Transcriptional response of Pseudomonas chenduensis strain MBR to cadmium toxicity

Genomic and transcriptomic analyses reveal insights into cadmium resistance mechanisms of Cupriavidus nantongensis strain E324

The cadmium-resistant Cupriavidus sp. strain E324 has been previously shown to have a high potential for use in cadmium (Cd) remediation, due to its high capacity for cadmium bioaccumulation. According to the comparative genomic analysis, the strain E324 was most closely related to C. nantongensis X1T, indicating that the strain E324 should be re-identified as C. nantongensis. To unravel the Cd tolerance mechanisms of C. nantongensis strain E324, the transcriptional response of this strain to acute Cd exposure was assessed using RNA-seq-based transcriptome analysis, followed by validation through qRT-PCR. The results showed that the upregulated Differentially Expressed Genes (DEGs) were significantly enriched in categories related to metal binding and transport, phosphate transport, and oxidative stress response. Consistently, we observed significant increases in both the cell wall and intracellular contents of certain essential metals (Cu, Fe, Mn, and Zn) upon Cd exposure. Among these, only the Zn pretreatment resulting in high Zn accumulation in the cell walls could enhance bacterial growth under Cd stress conditions through its role in inhibiting Cd accumulation. Additionally, the promotion of catalase activity and glutathione metabolism upon Cd exposure to cope with Cd-induced oxidative stress was demonstrated. Meanwhile, the upregulation of phosphate transport-related genes upon Cd treatment seems to be the bacterial response to Cd-induced phosphate depletion. Altogether, our findings suggest that these adaptive responses are critical mechanisms contributing to increased Cd tolerance in C. nantongensis strain E324 via the enhancement of metal-chelating and antioxidant capacities of the cells.

Transcriptome sequencing analysis of gene expression in phosphate-solubilizing bacterium 'N3' and grafted watermelon plants coping with toxicity induced by cadmium

Cadmium (Cd) is a harmful metal in soil, and reducing Cd accumulation in plants has become a vital prerequisite for maintaining food safety. Phosphate-solubilizing bacteria (PSB) can not only improve plant growth but also inhibit the transportation of metals to roots. However, data on gene expression in PSB Burkholderia sp. strain 'N3' and grafted watermelon plants dealing with Cd remain to be elucidated. In this study, core genes and metabolic pathways of strain 'N3' and grafted plants were analyzed by Illumina sequencing. Results showed that 356 and 2527 genes were upregulated in 'N3' and grafted watermelon plants, respectively, whereas 514 and 1540 genes were downregulated in 'N3' and grafted watermelon plants, respectively. Gene ontology enrichment analysis showed that signal transduction, inorganic ion transport, cell motility, amino acid transport, and metabolism pathways were marked in 'N3'. However, pathways such as secondary metabolite biosynthesis, oxidation-reduction process, electron transfer activity, and channel regulator activity were marked in the grafted plants. Six genes related to pentose phosphate, glycolysis, and gluconeogenesis metabolism were upregulated in the grafted plants. This study paves the way for developing potential strategies to improve plant growth under Cd toxicity.

Cysteine and thiosulfate promoted cadmium immobilization in strain G303 by the formation of extracellular CdS

Bacteria have evolved a variety of strategies to defend themselves against cadmium toxicity, however, the specific mechanisms involved in the enhancement of bacterial cadmium resistance by sulfur sources are unclear. In this study, a novel cadmium (Cd)-tolerant bacterium, Stenotrophomonas geniculata G303, was isolated from activated sludge. The growth of strain G303 under diverse Cd concentrations was investigated, and the minimum inhibitory concentration of Cd was found to be 1 mM. Strain G303 effectively remove 94.7 % of Cd after 96 h of culture. Extracellular CdS was detected using multiple methods, with the CdS formed being aggregated in the biofilm. The addition of cysteine and thiosulfate to the medium significantly enhanced the Cd resistance and removal capacity of strain G303. Integrated genomic and proteomic analyses revealed that heavy metal transporters cooperate to resist Cd stress. Cysteine and thiosulfate improved Cd tolerance in strain G303 by upregulating nitrogen and energy metabolism. Proteins associated with nitrate reduction likely played a pivotal role in cysteine and thiosulfate metabolism. Notably, cysteine synthase and the SUF system played crucial roles in CdS formation. This study systematically explored the impact of cysteine and thiosulfate on the Cd resistance of strain G303, deepening our understanding of the microbial response mechanism to heavy metals.

