Vitamin B 12 is not shared by all marine prototrophic bacteria with their environment

• Published in: The ISME Journal Vol. 17; no. 6; p. 836
• Main Authors: Sultana, Sabiha, Bruns, Stefan, Wilkes, Heinz, Simon, Meinhard, Wienhausen, Gerrit
• Format: Journal Article
• Language: English
• Published: England 01.06.2023
• Subjects: Bacteria - genetics; Bacteria - metabolism; Diatoms - metabolism; Vitamin B 12 - metabolism; Vitamins - metabolism
• ISSN: 1751-7370
• DOI: 10.1038/s41396-023-01391-3

Vitamin B (cobalamin, herein B ) is an essential cofactor involved in amino acid synthesis and carbon resupply to the TCA cycle for most prokaryotes, eukaryotic microorganisms, and animals. Despite being required by most, B is produced by only a minor fraction of prokaryotes and therefore leads to complex interaction between prototrophs and auxotrophs. However, it is unknown how B is provided by prototrophs to auxotrophs. In this study, 33 B prototrophic alphaproteobacterial strains were grown in co-culture with Thalassiosira pseudonana, a B auxotrophic diatom, to determine the bacterial ability to support the growth of the diatom by sharing B . Among these strains, 18 were identified to share B with the diatom, while nine were identified to retain B and not support growth of the diatom. The other bacteria either shared B with the diatom only with the addition of substrate or inhibited the growth of the diatom. Extracellular B measurements of B -provider and B -retainer strains confirmed that the cofactor could only be detected in the environment of the tested B -provider strains. Intracellular B was measured by LC-MS and showed that the concentrations of the different B -provider as well as B -retainer strains differed substantially. Although B is essential for the vast majority of microorganisms, mechanisms that export this essential cofactor are still unknown. Our results suggest that a large proportion of bacteria that can synthesise B de novo cannot share the cofactor with their environment.