Impact of microcystin on RubisCO and the carbon concentrating mechanism of Microcystis aeruginosa
Final Report Abstract
Growth of cyanobacteria is closely linked to CO2 fixation by the enzyme RubisCO. However, the activity of RubisCO is compromised by the alternative fixation of O2 that leads to photorespiration. In model cyanobacteria, robust carbon fixation by RubisCO under limiting Ci conditions is ensured by the carbon-concentrating mechanism (CCM). Recent studies have shown a pronounced genotypic plasticity among Microcystis strains that individually lack components bicarbonate uptake transporter genes and differ in their adaptation to Ci-limiting conditions. The current project has uncovered that differences in the CCM of Microcystis go beyond the bicarbonate uptake transport but also concern the carboxysomal localization of RubisCO. The study has not only revealed a non-canonical localization of RubisCO under high light conditions and high cell densities underneath the cytoplasmic membrane but also highlighted differences between the microcystin-producing wild-type strain M. aeruginosa and the DmcyB mutant. We have found evidence that microcystin promotes condensate formation in vivo and closely interacts with RbcS and enzymes of the Calvin-Benson cycle. Further, we have observed pronounced diel dynamics of extracellular microcystin under higher cell densities that influence the subcellular localization dynamics as external stimuli. The large of the small subunit of RubisCO are conditionally separate in Microcystis. Our data suggest that microcystin and possibly other small molecules in Microcystis may be part of a rapid response mechanism to conditions of high light. We have further identified and characterized new regulatory proteins controlling Calvin cycle proteins, the CBS-CP12 fusion proteins that also show pronounced light-dependent regulation and a localization underneath the cytoplasmic membrane.4 Additionally, we have studied the impact of heterotrophic bacteria for the localization of RubisCO and found evidence for a tight and specific interaction of facilitating heterotrophic bacteria that may provide CO2 through their respiratory activities.
Publications
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(2018) Structural and functional insights into the unique CBS-CP12 fusion protein family in cyanobacteria. Proc Natl Acad Sci 115: 7141-7146
Hackenberg, C., Hakanpää, J., Cai, F., Antonyuk, S., Eigner, S., Meissner, S., Laitaoja, M., Jänis, J., Kerfeld, C.A., Dittmann, E., Lamzin, V.S.
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(2019) Non-canonical localization of RubisCO under high light conditions in the toxic cyanobacterium Microcystis aeruginosa PCC7806. Environ Microbiol 21: 4836-4851
Barchewitz, T., Guljamow, A., Meissner, S., Timm, S., Henneberg, M., Baumann, O., Hagemann, M., Dittmann, E.
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(2021) Diel variations of extracellular microcystin influence the subcellular dynamics of RubisCO in Microcystis aeruginosa PCC7806. Microorganisms
Guljamow, A., Barchewitz, T., Große, R., Timm, S., Hagemann, M., Dittmann, E.
