258 F. L. Bunnell et al. 



Anaerobic and Facultative Anaerobic Bacteria 



While some earlier tundra studies (Levin 1899, Omdliansky 1911) 

 failed to document the presence of anaerobes in tundra soils, recent re- 

 views (Dunican and Rosswall 1974, Clarholm et al. 1975) reported anaer- 

 obes from Swedish and Norwegian tundra and a British peat bog. Evi- 

 dence from the coastal tundra at Barrow indicates that anaerobic bac- 

 teria are present and may be important in decomposition. 



The presence of anaerobic bacteria is indicated by low aerobic plate 

 counts, but high direct microscopic counts and significant quantities of 

 adenosine triphosphate (ATP) in regions of low concentrations of soil 

 oxygen. The observations suggest a living microflora at depth, only a 

 small portion of which can be attributed to fungi, which decrease mark- 

 edly with depth. Significant amounts of methane were evolved only from 

 artificially heated or extremely wet soils. Benoit (unpubl.) isolated both 

 methane oxidizers and methane producers from wet meadow soils using 

 enrichment cultures. Oxidizers would reduce the quantity of methane re- 

 leased from the system, making the detection of anaerobes such as Meth- 

 anomonas more difficult. The most probable number (MPN) of soil an- 

 aerobes obtained in pre-reduced broth media in anaerobic jars was 

 always tenfold greater than the most probable number from the same soil 

 incubated under aerobic conditions. Many of these anaerobes are facul- 

 tative; strict anaerobes constitute less than half of the anaerobic popula- 

 tion. Ahhough facultative anaerobic bacteria are estimated to constitute 

 50 to 10% of the aerobically plateable populations below 10 cm depth, 

 they do not increase in numbers with depth as might be expected in wet 

 soils (Clarholm et al. 1975). The reason appears to be lower temperatures 

 with depth rather than lack of favorable substrates. Heated soils showed 

 a marked loss in caloric content despite low oxygen concentrations. 



Nitrogen, Sulfur, and Iron Bacteria 



Free-living, aerobic, nitrogen-fixing bacteria (e.g. Azotobacterspp.) 

 are generally absent in tundra soils (Dunican and Rosswall 1974), while 

 anaerobic Clostridium spp. often occur (Mishustin and Mirzoeva 1972). 

 Although Azotobacter has been identified from both arctic and antarctic 

 soils, reported numbers are very low and fixation of nitrogen has not 

 been demonstrated (Boyd and Boyd 1962, Boyd et al. 1966, Stutz 1977). 

 Present studies confirm that all three species of /I zo/o^ac/er described in 

 Bergey's manual (Breed et al. 1957) occur in low numbers in the soils at 

 Barrow, but nitrogen fixation by isolates could not be demonstrated. 

 Some nitrogen-fixing activity has been observed in wet meadows in plots 



