Heavy metals bioremediation and water softening using ureolytic strains Metschnikowia pulcherrima and Raoultella planticola

Abstract

BACKGROUND: The recalcitrant nature of lead (Pb) and mercury (Hg) to degradation represents a real risk to living creatures and their surrounding ecosystems. Therefore, this study employed ureolytic fungal strain Metschnikowia pulcherrima (29A) and bacterial strain Raoultella planticola (VIP) in their removal using the promising CaCO 3 bioprecipitation technique, for the first time.RESULTS: Out of 50 isolates, strains 29A and VIP were selected based on their highest ureolytic activity, followed by minimum inhibitory concentration assay using 350 ppm of Pb 2+ and Hg 2+ . Throughout 7 days of incubation at 30°C and 150 rpm with 10 8 CFU mL −1 inoculum, the maximum urease activity was 884 and 639 U mL −1 for 29A and VIP at 24 and 30 h of incubation, respectively. Complete removal of Pb 2+ was achieved at 42 h (29A) and 90 h (VIP), while Hg 2+ was totally removed at 60 h (29A) and 102 h (VIP). Remarkable removal of Ca 2+ (>95%) was achieved by the end of the experiments, which would address the hardness problem in water treatment processes. Further, energy-dispersive X-ray analysis (EDX), scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the remediated precipitates. EDX profiles showed characteristic peaks of C, O and Ca besides Pb and Hg. SEM illustrated the presence of microbial imprints and calcinated cells in the remediated bioliths. However, XRD confirmed transformation of soluble metals to insoluble forms entrapped in calcite or vaterite lattice.CONCLUSIONS: Such a bioremediation approach ensures the detoxification and sequestration of heavy metals in stable and durable matrices, hindering their leaching from carbonate complex trap to the environment.

Statistical modeling of methylene blue degradation by yeast-bacteria consortium; optimization via agro-industrial waste, immobilization and application in real effluents

“…Despite they were screened from different environmental habitats with different contamination content. Some of them exhibited characteristic bioremediation capabilities [ 16 ]. The diversity of their phylogeny, namely Basidiomycota, Proteobacteria , and Firmicutes , revealing their metabolic performance to utilize and detoxify xenobiotic compounds.…”

“…Moreover, it is a time consuming, laborious practice and cost-effective. Recently, DOS has been utilized in media engineering to procure the optimal operating conditions for several purposes such as heavy metal removal [ 16 ], enzyme production [ 75 ] protein-drug production [ 74 ] and dye biosorption [ 63 ]. Initially PBD was utilized to screen the most significant factors, based on p-value, which were MB concentration, pH, molasses concentration, inoculum size and NaNO 3 concentration.…”

“…Moreover, the presence of azo dyes or their aromatic by-products in water causes shortness of breath, vomiting, diarrhea, sweating, allergy and hypopigmentation. Notably, some carcinogenic, mutagenic and neurotoxic effects of them have also been reported [ 7 , 15 , 16 ]. Therefore, to reduce these environmental pollution and human health risks, the environmental legislation has enforced dyestuff manufacturers to treat effluents contaminated with dyes prior to their discharge into open streams [ 7 ].…”

Draft genome of Raoultella planticola, a high lead resistance bacterium from industrial wastewater

“…Also, it was reported that R. planticola (R3) can grow at 1500 ppm lead and was reported that it can remove several heavy metals like lead, manganese, cadmium, copper, zinc and nickel (Bowman et al 2018 ). Raoultella planticola (VIP) was determined the minimum inhibition concentration reached to 350 ppm and completely removed lead at 90 h (Eltarahony et al 2021 ) while the MIC for R. planticola FACU 3 was to 2800 ppm. In this study, TEM was used to investigate the morphological Pb response of two bacterial strains, the highest strain ( R. planticola FACU 3) and lowest strains ( S. xylosus FACU) in cell viability, efficiency of biosorption and Pb uptake.…”

Heavy metal bioremediation using microbially induced carbonate precipitation: Key factors and enhancement strategies

“…Raoultella planticola , a ureolytic bacterial strain, transformed Pb 2+ into light grey cerussite (PbCO 3 ), whereas Metschnikowia pulcherrima , a ureolytic fungal strain, transformed Pb 2+ into CaPbO 3 . Such instances were also disclosed by Hg 2+ remediation ( Eltarahony et al, 2021 ). Supplementary Table S1 also lists the final products of different representative HMs formed in MICP.…”