Fibrivirga algicola gen. nov., sp. nov., an algicidal bacterium isolated from a freshwater river.

An aerobic, gram-stain-negative, pink-colored, non-motile and rod-shaped algicidal bacterium, designated as JA-25T was isolated from freshwater in Geumgang River, Republic of Korea. Strain JA-25T grew at 15-30 °C and pH 6-9, and did not require NaCl. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain JA-25T belongs to the family 'Spirosomaceae' and is most closely related to Fibrella aestuarina BUZ 2T (93.6%). Strain JA-25T showed < 90% sequence similarity to other members of the family 'Spirosomaceae'. The average nucleotide identity(ANI), in silico DNA-DNA hybridization and average amino acid identity(AAI) values based on the genomic sequences of JA-25T and F. aestuarina BUZ 2T were 74.4, 20.5, and 73.6%, respectively. Strain JA-25T showed an algicidal effect on the marine flagellate alga Heterocapsa triquetra, but no effect on fresh water cyanobacterium (Nostoc). In genome analysis, RIPP-like peptides were detected and predicted to resemble the indolmycin biosynthetic gene cluster, which possibly influence its algicidal effect. Furthermore, a bacteriorhodopsin gene with photoheterotrophic characteristics was detected. The genomic DNA G + C content was 52.5 mol%. The major cellular fatty acids were summed feature 3 (C16:1 ω6c/C16:1 ω7c), C16:1 ω5c, C16:0 (> 10%). The major respiratory quinone was menaquinone 7 and major polar lipids were phosphatidylethanolamine, two unidentified aminolipids, two phospholipids, and five unidentified lipids. Considering the phylogenetic inference, phenotypic, and chemotaxonomic data, strain JA-25T should be classified as a novel species in the novel genus Fibrivirga, with the proposed name Fibrivirga algicola sp. nov. The type strain is JA-25T (= KCCM 43334T = NBRC 114259T).

Interpretation of ensemble learning to predict water quality using explainable artificial intelligence.

Algal bloom is a significant issue when managing water quality in freshwater; specifically, predicting the concentration of algae is essential to maintaining the safety of the drinking water supply system. The chlorophyll-a (Chl-a) concentration is a commonly used indicator to obtain an estimation of algal concentration. In this study, an XGBoost ensemble machine learning (ML) model was developed from eighteen input variables to predict Chl-a concentration. The composition and pretreatment of input variables to the model are important factors for improving model performance. Explainable artificial intelligence (XAI) is an emerging area of ML modeling that provides a reasonable interpretation of model performance. The effect of input variable selection on model performance was estimated, where the priority of input variable selection was determined using three indices: Shapley value (SHAP), feature importance (FI), and variance inflation factor (VIF). SHAP analysis is an XAI algorithm designed to compute the relative importance of input variables with consistency, providing an interpretable analysis for model prediction. The XGB models simulated with independent variables selected using three indices were evaluated with root mean square error (RMSE), RMSE-observation standard deviation ratio, and Nash-Sutcliffe efficiency. This study shows that the model exhibited the most stable performance when the priority of input variables was determined by SHAP. This implies that on-site monitoring can be designed to collect the selected input variables from the SHAP analysis to reduce the cost of overall water quality analysis. The independent variables were further analyzed using SHAP summary plot, force plot, target plot, and partial dependency plot to provide understandable interpretation on the performance of the XGB model. While XAI is still in the early stages of development, this study successfully demonstrated a good example of XAI application to improve the interpretation of machine learning model performance in predicting water quality.

Nanoparticle-embedded hydrogel synthesized electrodes for electrochemical oxidation of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS).

In this study, sliver (Ag) and gold (Au) nanoparticles (NPs) were embedded on poly (acrylic acid) (PAA)/poly (allylamine) hydrochloride (PAH) hydrogel fibers for improved electrochemical oxidation (EO) of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) removal. The NPs-loaded PAA/PAHs shows the better charge transport compared to the ceramic nanofiber membranes (CNM) electrodes. At 10 mA cm-2 of current density, the Ag-PAA/PAH electrodes showed a faster removal of PFAS compared to the Ag-CNM electrode probably due to large surface area-volume ratio and high porosity from the hydrogel. Among NPs-loaded PAA/PAH electrodes, the Ag/Au-PAA/PAH electrodes showed the highest removal of PFOA (72%) and PFOS (91%) in 2 h with the maximum removal rate of PFOA (0.0046 min-1) and PFOS (0.0093 min-1). The rapid PFOS removal is possibly due to the high activity of electron transfer with a higher redox potential of SO4•- than •OH. The highly stable F- generation was obtained from each electrode during reproducibility (n = 3). The net energy consumption from Ag/Au-PAA/PAH electrode was 164.9 kWh m-3 for 72% PFOA removal and 90 kWh m-3 for 91% PFOS removal, respectively. The developed Au-PAA/PAH electrodes were applied to lake water samples and showed acceptable PFOS removal (65%) with relative standard deviations (RSD) of 10.2% (n = 3) at 10 mA cm-2 of current density. Overall, the NP-embedded hydrogel nanofibers were proven to be a promising sustainable catalyst for the electrochemical PFAS oxidation in water.

Recent advances in biosensors for detecting viruses in water and wastewater.

