Salinity as a Determinant Structuring Microbial Communities in Coastal Lakes

Metagenomics analysis reveals effects of salinity fluctuation on diversity and ecological functions of high and low nucleic acid content bacteria

Salinity is a critical environmental factor in marine ecosystems and has complex and wide-ranging biological effects. However, the effects of changing salinity on diversity and ecological functions of high nucleic acid (HNA) and low nucleic acid (LNA) bacteria are not well understood. In this study, we used 16S rRNA sequencing and metagenomic sequencing analysis to reveal the response of HNA and LNA bacterial communities and their ecological functions to salinity, which was decreased from 26 ‰ to 16 ‰. The results showed that salinity changes had significant effects on the community composition of HNA and LNA bacteria. Among LNA bacteria, 14 classes showed a significant correlation between relative abundance and salinity. Salinity changes can lead to the transfer of some bacteria from HNA bacteria to LNA bacteria. In the network topology relationship, the complexity of the network between HNA and LNA bacterial communities gradually decreased with decreased salinity. The abundance of some carbon and nitrogen cycling genes in HNA and LNA bacteria varied with salinity. Overall, this study demonstrates the effects of salinity on diversity and ecological functions and suggests the importance of salinity in regulating HNA and LNA bacterial communities and functions.

Investigation of the marine bacterial community along the coastline of the Gulf of Thailand

The Gulf of Thailand provides many services to the Thai population, and human activities may influence the diversity of microorganisms in the seawater. Information of the microorganisms' profile which inhabit the coastline can be used to monitor the water quality. This study aimed to investigate the bacterial community in the waters along the coastline provinces, including Rayong, Chonburi, Prachuap Kiri Khan, and Nakhon Sri Thammarat. Seawater samples were collected at each site, and the conductivity, pH, salinity, temperature, and turbidity were measured. The samples were subjected to whole DNA extraction, 16S rRNA amplification, next-generation sequencing, and statistical analysis to identify the bacterial diversity and analyse the effects of water parameters on the bacterial community. The dominant bacterial phyla found were Proteobacteria, Bacteroidota, and Cyanobacteria. Spearman rank correlation analysis revealed a high correlation of Pseudoalteromonas, the NS5 marine group, Lachnospiraceae, Marinobacterium, Mariviven, and Vibrio with the seawater parameters. The predatory bacteria Peredibacter and Halobacteriovorax were reported among these bacterial communities for the first time in the Gulf of Thailand. Interestingly, Akkermansia, a novel candidate for next-generation probiotics to improve human health, was also found in the sample from Nakhon Sri Thammarat Province. Although the rich-ness and diversity of the bacterial communities differed among sampling sites, it is a possible source of many valuable bacteria for future use.

Hypoxia and salinity constrain the sediment microbiota-mediated N removal potential in an estuary: A multi-trophic interrelationship perspective

Reactive nitrogen (N) enrichment is a common environmental problem in estuarine ecosystems, while the microbial-mediated N removal process is complicated for other multi-environmental factors. Therefore, A systematic investigation is necessary to understand the multi-trophic microbiota-mediated N removal characteristics under various environmental factors in estuaries. Here, we studied how multiple factors affect the multi-trophic microbiota-mediated N removal potential (denitrification and anammox) and N2O emission along a river-estuary-bay continuum in southeastern China using the environmental DNA (eDNA) approach. Results suggested that hypoxia and salinity were the dominant environmental factors affecting multi-trophic microbiota-mediated N removal in the estuary. The synergistic effect of hypoxia and salinity contributed to the loss of taxonomic (MultiTaxa) and phylogenetic (MultiPhyl) diversity across multi-trophic microbiota and enhanced the interdependence among multi-trophic microbiota in the estuary. The N removal potential calculated as the activities of key N removal enzymes was also significantly constrained in the estuary (0.011), compared with the river (0.257) and bay (0.461). Structural equation modeling illustrated that metazoans were central to all sediment N removal potential regulatory pathways. The top-down forces (predation by metazoans) restrained the growth of heterotrophic bacteria, which may affect microbial N removal processes in the sediment. Furthermore, we found that the hypoxia and salinity exacerbated the N2O emission in the estuary. This study clarifies that hypoxia and salinity constrain estuarine multi-trophic microbiota-mediated N removal potential and highlights the important role of multi-trophic interactions in estuarine N removal, providing a new perspective on mitigating estuarine N accumulation.

Different Responses of Bacteria and Archaea to Environmental Variables in Brines of the Mahai Potash Mine, Qinghai-Tibet Plateau

Salt mines feature both autochthonous and allochthonous microbial communities introduced by industrialization. It is important to generate the information on the diversity of the microbial communities present in the salt mines and how they are shaped by the environment representing ecological diversification. Brine from Mahai potash mine (Qianghai, China), an extreme hypersaline environment, is used to produce potash salts for hundreds of millions of people. However, halophiles preserved in this niche during deposition are still unknown. In this study, using high-throughput 16S rRNA gene amplicon sequencing and estimation of physicochemical variables, we examined brine samples collected from locations with the gradient of industrial activity intensity and discrete hydrochemical compositions in the Mahai potash mine. Our findings revealed a highly diverse bacterial community, mainly composed of Pseudomonadota in the hypersaline brines from the industrial area, whereas in the natural brine collected from the upstream Mahai salt lake, most of the 16S rRNA gene reads were assigned to Bacteroidota. Halobacteria and halophilic methanogens dominated archaeal populations. Furthermore, we discovered that in the Mahai potash mining area, bacterial communities tended to respond to anthropogenic influences. In contrast, archaeal diversity and compositions were primarily shaped by the chemical properties of the hypersaline brines. Conspicuously, distinct methanogenic communities were discovered in sets of samples with varying ionic compositions, indicating their strong sensitivity to the brine hydrochemical alterations. Our findings provide the first taxonomic snapshot of microbial communities from the Mahai potash mine and reveal the different responses of bacteria and archaea to environmental variations in this high-altitude aquatic ecosystem.

