AME 26:305-311 (2002)  -  doi:10.3354/ame026305

photoreactivity and bacterioplankton availability of aliphatic versus aromatic amino acids and a protein

Bettina Reitner1, Alois Herzig2, Gerhard J. Herndl3,*

1Institute of Ecology and Conservation Biology, University of Vienna, Althanstr. 14, 1090 Vienna, Austria
2Biological Station Neusiedler See, 7142 Illmitz, Austria
3Department of Biological Oceanography, Netherlands Institute for Sea Research (NIOZ), PO Box 59, 1790 AB Den Burg, Texel, The Netherlands
*Corresponding author. E-mail:

ABSTRACT: In batch culture experiments with natural bacerial assemblages collected from a humic-rich lake (Lake Neusiedl, Austria), labile organic nitrogen containing model substrates (alanine [Ala], an aliphatic amino acid, tryptophan [Trp], an aromatic amino acid, and bovine serum albumin [BSA], as protein) were added to 0.2 μm filtered lake water prior to exposure (for 9 h) to surface levels of the full range of solar radiation or being held in the dark. These organic nitrogen species were chosen to investigate compound-specific differences in the photochemical transformation of labile dissolved organic matter (DOM) and its subsequent availability to bacteria. ŒPhotocoloring¹ or humification in the Trp-amended water exposed to natural solar radiation and significant dissolved organic carbon (DOC) loss (120 μM C over 9 h exposure) resulted, after inoculation of the natural bacterial assemblage, in a lower maximum bacterial abundance in the previously solar radiation-exposed treatments as compared to the dark control. In contrast, the absorbance characteristics of solar-irradiated Ala- and BSA-amended water were almost identical to the unamended control and to the Ala- and BSA-amended treatments kept in the dark. Also, no significant difference in the maximum bacterial abundance of the solar radiation-exposed Ala- and BSA-amended treatments was detectable as compared to the corresponding dark controls. Our data indicate that Trp is a potential source of solar radiation-mediated humification in Lake Neusiedl.

KEY WORDS: Shallow lake · Dissolved organic matter · UV radiation · Photoreactivity · Bioreactivity

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