Mutualistic interactions between vitamin B12-dependent algae and heterotrophic bacteria exhibit regulation

Kazamia, Elena, Czesnick, Hjördis, Nguyen, Thi Thanh Van, Croft, Martin Tom, Sherwood, Emma, Sasso, Severin, Hodson, Sarah James, Warren, Martin James ORCID: https://orcid.org/0000-0002-6028-6456 and Smith, Alison Gail (2012) Mutualistic interactions between vitamin B12-dependent algae and heterotrophic bacteria exhibit regulation. Environmental Microbiology, 14 (6). pp. 1466-1476. ISSN 1462-2912

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Abstract

Many algae are auxotrophs for vitamin B12 (cobalamin), which they need as a cofactor for B12-dependent methionine synthase (METH). Because only prokaryotes can synthesize the cobalamin, they must be the ultimate source of the vitamin. In the laboratory, a direct interaction between algae and heterotrophic bacteria has been shown, with bacteria supplying cobalamin in exchange for fixed carbon. Here we establish a system to study this interaction at the molecular level. In a culture of a B12-dependent green alga Chlamydomonas nivalis, we found a contaminating bacterium, identified by 16S rRNA analysis as Mesorhizobium sp. Using the sequenced strain of M.loti (MAFF303099), we found that it was able to support the growth of B12-dependent Lobomonas rostrata, another green alga, in return for fixed carbon. The two organisms form a stable equilibrium in terms of population numbers, which is maintained over many generations in semi-continuous culture, indicating a degree of regulation. However, addition of either vitamin B12 or a carbon source for the bacteria perturbs the equilibrium, demonstrating that the symbiosis is mutualistic and facultative. Chlamydomonas reinhardtii does not require B12 for growth because it encodes a B12-independent methionine synthase, METE, the gene for which is suppressed by addition of exogenous B12. Co-culturing C.reinhardtii with M.loti also results in reduction of METE expression, demonstrating that the bacterium can deliver the vitamin to this B12-independent alga. We discuss the implications of this for the widespread distribution of cobalamin auxotrophy in the algal kingdom.

Item Type: Article
Uncontrolled Keywords: microbiology,ecology, evolution, behavior and systematics ,/dk/atira/pure/subjectarea/asjc/2400/2404
Faculty \ School: Faculty of Science
Faculty of Science > School of Biological Sciences
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Depositing User: LivePure Connector
Date Deposited: 20 Sep 2022 15:30
Last Modified: 03 Oct 2022 07:33
URI: https://ueaeprints.uea.ac.uk/id/eprint/88509
DOI: 10.1111/j.1462-2920.2012.02733.x

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