Mechanisms involved in the sequestration and resistance of cadmium for a plant-associated Pseudomonas strain

Understanding Cd-resistant bacterial cadmium (Cd) resistance systems is crucial for improving microremediation in Cd-contaminated environments. However, these mechanisms are not fully understood in plant-associated bacteria. In the present study, we investigated the mechanisms underlying Cd sequestration and resistance in the strain AN-B15. These results showed that extracellular Cd sequestration by complexation in strain AN-B15 was primarily responsible for the removal of Cd from the solution. Transcriptome analyses have shown that the mechanisms of Cd resistance at the transcriptional level involve collaborative processes involving multiple metabolic pathways. The AN-B15 strain upregulated the expression of genes related to exopolymeric substance synthesis, metal transport, Fe-S cluster biogenesis, iron recruitment, reactive oxygen species oxidative stress defense, and DNA and protein repair to resist Cd-induced stress. Furthermore, inoculation with AN-B15 alleviated Cd-induced toxicity and reduced Cd uptake in the shoots of wheat seedlings, indicating its potential for remediation. Overall, the results improve our understanding of the mechanisms involved in Cd resistance in bacteria and thus have important implications for improving microremediation.

Multiple mechanisms collectively mediate tungsten homeostasis and resistance in Citrobacter sp. Lzp2

Tungsten (W) is an emerging contaminant, and current knowledge on W resistance profiles of microorganisms remains scarce and fragmentary. This study aimed to explore the physiological responses of bacteria under W stress and to resolve genes and metabolic pathways involved in W resistance using a transcriptome expression profiling assay. The results showed that the bacterium Citrobacter sp. Lzp2, screened from W-contaminated soil, could tolerate hundreds of mM W(VI) with a 50% inhibiting concentration of ∼110 mM. To cope with W stress, Citrobacter sp. Lzp2 secreted large amounts of proteins through the type VI secretory system (T6SS) to chelate W oxoanions via carboxylic groups in extracellular polymeric substances (EPS), and could transport cytosolic W outside via the multidrug efflux pumps (mdtABC and acrD). Intracellular W is probably bound by chaperone proteins and metal-binding pterin (tungstopterin) through the sulfur relay system. We propose that tetrathionate respiration is a new metabolic pathway for cellular W detoxification likely producing thio-tungstate. We conclude that multiple mechanisms collectively mediate W homeostasis and resistance in Citrobacter sp. Lzp2. Our results have important implications not only for understanding the intricate regulatory network of W homeostasis in microbes but also for bio-recovery and bioremediation of W in contaminated environments.

Gap junction intercellular communication mediates cadmium-induced apoptosis in hepatocytes via the Fas/FasL pathway

