Optimizing the Management of Cadmium Bioremediation Capacity of Metal-Resistant Pseudomonas sp. Strain Al-Dhabi-126 Isolated from the Industrial City of Saudi Arabian Environment

Bioremediation of Heavy Metals by the Genus Bacillus

Environmental contamination with heavy metals is one of the major problems caused by human activity. Bioremediation is an effective and eco-friendly approach that can reduce heavy metal contamination in the environment. Bioremediation agents include bacteria of the genus Bacillus, among others. The best-described species in terms of the bioremediation potential of Bacillus spp. Are B. subtilis, B. cereus, or B. thuringiensis. This bacterial genus has several bioremediation strategies, including biosorption, extracellular polymeric substance (EPS)-mediated biosorption, bioaccumulation, or bioprecipitation. Due to the above-mentioned strategies, Bacillus spp. strains can reduce the amounts of metals such as lead, cadmium, mercury, chromium, arsenic or nickel in the environment. Moreover, strains of the genus Bacillus can also assist phytoremediation by stimulating plant growth and bioaccumulation of heavy metals in the soil. Therefore, Bacillus spp. is one of the best sustainable solutions for reducing heavy metals from various environments, especially soil.

Molybdenum and cadmium co-exposure induces endoplasmic reticulum stress-mediated apoptosis by Th1 polarization in Shaoxing duck (Anas platyrhyncha) spleens

Excessive molybdenum (Mo) and cadmium (Cd) are deleterious to animals, but immunotoxicity co-induced by Mo and Cd remains unclear. To ascertain the confederate impacts of Mo and Cd on endoplasmic reticulum (ER) stress-mediated apoptosis by Helper T (Th) cells 1 polarization in the spleen of ducks, we randomly allocated forty 8-day-old Shaoxing ducks (Anas platyrhyncha) into 4 groups and reared them with having different doses of Mo and/or Cd basic diet. At the 16th week of the experiment, serum and spleen tissues were extracted. Data confirmed that Mo and/or Cd strikingly promoted their levels in spleen, caused histological abnormality and trace elements imbalance, and disrupted Th1/Th2 balance to divert toward Th1, then triggered ER stress by increasing three branches PERK/eIF2α/CHOP, IRE1/Caspase-12 and TRAF2/JNK signaling pathways-related genes mRNA and proteins levels, which stimulated apoptosis by elevating Bak-1, Bax, Caspase-9, Caspase-3 mRNA expression, and cleaved-Caspase-9/Caspase-9, cleaved-Caspase-3/Caspase-3 proteins expression as well as apoptosis rate, and decreasing Bcl-xL, Bcl-2 mRNA expression and Bcl-2/Bax ratio. Besides, the variation in combined group was most evident. Briefly, the study indicates that Mo and/or Cd exposure trigger ER stress-induced apoptosis via Th1 polarization in duck spleens, and its mechanism is somehow closely linked with the deposition of Cd and Mo, which may aggravate toxic damage to spleen.

Factors affecting seasonal variation of microbial community structure in Hulun Lake, China

Microbial communities play an important role in water quality regulation and biogeochemical cycling in freshwater ecosystems. However, there is a lack of research on the seasonal variation in lake water microorganisms in cold environments. In this study, 16S rRNA gene high-throughput sequencing was used to explore the microbial community and its influencing factors in Hulun Lake water during different seasons. The results showed that Proteobacteria, Actinobacteria, and Bacteroidetes were the most important phyla in the microbial community of Hulun Lake, but they had significant seasonal differences in their distribution. In addition, significant seasonal differences were observed in the α diversity of microorganisms, with bacterial diversity being higher in winter than in summer. Changes in environmental variables were significantly correlated with changes in the microbial community, and the rapid changes in temperature, pH, and dissolved oxygen are potentially the major factors influencing seasonal bacterial diversity trends. The findings of the present study enhance our understanding of the microbial communities in alpine lake ecosystems and are of great significance for the management and protection of lake ecosystems.

Comparative Study of Heavy Metal Uptake and Analysis of Plant Growth Promotion Potential of Multiple Heavy Metal-Resistant Bacteria Isolated From Arable Land

