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Autotrophic and heterotrophic acquisition of carbon and nitrogen by a mixotrophic chrysophyte established through stable isotope analysis

Terrado, Ramon and Pasulka, Alexis L. and Lie, Alle A.-Y. and Orphan, Victoria J. and Heidelberg, Karla B. and Caron, David A. (2017) Autotrophic and heterotrophic acquisition of carbon and nitrogen by a mixotrophic chrysophyte established through stable isotope analysis. ISME Journal, 11 (9). pp. 2022-2034. ISSN 1751-7362. PMCID PMC5563956. doi:10.1038/ismej.2017.68.

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Collectively, phagotrophic algae (mixotrophs) form a functional continuum of nutritional modes between autotrophy and heterotrophy, but the specific physiological benefits of mixotrophic nutrition differ among taxa. Ochromonas spp. are ubiquitous chrysophytes that exhibit high nutritional flexibility, although most species generally fall towards the heterotrophic end of the mixotrophy spectrum. We assessed the sources of carbon and nitrogen in Ochromonas sp. strain BG-1 growing mixotrophically via short-term stable isotope probing. An axenic culture was grown in the presence of either heat-killed bacteria enriched with ^(15)N and ^(13)C, or unlabeled heat-killed bacteria and labeled inorganic substrates (^(13)C-bicarbonate and ^(15)N-ammonium). The alga exhibited high growth rates (up to 2 divisions per day) only until heat-killed bacteria were depleted. NanoSIMS and bulk IRMS isotope analyses revealed that Ochromonas obtained 84–99% of its carbon and 88–95% of its nitrogen from consumed bacteria. The chrysophyte assimilated inorganic ^(13)C-carbon and ^(15)N-nitrogen when bacterial abundances were very low, but autotrophic (photosynthetic) activity was insufficient to support net population growth of the alga. Our use of nanoSIMS represents its first application towards the study of a mixotrophic alga, enabling a better understanding and quantitative assessment of carbon and nutrient acquisition by this species.

Item Type:Article
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Orphan, Victoria J.0000-0002-5374-6178
Additional Information:© 2017 The Authors. This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit Received 21 October 2016; Revised 20 March 2017; Accepted 3 April 2017; Advance online publication 19 May 2017. This collaborative research was supported by the Gordon and Betty Moore Foundation through Grant GBMF3299 to DAC and KBH at USC, and Grant (GBMF3780) to VJO at California Institute of Technology. The authors declare no conflict of interest.
Funding AgencyGrant Number
Gordon and Betty Moore FoundationGBMF3299
Gordon and Betty Moore FoundationGBMF3780
Issue or Number:9
PubMed Central ID:PMC5563956
Record Number:CaltechAUTHORS:20170522-080446020
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:77616
Deposited By: Tony Diaz
Deposited On:22 May 2017 15:58
Last Modified:15 Nov 2021 17:32

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