There is much evidence that the environment is a reservoir of antibiotic resistance genes (ARGs). For ARG latency and stability, environmental factors should play a role since ARGs are transferred among bacterial species, which results in their evolution and dissemination. Recent findings have expanded the novel mechanisms of horizontal gene transfer (HGT) beyond classically accepted HGT mechanisms such as conjugation, transformation, and transduction. In these HGT processes, environmental factors directly or indirectly affect the transfer rate and mechanism. Here, we focus on the effect of protists that affect HGT, because HGT is regulated among the microbial community, in which protist grazing is one factor that enhances HGT. Protist grazing eliminates planktonic bacteria. However, it is reported that environmental DNA release and HGT in protist vacuoles are increased by the grazing, although the effect is not uniform and depends on the environmental conditions. Biofilms protect bacteria and accelerate HGT. In these processes, quorum sensing and organic matter contribute to HGT. Although HGT occurs between bacterial cells, other microorganisms such as protists should be recognized as factors relating to HGT. We should pay attention to microbial ecosystem when consider ARG risk from water environment in terms of “one health” aspect.

The Ministry of the Environment, Japan has listed 207 items of emerging contaminants that are to be surveyed (“Items to be surveyed”, Youchousa-koumoku) to study the contamination in the water environment. Wastewater treatment plants (WWTPs) are one of the main sources of these contaminants in the water environment. In the current study, 84 compounds in the list of “Items to be surveyed” were concurrently analyzed in samples from 10 different WWTPs in Japan using liquid chromatography and high-resolution mass spectrometry. Samples were collected at three stages; i) primary effluent, ii) secondary effluent, and iii) final effluent. Impact of solid phase extraction and wastewater matrix on the recovery of the compounds was evaluated. 29 compounds were detected in at least 4 WWTPs. Triethanolamine, N,N-dimethyldodecylamine, 2-(2-ethoxyethoxy) ethanol, diethanolamine, and N,N-dimethyalacetamide had high removal (> 60%) in at least 6 treatment plants. The conventional activated sludge process was found to have lower removal efficiency for some compounds than the other processes. Decanoic acid had a concentration higher than its predicted no effect concentration (PNEC) and other three compounds had concentrations greater than PNEC/10 in final effluent.

This study investigated the relationship between nitrogen (N) and phosphorus (P) mass ratio in the medium and cellular N (N_c) and P (P_c) mass ratio in Microcystis cell. Monoculture experiments were conducted with the phosphorus concentration fixed at 0.110 mg L^–1 and the initial N:P mass ratios of 1, 10, 18, 50, 70, and 100. The results showed that the cell density of Microcystis sp. was highest at the initial N:P mass ratio of 50. Although it has been disputed that a low total N:P (TN:TP) ratio (< 29) in water was a cause of the development of cyanobacterial blooms or a result of its occurrence, this study could support the latter trend. This assumption could be supported by the results of elemental analysis (i.e., cellular N_c:P_c mass ratio of Microcystis sp.). At the end of the culture experiment, the N_c:P_c ratios ranged from 13.2 to 20.3, which were similar to the initial value (12.7). In general, the dissolved N and P concentrations in lake water are completely consumed when cyanobacterial blooms occur. Therefore, the present study suggests that the low TN:TP ratio may reflect the cellular N_c:P_c ratio of Microcystis sp. following assimilation of N and P in lake water.

This study is aimed at improving calculation quality for IWA Anaerobic Digestion Model No.1 (ADM1) to simulate acidic failure of the methane fermentation systems and its performance recovery. The methanogen collected from digestate at a municipal wastewater treatment plant was cultivated in a lab-scale continuous reactor receiving acetate as a sole organic source. By varying the influent concentration during 400 days of operation, 6 datasets of acidification events were obtained to simulate the concentrations of acetate, VSS, pH, and the methane production rate. The ADM1 equipped with either pH sub-model or undissociated acetate sub-model could reproduce the deterioration of reactor performance in the acidic failure but totally failed to simulate the recovery in the subsequent lowered volumetric loading rate. The statistical analysis revealed both ADM1 models had relatively low correlation coefficient (Nash-Sutcliffe model efficiency coefficient (NSE)) of 0.31–0.38 although these were considerably improved from that without parameter calibration (NSE = −0.04). To cope with the mismatch, a lag phase sub-model was developed. The sub-model is composed of the remaining relative activity of the microorganism at which the inhibition peaked, and the half-saturation coefficient to express the specific length of lag phase. By adding the sub-model into the calibrated ADM1, NSE was significantly improved to 0.49–0.53.