Heavy metal-induced pollution is a serious environmental concern. This study was aimed at exploring indigenous heavy metal-resistant and plant growth promoting bacteria from arable land that might be useful for developing green strategies to counter the challenges related to bioremediation and sustainable agriculture. A thorough screening and characterization of all the twenty heavy metal-resistant bacterial isolates obtained in this study was done. Of these, three potent isolates were further analyzed to unravel their heavy metal resistance and uptake potentiality. Minimum inhibitory concentration determination depicted considerable tolerance (≥ 500 µg/mL) of the three isolates to Ni, Zn, Fe, Cd, Cu, etc. Growth kinetics of the isolates in presence of various heavy metals indicated differences between normal and metal-induced growth. pH tolerance and pigmentation ability of the isolates were also analyzed. Inductively Coupled Plasma-Mass Spectrometry study revealed maximum Cd uptake by the isolates during exponential phase of growth. One of the isolates demonstrated plant growth promotion ability detected using different in vitro qualitative screening tests. Molecular identification using 16S rRNA depicted the isolates as strains of Pseudomonas aeruginosa. This was the first study of heavy metal-resistant and plant growth promoting bacteria from this region. Further exploration of such multi metal-resistant indigenous bacteria may pave the way for designing effective strategies for bioremediation and sustainable agriculture.

Recent advances in bacterial biosensing and bioremediation of cadmium pollution: a mini-review

Cadmium (Cd) pollution has become a global environmental issue because Cd gets easily accumulated and translocated in the food chain, threatening human health. Considering the detrimental effects and non-biodegradability of environmental Cd, this is an urgent issue that needs to be addressed through the development of robust, cost-effective, and eco-friendly green routes for monitoring and remediating toxic levels of Cd. This article attempts to review various bacterial approaches toward biosensing and bioremediation of Cd in the environment. This review focuses on the recent development of bacterial cell-based biosensors for the detection of bioavailable Cd and the bioremediation of toxic Cd by natural or genetically-engineered bacteria. The present limitations and future perspectives of these available bacterial approaches are outlined. New trends for integrating synthetic biology and metabolic engineering into the design of bacterial biosensors and bioadsorbers are additionally highlighted.

Effective removal of pharmaceutical impurities and nutrients using biocatalyst from the municipal wastewater with moving bed packed reactor

The presence of antibiotics in the wastewater is one of the important issues related to environmental management. In this study, antibiotics-degrading bacteria were screened from the enriched sewage sludge sample. Among the isolated bacterial strains, Bacillus subtilis AQ03 showed maximum antibiotic tolerance (>2000 ppm). The characterized strain B. subtilis AQ03 degraded sulfamethaoxazole and sulfamethoxine and the optimum nutrient and physical-factors were analyzed. B. subtilis AQ03 degraded 99.8 ± 1.3 % sulfamethaoxazole, and 93.3 ± 6.2 % sulfamethoxine. Sodium nitrate and ammonium chloride were improved antibiotics degradation (<90 %). The optimized conditions were maintained in a moving bed bioreactor for the removal of antibiotics and nutrients from the wastewater. The selected strain considerably produced proteases (109.4 U/mL), amylases (55.1 U/mL), cellulase (9.6 U/mL) and laccases (15.2). In moving bed reactor, sulfamethaoxazole degradation was maximum after 8 days (100 ± 1.5 %) and sulfamethoxazole (100 ± 0) was removed completely from wastewater after 10 days. In moving bed reactor, biological oxygen demand (92.1 ± 2.8 %), chemical oxygen demand (79.6 ± 1.2 %), nitrate (89.4 ± 3.9 %) and phosphate (91.8 ± 1.2) were removed from the wastewater along with antibiotics after 10 days of treatment. The findings indicate that the indigenous bacterial communities and the ability to survive in the presence of high antibiotic concentrations and xenobiotics. Moving bed bioreactor is useful for the removal of nutrients and antibiotics from wastewater.

Heavy metals assessment in water, soil, vegetables and their associated health risks via consumption of vegetables, District Kasur, Pakistan

The consumption of contaminated vegetables has a great impact on human health. Due to this fact, we conduct the study to estimate the heavy metals in groundwater, soil, and vegetables by using the atomic adsorption spectroscopy (AAS) and find out the health risk using THQ and TCR caused by using these vegetables. The mean concentrations of As (0.015–0.40 mg/L), Cd (0.02–0.029 mg/L), Co (0.31–0.38 mg/L), Cr (1.02–1.09 mg/L), Cu (2.14–2.17 mg/L), and Hg (0.01–0.04 mg/L) are high in groundwater from threshold values given by WHO. The mean concentrations of As (22.17–23.14 mg/kg), Cd (4.21–4.54 mg/kg), Cu (21.24–24.36 mg/kg), and Pb (32.12–33.48 mg/kg) are high in soil samples from threshold values given by WHO. The mean concentrations of As, Cd, Pb, Cr, Fe, Hg, and Mn values exceeded the recommended values with concentration ranges: 1.75–4.56, 0.41–0.67, 2.12–3.12, 1.44–4.56, 87.12–135.25, 2.09–2.64, and 33.41–129.32 mg/Kg, respectively. The vegetable sample’s average concentration of heavy metals was in decreasing order cabbage ˃ brinjal ˃ okra ˃ tomato. The EDI values for As, Co, and Hg calculated for both adults and children is high. The target hazard quotients (THQ) for As, Co, and Hg are greater than the threshold value by consuming vegetables, which indicated the health risk for both adults and children. Similarly, HI due to tomato, cabbage, okra, and brinjal’s consumption is ˃ 1, with HI values 8.1975, 15.3077, 8.7312, and 10.2306, respectively. This advised the possible health effect in this area by using these vegetables. Target Cancer risk (TCR) exposed the adverse cancer risk persuaded by As, Cr, and Hg as their values exceeded the normal range by USEPA by consumption of these vegetables. This study concluded that vegetables imply the total health risk on local people, and regular monitoring of heavy metals is strongly suggested in this region.

