Search

Far-UVC irradiation (222 nm) is an emerging approach for disinfection due to its effectiveness and potentially harmless nature to humans by direct irradiation compared with other UV wavelengths. However, the indirect risk caused by 222 nm irradiance, such as changes in the inhalation hazard of irradiated bioaerosols, is poorly studied. In particular, Gram-negative bacteria (GNB) lysis releases endotoxins, which can cause respiratory diseases viainhalation. Herein, we measured the endotoxin activity of illuminated GNB bioaerosols in a chamber using the limulus amebocyte lysate (LAL) assay. A 4-fold higher endotoxin activity ratio (EAR) of the UV-irradiated cells to fresh cells was found in the GNB bioaerosols illuminated by 222 nm than 254 nm, which can be explained by the different inactivation mechanisms. Compared with 254 nm, 222 nm illumination excited the cell membrane components (e.g., proteins) more effectively, leading to the formation of more reactive oxygen species (ROS) and membrane damage, followed by exposing lipid A to release the free-endotoxins into the aqueous environment of the aerosols. The increase in EAR, membrane damage, and ROS level at 222 nm were significantly higher than at 254 nm (p< 0.05). The EAR increased linearly with the UV dose up to 50 mJ cm−2. The EAR increase rate constant (kEAR) was insensitive to the KCl concentration in the aerosol, but it decreased by more than 80% when the droplets became solid particles. At a 222 nm UV dose of 50 mJ cm−2, the increase in indoor endotoxin activity due to illuminated GNB in typical indoor environments was estimated to be 3 orders of magnitude lower than the pre-existing endotoxin activity. Thus, our work suggests a negligible increase in endotoxic risk due to 222 nm indoor disinfection.

Currently, there is a lack of understanding on the variations of the indoor airborne microbiotas of different building types within a city, and how operational taxonomic unit (OTU)- and amplicon sequence variant (ASV)-based analyses of the 16S rRNA gene sequences affect interpretation of the indoor airborne microbiota results. Therefore, in this study, the indoor airborne bacterial microbiotas between commercial buildings, residences, and subways within the same city were compared using both OTU- and ASV-based analytic methods. Our findings suggested that indoor airborne bacterial microbiota compositions were significantly different between building types regardless of the bioinformatics method used. The processes of ecological drift and random dispersal consistently played significant roles in the assembly of the indoor microbiota across building types. Abundant taxa tended to be more centralized in the correlation network of each building type, highlighting their importance. Taxonomic changes between the microbiotas of different building types were also linked to changes in their inferred metabolic function capabilities. Overall, the results imply that customized strategies are necessary to manage indoor airborne bacterial microbiotas for each building type or even within each specific building.

Microbial communities in full-scale engineered systems undergo dynamic compositional changes. However, mechanisms governing assembly of such microbes and succession of their functioning and genomic traits under various environmental conditions are unclear. In this study, we used the activated sludge and anaerobic treatment systems of four full-scale industrial wastewater treatment plants as models to investigate the niches of microbes in communities and the temporal succession patterns of community compositions. High-quality representative metagenome-assembled genomes revealed that taxonomic, functional, and trait-based compositions were strongly shaped by environmental selection, with replacement processes primarily driving variations in taxonomic and functional compositions. Plant-specific indicators were associated with system environmental conditions and exhibited strong determinism and trajectory directionality over time. The partitioning of microbes in a co-abundance network according to groups of plant-specific indicators, together with significant between-group differences in genomic traits, indicated the occurrence of niche differentiation. The indicators of the treatment plant with rich nutrient input and high substrate removal efficiency exhibited a faster predicted growth rate, lower guanine–cytosine content, smaller genome size, and higher codon usage bias than the indicators of the other plants. In individual plants, taxonomic composition displayed a more rapid temporal succession than functional and trait-based compositions. The succession of taxonomic, functional, and trait-based compositions was correlated with the kinetics of treatment processes in the activated sludge systems. This study provides insights into ecological niches of microbes in engineered systems and succession patterns of their functions and traits, which will aid microbial community management to improve treatment performance.