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Applied and Environmental Microbiology, October 2005, p. 6267-6275, Vol. 71, No. 10
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.10.6267-6275.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Effect of Humic Substance Photodegradation on Bacterial Growth and Respiration in Lake Water

Alexandre M. Anesio,¹ Wilhelm Granéli,² George R. Aiken,³ David J. Kieber,⁴ and Kenneth Mopper^5*

Institute of Biological Sciences, University of Wales, Aberystwyth SY23 3DA, United Kingdom,¹ Department of Ecology/Limnology, Lund University, Ecology Building, S 223 62 Lund, Sweden,² U.S. Geological Survey, Boulder, Colorado 80303,³ Department of Chemistry, College of Environmental Science and Forestry, State University of New York, Syracuse, New York 13210,⁴ Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, Virginia 23529⁵

Received 21 December 2004/ Accepted 13 May 2005

This study addresses how humic substance (HS) chemical composition and photoreactivity affect bacterial growth, respiration, and growth efficiency (BGE) in lake water. Aqueous solutions of HSs from diverse aquatic environments representing different dissolved organic matter sources (autochthonous and allochthonous) were exposed to artificial solar UV radiation. These solutions were added to lake water passed through a 0.7-µm-pore-size filter (containing grazer-free lake bacteria) followed by dark incubation for 5, 43, and 65 h. For the 5-h incubation, several irradiated HSs inhibited bacterial carbon production (BCP) and this inhibition was highly correlated with H₂O₂ photoproduction. The H₂O₂ decayed in the dark, and after 43 h, nearly all irradiated HSs enhanced BCP (average 39% increase relative to nonirradiated controls, standard error = 7.5%, n = 16). UV exposure of HSs also increased bacterial respiration (by 18%, standard error = 5%, n = 4), but less than BCP, resulting in an average increase in BGE of 32% (standard error = 10%, n = 4). Photoenhancement of BCP did not correlate to HS bulk properties (i.e., elemental and chemical composition). However, when the photoenhancement of BCP was normalized to absorbance, several trends with HS origin and extraction method emerged. Absorbance-normalized hydrophilic acid and humic acid samples showed greater enhancement of BCP than hydrophobic acid and fulvic acid samples. Furthermore, absorbance-normalized autochthonous samples showed 10-fold greater enhancement of BCP than allochthonous-dominated samples, indicating that the former are more efficient photoproducers of biological substrates.

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* Corresponding author. Mailing address: Department of Chemistry and Biochemistry, Old Dominion University, Rm. 110 Alfriend Bldg., 4541 Hampton Blvd., Norfolk, VA 23529. Phone: (757) 683-4094. Fax: (757) 683-4628. E-mail: kmopper{at}odu.edu.

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Applied and Environmental Microbiology, October 2005, p. 6267-6275, Vol. 71, No. 10
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.10.6267-6275.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

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