Graduate Thesis Or Dissertation
 

Vitamin B₁₂ production and depletion in a naturally eutrophic lake

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  • The vitamin B₁₂ concentrations in both the water and sediments of Klamath Lake were found to vary significantly during a one-year period. The patterns of B₁₂ distribution were remarkably similar among the three main sites. In all cases there was an extremely sharp gradation in concentration in relation to depth of sediment, with the highest concentrations being found at the water-sediment interface. Maximum concentrations in the water layer occurred shortly after the onset of bloom conditions in mid May 1969. In the upper sediment layers, however, maximum concentrations occurred in early fall, concurrent with the die-off of the bloom, followed by an abrupt decrease shortly thereafter. Concentrations of up to 400 μμg/ml of water (June 1969) and 1.8 μg/g of dry sediment (September 1969) were demonstrated. In conjunction with the analysis of environmental variations of B₁₂, various aspects of its production and depletion were examined. Of 42 bacterial isolates from Klamath Lake water and sediments 20 were found capable of producing 50 μμg or more B₁₂/ml of culture medium. Mixed cultures of Klamath Lake organisms were found capable of producing up to 23 mμg B₁₂/ml of medium. This is more than 30 times the highest rate found using pure culture techniques. Phytoplankton samples were found to contain up to 5 μg B₁₂/g dry material and significant B₁₂ production was found to occur in unialgal cultures of Aphanizomenon flos-aquae. Degradation of B₁₂ occurred in sterilized sediment samples as well as in a sediment-perfusion column containing an initially high concentration of the vitamin.
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