K. Suthindhiran

Magnetotactic bacteria and magnetosomes - Scope and challenges.

Geomagnetism aided navigation has been demonstrated by certain organisms which allows them to identify a particular location using magnetic field. This attractive technique to recognize the course was earlier exhibited in numerous animals, for example, birds, insects, reptiles, fishes and mammals. Magnetotactic bacteria (MTB) are one of the best examples for magnetoreception among microorganisms as the magnetic mineral functions as an internal magnet and aid the microbe to move towards the water columns in an oxic-anoxic interface (OAI). The ability of MTB to biomineralize the magnetic particles (magnetosomes) into uniform nano-sized, highly crystalline structure with uniform magnetic properties has made the bacteria an important topic of research. The superior properties of magnetosomes over chemically synthesized magnetic nanoparticles made it an attractive candidate for potential applications in microbiology, biophysics, biochemistry, nanotechnology and biomedicine. In this review article, the scope of MTB, magnetosomes and its challenges in research and industrial application have been discussed in brief. This article mainly focuses on the application based on the magnetotactic behaviour of MTB and magnetosomes in different areas of modern science.

1,2,4-Triazolo-quinazoline-thiones: Non-conventional synthetic approach, study of solvatochromism and antioxidant assessment.

A non-conventional methodology has been utilized for the synthesis of a series of 1,2,4-triazolo-quinazoline-thiones (2a-l). Here the reaction was carried out between 1,2,4-triazolo-quinazolinones (1a-l), in the presence of 1,4-dioxane. The mixture was irradiated under microwave (100W) for 7min to obtain targeted molecules (2a-l). All the synthesized molecules were confirmed by (1)H, (13)C NMR and HRMS. The solvatochromic property (absorption spectra) of compounds (2a-l) in solvents of different polarities was studied. The compounds (2a-l) were further subjected for their in vitro free radical screening using 2,2-diphenyl-1-picrylhydrazyl (DPPH) method and also screened for their in vitro anti-fungal property against Aspergillus flavus (A. flavus) and Aspergillus niger (A. niger). The results from free radical scavenging assay showed promising activity for compounds 2a, e-i, whereas compound 2d showed significant antioxidant activity when compared to ascorbic acid. In vitro anti-fungal study showed that the 1,2,4-triazolo-quinazoline-thiones (2a-l) had significant activity against A. flavus and A. niger compared with widely used antifungal agent Fluconazole.

Isolation, characterisation and kinetics of perchlorate reducing Magnetospirillum species

ABSTRACT Perchlorate reducing bacteria reduce perchlorate to chlorate (ClO3−), which, in turn, is reduced to chlorite (ClO2−) and ultimately to chloride (Cl−). Magnetospirillum strains are reported to use chlorate/perchlorate as electron acceptors. This study describes the perchlorate reducing property of strain VITRJS5, a Magnetopsirillum isolated from freshwater sediment collected from Chelur freshwater lake, Kerala, India. The strain was microaerophile and was phylogenetically related to a Magnetospirillum sp., a member of the α-subclass of the class Proteobacteria. The placement of the isolate in the genus Magnetospirillum has further confirmed the presence of four key magnetosome membrane genes. PCR amplification and phylogenetic analysis of central metabolic genes such as nifH (nitrogenase) and cbbM (type II RubisCo) displayed the highest similarity (97% and 81%, respectively) with Magnetospirillum sp. BB-1 The growth kinetic parameters of the isolate were studied with acetate as the electron donor in batch experiments. Monods substrate utilization model has been established with oxygen, nitrate and perchlorate as electron acceptors separately. The maximum specific growth rate (µmax) and half-saturation constant (ksconc) for the bacterium varied while utilizing different electron acceptors. The maximum specific growth rate was 0.226, 0.190 and 0.096 per hour and half-velocity constant Ks was 25.09, 33.36 and 65.37 mg acetate/l for oxygen, nitrate and perchlorate, respectively. The reduction of perchlorate has been analyzed using kinetic studies of the substrate uptake by the bacteria and the half-velocity constant Ks was found to be 52.8 mg/l. The results indicate that the strain VITRJS5 effectively reduces perchlorate by using it as an electron acceptor.

The chemistry of magnetosomes

Abstract Magnetite nanoparticles are becoming increasingly important for the development of novel biomedical and nanotechnology applications. What if these magnetite nanoparticles are synthesized with uniform shape, size, and dispersion? This leads to the significance of magnetosomes of magnetotactic bacteria (MTB). MTB are aquatic microorganisms that have the ability to biomineralize membrane-bound iron mineral nanocrystals called magnetosomes. Magnetosomes can be easily functionalized because of the presence of various chemical groups at their surface. To explore the world of magnetosomes, it is important to understand their surface chemistry. The two major components of magnetosomes are the magnetosome membrane (MM) and magnetite mineral. MM consists of lipids and proteins. The MM lipids are divided into three major groups of fatty acids phospholipids, glycolipids, and neutral lipids. The proteins present in MM are designated as “Mam” and “mms” proteins. Magnetosome magnetite crystals have unique properties over synthetic nanoparticles such as narrow size distribution, superior shape control, high purity with limited defects, better T2 reducing effect, and chain-like alignment. The genetic manipulation of biomolecules present in the membrane and the excellent characteristics of magnetite make magnetosomes a better candidate for biomedical applications.

