Oxygen tolerance and detoxification mechanisms of highly enriched planktonic anaerobic ammonium-oxidizing (anammox) bacteria.

Oxygen is a key regulatory factor of anaerobic ammonium oxidation (anammox). Although the inhibitory effect of oxygen is evident, a wide range of oxygen sensitivities of anammox bacteria have been reported so far, which makes it difficult to model the marine nitrogen loss and design anammox-based technologies. Here, oxygen tolerance and detoxification mechanisms of four genera of anammox bacteria; one marine species ("Ca. Scalindua sp.") and four freshwater anammox species ("Ca. Brocadia sinica", "Ca. Brocadia sapporoensis", "Ca. Jettenia caeni", and "Ca. Kuenenia stuttgartiensis") were determined and then related to the activities of anti-oxidative enzymes. Highly enriched planktonic anammox cells were exposed to various levels of oxygen, and oxygen inhibition kinetics (50% inhibitory concentration (IC50) and upper O2 limits (DOmax) of anammox activity) were quantitatively determined. A marine anammox species, "Ca. Scalindua sp.", exhibited much higher oxygen tolerance capability (IC50 = 18.0 µM and DOmax = 51.6 µM) than freshwater species (IC50 = 2.7-4.2 µM and DOmax = 10.9-26.6 µM). The upper DO limit of "Ca. Scalindua sp." was much higher than the values reported so far (~20 µM). Furthermore, the oxygen inhibition was reversible even after exposed to ambient air for 12-24 h. The comparative genome analysis confirmed that all anammox species commonly possess the genes considered to function for reduction of O2, superoxide anion (O2•-), and H2O2. However, the superoxide reductase (Sor)-peroxidase dependent detoxification system alone may not be sufficient for cell survival under microaerobic conditions. Despite the fact that anaerobes normally possess no or little superoxide dismutase (Sod) or catalase (Cat), only Scalindua exhibited high Sod activity of 22.6 ± 1.9 U/mg-protein with moderate Cat activity of 1.6 ± 0.7 U/mg-protein, which was consistent with the genome sequence analysis. This Sod-Cat dependent detoxification system could be responsible for the higher O2 tolerance of Scalindua than other freshwater anammox species lacking the Sod activity.

Relationship between university students' emotional expression on tweets and subjective well-being: Considering the effects of their self-presentation and online communication skills.

This study investigated how personal characteristics such as generalized trust, self-consciousness and friendship, and desire for self-presentation are related to the subjective well-being of university students who use Twitter in Japan, including the effects of their online communication skills. We conducted a survey in May 2021 with Twitter users and analyzed their log data between January 2019 and June 2021. The log data of 501 Twitter users, including the number of public tweets, retweets, and emotional expressions among different patterns of social media (e.g., Twitter only, Twitter + Instagram, Twitter + LINE + Instagram, etc.) and academic standings, were analyzed using ANOVA and stepwise regression analyses. The results showed that the number of tweets and retweets, with and without photos/videos, increased in 2020 and 2021 compared to 2019, and the ratio of positive sentences remained almost the same for the two-and-a-half-year period of this study. However, the proportion of negative sentences increased slightly. It is clear that the factors which affected the university students' subjective well-being differed depending on the respective patterns of social media use.