assimilation versus temperature data for acetate (Table 9) 

 suggest that this organic substrate is perhaps utilized by a 

 specialized sub-population which displayed a much more narrow 

 tolerance with respect to temperature. Similar experiments were 

 also performed to determine the temperature optimum for the 

 metabolism of 14 CH 4 . Using the Niskin bottle collected sample 

 from Pisces V dive #25 (see Tables 6 and 7) we determined a 

 metabolic maximum at 37°C with 62.2% of this maximum 14 CH 4 

 oxidation activity still remaining at an incubation temperature 

 of 60°C. In this regard the temperature dependence of CH4 

 oxidation was similar to that measured for the nucleic acid 

 precursors (see Table 9). On the basis of these experiments we 

 conclude that the Pele's Vent bacterial populations are adapted 

 for growth at warm (35-60°C) temperatures and probably decrease 

 their rates of metabolism by factors of 20-100 fold when they are 

 injected into the cold ( 4°C ) ambient bottom seawater surrounding 

 the vent field. 



Enrichment Culture Results 



Our first attempts at pure culture isolation were, in 

 general, unsuccessful. The enrichment cultures failed to recover 

 any organisms with the exception of proteolytic bacteria. Our 

 selective medium (see Table 2) recovered gelatinase positive 

 bacteria with a most probable number of 750 cells ml - -'- for the 

 rock scraping suspension and 550 cells ml -1 for the titanium 

 sample from dive #29. The negative results obtained with the 

 other enrichment culture media should not be interpreted as 

 conclusive evidence for the absence of the "target" organisms. 

 As with any enrichment experiment, negative results cannot 

 preclude the presence of a particular group of microorganisms but 

 could alternately reflect improper incubation or enrichment 

 conditions. This is especially true for the unique habitat of 

 Pele's Vent. Improper conditions, with respect to temperature, 

 pH-alkalinity, dissolved gases, eH or specific organic or 

 inorganic growth factors could have significantly affected the 

 potential growth of the vent bacteria. The presence of 

 heterotrophic bacteria able to hydrolyse protein is not 

 startling. Our investigation of the temperature of maximum 

 growth might help in future studies to define the actual habitat 

 for these organisms while other conditions could be studied to 

 help in defining proper enrichment conditions for the other 

 micro-organisms present. The effects of high concentrations of 

 dissolved CO2 and its effect on bacterial metabolism may also 

 need to be evaluated in future experiments. 



Structure and Composition of Bacterial Mats 



One of the most conspicuous features of Pele's Vent is the 

 extensive reddish-brown bacterial mat, or more precisely carpet, 

 which covers large areas of the hydrothermal habitat (Fig. 2b). 

 When viewed under bright-field (Fig. 8) or scanning electron 



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