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Applied and Environmental Microbiology, November 2009, p. 7221-7228, Vol. 75, No. 22
0099-2240/09/$08.00+0     doi:10.1128/AEM.00960-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

High Ratio of Bacteriochlorophyll Biosynthesis Genes to Chlorophyll Biosynthesis Genes in Bacteria of Humic Lakes {triangledown}

Alexander Eiler,1,3 Sara Beier,1 Christin Säwström,2,4 Jan Karlsson,2 and Stefan Bertilsson1*

Limnology/Department of Ecology & Evolution, Uppsala University, Uppsala, Sweden,1 Climate Impacts Research Centre (CIRC), Department of Ecology and Environmental Science, Umeå University, Box 62, 98107 Abisko, Sweden,2 Hawaii Institute of Marine Biology, SOEST, University of Hawaii at Manoa, Kaneohe, Hawaii,3 Australian Rivers Institute, Griffith University, Nathan, Queensland 4111, Australia4

Received 28 April 2009/ Accepted 22 September 2009

Recent studies highlight the diversity and significance of marine phototrophic microorganisms such as picocyanobacteria, phototrophic picoeukaryotes, and bacteriochlorophyll- and rhodopsin-holding phototrophic bacteria. To assess if freshwater ecosystems also harbor similar phototroph diversity, genes involved in the biosynthesis of bacteriochlorophyll and chlorophyll were targeted to explore oxygenic and aerobic anoxygenic phototroph composition in a wide range of lakes. Partial dark-operative protochlorophyllide oxidoreductase (DPOR) and chlorophyllide oxidoreductase (COR) genes in bacteria of seven lakes with contrasting trophic statuses were PCR amplified, cloned, and sequenced. Out of 61 sequences encoding the L subunit of DPOR (L-DPOR), 22 clustered with aerobic anoxygenic photosynthetic bacteria, whereas 39 L-DPOR sequences related to oxygenic phototrophs, like cyanobacteria, were observed. Phylogenetic analysis revealed clear separation of these freshwater L-DPOR genes as well as 11 COR gene sequences from their marine counterparts. Terminal restriction fragment length analysis of L-DPOR genes was used to characterize oxygenic aerobic and anoxygenic photosynthesizing populations in 20 lakes differing in physical and chemical characteristics. Significant differences in L-DPOR community composition were observed between dystrophic lakes and all other systems, where a higher proportion of genes affiliated with aerobic anoxygenic photosynthetic bacteria was observed than in other systems. Our results reveal a significant diversity of phototrophic microorganisms in lakes and suggest niche partitioning of oxygenic and aerobic anoxygenic phototrophs in these systems in response to trophic status and coupled differences in light regime.

* Corresponding author. Mailing address: Limnology/Department of Ecology and Evolution, Uppsala University, Norbyv. 18D, SE-75239 Uppsala, Sweden. Phone: 46-18-4712712. Fax: 46-18-531134. E-mail: stebe{at}ebc.uu.se

{triangledown} Published ahead of print on 2 October 2009.

Applied and Environmental Microbiology, November 2009, p. 7221-7228, Vol. 75, No. 22
0099-2240/09/$08.00+0     doi:10.1128/AEM.00960-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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