Lead biosorption efficiency of Levilactobacillus brevis MZ384011 and Levilactobacillus brevis MW362779: A response surface based approach

Molecular and eco-physiological responses of soil-borne lead (Pb2+)-resistant bacteria for bioremediation and plant growth promotion under lead stress

Lead (Pb) is the 2nd known portentous hazardous substance after arsenic (As). Being highly noxious, widespread, non-biodegradable, prolonged environmental presence, and increasing accumulation, particularly in arable land, Pb pollution has become a serious global health concern requiring urgent remediation. Soil-borne, indigenous microbes from Pb-polluted sites have evolved diverse resistance strategies, involving biosorption, bioprecipitation, biomineralization, biotransformation, and efflux mechanisms, under continuous exposure to Pb in human-impacted surroundings. These strategies employ a wide range of functional bioligands to capture Pb and render it inaccessible for leaching. Recent breakthroughs in molecular technology and understanding of lead resistance mechanisms offer the potential for utilizing microbes as biological tools in environmental risk assessment. Leveraging the specific affinity and sensitivity of bacterial regulators to Pb2+ ions, numerous lead biosensors have been designed and deployed worldwide to monitor Pb bioavailability in contaminated sites, even at trace levels. Besides, the ongoing degradation of croplands due to Pb pollution poses a significant challenge to meet the escalating global food demands. The accumulation of Pb in plant tissues jeopardizes both food safety and security while severely impacting plant growth. Exploring Pb-resistant plant growth-promoting rhizobacteria (PGPR) presents a promising sustainable approach to agricultural practices. The active associations of PGPR with host plants have shown enhancements in plant biomass and stress alleviation under Pb influence. They thus serve a dual purpose for plants grown in Pb-contaminated areas. This review aims to offer a comprehensive understanding of the role played by Pb-resistant soil-borne indigenous bacteria in expediting bioremediation and improving the growth of Pb-challenged plants essential for potential field application, thus broadening prospects for future research and development.

Optimization of desorption parameters using response surface methodology for enhanced recovery of arsenic from spent reclaimable activated carbon: Eco-friendly and sorbent sustainability approach

Desorption and adsorbent regeneration are imperative factors that are required to be taken into account when designing the adsorption system. From the environmental, economic, and practical points of view, regeneration is necessary for evaluating the efficiency and sustainability of synthesized adsorbents. However, no study has investigated the optimization of arsenic species desorption from spent adsorbents and their regeneration ability for reuse as well as safe disposal. This study aims to investigate the desorption ability of arsenic ions adsorbed on hybrid granular activated carbon and the optimization of the independent factors influencing the efficient recovery of arsenic species from the spent activated carbon using central composite design of the response surface methodology. The activated carbon before the sorption process and after the adsorption-desorption of arsenic ions have been characterized using SEM-EDX, FTIR, and TEM. The study found that all the investigated independent desorption variables greatly influence the retrievability of arsenic ions from the spent activated carbon. Using the desirability function for the optimization of the independent factors as a function of desorption efficiency, the optimum experimental conditions were solution pH of 2.00, eluent concentration of 0.10 M, and temperature of 26.63 ℃, which gave maximum arsenic ions recovery efficiency of 91 %. The validation of the quadratic model using laboratory confirmatory experiments gave an optimum arsenic ions desorption efficiency of 97 %. Therefore, the study reveals that the application of the central composite design of the response surface methodology led to the development of an accurate and valid quadratic model, which was utilized in the enhanced optimization of arsenic ions recovery from the spent reclaimable activated carbon. More so, the desorption isotherm and kinetic data of arsenic were well correlated with the Langmuir and the pseudo-second-order models, while the thermodynamics studies indicated that arsenic ions desorption process was feasible, endothermic, and spontaneous.

Levilactobacillus brevis MZ384011 and Levilactobacillus brevis MW362779 can mitigate lead induced hepato-renal damage by regulating visceral dispersion and fecal excretion

Heavy metal pollution is a global issue. Current study provides evidence on Pb toxicity ameliorative potential and safe nature of Levilactobacillus brevis MZ384011 (S1) and Levilactobacillus brevis MW362779 (S2), isolated from carnivore gut and human milk, respectively. In a 60-days experiment, the rats were distributed into six groups. G-I, G-V and G-VI were kept on normal diet, while GII-IV were fed on lead nitrate (500 mg/kg) supplemented food, throughout experiment. After confirmation of Pb toxicity in GII-IV at 15th day, S1 was orally administered to G-III and G-V while S2 was given to G-IV and G-VI at a dose of 1 × 109 CFU/animal/day. On day 60 of experiment, positive control (G-II) displayed significant reduction in body weight, total protein, albumin, globulin, mineral profile, erythrocyte count, hemoglobin, hematocrit and hematological indices and elevation in leukocyte count, alanine aminotransferase, aspartate aminotransferase, bilirubin, uric acid and creatinine along with alterations in hepato-renal architecture. With reference to G-II, the G-III and G-IV displayed significant improvement in all aforementioned parameters, 40-60% reduction in tissue Pb levels (blood, liver, kidney and adipose tissue) and elevation in fecal Pb contents (p = 0.000). The groups V and VI did not show any sign of toxicity. The findings confirm that strains are safe for biological application and can reverse Pb toxicity by facilitating fecal Pb excretion and reducing its systemic dispersal. To best of our information this is the first report on Pb toxicity ameliorative role of Levilactobacillus brevis from human milk, the safest source.