Phosphorus cycling in a subterranean estuary seepage face: A seasonal view on inventory composition and linkage with nitrate transformations.

Seasonal field surveys (April 2018 to February 2019) were conducted in a subterranean estuary (STE) seepage face in Sanggou Bay (China) aiming to explore the transport and reactivity of phosphorus (P) and biogeochemical linkages with the cycling of nitrogen (N) prior to discharge. Porewater dissolved inorganic phosphorus (DIP) and dissolved organic phosphorus (DOP) together with different fractions of sedimentary P were analyzed in the upper, middle and lower intertidal covering the top 20 cm of sediment (1-4 cm, 5-8 cm, 9-12 cm, 13-16 cm and 17-20 cm depth). The accumulation of sedimentary organic P stimulated the growth of phosphate-solubilizing microorganisms and led to porewater DOP enrichment during spring. During summer, total P (TP), porewater DIP and DOP concentrations decreased, potentially due to enhanced mineralization driven by high ambient temperature. From autumn to winter, pelagic organic matter into the STE lowered, triggering a drop of TP standing stocks. Compared with the significant seasonality, sedimentary P storage was statistically identical along the intertidal. Such spatial homogeneity likely results from the rebalance driven by P adsorption dynamics and pelagic organic matter delivered by tide and wave setup. The vertical distribution of DIP, DOP, and sedimentary TP were linked to nitrate transformations. In the sediment layer with active mineralization and nitrification, concentrations of DOP, sedimentary redox and clay P increased. In the layer with active nitrate removal (2-5 cm depth), both DIP and DOP concentrations decreased. The sedimentary loosely-bound and organic P were also lower there. Notably, a substantial quantity of soluble P seeped out, acting as an important contributor to the dissolved P pool of the receiving waters. The spatial and temporal overlap of high concentrations of N and P in STEs adds variabilities and uncertainties in P out-drainage fluxes and nutrient stoichiometry balances, which should draw attention from coastal researchers and stakeholders.

Assessment of Joint Toxicity of Arsenate and Lead by Multiple Endpoints in Chlamydomonas reinhardtii.

In aquatic ecosystems, arsenate (As(V)) and lead (Pb(II)) frequently coexist but their joint toxicity on microalgae remains unknown. In this study, Chlamydomonas reinhardtii was exposed to various levels of combined As(V) and Pb(II) treatments. The cell growth, respiration, pigment synthesis, polysaccharides and protein secretion as well as As speciation of C. reinhardtii were analyzed. The low-level coexistence of As(V) and Pb(II) had a stimulatory effect, as indicated by enhanced cell proliferation. In the middle-level coexistence, the cells resisted the toxicity by significant increasing protein secretion. Under high-level coexistence, the presence of Pb(II) inhibited the efflux of As and caused the decline of cell numbers and occurrence of cell lysis, indicating that the interaction mode between As(V) and Pb(II) switched to synergistic. Taken together, the above findings may deepen the understanding of detoxification mechanisms of algae upon exposure to combined metal(loid)s in aqueous environments.

Sufficient Phosphorus Enhances Resistance and Changes Accumulation of Lead in Chlamydomonas reinhardtii.

Phosphorus (P) is critical for algal growth and resistance to environmental stress. However, little is known about the effects of P supply on the lead (Pb) toxicity and accumulation in microalgae. We set up two P concentrations, 315 (PL ) and 3150 µg L-1 (PH ), in algal culture, and the responses of Chlamydomonas reinhardtii to various Pb treatments (0, 200, 500, 1000, 2000, and 5000 µg L-1 ) were investigated. Compared with the PL condition, PH promoted cell growth but reduced cellular respiration by approximately 50%. Moreover, PH alleviated damage to the photosynthetic system in algal cells after Pb stress. After exposure to 200-2000 µg L-1 Pb, higher Pb2+ concentrations and Pb removal were observed in the PL medium. However, under exposure to 5000 µg L-1 Pb, less Pb2+ was present but more Pb was removed by the algal cells in the PH medium. More P supply enhanced the secretion of extracellular fluorescent substances by C. reinhardtii. Transcriptomic analysis showed that genes associated with synthesis of phospholipids, tyrosine-like proteins, ferredoxin, and RuBisCO were up-regulated after Pb exposure. Together the findings of our study demonstrated the critical roles of P in Pb accumulation and resistance in C. reinhardtii. Environ Toxicol Chem 2023;42:1960-1970. © 2023 SETAC.

