Chinmay Hazra

Ultrasound-assisted/biosurfactant-templated size-tunable synthesis of nano-calcium sulfate with controllable crystal morphology.

Nano-sized crystals of alpha calcium sulfate hemihydrate (α-HH) with considerable morphology-dependent properties find promising applications in the clinical fields as a cementitious material. Towards this end, ultrasound-assisted rhamnolipid and surfactin biosurfactant-template route is explored to control the morphology and aspect ratio of nano-CaSO4 by adjusting the mass ratio of rhamnolipid/H2O, surfactin/H2O and rhamnolipid/surfactin. The change in the molar ratio of [SO4(2-)]:[Ca(2+)] results in modification in variable morphology and size of nano-CaSO4 including long, short rods and nanoplates. With increase in the rhamnolipid/H2O ratio from 1.3 to 4.5, the crystal length decreases from 3 μm to 600 nm with the corresponding aspect ratio reduced sharply from 10 to 3. Similarly, the crystal morphology gradually changes from submicrometer-sized long rod to hexagonal plate, and then plate-like appearance with increase in surfactin concentration. The preferential adsorption of rhamnolipid on the side facets and surfactin on the top facets contributes to the morphology control. The process using 50% amplitude with a power input of 45.5 W was found to be the most ideal as observed from the high yields and lower average l/w aspect ratio, leading to more than 94% energy savings as compared to that utilized by the conventional process. As a morphology and crystal habit modifier, effects of Mg(2+) and K(+) ions on α-HH growth were investigated to find an optimal composition of solution for α-HH preparation. Mg(2+) ions apparently show an accelerating effect on the α-HH growth; however, the nucleation of α-HH is probably retarded by K(+) ions. Thus, the present work is a simple, versatile, highly efficient approach to controlling the morphology of α-HH and thereby, offers more opportunities for α-HH multiple applications.

Extracellular biosynthesis of zinc oxide nanoparticles using Rhodococcus pyridinivorans NT2: Multifunctional textile finishing, biosafety evaluation and in vitro drug delivery in colon carcinoma

In this study, zinc oxide (ZnO) nanoparticles (NPs) were rapidly synthesized from zinc sulfate solution at room temperature using a metabolically versatile actinobacteria Rhodococcus pyridinivorans NT2. The morphology, structure and stability of the synthesized ZnO NPs were studied using UV-visible absorption spectroscopy, X-ray Diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM) with energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), Zeta potential, and thermogravimetry. The data indicated that the synthesized nanoparticles were moderately stable, hexagonal phase, roughly spherical with average particle diameter in the range of 100-120 nm. Results obtained on examination of protein expression revealed that cell enzymes and extracellular protein systems of Rhodococcus sp. may take part in synthesis process. Furthermore, the ZnO NPs were coated onto textile fabrics to enhance UV-blocking, self-cleaning and antibacterial properties. Ultraviolet protecting factor (UPF) indicating UV-blocking properties of ZnO NPs coated textile fabrics were determined as 65, 88, 121, 172 and 241 for 1, 2, 3, 4 and 5 gm(-2) of ZnO NPs, respectively. Besides, self-cleaning activity was assessed by investigating photocatalytic activity on malachite green as well as antibacterial activity against aerobic Gram-positive Staphylococcus epidermidis NCIM 2493 (ATCC 12228). The antibacterial effects of these textiles were evaluated using ISO 20743 standard. In addition, ZnO NPs exhibited a preferential ability to kill HT-29 cancerous cells as compared with normal peripheral blood mononuclear cells (PBMCs).

Biosurfactant-Assisted Bioaugmentation in Bioremediation

Surface active compounds (SACs) are basically amphipathic in nature, which alter the properties of fluid interfaces, partition at interface between fluid phases leading to formation of micro-emulsion and impart better wetting, spreading, foaming and detergent traits, thereby rendering them as most versatile process chemicals to be utilized in surfactant-enhanced bioremediation practices. Use of chemical surfactants as an additive, however, warrant (i) toxicity, (ii) carcinogenicity, (iii) non-biodegradibility, (iv) bioaccumulation and (v) inconsistent performance with slow desorption kinetics. Therefore, attention has been focused on alternative amphiphilic surfactants of biological origin, which have predilection for interfaces of dissimilar polarities (liquid-air/liquid-liquid) and are soluble in both organic (non-polar) and aqueous (polar) milieu. The mechanisms of biosurfactant-assisted bioaugmentation in bioremediation include: (i) lowering of interfacial tension, (ii) biosurfactant solubilization of hydrophobic contaminants, and (iii) the phase transfer of pollutants from soil-sorbed to pseudo-aqueous phase. Hence, microbial surfactants have potential attributes as alternative to synthetic surfactants. This article reviews key aspects of microbial tensioactives for applications in bioremediation and biodegradation of environmental pollutants with focus on properties and physiological roles, followed by its laboratory, field demonstrations and full-scale applications. Finally, it is concluded with a concise appraisal on in situ and ex situ biosurfactant-assisted bioaugmentation, along-with impediments and future challenges.

