Diatoms are one of the most prominent oceanic primary producers and are now recognized to be distributed throughout the world. They maintain their population despite predators, infections, and unfavourable environmental conditions. One of the smallest diatoms, Chaetoceros tenuissimus, can coexist with infectious viruses during blooms. To further understand this relationship, we sequenced the C. tenuissimus strain NIES-3715 genome. A gene fragment of a replication-associated gene from the infectious ssDNA virus (designated endogenous virus-like fragment, EVLF) was found to be integrated into each 41 Mb of haploid assembly. In addition, the EVLF was transcriptionally active and conserved in nine other C. tenuissimus strains from different geographical areas, although the primary structures of their proteins varied. The phylogenetic tree further suggested that the EVLF was acquired by the ancestor of C. tenuissimus. Additionally, retrotransposon genes possessing a reverse transcriptase function were more abundant in C. tenuissimus than in Thalassiosira pseudonana and Phaeodactylum tricornutum. Moreover, a target site duplication, a hallmark for long interspersed nuclear element retrotransposons, flanked the EVLF. Therefore, the EVLF was likely integrated by a retrotransposon during viral infection. The present study provides further insights into the diatom-virus evolutionary relationship.

Induction of mutation in Monascus purpureus isolated from Thai fermented food to develop low citrinin-producing strain for application in the red koji industry

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Screening for new sake yeasts can expand the sensory diversity of sake, due to their production of metabolites that characterize sake's aroma and taste. In this study, mud from tidal flats in the Ariake Sea was screened for Saccharomyces cerevisiae strains with ethanol productivity suitable for sake brewing, and the brewing characteristics of isolated strains were evaluated. Five strains (H1-1, H1-2, H1-3, H3-1, and H3-2) classified as S. cerevisiae were isolated. Karyotype analysis by pulsed-field gel electrophoresis showed that five isolated strains were closely related to sake yeast strains (K7, K701, K9, K901, and Y52) instead of laboratory yeast strain. Results of small-scale brewing tests including sake yeast strains K701, K901, and Y52 showed that the five isolated strains have fermentation activity comparable to sake yeast strains. Principal component analysis (PCA) revealed that the five isolated strains produce higher levels of ethyl caproate and lower levels of acidic compounds than sake yeasts. In addition, isolated strains H3-1 and H3-2 produce higher levels of isoamyl acetate and lower levels of acetic acid than other isolated strains. Consequently, five S. cerevisiae strains that have high fermentation activity and differ from common sake yeast strains in terms of brewing characteristics were successfully isolated from the Ariake Sea.

No abstract