The University of Tokyo · Environmental Science
Professor Koji Hamasaki's research lab specializes in microbial ecology and environmental microbiology, with a focus on understanding the physiological responses of marine microorganisms to environmental stressors such as temperature, salinity, and light. The lab employs innovative molecular and immunocytochemical techniques—such as BrdU labeling and BUMP-DGGE—to study microbial growth dynamics, community assembly, and functional diversity in marine and aquatic ecosystems. Additional research explores the impacts of climate change on host-microbe interactions, particularly in marine fish and invertebrates, highlighting the ecological consequences of shifting environmental conditions. The lab also investigates the biophysical properties of advanced materials, including superconducting thin films, demonstrating a multidisciplinary approach bridging biology and materials science.
Figures are computed from collected data and may differ slightly.
The variability of cellular toxin content in the dinoflagellate Alexandrium tamarense isolated from Hiroshima Bay was analyzed under a variety of culture conditions. Growth and toxicity were represented as a function of light (80, 90, 110, 160 and 350 μmol m–2 s –1), temperature (12, 17 and 22°C), salinity (13, 16.5, 19.5, 25, 29, 33, 36.5 and 38 PSU) and ammonium concentration (0.11, 0.22 and 0.44 mM). Toxicity was measured by the tissue culture bioassay using mouse neuroblastoma cells, and exp
A fundamental question in microbial oceanography concerns the relationship between prokaryote diversity and biogeochemical function in an ecosystem context. We combined bromodeoxyuridine (BrdU) magnetic bead immunocapture and PCR-denaturing gradient gel electrophoresis (BUMP-DGGE) to examine phylotype-specific growth in natural marine assemblages. We also examined a broad range of marine bacterial isolates to determine their abilities to incorporate BrdU in order to test the validity of the meth
Fish-associated microbiota are an integral part to the health of the host fish. The ongoing climate changes including global warming of water may disrupt the composition and diversity of host-microbiota, and subsequently, destabilize the fish homeostasis. Since the knowledge on temperature-sensitive marine fish and environmental bacteria is scarce, we investigated the effects of rearing temperatures on community structure, diversity and assembly process of bacteria on chum salmon ( Oncorhynchus
We tested the application of 5-bromo-2’-deoxyuridine (BrdU), a thymidine analogue that becomes incorporated into DNA during growth, to measure growth rates of individual marine bacteria cells. Immunocytochemical detection of BrdU incorporation into bacterial DNA has the potential for single-cell-based growth measurement. Optimized procedure for immunocytochemistry was applicable to 14 marine heterotrophic bacterial isolates belonging to g-proteobacteria, α-proteobacteria, Cytophaga-Flavobacteriu
We investigated patterns of larval growth and development in terrestrial hermit crabs of the family Coenobitidae (genera Coenobita and Birgus). Larvae of 5 species (C. cavipes, C. purpureus, C. rugosus, C. violascens, and B. latro) were cultured individually at ~28C, and their moulting, growth and developmental duration were analysed in conjunction with published data for coenobitid species (C. brevimanus, C. cavipes, C. clypeatus, C. compressus, C. purpureus, C. rugosus, C. scaevola, C. variabi
Critical currents in thin films of Chevrel-phase lead molybdenum sulfide have been measured as a function of applied magnetic field up to 8.5 T. The magnetic field was perpendicular or parallel to the film plane, and a 5-μV/cm criterion was used to define the critical current density Jc. The maximum value of critical current density was above 106 A/cm2 at zero field and 5×104 A/cm2 at 8 T. These values are greater than the best reported so far.
A tissue culture bioassay, using the mouse neuroblastoma cell line (Neuro2A), was improved to provide a simple and sensitive bioassay for TTX. The tetrazolium salt, 3-(4, 5-dimethy1-2-thiazoly1)-2, 5-dipheny1-2H tetrazolium bromide (MTT) was applied to replace the time-consuming and incomplete procedure of the original method with automatic measurement, using a microplate reader. TTX was used as a standard and an S-shaped dose-response curve was obtained. In additionto the relative ease of use a
An electro-plating and diffusion method has been developed for the production of superconducting ternary lead molybdenum sulfide (PbMo <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> S <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</inf> ) tapes. These tapes were prepared by plating a Mo tape with lead, and with subsequent heat treatment in sulfur (S) vapour from molybdenum sulfide (MoS <inf
All-NbN nanobridges with gap structure in I-V curves have been reproducibly constructed using RIE and lift-off techniques. The nanobridges had a width of 2 μm, and a thickness of < 30 nm. The length or nanobridge was about of the order of 3 to 5 coherence length of epitaxial NbN films. The nanobridges had nearly ideal characteristics: sharply defined critical current, high resistance, well-defined gap structure at about 4 mV, large I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlin
The "rare biosphere" consisting of thousands of low-abundance microbial taxa is important as a seed bank or a gene pool to maintain microbial functional redundancy and robustness of the ecosystem. Here we investigated contemporaneous growth of diverse microbial taxa including rare taxa and determined their variability in environmentally distinctive locations along a north-south transect in the Pacific Ocean in order to assess which taxa were actively growing and how environmental factors influen
Open papers in the app to read, cite, and organize with AI.
