Remarkably high Pb2+ binding capacity of a novel, regenerable bioremediator Papiliotrema laurentii RY1: Functional in both alkaline and neutral environments.

The ability of P. laurentii strain RY1 to remediate lead (Pb2+) from water was investigated in batch and column studies. The lead removal ability of non-viable biomass, non-viable biomass immobilised on agar-agar (biobeads) and agar-agar at different pH was compared in batch studies. It was found that among the three, biobeads have maximum ability to remove Pb2+ followed by biomass and agar-agar beads. Maximum and almost equal lead removal by biobeads was observed at both neutral and alkaline pH making it a novel and more applicable bioremediator as all other reported bioremediators have a single pH for optimum activity. Studies were performed to determine the optimum conditions for lead removal from aqueous solutions for biobeads. The physical and chemical characterization of the biobeads before and after Pb2+ biosorption was done by using S.E.M. and F.T.I.R. respectively. The adsorption of Pb2+ on biobeads obeyed the Langmuir adsorption isotherm and pseudo first order kinetics. These mean that the Pb2+ binding sites are identical, located on the surface of the adsorbant and the rate of Pb2+ removal from aqueous solution is directly proportional to the number of Pb2+ binding sites on the biobeads. The thermodynamics of the biosorption process is also investigated. The binding capacity of the biobeads in batch study was found to be 52.91mg/gm which is higher in comparison to other reported yeast bioremediators. The used biobeads can be desorbed using 0.1(M) CaCl2. The desorbed biobeads can be used subsequently for several cycles of lead removal making it cost-effective. Column studies were also performed for biobeads with the help of Thomas model for examining its suitability for industrial application. Maximum specific lead uptake of the biobeads when applied in the column was found to be 58.26mg/gm which being promising makes it suitable for application in industries involved in the treatment of wastewater contaminated with high amounts of lead. The high mass transfer co-efficient indicate that small sized column can be used effectively to remove high amounts of lead which makes the bioremediation process by the biobeads more economical and advantageous for industrial application. Several factors like effectiveness of the biobeads in Pb2+removal at both neutral and alkaline pH, reusability, high mass transfer co-efficient, regenerability and high binding capacity makes it a novel versatile, cost-effective and high utility bioremediator.

Removal of Pb (II), As (III), and Cr (VI) by nitrogen-starved Papiliotrema laurentii strain RY1.

Heavy metals such as lead, chromium, and metalloid like arsenic dominate the pinnacle in posing a threat to life. Being environment-friendly, elucidating the mechanism by which microorganisms detoxify such elements has always been an active field of research hitherto. In the present study, we have investigated the capability of nitrogen-deprived Papiliotrema laurentii strain RY1 toward enhanced tolerance and neutralizing toxic elements. There were biosorption and bioprecipitation of lead and chromium at the cell surfaces. Bioprecipitation mechanisms included the formation of lead phosphates and pyromorphites from lead, grimaldite from chromium. Transcripts such as metallothionein, aquaporins, and arsenical pump-driving ATPase have been surmised to be involved in the detoxification of elements. Furthermore, activation of antioxidant defense mechanisms for the cells for each of the elements should contribute towards yeast's propagation. The efficiency of removal of elements for live cells and immobilized cells were high for lead and chromium. To the best of our knowledge, this is the first report of such high tolerance of lead, arsenic, and chromium for any yeast. The yeast showed such varied response under dual stress due to nitrogen starvation and in the presence of respective elements. The yeast possesses promising potentials in nitrogen deprived and enriched environments to aid in bioremediation sectors.

A new approach to calculating fiber fields in 2D vessel cross sections using conformal maps.

