Immobilization of heavy metals by microbially induced carbonate precipitation using hydrocarbon-degrading ureolytic bacteria

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Heavy metal toxicity to hydrocarbon-degrading ureolytic bacteria is Cd > Ni > Cr > Cu > Zn.

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The ureolytic bacteria can tolerate heavy metals and co-precipitate heavy metals.

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The precipitated minerals shifted between calcite and brushite depending on the heavy metal.

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The immobilization of heavy metals resulted in removal efficiency reaching 100%.

Crude oil contamination introduces multiple threats to human health and the environment, most of which are from toxic heavy metals. Heavy metals cause significant threats because of their persistence, toxicity, and bio-accumulation. Biomineralization, performed through many microbial processes, can lead to the immobilization of heavy metals in formed minerals. The potential of the microbially carbonate-induced precipitation (MICP) in removal by biomineralization of several heavy metals was investigated. A collection of diverse 11 bacterial strains exhibited ureolytic activity and tolerance to heavy metals when growing in Luria-Bertani (LB) and urea medium. Determination of the minimum inhibitory concentrations (MIC) revealed that heavy metal toxicity was arranged as Cd > Ni > Cr > Cu > Zn. Three hydrocarbon-degrading bacterial strains (two of Pseudomonas aeruginosa and one of Providencia rettgeri) exhibited the highest tolerance (MIC > 5 mM) to Cu, Cr, Zn, and Ni, whereas Cd exerted significantly higher toxicity with MIC <1 mM. At all MICP conditions, different proportions of calcium carbonate (calcite) and calcium phosphate (brushite) were formed. Pseudomonas aeruginosa strains (QZ5 and QZ9) exhibited the highest removal efficiency of Cr (100%), whereas Providencia rettgeri strain (QZ2) showed 100% removal of Zn. Heavy metal complexes were found as well. Cd removal was evidenced by the formation of cadmium phosphate induced by Providencia rettgeri bacterial activity. Our study confirmed that hydrocarbon-degrading ureolytic bacteria not only can tolerate heavy metal toxicity but also have the capability to co-precipitate heavy metals. These findings indicate an effective and novel biological approach to bioremediate petroleum hydrocarbons and immobilize multiple heavy metals with mineral formation. This is of high importance for ecological restoration via stabilization of soil and alleviation of heavy metal toxicity.

Wound healing property of a gel prepared by the combination of Pseudomonas aeruginosa alginate and Alhagi maurorum aqueous extract in rats

Although alginate has been known to be a good wound dressing, it does not have antimicrobial properties, has low availability, and is expensive. To overcome these problems, the present study was conducted, where the extraction of this material from an available small factory Pseudomonas aeruginosa and the improvement of its wound healing property by its combination with herb extract, Alhagi maurorum, done. Nineteen P. aeruginosa strains were isolated and identified from burned skin, and the one isolated strain with the highest ability of alginate production was selected. A. maurorum aqueous extract was prepared, and the toxicity of each material was determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5diphenyltetrazolium bromide assay. A mixture of nontoxic doses of each substance was then prepared. Thirty-two Wistar rats were divided into four groups (n = 8). The control group and the rest three groups, which were treated by alginate, A. maurorum extract, and alginate- A. maurorum extract. Throughout the 21 days of treatment, the open wound sites were checked. Finally, the rats were sacrificed and the effect of each substance on their skin tissue was evaluated. The results showed that the high alginate production without any toxic effect was obtained from the P. aeruginosa strain K1. A. maurorum aqueous extract had dose-dependent toxicity. The aqueous solution of alginate- A. maurorum extract complex group showed the best wound healing activity in both macroscopic and microscopic examinations. Recent research has introduced a new type of wound dressing with high wound healing properties. This could decrease the time for re-epithelialization and increase wound contraction percentage.

Chromosomal organization and transcription analysis of genes in the vicinity of Pseudomonas aeruginosa glmM gene encoding phosphoglucosamine mutase

A computer-aided analysis of the Pseudomonas aeruginosa PAO1 genome surrounding the glmM gene was carried out and the organization of this chromosomal region was compared with the equivalent regions in other gamma-proteobacteria species with the genome sequence available. glmM encodes the enzyme phosphoglucosamine mutase which catalyses the interconversion of glucosamine-6-phosphate into glucosamine-1-phosphate in the biosynthetic pathway leading to the synthesis of UDP-N-acetylglucosamine which is simultaneously a precursor for the biosynthesis of cell-wall peptidoglycan and outer membrane lipopolysaccharide. Northern blot analysis suggests that glmM may be a part of the five-cistron operonic structure composed by the Escherichia coli homologues ftsJ, ftsH, folP, glmM, and tpiA. The secG gene, downstream tpiA, does not make part of this polygenic organization, being actively transcribed as a monocistronic mRNA during transition to the stationary phase of growth. Differently, transcription of genes in the glmM operon is more active in the early exponential phase, decreasing with the increase of cell density during exponential growth and reaching negligible values in stationary phase cells.

