678 Marine Microbiology 



during the length of the experiment. The organic bound carbon 

 decreased significantly due to tlie activity of the bacteria. 



mV 



-400 h 



1 



time in weeks 



Fig. 2. First experimental series. Sulfate-sulfur (c), sulfide-sulfur (b), 



product of both (a), organic bound carbon and Eh after different times. 



Sediment tiapped in plastic tubes and left in the natvual environment. 



Figure 3 shows the numbers of aerobic, anaerobic, bacteria 

 which transform organic sulfur to sulfide and sulfate reducing 

 bacteria in a semi-logarithmic plot. About 100 times more bac- 

 teria were found which had the potency to form hydrogen sul- 

 fide from organic sources than sulfate reducers. Most bacterial 

 numbers decreased during the length of the experiment, only the 

 sulfate reducing bacteria increased. 



Figure 4 shows another series of experiments. A suspension 

 of an anaerobic mud was added to a medium made of aged sea 

 water and containing among other ingredients Difco neopeptone, 

 yeast extract and sodium lactate. The redox potential was reduced 

 to minus 112 mV by bubbling hydrogen through it before the 