Physiological and proteomic responses of Chlamydomonas reinhardtii to arsenate and lead mixtures.

Arsenic (As) and lead (Pb) are frequently emitted from various sources into environment, but microbial responses to their combined toxicity have not been systematically investigated. In this study, Chlamydomonas reinhardtii was exposed to two levels of arsenate (As (V), 50, 500 µg/L), Pb (II) (500, 5000 µg/L) and their mixture (50 µg/L As (V) + 500 µg/L Pb (II); 500 µg/L As (V) + 5000 µg/L Pb (II)). The growth of C. reinhardtii was inhibited more remarkably by As (V) than by Pb (II). The As stress was alleviated by Pb in the 50 µg/L As (V) + 500 µg/L Pb (II) treatment, but was enhanced upon the 500 µg/L As (V) + 5000 µg/L Pb (II) exposure, with more pronounced changes in a number of physiological parameters of the algal cells. Proteomic results showed that 71 differently expressed proteins (DEPs) in the treatment of 50 µg/L As (V) + 500 µg/L Pb (II), and 167 DEPs were identified in that of 500 µg/L As (V) + 5000 µg/L Pb (II). These proteins were involved in energy metabolism, photosynthetic carbon fixation, reactive oxygen scavenging and defense, and amino acid synthesis. Taken together, these physiological and proteomic data demonstrated that C. reinhardtii could resist the As (V) and Pb (II) combined treatments through extracellular complexation and intracellular pathways.

Contributions of polysaccharides to arsenate resistance in Chlamydomonas reinhardtii.

Polysaccharides supply energy for various metabolic processes in cells. However, their roles in the arsenate (As(V)) resistance in microalgae remain largely unknown. Here, we explored the synthesis and transformation of polysaccharides in Chlamydomonas reinhardtii upon various levels of As(V) stress, using a number of physiological indexes along with transmission electron microscopic (TEM) and proteomic analyses. When exposed to low concentration of As(V) (0-20 µg/L), C. reinhardtii accumulated starch and produced more extracellular polysaccharides. At 50 µg/L As(V) treatment, starch accumulation gradually shifted to polysaccharides decomposition in the algal cells. Under higher As(V) concentration (500 µg/L), significantly more proteins in fatty acid metabolic pathway were differentially expressed, indicating that cells redirected carbon flux and transformed lipids into polysaccharides. The findings of this study demonstrate that polysaccharides may be critically involved in the As(V) resistance of C. reinhardtii.

An effect analysis of vestibular rehabilitation training in vertigo treatment.

OBJECTIVE: This study aimed to explore the clinical safety and effectiveness of vestibular rehabilitation training in the treatment of vertigo. METHODS: Patients with vertigo were randomly divided into an experimental group (51 cases) or a control group (51 cases) and were treated for 4 weeks. The Berg balance scale scores (BBS), the vestibular symptom index (VSI) scores, the balance experiment scores, the UCIA vertigo scores, and the vertigo symptom changes before and after the treatment were recorded, and the treatment success was investigated. At the same time, the patient satisfaction scores and the dizziness handicap inventory (DHI) scores were recorded, and the quality of life after the treatment was evaluated. RESULTS: After four weeks of treatment, the BBS, VSI, balance test, and UCIA vertigo scores in the experimental group were higher than the corresponding scores in the control group (P<0.05). Meanwhile, the total effective rate and the patient satisfaction in the experimental group were higher than they were in the control group (P<0.05). Compared with the control group, the total index and sub-indexes of the DHI (DHI-P (physical), DHI-F (function), and DHI-E (emotion)) in the experimental group were significantly improved, and the differences were statistically significant (P<0.05). The BBS, VSI, balance test, and UCIA vertigo scores in the two groups after the treatment were better than they were before the treatment (P<0.05). CONCLUSION: Compared with drug therapy alone, vestibular rehabilitation training combined with common drug therapy can significantly improve the patients' quality of life, better eliminate their vertigo symptoms, and improve their satisfaction.