Effect of oxygen on formation and structure of Azotobacter vinelandii alginate and its role in protecting nitrogenase

The activity of nitrogenase in the nitrogen-fixing bacterium Azotobacter vinelandii grown diazotrophically under aerobic conditions is generally considered to be protected against O(2) by a high respiration rate. In this work, we have shown that a high rate of respiration is not the prevailing mechanism for nitrogenase protection in A. vinelandii grown in phosphate-limited nitrogen-free chemostat culture. Instead, the formation of alginate appeared to play a decisive role in protecting the nitrogenase that is required for cell growth in this culture. Depending on the O(2) tension and cell growth rate, the formation rate and composition of alginate released into the culture broth varied significantly. Furthermore, transmission electron microscopic analysis of cell morphology and the cell surface revealed the existence of an alginate capsule on the surface of A. vinelandii. The composition, thickness, and compactness of this alginate capsule also varied significantly. In general, increasing O(2) tension led to the formation of alginate with a higher molecular weight and a greater L-guluronic acid content. The alginate capsule was accordingly thicker and more compact. In addition, the formation of the alginate capsule was found to be strongly affected by the shear rate in a bioreactor. Based on these experimental results, it is suggested that the production of alginate, especially the formation of an alginate capsule on the cell surface, forms an effective barrier for O(2) transfer into the cell. It is obviously the quality, not the quantity, of alginate that is decisive for the protection of nitrogenase.

Structures and properties of gellan polymers produced by sphingomonas paucimobilis ATCC 31461 from lactose compared with those produced from glucose and from cheese whey

The dairy industry produces large quantities of whey as a by-product of cheese production and is increasingly looking for new ways to utilize this waste product. Gellan gum is reliably produced by Sphingomonas paucimobilis in growth media containing lactose, a significant component of cheese whey, as a carbon source. We studied and compared polysaccharide biosynthesis by S. paucimobilis ATCC 31461 in media containing glucose, lactose (5 to 30 g/liter), and sweet cheese whey. We found that altering the growth medium can markedly affect the polysaccharide yield, acyl substitution level, polymer rheological properties, and susceptibility to degradation. Depression of gellan production from lactose compared with gellan production from glucose (approximately 30%) did not appear to occur at the level of synthesis of sugar nucleotides, which are the donors of monomers used for biosynthesis of the repetitive tetrasaccharide unit of gellan. The lactose-derived biopolymer had the highest total acyl content; the glucose- and whey-derived gellans had similar total acyl contents but differed markedly in their acetate and glycerate levels. Rheological studies revealed how the functionality of a gellan polysaccharide is affected by changes in the acyl substitution.

Bacterial alginate biosynthesis--recent progress and future prospects

The extracellular polysaccharide alginate has been widely associated with chronic Pseudomonas aeruginosa infections in the cystic fibrosis lung. However, it is clear that alginate biosynthesis is a more widespread phenomenon. Alginate plays a key role as a virulence factor of plant-pathogenic pseudomonads, in the formation of biofilms and with the encystment process of Azotobacter spp.

Oxygen-dependent upregulation of transcription of alginate genes algA, algC and algD in Pseudomonas aeruginosa

The mRNA levels of algA, algC and algD genes increased, coordinately, in cells of the highly mucoid Pseudomonas aeruginosa 8821M grown under increasing dissolved oxygen tensions (DOT) of up to 70% of air saturation. These genes encode the bifunctional protein with phosphomannose isomerase (PMI) and GDP-mannose pyrophosphorylase (GMP) activities (algA), the phosphomannomutase (PMM) (algC) and the GDP-mannose dehydrogenase (GMD) (algD). These four enzyme activities are necessary for the synthesis of GDP-mannuronic acid, which is the activated sugar precursor for alginate polymerization. For growth-limiting DOT--lower than 10% of air saturation--the increase in mRNA levels of algA, algC and algD with oxygen concentration was accompanied by a strong increase in the activity of the encoded enzymes and the consequent increase in alginate synthesis. However, and despite the upregulation of alginate gene transcription by DOT above 10% of air saturation, the activities of the encoded enzymes either maintained (GMP and GMD) or decreased (PMI and PMM) their levels at high oxygen tensions, leading to a slight decrease in alginate synthesis. This has previously been attributed to the oxidative inactivation of alginate enzymes, particularly of PMM and PMI activities.