As there is a considerable number of virus particles in wastewater which cause numerous infectious diseases, it is necessary to eliminate viruses from domestic wastewater before it is released in the environment. In addition, on-site detection of viruses in wastewater can provide information on possible virus exposures in the community of a given wastewater catchment. For this purpose, the pre-detection of different strains of viruses in wastewaters is an essential environmental step. Epidemiological studies illustrate that viruses are the most challenging pathogens to be detected in water samples because of their nano sizes, discrete distribution, and low infective doses. Over the past decades, several methods have been applied for the detection of waterborne viruses which include polymerase chain reaction-based methods (PCR), enzyme-linked immunosorbent assay (ELISA), and nucleic acid sequence-based amplification (NASBA). Although they have shown acceptable performance in virus measurements, their drawbacks such as complicated and time-consuming procedures, low sensitivity, and high analytical cost call for alternatives. Although biosensors are still in an early stage for practical applications, they have shown great potential to become an alternative means for virus detection in water and wastewater. This comprehensive review addresses the different types of viruses found in water and the recent development of biosensors for detecting waterborne viruses.

Silica-quaternary ammonium "Fixed-Quat" nanofilm coated fiberglass mesh for water disinfection and harmful algal blooms control.

Intensification of pollution loading worldwide has promoted an escalation of different types of disease-causing microorganisms, such as harmful algal blooms (HABs), instigating detrimental impacts on the quality of receiving surface waters. Formation of unwanted disinfection by-products (DBPs) resulting from conventional disinfection technologies reveals the need for the development of new sustainable alternatives. Quaternary Ammonium Compounds (QACs) are cationic surfactants widely known for their effective biocidal properties at the ppm level. In this study, a novel silica-based antimicrobial nanofilm was developed using a composite of silica-modified QAC (Fixed-Quat) and applied to a fiberglass mesh as an active surface via sol-gel technique. The synthesized Fixed-Quat nanocoating was found to be effective against E. coli with an inactivation rate of 1.3 × 10-3 log reduction/cm min. The Fixed-Quat coated fiberglass mesh also demonstrated successful control of Microcystis aeruginosa with more than 99% inactivation after 10 hr of exposure. The developed antimicrobial mesh was also evaluated with wild-type microalgal species collected in a water body experiencing HABs, obtaining a 97% removal efficiency. Overall, the silica-functionalized Fixed-Quat nanocoating showed promising antimicrobial properties for water disinfection and HABs control, while decreasing concerns related to DBPs formation and the possible release of toxic nanomaterials into the environment.

Effect of salt type and concentration on the growth and lipid content of Chlorella vulgaris in synthetic saline wastewater for biofuel production.

Microalgae can offer several benefits for wastewater treatment with their ability to produce large amounts of lipids for biofuel production and the high economic value of harvested biomass for biogas and fertilizer. This study found that salt concentration (∼45gL-1) had more of an effect than salt type on metabolisms of Chlorella vulgaris for wastewater treatment and biofuel production. Salinity stress decreased the algal growth rate in wastewater by 0.003day-1permScm-1 and slightly reduced nutrient removal rates. However, salinity stress was shown to increase total lipid content from 11.5% to 16.1% while also increasing the saturated portions of fatty acids in C. vulgaris. In addition, salinity increased the algal settling rate from 0.06 to 0.11mday-1 which could potentially reduce the cost of harvesting for algal biofuel production. Overall, C. vulgaris makes a suitable candidate for high salinity wastewater cultivation and biofuel production.

Recent advances in ultrasonic treatment: Challenges and field applications for controlling harmful algal blooms (HABs).

Algal blooms are a naturally occurring phenomenon which can occur in both freshwater and saltwater. However, due to excess nutrient loading in water bodies (e.g. agricultural runoff and industrial activities), harmful algal blooms (HABs) have become an increasing issue globally, and can even cause health effects in humans due to the release of cyanotoxins. Among currently available treatment methods, sonication has received increasing attention for algal control because of its low impact on ecosystems and the environment. The effects of ultrasound on algal cells are well understood and operating parameter such as frequency, intensity, and duration of exposure has been well studied. However, most studies have been limited to laboratory data interpretation due to complicated environmental conditions in the field. Only a few field and pilot tests in small reservoirs were reported and the applicability of ultrasound for HABs prevention and control is still under question. There is a lack of information on the upscaling of ultrasonication devices for HAB control on larger water bodies, considering field influencing factors such as rainfall, light intensity/duration, temperature, water flow, nutrients loading, and turbidity. In this review article, we address the challenges and field considerations of ultrasonic applications for controlling algal blooms. An extensive literature survey, from the fundamentals of ultrasound techniques to recent ultrasound laboratory and field studies, has been thoroughly conducted and summarized to identify future technical expectations for field applications. Case studies investigating spatial distribution of frequency and pressure during sonication are highlighted with future implications.

Discovery of an intermolecular disulfide bond required for the thermostability of a heterodimeric protein from the thermophile Hydrogenobacter thermophilus.

Factors that increase protein thermostability are of considerable interest in both scientific and industrial fields. Disulfide bonds are one of such factors that increase thermostability, but are rarely found in intracellular proteins because of the reducing environment of the cytosol. Here, we report the first example of an intermolecular disulfide bond between heteromeric subunits of a novel-type phosphoserine phosphatase from a thermophilic bacterium Hydrogenobacter thermophilus, which contributes to the protein thermostability at the physiological temperature. Comparison of remaining soluble proteins between wild-type and cysteine-deleted mutant using SDS-PAGE revealed that the disulfide bond increases the thermostability of the whole protein by tightly connecting a subunit with low solubility to the partner with higher solubility. Furthermore, it was strongly suggested that the disulfide bond is formed and contributes to the stability in vivo. This finding will open new avenues for the design of proteins with increased thermostability.