Genome biological studies on marine microbial eukaryotes
Ryoma Kamikawa（Graduate School of Agriculture, Kyoto University）
kamikawa.ryoma.7v@kyoto-u.ac.jp
Abstract
Microbial eukaryotes play primary roles in marine environments. Photosynthetic microbial eukaryotes are
responsible for major parts of the annual net primary production in the ocean. On the other hand, heterotrophic
microbial eukaryotes function as intermediate “connectors” in the marine food web. Importantly, some of
microbial eukaryotes form toxic and/or harmful blooms called red tides that would cause mass mortalities ofcultivated fish and bivalves in the coastal areas of Japan. Unveiling genetic and genomic diversity in microbial
eukaryotes would contribute not only to deeper understanding of material circulations in the ocean but also
to development of useful genetic resources as well as of methods for accurate and rapid identification andquantification of toxic and/or harmful bloom-forming species.
Cysts (or resting spores) of those toxic/harmful species present in the marine sediments on theJapanese coastal areas function as a seed population for the next generation red tides and highly useful toevaluate potential of occurrence of toxic and harmful red tides. However, it is difficult to accurately identify
cysts of toxic and harmful species on the basis of morphological characters under microscopy. Therefore, I
developed a method to rapidly and accurately detect and quantify cysts of toxic species from marine
sediments, by using the real-time quantitative PCR targeting that species-specific gene sequences1). I was also
engaged in accumulation of genetic resources in microbial eukaryotes of which genomic and transcriptomic
data have not been fully analyzed. Many microalgal species are known to have lost photosynthesis
secondarily and have shifted their lifestyles to hetertrophy. I have isolated such non-photosynthetic microalgal
species from environmental samples and analyzed their genomes and transcriptomes to reveal theirevolutionary background and cellular functions. Especially, the genomic and transcriptomic analyses
unveiled that the non-photosynthetic microalgal species still retain plastids that are incapable ofphotosynthesizing but capable of biosynthesizing various compounds including fatty acids and carotenoids,some of which are well known as useful anti-oxidants2). I also focused on anaerobic microbial eukaryotes
that are capable of thriving in low oxygen or anaerobic environments such as marine sediments and humanintestines. Genomic and transcriptomic analyses allowed us to obtain gene sequences that encode proteinsfor hydrogen gas production in their anaerobic mitochondrion-related organelles3).
References
1) Kamikawa R., Nagai S., Hosoi-Tanabe S., Itakura S., Yamaguchi M., Uchida Y., Baba T. and Sako Y.:Harmful Algae 6:413-420 (2007)
2) Kayama M., Chen JF., Nakada T., Nishimura Y., Azuma T., Miyashita T., Shikanai T., Takaichi S.,
Kashiyama Y. and Kamikawa R.: BMC Biology 18:126 (2020)
3) Leger M., Kolisko M., Kamikawa R., Stairs CW., Kume K., Čepicka I., Silberman JD., Andersson JO., Xu F.,Yabuki A., Eme L., Zhang Q., Takishita K., Inagaki Y., Simpson AGB., Hashimoto T. and Roger AJ.: NatureEcology and Evolution 1:0092 (2017)