Biodegradation of 2,4-dinitrotoluene with Rhodococcus pyridinivorans NT2: characteristics, kinetic modeling, physiological responses and metabolic pathway

2,4-Dinitrotoluene (2,4-DNT), a major by-product during the synthesis of 2,4,6-trinitrotoluene, is widely used as a gelatinizing, waterproofing and plasticizing agent in explosives and propellants. Since DNTs and its metabolites exhibit toxicity to human beings, fish, algae and microorganisms, they are treated as priority pollutant in several countries. This study describes the biodegradation of 2,4-DNT in batch mode by Rhodococcus pyridinivorans NT2 in the range of 0.5–2 mM. At initial concentration of 0.54 mM, degradation kinetics were described well by zero-order model. However, modeling of the biodegradation at higher concentrations indicated that the Andrews–Haldane model predicts the experimental data fairly well. During growth and biodegradation, changes in saturated/unsaturated ratio of fatty acids, total cyclo fatty acids, and the ratio of anteiso:iso-branching were observed. This was accompanied by increased cell size, alternation in enzymatic and non-enzymatic antioxidant defense systems, accumulation of biosurfactants and carotenoids. Biodegradation of 2,4-DNT by this strain proceeded through a pathway involving intermediates such as 2-amino-4-nitrotoluene and 2,4-diaminotoluene. The strain NT2 harbored plasmid that was found to be associated with biodegradation.

Surfactin-functionalized poly(methyl methacrylate) as an eco-friendly nano-adsorbent: from size-controlled scalable fabrication to adsorptive removal of inorganic and organic pollutants

Poly(methyl methacrylate) (PMMA), a non-toxic, cheap and easy-to-obtain compatible polymer, has widespread applications in biomedical and environmental nanotechnology. This work presents an environmentally-friendly sonochemical approach to synthesizing PMMA nanoparticles surface-functionalized with surfactin to develop multifunctional polymer nanoparticles with enhanced sorption properties. The advantages of sonochemical emulsion polymerization over conventional polymerization included (i) higher monomer conversion, (ii) enhanced latex yield, (iii) better surfactin functionalization and (iv) higher colloidal stability. The TEM micrographs showed that spherical nanoparticles with average sizes of 60 and 72 nm were formed by sonochemical and conventional emulsion polymerization, respectively. These nanoparticles were used for the selective removal of Pb2+, Cd2+, Cu2+, Fe2+, Ni2+, Co2+, Zn2+ and Cr3+ from water. Metal ions were removed either by forming chelate complexes or by electrostatic interactions. The observed affinity order for adsorption was Co2+ > Zn2+ > Ni2+ > Cr3+ > Fe2+ > Cu2+ > Cd2+ > Pb2+ under single-component non-competitive conditions. These nanoparticles were suitable for four adsorption–desorption cycles without appreciable loss of adsorption capacity. The rate of adsorption was described well by a pseudo-second-order rate equation and the Sips and Redlich–Peterson isotherms provided the best theoretical correlation with the experimental equilibrium data. The quality of the results was measured and the most influential parameter in each model was identified by a sensitivity analysis of the fitted model parameters. The adsorption thermodynamics were spontaneous and exothermic. The nanoparticles were also a good adsorbent for phenol and β-naphthol, but not for 1-naphthylamine. Furthermore, the sonochemically synthesized and surfactin-functionalized PMMA exhibited bactericidal action (300 μg mL−1) against E. coli, with 80% killing efficacy and low haemolytic toxicity (45%), even at high concentrations up to 500 μg mL−1. Therefore, these nano-adsorbents care suitable for environmental engineering applications.

Bioremediation Potential of Rhodococcus pyridinivorans NT2 in Nitrotoluene-Contaminated Soils: The Effectiveness of Natural Attenuation, Biostimulation and Bioaugmentation Approaches

ABSTRACT This work evaluated the effect of bioremediation treatments including natural attenuation, bioaugmentation, biostimulation as well as combined biostimulation and bioaugmentation on degradation of 4-nitrotoluene (4-NT), 2,4-dinitrotoluene (2,4-DNT) and 2,6-dinitrotoluene (2,6-DNT) in soil microcosms. Bioaugmentation with a previously isolated NTs-degrading bacterium, Rhodococcus pyridinivorans NT2, showed an 86–88% decrease in 4-NT, 2,4-DNT or 2,6-DNT after 60 days. Irrespective of the substrate types, least degradation (6–6.5%) was observed in abiotic control. The addition of β-cyclodextrin or rhamnolipid significantly improved NTs degradation efficiency in soil (18.5–74%) than natural attenuation (22–25%). Exogenous addition of preselected bacterial isolate NT2 along with β-cyclodextrin/rhamnolipid resulted in the greatest number (1.8× and 2.5× high) of total heterotrophic aerobic bacteria and NT degraders, respectively, compared to natural attenuation. Irrespective of the treatment types, the population of NT degraders increased steadily in the first 5 weeks of incubation followed by a plateau within the next few weeks. The treatment BABS2 (Soil + rhamnolipid + NT2) yielded highest microbial-C and -N and dehydrogenase activity, consistent with results of NTs degradation and microbial counts in combined bioaugmentation and biostimulation. Thus the results of this study suggest that bioaugmentation by R. pyridinivorans NT2 may be a promising bioremediation strategy for nitroaromatics-contaminated soils.

Bioremediation of Nitroaromatics (NACs)-Based Explosives: Integrating ‘-Omics’ and Unmined Microbiome Richness

This review aims to be a pragmatic primer in the field of post-genomic bioremediation of NACs-based explosives with special emphasis on the ‘omics’ technologies. After an introduction in the concepts and methodologies of high-throughput molecular approaches and a discussion of the numerous emerging variations on the basic theme, a short overview of the success stories of ‘omics’ in bioremediation of NACs are revisited, followed by a brief discussion about the technical, methodological, and computational resources that embody the landscape of microbial epimetabolome. The review ends with a note on the research-commercialization gap, taking into account the containment technologies pertaining to biosafety issues and technical safeguards.