Response of Macrophyte Diversity in Coastal Lakes to Watershed Land Use and Salinity Gradient

Coastal lakes are subject to multiple stressors, among which land use, hydrological connectivity, and salinity have the greatest effect on their biodiversity. We studied the effects that various land cover types (CORINE) of coastal lake watersheds had on macrophyte diversity in ten coastal lakes along the southern Baltic coast as characterised by twelve phytocenotic indices: these being a number of communities, Shannon-Wiener diversity, evenness, and indices of taxonomic distinctiveness of plant communities: vegetation coverage; colonisation index; share of the phytolittoral area in the total lake area, as well as shares of nympheides, pondweeds, charophytes, marine, emerged and submerged communities in the total lake area. The effects were checked for three groups of lakes distinguished by differences in salinity-freshwater (F, 5), transitional (T, 4), and brackish (B, 1)-in which a total of 48 macrophyte communities were identified. The most abundant in aquatic phytocoenoses were lakes of T type. A partial least squares regression model (PLS-R) showed a stronger impact of land-use types in immediate vicinities and entire watersheds than the impact of physico-chemical properties of water on phytocenotic indices in the lakes. Macrophyte diversity was relatively low in urban and agricultural catchments and relatively high in forest and wetland areas. Agriculture had a negative impact on the number of macrophyte communities in F lakes and, in T lakes, on the number of macrophyte communities, biodiversity, evenness, and proportion of emerged, submerged, and marine communities. Urban areas contributed to lower values of evenness, vegetation coverage, and share of marine communities in F, but, in T, to lower the number of macrophyte communities, evenness, and proportion of submerged and marine communities. Our results confirm the significant impact of land use on macrophyte diversity in coastal aquatic ecosystems. Combined analysis of anthropogenic and natural descriptors is a prerequisite for analysing human threats to biodiversity in coastal lakes. Macrophyte community-based measures of biodiversity are sensitive indicators of anthropogenic impact on the ecological condition of coastal ecosystems.

Microbial marker for seawater intrusion in a coastal Mediterranean shallow Lake, Lake Vrana, Croatia

Climate change-induced rising sea levels and prolonged dry periods impose a global threat to the freshwater scarcity on the coastline: salinization. Lake Vrana is the largest surface freshwater resource in mid-Dalmatia, while the local springs are heavily used in agriculture. The karstified carbonate ridge that separates this shallow lake from the Adriatic Sea enables seawater intrusion if the lakes' precipitation-evaporation balance is disturbed. In this study, the impact of anthropogenic activities and drought exuberated salinization on microbial communities was tracked in Lake Vrana and its inlets, using 16S rRNA gene sequencing. The lack of precipitation and high water temperatures in summer months introduced an imbalance in the water regime of the lake, allowing for seawater intrusion, mainly via the karst conduit Jugovir. The determined microbial community spatial differences in the lake itself and the main drainage canals were driven by salinity, drought, and nutrient loading. Particle-associated and free-living microorganisms both strongly responded to the ecosystem perturbations, and their co-occurrence was driven by the salinization event. Notably, a bloom of halotolerant taxa, predominant the sulfur-oxidizing genus Sulfurovum, emerged with increased salinity and sulfate concentrations, having the potential to be used as an indicator for salinization of shallow coastal lakes. Following summer salinization, lake water column homogenization took from a couple of weeks up to a few months, while the entire system displayed increased salinity despite increased precipitation. This study represents a valuable contribution to understanding the impact of the Freshwater Salinization Syndrome on Mediterranean lakes' microbial communities and the ecosystem resilience.

Habitat Conditions of the Microbiota in Ballast Water of Ships Entering the Oder Estuary

Ballast water is a vector for the transfer of microorganisms between ecospheres that can subsequently have a negative impact on native species of aquatic fauna. In this study, we determined the microbiota and selected physicochemical properties of ballast water from long- and short-range ships entering a southern Baltic port within a large estuary in autumn and winter (Police, Poland). Microbiological tests of the ballast water samples were carried out according to ISO 6887-1, and physicochemical tests were performed according to standard methods. Low amounts of oxygen (1.6-3.10 mg/dm3 in autumn and 0.60-2.10 mg/dm3 in winter) were recorded in all ship ballast water samples, with pH (above 7.90) and PSU (above 1.20) were higher than in the port waters. Yeast, mold, Pseudomonas bacteria (including Pseudomonas fluorescens), and halophilic bacteria as well as lipolytic, amylolytic, and proteolytic bacteria were found in the ballast water samples. Heterotrophic bacteria and mold fungi (log. 2.45-3.26) dominated in the autumn period, while Pseudomonas bacteria (log. 3.32-4.40) dominated in the winter period. In addition, the ballast water samples taken during the autumn period were characterized by a statistically significantly higher (p < 0.1) abundance of microorganisms (log 1.97-2.55) than in the winter period (log 1.39-2.27).