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 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
Related URLs:	http://www.scopus.com/inward/record.url?...
Depositing User:	LivePure Connector
Date Deposited:	20 Sep 2022 15:30
Last Modified:	06 Feb 2025 10:58
URI:	https://ueaeprints.uea.ac.uk/id/eprint/88509
DOI:	10.1111/j.1462-2920.2012.02733.x

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