Banerjee RV

Frigaard N-U

Pejchal R

Rippka R

Sakamoto T

Sakuragi Y

Shen G

Swift D

Yoshimura T

ABSTRACT
          
            The euryhaline cyanobacterium
            Synechococcus
            sp. strain PCC 7002 has an obligate requirement for exogenous vitamin B
            12
            (cobalamin), but little is known about the roles of this compound in cyanobacteria. Bioinformatic analyses suggest that only the terminal enzyme in methionine biosynthesis, methionine synthase, requires cobalamin as a coenzyme in
            Synechococcus
            sp. strain PCC 7002. Methionine synthase (MetH) catalyzes the transfer of a methyl group from
            N
            5
            -methyl-5,6,7,8-tetrahydrofolate to
            l
            -homocysteine during
            l
            -methionine synthesis and uses methylcobalamin as an intermediate methyl donor. Numerous bacteria and plants alternatively employ a cobalamin-independent methionine synthase isozyme, MetE, that catalyzes the same methyl transfer reaction as MetH but uses
            N
            5
            -methyl-5,6,7,8-tetrahydrofolate directly as the methyl donor. The cobalamin auxotrophy of
            Synechococcus
            sp. strain PCC 7002 was complemented by using the
            metE
            gene from the closely related cyanobacterium
            Synechococcus
            sp. strain PCC 73109, which possesses genes for both methionine synthases. This result suggests that methionine biosynthesis is probably the sole use of cobalamin in
            Synechococcus
            sp. strain PCC 7002. Furthermore, a cobalamin-repressible gene expression system was developed in
            Synechococcus
            sp. strain PCC 7002 that was used to validate the presence of a cobalamin riboswitch in the promoter region of
            metE
            from
            Synechococcus
            sp. strain PCC 73109. This riboswitch acts as a cobalamin-dependent transcriptional attenuator for
            metE
            in that organism.
          
          
            IMPORTANCE
            Synechococcus
            sp. strain PCC 7002 is a cobalamin auxotroph because, like eukaryotic marine algae, it uses a cobalamin-dependent methionine synthase (MetH) for the final step of
            l
            -methionine biosynthesis but cannot synthesize cobalamin
            de novo
            . Heterologous expression of
            metE
            , encoding cobalamin-independent methionine synthase, from
            Synechococcus
            sp. strain PCC 73109, relieved this auxotrophy and enabled the construction of a truly autotrophic
            Synechococcus
            sp. strain PCC 7002 more suitable for large-scale industrial applications. Characterization of a cobalamin riboswitch expands the genetic toolbox for
            Synechococcus
            sp. strain PCC 7002 by providing a cobalamin-repressible expression system.
          </jats:p

Adam A. Pérez

Zhenfeng Liu

Dmitry A. Rodionov

Zhongkui Li

Donald A. Bryant

Crossref

Journal of Bacteriology

Complementation of Cobalamin Auxotrophy in Synechococcus sp. Strain PCC 7002 and Validation of a Putative Cobalamin Riboswitch
            <i>In Vivo</i>

Complementation of Cobalamin Auxotrophy in Synechococcus sp. Strain PCC 7002 and Validation of a Putative Cobalamin Riboswitch In Vivo

Complementation of Cobalamin Auxotrophy in Synechococcus sp. Strain PCC 7002 and Validation of a Putative Cobalamin Riboswitch In Vivo

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