Abstract
Thraustochytrids are cosmopolitan osmotrophic or heterotrophic microorganisms that are considered as important decomposers in coastal ecosystems. However, because of a lack of estimation method for each genus or systematic group of them, relatively little is known about their ecology in situ. Previously, we reported two distinct types of virus infecting thraustochytrids (AuRNAV: reported as SssRNAV, and SmDNAV) suggesting they have wide distributions in the host-virus systems of coastal environments. Here we conducted a field survey from 2004 through 2005 to show the fluctuation pattern of thraustochytrids and their viruses in Hiroshima Bay, Japan. During the field survey, we monitored the dynamics of the two types of thraustochytrid-infecting virus: small viruses causing lysis of Aurantiochytrium sp. NIBH N1-27 (identified as AuRNAV) and the large viruses of Sicyoidochytrium minutum NBRC 102975 (similar to SmDNAV in physiology and morphology). Fluctuation patterns of the two distinct types of virus were different from each other. This may reflect the difference in the preference of organic substrates; i.e., it may be likely the host of AuRNAV (Aurantiochytrium sp.) increases utilizing algal dead bodies or feeble cells as the virus shows a large increase in abundance following raphidophyte blooms; whereas, the trophic nutrient supply for S. minutum may primarily depend on other constantly-supplied organic compounds because it did not show any significant change in abundance throughout the survey. Further study concerning the population composition of thraustochytrids and their viruses may demonstrate the microbial ecology (especially concerning the detrital food web) of marine environments.
Highlights
IntroductionThraustochytrids are non-photosynthetic marine/estuarine stramenopile protists that are frequently observed and/or isolated from marine and estuarine waters, sediments, algal and plant materials both as saprotrophs and parasites [1]
Thraustochytrids are non-photosynthetic marine/estuarine stramenopile protists that are frequently observed and/or isolated from marine and estuarine waters, sediments, algal and plant materials both as saprotrophs and parasites [1]. Their bio-volume in coastal waters is estimated at 43% of that of the bacterioplankton [2]
The ubiquitousness and ability to use a wide variety of organic substrates argue for their ecological importance as decomposers [3, 4]. Due to their high production of PUFAs such as docosahexaenoic acid and docosapentaenoic acid [5], they are considered very important as food resources for higher organisms in marine systems [6,7,8]
Summary
Thraustochytrids are non-photosynthetic marine/estuarine stramenopile protists that are frequently observed and/or isolated from marine and estuarine waters, sediments, algal and plant materials both as saprotrophs and parasites [1] Their bio-volume in coastal waters is estimated at 43% of that of the bacterioplankton [2]. Due to their high production of PUFAs (polyunsaturated fatty acids) such as docosahexaenoic acid and docosapentaenoic acid [5], they are considered very important as food resources for higher organisms in marine systems [6,7,8] Because of these distinctive features of the thraustochytrids, their ecological significance in the coastal ecosystems has been studied [9, 10]. In spite of their ecological significance, relatively little is known about their ecological influence and impact in situ
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