 



Effect on hydrogen-ion concentration : — As has been stated before, 

 microorganisms are probably the principal dynamic agencies which alter 

 the hydrogen-ion concentration, oxidation -reduction potential, gas ten- 

 sion, and other physico-chemical conditions in bottom deposits. De- 

 pending primarily upon the numbers and kinds of microorganisms present, 

 the chemical composition of the substrate, and various environmental 

 conditions, they may tend to increase or to decrease the hydrogen-ion 

 concentration or pH. The following microbiologically activated processes 

 tend to increase the hydrogen-ion concentration or to decrease the pH.: 

 (i) Production of CO2 by respiring cells, (2) production of organic acids 

 such as lactic, butyric, acetic, and formic acids, for example, from the 

 decomposition of carbohydrates, lipids, proteins, etc., (j) oxidation of 

 H2S or sulfur to sulfuric acid or other acid sulfates, {4) reduction of sulfur 

 to H2S, (5) formation of nitrite or nitrate, (6) assimilation of ammonium 

 as a source of nitrogen or its oxidation as a source of energy, and (7) the 

 liberation of phosphate from organic compounds. The extent to which 

 these reactions may occur in the marine environment is discussed else- 

 where in this volume. 



