Laboratory of Aquatic Ecology
Maiko Kagami
We are interested in discovering diversity and functions of microbes in lakes, rivers and oceans. Our tools are various, including field observations, microscopes, DNA analysis and incubation experiments.
Diversity and functions of phytoplankton
EUTROPHICATION often promotes the dominance of large phytoplankton and cyanobacteria, which are less edible to zooplankton. The functions of large inedible species must be different from those of small edible algae.
Those inedible species are thought to sink into the bottom without being incorporated in the food webs. The increase in sinking fluxes causes the anoxic zone in the lake bottom. Some of inedible species, however, are infected by parasitic chytrids. Those infected algae might be incorporated into food webs in the surface zone instead of sinking into the bottom (Fig 1).
The responses of large and small phyotplankton to eutrophication and global warming must be different, since the growth characteristics are partly determined by cell size. Considering ECOLOGICAL TRAITS, such as cell size and nutrient affinities, we can better predict how phytoplankton respond to environmental changes, and develop the sustainable way to control algal blooms and maintain the water quality of lakes.
Large inedible diatoms are utilized by chytrids, whose zoospores are eaten by daphnia.
Aquatic Food Web including parasites
Parasitic fungi, CHYTRIDS, are major parasites infecting various organisms. The most famous chytrid must be Batrachochytrium infecting amphibians. The other chytrids infect diverse phytoplankoton. The zoospores of chytrids are good food sources for zooplankton due to their small sizes (2-5 µm) and their quality (rich in cholesterols and PUFAs). Parasitic chytrids can transfer the materials from large inedible algae to zooplankton. The pathway from large inedible algae to zooplankton via chytrid was named as MYCOLOOP, based on mycology and my name (Maiko).
Mycoloop (Kagami et al. 2007）
References
Kagami et al. (2014) Mycoloop: chytrids in aquatic food webs. Frontiers in Microbiology 5:166.
Major Research Grants
-
Quantifying material flows mediated by parasites in lake, JSPS Grant-in Aid for Young Scientists (B), Coorinator, 2007-2009
-
Ecology of fungi and their roles in decomposing refractory organic matters in lakes and ponds, JSPS Grant-in Aid for Young Scientists (B), Coordinator, 2010-2013
-
Diversity and functional importance of chytrids in lake ecosystems, Japan-France Integrated Action Program (SAKURA) , Coordinator, 2010-2012
-
Diversity and functions of chytrids in lakes and oceans, JSPS Grant-in Aid for Scientific Research (B), Coordinator, 2013-2016
-
Diversity and functions of chytrids in lakes and oceans, JSPS Grants-in-Aid for Scientific Research (KAKENHI) - “Fund for the Promotion of Joint International Research (Fostering Joint International Research), Coordinator, 2016-2017
Host-parasite interactions between phytoplankton and diverse eukaryotes
Phytoplankton can be infected by various organisms including virus, bacteria, fungi and protists. Recently, fungi especially chytr chytridiomycetes (chytrids) are found to be important parasites infecting phytoplankton in lakes and coastal areas. However, due to the lack of DNA database and distinct morphological characteristics, chytrids cannot be identified in the field only by DNA analysis or by microscopic observation.
SINGLE SPORE PCR method was developed to identify fungi infecting phytoplankton in the field. By applying the method, we identified various fungi, including not only chytrids but also Cryptomycota and Aphelida. Diverse fungi must be discovered with more sampling efforts with Single Spore PCR methods.
Not only chytrids but also Cryptomycota and Aphelida were found from single diatom species, Aulacoseira granulata, in Lake Inba, Japan (Kagami et al. unpublished).
Single Spore PCR method
We pick up single host-parasite pair from the water, extract DNA, and identify both parasitic fungi and phytopankton by using specific primers
(Ishida et al. 2015, Wurzbacher et al. 2018).
References
Seiji Ishida, Daiki Nozaki, Hans-Peter Grossart, Maiko Kagami (2015) Novel basal fungal lineages from freshwater phytoplankton and lake samples. Environmental Microbiology Reports 7(3), 435-441.
Kensuke Seto, Maiko Kagami, Yosuke Degawa (2016) Phylogenic Position of Parasitic Chytrids on Diatoms: Characterization of a Novel Clade in Chytridiomycota. Journal of Eukaryotic Microbiology (64) 383-393. 10.1111/jeu.12373
Silke van den Wyngaert, Kensuke Seto, Keilor Rojas-Jimenez, Maiko Kagami, Hans-Peter Grossart (2017) A new parasitic chytrid, Staustromyces oculus (Rhizophydiales, Staurastromycetaceae fam. nov.), infecting the freshwater desmid Stauastrum sp.. Protist (in print) 10.1016/j.protis.2017.05.001
Christian Wurzbacher, Ellen Larsson, Johan Bengtsson-Palme, Silke Van den Wyngaert, Sten Svantesson, Erik Kristiansson, Maiko Kagami, Henrik Nilsson (2018) Introducing ribosomal tandem repeat barcoding for fungi. Molecular Ecology Resources (accepted).
Major grants
-
Diversity and functions of chytrids in lakes and oceans, JSPS Grant-in Aid for Scientific Research (B), Coordinator, 2013-2016
-
Diversity and functions of chytrids in lakes and oceans, JSPS Grants-in-Aid for Scientific Research (KAKENHI) - “Fund for the Promotion of Joint International Research (Fostering Joint International Research), Coordinator, 2016-2017
-
Host-parasite interactions between phytoplankton and diverse fungi under environmental fluctuations, JSPS Grant-in Aid for Scientific Research (B), Coordinator, 2016-2020
Regime shift
In many shallow eutrophic lakes, floating-leaved macrophytes became dominant instead of cyanobacteria bloom. Floating-leaved macrophytes, such as water chestnuts (Trapa natans, Trapa japonicus), expand leaves on the lake surface, which decrease the light penetration and oxygen in the water column. While, leaves created habitats for water birds, insects and fishes. We examine the positive and negative effects of floating-leaved macrophytes on lake ecosystems, and suggest the sustainable way to control the overgrown macrophyte.
Major publications
Masayuki Kawatsu, Gen Morimoto, Maiko Kagami (2015) Seasonal changes in the water bird community in Lake Inba; influence of floating-leaved macrophytes on habitat selection. Aquatic Botany 126, 32-37.
Yurie Otake, Maiko Kagami, Takeo Kuriyama, Takehito Yoshida (2018) Spatial heterogeneity in induced defense of Brachionus calyciflorus within a single lake caused by the bed of floating-leaved macrophyte Trapa species”. Limnology (accepted)
On Saito, Tatsuya Kobayashi, Maiko Hiroi, Masayuki Kawatsu, Shun Takagi, Jun Nishihiro, Maiko Kagami (2018) Seasonal changes in the biomass of floating leaved plant, Trapa spp., and its relation with a leaf beetle, Galerucella nipponensis, in Lake Inba, Japan. Limnology (accepted)
Shun Takagi, Natsumi Nakanishi, Shota Tanimura, Takeo Kuriyama, Maiko Kagami (2018) Utilization of emergent plants as an aestivation habitat by the Trapa-feeding leaf beetle (Galerucella nipponensis) in Lake Inba, Japan. Limnology (accepted), https://link.springer.com/article/10.1007/s10201-018-0545-3
Daphnia fortune telling (only in Japanese)
We are creating educational tools to teach diversity and ecosystem functions using plankton. We developed "daphnia fortune telling" based on our survey of daphnids in Lake Inba, Japan. After you answer several easy questions (e.g.Do you like party? Do you feel lonely?), you will find out which daphnia you are.