As a common environmental pollutant, cadmium (Cd) causes damage to many organs of the body. Gap junction intercellular communication (GJIC) represents one of the most important routes of rapid signaling between cells. However, the mechanisms underlying GJIC's role in hepatotoxicity induced by Cd remain unknown. We established a Cd poisoning model in vitro by co-culturing Cd-exposed and unexposed hepatocytes and found that 18β-glycyrrhetinic acid (GA), a GJIC inhibitor, can effectively reduce the apoptosis rate of healthy cells co-cultured with apoptotic cells treated with Cd. We also found that anti-FasL antibody had the same effect. However, in mono-cultured cells, GA treatment in combination with Cd was found to aggravate the damage induced by Cd exposure, increase the level of oxidative stress and protein expression of HO-1, decrease the mitochondrial membrane potential, incur more serious morphological damage to mitochondria than Cd treatment alone. Moreover, compared with Cd-only exposure, GA and Cd co-treatment further increased the expression levels of the apoptosis-related proteins Fas, FasL, FADD and the ratio of Bax/Bcl-2, inhibited the protein expression of ASK1 and Daxx. We also found that the protein expression of Daxx in siFADD + Cd hepatocytes was significantly higher than in Cd-treated cells. Thus, our study suggests that gap junction inhibition may play a dual role in Cd-induced cell damage by inhibiting the transmission of death signals from damaged cells to healthy cells but also aggravating the transmission of death signals between damaged cells, and that the Fas/FasL-mediated death receptor pathway may play an important role in this process.

Comparative transcriptomics reveal different genetic adaptations of biofilm formation in Bacillus subtilis isolate 1JN2 in response to Cd2+ treatment

Biofilm plays important roles in the life cycle of Bacillus species, such as promoting host and object surface colonization and resisting heavy metal stress. This study utilized transcriptomics to evaluate the impacts of cadmium on the components, morphology, and function of biofilms of Bacillus subtilis strain 1JN2. Under cadmium ion stress, the morphology of the B. subtilis 1JN2 biofilm was flattened, and its mobility increased. Moreover, differential gene expression analysis showed that the main regulator of biofilm formation, Spo0A, decreased in expression under cadmium ion stress, thereby inhibiting extracellular polysaccharide synthesis through the SinI/SinR two-component regulatory system and the AbrB pathway. Cadmium ion treatment also increased the SigD content significantly, thereby increasing the expression of the flagella encoding and assembly genes in the strain. This promoted poly-γ-glutamic acid production via the DegS/DegU two-component regulatory system and the conversion of biofilm extracellular polysaccharide to poly-γ-glutamic acid. This conferred cadmium stress tolerance in the strain. Additionally, the cadmium ion-mediated changes in the biofilm composition affected the colonization of the strain on the host plant root surface. Cadmium ions also induced surfactin synthesis. These findings illustrate the potential of Bacillus species as biocontrol strains that can mitigate plant pathogenic infections and heavy metal stress. The results also provide a basis for the screening of multifunctional biocontrol strains.

Cadmium exposure triggers oxidative stress, necroptosis, Th1/Th2 imbalance and promotes inflammation through the TNF-α/NF-κB pathway in swine small intestine

Cadmium (Cd) is a toxic environmental pollutant and induces toxic effects to organism. Nevertheless, the mechanism of Cd-induced toxicity in swine remains obscure. To explore this, 10 healthy 6-week-old weaned swine were placed into two groups stochastically, the Cd group was treated with a commercial diet containing 20 mg/kg Cd for 40 days. The results of histopathological and ultrastructural observations showed typical necrosis features and inflammatory cell infiltration in Cd group. Excessive Cd suppressed T-AOC and SOD activities, increased MDA content and ROS levels. Cd diet elevated the expression of RIPK1, RIPK3, and MLKL to activate the RIPK3-dependent necroptosis pathway. Results of Th1 and Th2 cytokines indicated that the levels of IL-4, IL-6 and IL10 was increased, while the level of IFN-γ was decreased, illustrating Th1/Th2 immune imbalance leads to aggravate inflammatory responses. Cd activated the TNF-α/NF-κB pathway and induced inflammatory responses via increasing the expression of HO-1, IL-1β, iNOS, COX2. Heat shock proteins were notably elevated in response to inflammatory reactions. And these effects were inhibited by necrostatin-1 (Nec-1) and N-acetyl-cysteine (NAC). Altogether, these data demonstrated that Cd induced necroptosis and inflammation to aggravate small intestine injury in swine by increasing the excessive accumulation of ROS and imbalanced Th1/Th2, respectively.