Assessment of heavy metal bioremediation potential of bacterial isolates from landfill soils

Indiscriminate disposal of wastes on landfills has led to increase in heavy metal contamination in landfill soils. However, the ability of the indigenous microorganisms to remediate the polluted environment can be of great influence in reclamation of such soils. The objectives of this study were to assess the bioremediation potential of the screened indigenous bacteria and evaluate the effects of carbon source and pH in the enhancement of the bioremediation process. Bacterial isolates from landfill sites were screened for their capability to utilize heavy metal (Cd and Pb). Nutrient Agar was supplemented with five different concentrations of each metal (25 to 600 mgL^-1). Viable counts of the isolates were taken four times at two days interval. Pseudomonas aeruginosa, Klebsiella edwardsii and Enterobacter cloacae were selected based on their tolerance to heavy metal for remediation process. Peptone broth was also supplemented using different concentrations of heavy metals. The remediation process was assessed by monitoring the growth of biomass using UV spectrophotometer at 600 nm and the residual heavy metal was evaluated after 8 days of incubation using AAS. Pseudomonas aeruginosa exhibited the highest bioremediation potential among the bacterial isolates with 58.80 and 33.67 remediation percentage in 50 mg Cd L^-1 and 300 mg Pb L^-1 . However, higher remediation percentage (79.87 and 92.41) was observed by Klebsiella edwardsii through addition of carbon source (5 g/L) and varying the pH (6) of the media in the heavy metal contaminated medium. The results of this study indicate that the effectiveness of the indigenous bacteria in remediation process can be enhanced through the addition of carbon source and increase pH for effective reclamation of contaminated soil.

Removal of nitrogen from wastewater of date processing industries using a Saudi Arabian mesophilic bacterium, Stenotrophomonas maltophilia Al-Dhabi-17 in sequencing batch reactor

The main aim of the present study was to assess the technical feasibility of nutrients removal from the wastewater from the date processing industries in sequencing batch reactor. Heterotrophic nitrifying and aerobic denitrifying bacteria were isolated from the soil sediment samples. The bacterial strain Al-Dhabi-17 effectively removed nutrients than other isolates from the wastewater and characterized as Stenotrophomonas maltophilia Al-Dhabi-17. The nutrient removal efficacy was improved by optimizing process parameters. Removal of NH₄⁺ from the medium reached 42% within 60 h of cultivation and the nitrification rate was 111 ± 3.1 mg after 24 h. After 96 h, NO₃^- reached 6 ± 0.4 mg/mL concentration. The strain S. maltophilia Al-Dhabi-17 showed the ability to utilize NH₄⁺ ranged between 100 and 300 mg/L. The supplemented sucrose, glucose and date molasses reached maximum nitrification process after 72 h (p < 0.05). Reduction of NH₄⁺ -N reached 73.4% within 48 h time in the medium supplemented with date molasses. Nutrient removal was observed in the broad pH range (6.0-8.5) and maximum nutrient removal achieved at alkaline range (p < 0.05). Sequencing batch reactor was fed with wastewater and nutrient removal was analyzed under optimized condition. The associated chemical oxygen demand, phosphate and total nitrogen removal efficiencies for the suspended growth sequencing batch reactor were 96.5%, 97.9% and 88.4%, respectively. The sequencing batch reactor inoculated with S. maltophilia Al-Dhabi-17 showed promising for nitrogen removal.

