title: Extracellular proteases are released by ciliates in defined seawater microcosms.
abstract: The biodegradation of proteins in seawater requires various proteases which are commonly thought to be mainly derived from heterotrophic bacteria. We, however, found that protists showed a high protease activity and continuously produced trypsin-type enzymes. The free-living marine heterotrophic ciliate Paranophrys marina together with an associated bacterium was isolated and used for microcosm incubation with different concentrations of killed bacteria as food for 10 days. The results showed that the co-existence of the ciliate with its associated bacterium produced a significant protease activity in both cell-associated and cell-free fractions while that in the associated bacterium only microcosm was negligible. The protease profiles are different between cell-associated and cell-free fractions, and a trypsin-type enzyme hydrolyzing Boc-Val-Leu-Lys-MCA was detected throughout the period in the presence of ciliates. This suggests that ciliates release proteases into the surrounding environment which could play a role in protein digestion outside cells. It has been previously suggested that bacteria are the major transformers in seawater. We here present additional data which indicates that protists, or at least ciliates with their specific enzymes, are a potential player in organic matter degradation in water columns.
authors.affiliation: Center for Marine Environmental Studies (CMES), Ehime University, Matsuyama, Ehime, Japan; Faculty of Environment and Resources, Nong Lam University, Ho Chi Minh City, Vietnam.
authors.forename: Ngo Vy
authors.initials: NV
authors.lastname: Thao
authors.affiliation: Center for Marine Environmental Studies (CMES), Ehime University, Matsuyama, Ehime, Japan.
authors.forename: Akino
authors.initials: A
authors.lastname: Nozawa
authors.affiliation: Faculty of Life and Environmental Sciences, University of Tsukuba, Ibaraki, Japan.
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Obayashi
authors.affiliation: Center for Marine Environmental Studies (CMES), Ehime University, Matsuyama, Ehime, Japan.
authors.forename: Shin-Ichi
authors.initials: S
authors.lastname: Kitamura
authors.affiliation: Center for Marine Environmental Studies (CMES), Ehime University, Matsuyama, Ehime, Japan.
authors.forename: Taichi
authors.initials: T
authors.lastname: Yokokawa
authors.affiliation: Center for Marine Environmental Studies (CMES), Ehime University, Matsuyama, Ehime, Japan. Electronic address: ssuzuki@ehime-u.ac.jp.
authors.forename: Satoru
authors.initials: S
authors.lastname: Suzuki
mesh_terms: D016798:Ciliophora / Q000201:enzymology*; D010447:Peptide Hydrolases / Q000378:metabolism*; D015800:Protozoan Proteins / Q000378:metabolism*; D011550:Pseudomonas aeruginosa / Q000502:physiology*; D012623:Seawater / Q000737:chemistry* / Q000382:microbiology / Q000469:parasitology; D013559:Symbiosis
chemical_list: D015800:Protozoan Proteins; D010447:Peptide Hydrolases
keywords: Bacteria; Ciliate; Paranophrys marina; Protease; Pseudomonas aeruginosa; Seawater