We used molecular techniques to assess the phylogenetlc afflnlty of cultured and uncultured m~croorganis~ns from Toolik Lake, an ol~gotrophic lake In a r c t~c Alaska USA The phylogenetlc positions of cloned cultures of bacteria were determined by sequence analysls of PCR ampl~fled ribosomal RNA genes The Toollk Lake bacterial isolates showed a high degree of slmllarlty, 0 94 to 0 99, to a wlde variety of phyla that are well represented in the ribosomal RNA database The occurrence of species normally associated with a terrestrial habltat (Arthrobacter globiforn~is and B~~r k h o l d e n a solanacearum) or a more nutrient-rich environment (Cytophaga aquatills and Zoogloea r a m~y e r a ) suggests a particle-associated origln for these cell types consistent with the fact that w e used an unflltered sample In contrast, the analysls of rRNA genes cloned from a complex natural DNA community indlcated the predominance of beta-proteobacteria closely related to the rRNA hamology group I1 pseudomonads Alcalrgenes eutrophus and Pseudomonaspickett~l However, 2 of therRNA g e n e clones are deeply branching relatives (s~rnllarity = 0 88) of the alpha-proteobacteria SARI 1 cluster, previously detected only In marine environments Thls finding lndlcates a widespread aquatic dlstnbutlon for thls recently descnbed group KEY WORDS: Bactel-]a 1 6 s rRNA. Arctic. SARll
The biomass of bacteria in various waters can be estimated by measuring the amount of cellular bound lipopolysaccharide (LPS). LPS, which is present in the cell walls of gram-negative bacteria, including cyanobacteria, can be quantitated by using an extract of Limulus amebocytes. In one special environment, an oceanic water column below the euphotic zone, the results of the LPS technique agreed very well with those of the direct count and adenosine triphosphate techniques for measuring bacterial biomass.
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