Removal of Cr (III) and Ni (II) from tannery effluent using calcium carbonate coated bacterial magnetosomes

Heavy metal contamination of surface water bodies and ground water has been a major problem around the world. Calcium-based adsorbents are effective but cannot be separated easily after the treatment. Magnetosomes are biogenic magnetite synthesised as highly ordered chain-like structures by magnetotactic bacteria. In this study, we have prepared magnetically controlled calcite microcrystals using magnetosomes for the adsorption experiment. The ability of magnetic calcite as adsorbent was investigated for the removal of Cr (III) and Ni (II) ions from synthetic solution. Critical parameters, such as the effect of pH, temperature, contact time, initial ion concentration, and adsorbent dose, were optimised in comparison with calcite, magnetosomes, and activated carbon for maximum metal ion removal. The study showed that equilibrium was established in 1 h for both Cr (III) and Ni (II) at a pH of 6.0 and 8.0, respectively. The adsorption process follows pseudo-second-order reaction kinetics, along with Langmuir and Freundlich adsorption isotherms. The thermodynamics of adsorption of both metal ions on magnetic calcite showed that the adsorption was spontaneous and endothermic in nature. Magnetically controlled calcite crystals successfully removed Cr (III) and Ni (II) from collected tannery effluent and separated from the solution by applying magnetic field. Maximum removal of chromium and nickel (94 and 84%) by magnetic calcite is similar to calcite crystals but higher than magnetosomes and activated carbon. The results indicated that magnetic calcite could be used as an alternative adsorbent for removing heavy metals from tannery effluent.Industrial waste: Does it attract?Bacterial magnetosomes coated with calcite can adsorb heavy metals from industrial waste while being easily recoverable with a magnet. The tanning industry produces large volumes of wastewater contaminated with heavy metals, and these toxins require removal prior to waste discharge into the environment. Calcium carbonate adsorbs heavy metals with high efficiency, but is difficult to recover from treated water, lowering water quality. A team led by Krish Suthindhiran at VIT University in India combine environmentally-innocent magnetosomes—magnetic iron-based minerals enveloped by lipid membranes and produced by magnetotactic bacteria—with a calcium carbonate coating to achieve materials that not only remove Cr(III) and Ni(II) from tannery effluents with efficiencies of up to 94% and 84%, but are easily separated post-treatment by application of a magnetic field.

Combination of different marine algal extracts as biostimulant and biofungicide

ABSTRACT This study investigates the efficiency of seaweed liquid fertilizer (SLF) prepared from combinations of different seaweeds (Sargassum polyphyllum, Turbinaria ornata, Gelidiopsis sp., Padina tetrastomatica, Gracilaria corticata) as a stimulant for the growth of Vigna radiata (Mung) as well as its antagonistic activity against fungal pathogens (Alternaria solani, Rhizoctonia solani., Sarocladium oryzae). 100% SLF was prepared, which was further diluted to 60%, 40%, and 20%. Seeds were soaked in four different concentrations of the SLF (20%, 40%, 60%, and 100%) for 12 hr and planted. After 60 d, the root and shoot length were increased by 14% and 16%, respectively, with SLF (100%). The carbohydrate and protein concentrations were also increased by 70% and 86%, respectively, at 100% SLF. The concentration of chlorophyll a, chlorophyll b, and carotenoids were found to be increased by 20%, 43%, and 28%, respectively, with 100% SLF. Further, the SLF (60% and 100%) successfully inhibited the growth of fungal pathogen A. solani but the other tested strains were found to be resistant. The present study indicates that 100% SLF concentration acts as both biostimulant and biofungicide for A. solani and thus, this SLF could be used as a potential alternative to the chemical fertilizers.

Chapter 3 – Antimicrobial magnetosomes for topical antimicrobial therapy

Biofilms are microbial communities which survive in the hostile environment and are highly resistant to various antimicrobial agents and so very difficult to control, which leads to severity infections. There is an urgent need to eradicate these biofilm-forming bacteria. Nanomedicine is an emerging trend in the medical field, as nanoparticles have been well documented for their antagonistic activity against bacteria, fungi, and viruses and has given rise to new insights in antibiofilm research. Nanomaterials such as silver, gold, aluminum, titanium, iron, and zinc are known to inhibit microbial biofilm. However, they are toxic to the host cells and also to the ecosystem. Magnetosomes produced by magnetotactic bacteria are the iron crystals covered by a lipid membrane called magnetosome membrane. This makes them highly unique compared to the synthetic magnetic nanoparticles. Magnetosomes have received much attention due to their low toxicity, ecofriendly, and cost-efficient properties. Magnetosomes are capable of penetrating the biofilm matrix. Magnetosomes in combination with antibiotics/essential oils will be highly proficient in enhancing the wound-healing property. The carrier property of magnetosomes and antimicrobial activity of drugs/natural compound combination is a successful approach for the prevention of microbial biofilm formation.