〓 Research Area : Plant-Environmental Microbiology

Lanthanide-dependent enzyme and motility
in plant-associating methylotrophic bacteria
Plant emit large quantities of methanol through stomata as aresult of their growth and pectin degradation. Methanol canbe a good nutrient for bacteria and methanol-utilizing (methylotrophic) bacteria predominate on the aerial plant surface(phyllosphere). We focus on their methanol metabolism andsymbiosis with plants.
Methylobacterium species are commonly found in phyllosphere, and they can promote plant growth. They have methanol dehydrogenase (MDH) to oxidize methanol. Not only calcium-dependent MDH encoded by mxaF, recently it was foundthat lanthanide-dependent MDH is also encoded by xoxF in
the genomes of Methylobacterium species. This is the first enzyme described to date, to contain lanthanide. We investigate
the mechanism of expression switching between these MDHs,depending on the availability of lanthanide.
We also study molecular mechanism of the motility and chemotaxis in methylotrophs, which is important for the bacteria
to find and colonize plants. The chemotaxis is also affected by
the carbon source and lanthanide.

〓 Assoc. Prof.
TANI Akio

We have found new methylotrophic bacteria belonging tonovel genera. They have been isolated from rice rhizosphereusing lanthanide as an essential cofactor. They are named as
Oharaeibacter diazotrophicus SM30 and Novimethylophilus
kurashikiensis La2-4. Thus, lanthanide can be used for isolation of bacteria that contain xoxF, which can be found in manyso-believed non-methylotrophic bacteria and novel bacteria.

Methylobacterium aquaticum strain 22A

Strain 22A adhering plant root hair

Strain 22A chemotaxis toward methanol

Novimethylophilus kurashikiensis La2-4〓 Research Area : Plant-Environmental Microbiology

Study on dynamics of Phytoplankon in environment
Our group focuses on the study of Heterosigma akashiwo,
a unicellular alga that forms harmful algal bloom (commonlytermed ‘red tide’) . Algal bloom is typically caused by aberrant
propagation of a single species, resulting in its predominationin the local population. While environmental factors including
temperature and eutrophication are linked to bloom, the precise mechanism of its formation process is still obscure. We
isolated a bacterial strain, Altererythrobacter ishigakiensis,
a member of the class Alphaproteobacteria, that promotes
growth of Heterosigma akashiwo.This is the first example of
selective growth promotion of H. akashiwo by a marine bacterium, and may exemplify importance of symbiotic bacteriumon algal bloom forming process in general.

A bloom causative phytoplankton,
Heterosigma akashiwo

Study on interaction between a giant doube-stranded
DNA virus and its host〓 Assoc. Prof.
UEKI Shoko
HaV infect and lyse its host,Heterosigma akashiwo. Thevirus was identified as a bloomterminating factor.

H. akashiwo bloom is known to be terminated by algicidal bacteria
and viruses. Heterosigma akashiwo virus (HaV) was identified as oneof such bloom-terminating factors. We completed the sequencing of
its genomes. The virual genome was characterized to be a linear double stranded DNA (dsDNA), with an estimated size of ~290 kbp. It is amember of Phycodnaviridae, one of the viral families regarded as “giantdsDNA viruses” that possess genomes larger than several hundred-kbp
in size.
We are particularly interested in studying about the infection mechanismof HaV at cellular and molecular level. The study will provide insights
into infection strategies of a giant dsDNA virus, and the molecular mechanism of a major environmental phenomenon, bloom termination.
Graduate School of Environmental and Life Science, Okayama University57