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Background: The phylum Bacteroidota represents a significant proportion of heterotrophic bacteria found in marine ecosystems. Members of the phylum Bacteroidota are actively involved in the degradation of biopolymers such as polysaccharides and proteins. Bacteroidota genomes exhibit a significant enrichment of various enzymes, including carbohydrate-active enzymes (CAZymes), carboxypeptidases, esterases, isomerases, peptidases, phosphatases, and sulfatases. The genus Marivirga, a member of the family Marivirgaceae within the phylum Bacteroidota, comprises six documented species. During a microbial diversity study, three novel Marivirga strains (BKB1-2 T, ABR2-2, and BDSF4-3 T) were isolated from the West Sea, Republic of Korea. Results: To explore the taxonomic status and genomic characteristics of the novel isolates, we employed a polyphasic taxonomic approach, which included phylogenetic, chemotaxonomic and comprehensive genome analysis. The three isolates were Gram-stain-negative, aerobic, rod-shaped, moderately halophilic, and had a gliding motility. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values among the two isolates, BKB1-2 T and BDSF4-3 T, and the six reference strains were 70.5–76.5% for ANI and 18.1–25.7% for dDDH. Interestingly, the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that the strains harbor genes for a comprehensive pathway for dissimilatory nitrate reduction to ammonium (DNRA), as well as other nitrogen pathways for the reduction of nitrite, nitric oxide, and nitrous oxide. Additionally, the antiSMASH analysis indicated that the strains contained three to eight biosynthetic gene clusters (BGCs) associated with the synthesis of secondary metabolites. Furthermore, the strains carried a high number of CAZyme ranging from 53 to 152, which was also demonstrated by an in vitro analysis of degradation of the polysaccharide cellulose, chitin, laminarin, starch, and xylan. Additionally, all the strains carried genes for the metabolism of heavy metals, and exhibited tolerance to heavy metals, with minimum inhibitory concentrations (MICs) in millimoles (mM) in ranges of Co2+ (3–6), Cu2+ (0.2–0.4), Ni2+ (3–5), Zn2+ (2–4), Mn2+ (20–50), and Hg2+ (0.3). Conclusions: Based on polyphasic taxonomic approach, the three isolated strains represent two novel species names Marivirga arenosa sp. nov. (BKB1-2 T = KCTC 82989 T = InaCC B1618T), and Marivirga salinae sp. nov. (BDSF4-3 T = KCTC 82973 T = InaCC B1619T). [ABSTRACT FROM AUTHOR]

Nitrate in groundwater from alluvial and weathered granitic aquifers was monitored for 1-1.5 years on a monthly basis in an agricultural area with a high density of livestock feedlots to identify the main factors that control temporal variations in nitrate concentration. The baseline-loading group had median NO-N concentrations of 5-7 mg/L, with temporal variations of 5-34 % indicating less impact of nitrogen sources. This group was mainly located in paddy fields, areas that have limited rainfall recharge during summer monsoon. Upland wells and those near livestock facilities had median NO-N concentrations of 11-41 mg/L with temporal variations of 10-87 %, which were designated as the elevated-loading group. Overall, nitrate concentrations in groundwater decreased during dry/growing season of spring and fall due to the mixing of the groundwater in these areas with deeper groundwater because of heavy pumping, whereas nitrate concentrations increased during summer monsoon due to infiltration of the nitrate concentrated in the soil zone, and the level was maintained or rebounded during dry/fallow season. Multiple linear regression showed that nitrate was positively explained by SO, Cl, and DO, and negatively explained by pH and HCO indicating groundwater recharge and mixing of shallow and deep groundwater are important factors for nitrate contamination. These results show that nitrate concentrations in groundwater were controlled more by hydrologic processes than by biogeochemical processes, because most wells were considerably oxic. However, some of the wells were suboxic, and they exhibited increased Cl/NO ratio and concentrations of HCO and Mn(II) and decreased nitrate concentrations. Furthermore, NH-N was detected up to 2.6 mg/L with a sharp decrease in nitrate concentrations in one well, suggesting that dissimilatory nitrate reduction to ammonia and denitrification contributed to reduction in nitrate concentrations. This study revealed the effects of hydrologic and biogeochemical processes on temporal variations in nitrate concentrations in groundwater with high N loadings due to agricultural activity and a low potential for nitrate attenuation. [ABSTRACT FROM AUTHOR]