Adaptive characteristics of indigenous microflora in an organically contaminated high salinity groundwater

Salinity, a critical factor, could directly or indirectly affect the microbial community structure and diversity. Changes in salinity levels act as environmental filters that influence the transformation of key microbial species. This study investigates the adaptive characteristics of indigenous microflora in groundwater in relation to external organic pollutants under high salinity stress. A highly mineralized shallow groundwater in Northwest China was conducted as the study area, and six representative sampling points were chosen to explore the response of groundwater hydrochemical parameters and microflora, as well as to identify the tolerance mechanisms of indigenous microflora to combined pollution. The results revealed that the dominant genera found in high salinity groundwater contaminated with organic pollutants possess the remarkable ability to degrade such pollutants even under challenging high salinity conditions, including Halomonas, Pseudomonas, Halothiobacillus, Sphingomonas, Lutibacter, Aquabacterium, Thiomicrospira, Aequorivita, etc. The hydrochemical factors, including total dissolved solids (TDS), sulfide, nitrite, nitrate, oxidation reduction potential (ORP), NH3-N, Na, Fe, benzene series, phenols, and halogenated hydrocarbons, demonstrated a significant influence on microflora. High levels of sulphate and sulfide in groundwater can exhibit dual effects on microflora. On one hand, these compounds can inhibit the growth and metabolism of microorganisms. On the other hand, they can also serve as effective electron donors/receptors during the microbial degradation of organic pollutants. Microorganisms exhibit resilience to the inhibitory effects of high salinity and organic pollutants via a series of tolerance mechanisms, such as strengthening the extracellular membrane barrier, enhancing the synthesis of relevant enzymes, initiating novel biochemical reactions, improving cellular self-healing capabilities, responding to unfavorable environmental conditions by migration, and enhancing the S cycle for the microbial metabolism of organic pollutants.

Taxonomic identification and temperature stress tolerance mechanisms of Aequorivita marisscotiae sp. nov

The deep sea harbours microorganisms with unique life characteristics and activities due to adaptation to particular environmental conditions, but the limited sample collection and pure culture techniques available constrain the study of deep-sea microorganisms. In this study, strain Ant34-E75 was isolated from Antarctic deep-sea sediment samples and showed the highest 16 S rRNA gene sequence similarity (97.18%) with the strain Aequorivita viscosa 8-1bT. Strain Ant34-E75 is psychrotrophic and can effectively increase the cold tolerance of Chlamydomonas reinhardtii (a model organism). Subsequent transcriptome analysis revealed multiple mechanisms involved in the Ant34-E75 response to temperature stress, and weighted gene co-expression network analysis (WGCNA) showed that the peptidoglycan synthesis pathway was the key component. Overall, this study provides insights into the characteristics of a deep-sea microorganism and elucidates mechanisms of temperature adaptation at the molecular level.

Description of Aequorivita aurantiaca sp. nov. Isolated from Coastal Sediment, and Comparative Genomic Analysis and Biogeographic Distribution of the Genus Aequorivita

A novel Gram-stain-negative, facultatively anaerobic, and non-motile bacterial strain, designated SDUM287046T, was isolated from the coastal sediments of Jingzi Port of Weihai, China. Cells of strain SDUM287046T were rod-shaped with widths of 0.4-0.5 μm and lengths of 0.7-1.4 μm and could produce flexirubin-type pigments. Optimum growth of strain SDUM287046T occurred at 33-35 °C, pH 7.0, and with 2% (w/v) NaCl. Oxidase activity was negative, but catalase activity was positive. Phylogenetic analysis based on 16S rRNA gene sequence revealed that strain SDUM287046T was most closely related to Aequorivita aquimaris D-24T (98.3%). The main cellular fatty acids were iso-C15:0, anteiso-C15:0, iso-C17:0 3-OH, and summed feature 9 (comprised of iso-C17:1 ω9c and/or C16:0 10-methyl). The sole respiratory quinone was MK-6. The polar lipids consisted of phosphatidylethanolamine (PE), one aminolipid (AL), three unidentified glycolipids (GL), and three unidentified lipids (L). The DNA G + C content was 39.3 mol%. According to the integrated results of phylogenetic, physiological, biochemical, and chemotaxonomic characteristics, we propose that strain SDUM287046T represents a novel species of the genus Aequorivita, for which the name Aequorivita aurantiaca sp. nov. is proposed. The type strain is SDUM287046T (=KCTC 92754T = MCCC 1H01418T). Comparative genomic analysis showed that the 16 Aequorivita species shared 1453 core genes and differed mainly in amino acid metabolism, cofactor metabolism, and vitamin metabolism. Biogeographic distribution analysis indicated that the marine environments were the primary habitat of Aequorivita bacteria.