Bio-remediation approaches for alleviation of cadmium contamination in natural resources

Cadmium (Cd) is a harmful heavy metal that can cause potent environmental and health hazards at different trophic levels through food chain. Cd is relatively non-biodegradable and persists for a long time in the environment. Considering the potential toxicity and non-biodegradability of Cd in the environment as well as its health hazards, this is an urgent issue of international concern that needs to be addressed by implicating suitable remedial approaches. The current article specifically attempts to review the different biological approaches for remediation of Cd contamination in natural resources. Further, bioremediation mechanisms of Cd by microbes such as bacteria, fungi, algae are comprehensively discussed. Studies indicate that heavy metal resistant microbes can be used as suitable biosorbents for the removal of Cd (up to 90%) in the natural resources. Soil-to-plant transfer coefficient (TC) of Cd ranges from 3.9 to 3340 depending on the availability of metal to plants and also on the type of plant species. The potential phytoremediation strategies for Cd removal and the key factors influencing bioremediation process are also emphasized. Studies on molecular mechanisms of transgenic plants for Cd bioremediation show immense potential for enhancing Cd phytoremediation efficiency. Thus, it is suggested that nano-technological based integrated bioremediation approaches could be a potential futuristic path for Cd decontamination in natural resources. This review would be highly useful for the biologists, chemists, biotechnologists and environmentalists to understand the long-term impacts of Cd on ecology and human health so that potential remedial measures could be taken in advance.

Biosorption of heavy metals by dry biomass of metal tolerant bacterial biosorbents: an efficient metal clean-up strategy

Heavy metals discharge at an unrestrained rate from various industries into the environment pose serious human health problems. Considering this, the present study aimed at exploring the metal biosorbing potentials of bacterial strains recovered from polluted soils. The bacterial strains (CPSB1, BM2 and CAZ3) belonging to genera Pseudomonas, Bacillus and Azotobacter expressing multi-metal tolerance ability were identified to species level as P. aeruginosa, B. subtilis and A. chroococcum, respectively, by 16S rRNA partial gene sequence analysis. The biosorption of cadmium, chromium, copper, nickel, lead and zinc by three dead bacterial genera were studied as a function of metal concentration, variable pH of the medium and reaction (contact) time. The three bacterial strains exhibited a tremendous metal removal ability which continued even at the highest tested concentration of some metals. Later, a decline in the percentage of biosorbed metals was recorded as the metal concentration was increased with the simultaneous generation of a driving force to overcome mass transfer resistance for movement of metal ions between the solution and the surface of adsorbent. Among test bacteria, B. subtilis biosorbed a maximum of 96% chromium at 25 μg mL^-1 while the maximum percentage (91%) of biosorbed metals recorded at 400 μg Cd mL^-1 was observed for P. aeruginosa. The sorption of metal ions by dead biomass of three bacterial genera at optimum conditions followed the order-(i) B. subtilis BM2: Pb > Cu > Ni > Cd > Cr, (ii) A. chroococcum CAZ3: Cr > Cd > Cu > Ni > Pb and (iii) P. aeruginosa CPSB1: Cd > Cr > Ni > Cu > Pb > Zn. It was found that the optimum pH for metal adsorption ranged between pH 8 and 9 which, however, declined substantially at pH 5.0 for all three bacterial strains. In general, the biosorption of Cd, Cr, Cu, Ni and Pb by B. subtilis and A. chroococcum and such metals along with Zn by P. aeruginosa occurred maximally up to 60 min of bacterial growth. The adsorption data with regard to five metals provide an outstanding fit to the Langmuir and Freundlich isotherms. The biosorptive ability of three bacterial genera correlated strongly (r² > 0.9) with each metal. The bacteria belonging to two Gram-negative genera Pseudomonas (P. aeruginosa) and Azotobacter (A. chroococcum) and one Gram-positive genus Bacillus (B. subtilis) demonstrated exceptional metal removal efficiency and, hence, provides a comprehensive understanding of metal-bacteria sorption process which in effect paves the way for detoxifying/removing metals from contaminated environment.

Total Arsenic, pH, and Sulfate Are the Main Environmental Factors Affecting the Microbial Ecology of the Water and Sediments in Hulun Lake, China

Bacteria have the metabolic potential to produce a diverse array of secondary metabolites, which have important roles in biogeochemical cycling processes. However, for Hulun Lake and the rivers that enter into it, the bacterial community structures and their effects have not previously been widely studied, limiting our ecological understanding of this habitat. To address this, we have analyzed the bacterial communities in the water ecosystem of the Hulun Lake Basin. 16S rRNA high-throughput sequencing identified 64 phyla, 165 classes, 218 orders, 386 families, and 740 genera of bacteria across all samples. The dominant phyla in the central area of the lake were Proteobacteria, Actinobacteria, Firmicutes, and Cyanobacteria, while in all other areas, Proteobacteria, Actinobacteria, and Bacteroidetes were dominant. The microbial community structures were significantly affected by environmental factors [arsenic (As), pH, and sulfate (SO₄^2–)] and their location in the lake. The species richness in the sediments of Hulun Lake was higher than in the water, and this ecosystem harbored the highest proportion of unclassified sequences, representing unclassified bacteria. This study provides basic data for future investigations into the Hulun lake ecosystem and for water microbial monitoring and protection measures.