An arterial vessel has three layers, namely, the intima, the media and the adventitia. Each of these layers is modeled to have two families of strain-stiffening collagen fibers that are transversely helical. In an unloaded configuration, these fibers are coiled up. In the case of a pressurized lumen, these fibers stretch and start to resist further outward expansion. As the fibers elongate, they stiffen, affecting the mechanical response. Having a mathematical model of vessel expansion is crucial in cardiovascular applications such as predicting stenosis and simulating hemodynamics. Thus, to study the mechanics of the vessel wall under loading, it is important to calculate the fiber configurations in the unloaded configuration. The aim of this paper is to introduce a new technique of using conformal maps to numerically calculate the fiber field in a general arterial cross-section. The technique relies on finding a rational approximation of the conformal map. First, points on the physical cross section are mapped to points on a reference annulus using a rational approximation of the forward conformal map. Next, we find the angular unit vectors at the mapped points, and finally a rational approximation of the inverse conformal map is used to map the angular unit vectors back to vectors on the physical cross section. We have used MATLAB software packages to achieve these goals.

DMSO strengthens chitin deacetylase-chitin interaction: Physicochemical, kinetic, structural and catalytic insights.

Chitin deacetylase, an enzyme isolated from Cryptococcus laurentii RY1, catalyzes the hydrolysis of acetamido group of N-acetyl-D-glucosamine unit of chitin. The primary objective of this study was to characterize and comprehend the activation of chitin deacetylase by DMSO. The secondary structure of the protein was determined by circular dichroism(CD).The interaction of protein with DMSO was evaluated by CD and tryptophan fluorescence spectroscopy which revealed that DMSO had no effect on overall secondary structure, but induced change in the tertiary structure of the enzyme. The interaction of chitin deacetylase with chitin in DMSO system when investigated by molecular dynamics simulation revealed stronger chitin deacetylase-chitin interaction involving several amino acid residues. The enhanced activity of the enzyme in presence of DMSO along with the fact that its kcat is highest of all other reported chitin deacetylases makes it a superior candidate in the industrial sector involved in chitosan production from chitin.

Nitrogen deprivation elicits dimorphism, capsule biosynthesis and autophagy in Papiliotrema laurentii strain RY1.

Stress response due to the lack of essential nutrient(s) for an organism has been a focal point of several scientific investigations. The present study investigates the cellular adaptations behind the ability of Papiliotrema laurentii strain RY1 to perpetuate without added nitrogen and propagate robustly in growth- limiting amount of nitrogen. We executed phenotypic (using scanning electron microscopy, differential interference contrast microscopy and transmission electron microscopy), microbiological and computational analyses to show multiple responses of dimorphism, capsule formation and autophagy as a survival strategy by the yeast upon nitrogen starvation. The roles of phosphomannose isomerase, phosphomannomutase and several autophagy-related transcripts aiding in such a response have been discussed.

Investigation of conformational changes of levansucrase isolated from Acetobacter nitrogenifigens strain RG1 by mercuric and cadmium ion.

Levansucrase is a secretary enzyme of Acetobacter nitrogenifigens strain RG1. The enzyme shows enhanced activity in the presence of Hg2+ in spite of being inhibited by other heavy metal ion Cd2+. In this study the structural characterization of levansucrase in native state as well as in the presence of Hg2+ and Cd2+ by CD spectroscopy is done. The secondary structures of the native enzyme and the enzyme treated with Hg2+ and Cd2+ on comparison by their CD spectra revealed that their spectra showed no significant difference indicating that both Hg2+ as well as Cd2+ had no effect on the overall secondary structure of the protein. The respective CD spectra on analysis revealed that they have almost identical percentage of secondary structural elements. The interaction of levansucrase with Hg2+ as well as Cd2+ was studied further by tryptophan fluorescence spectroscopy which on analysis revealed static quenching indicating protein-heavy metal complex formation. A blue shift in the tryptophan fluorescence spectra of Hg2+ treated protein indicated that the tryptophan residues have moved to a more hydrophobic environment in the protein away from aqueous phase. The mechanism of interaction of enzyme with mercury and cadmium was determined from their tryptophan fluorescence spectra.

De novo RNA-Seq based transcriptome analysis of Papiliotrema laurentii strain RY1 under nitrogen starvation.

Nitrogen is a key nutrient for all cell forms. Most organisms respond to nitrogen scarcity by slowing down their growth rate. On the contrary, our previous studies have shown that Papiliotrema laurentii strain RY1 has a robust growth under nitrogen starvation. To understand the global regulation that leads to such an extraordinary response, we undertook a de novo approach for transcriptome analysis of the yeast. Close to 33 million sequence reads of high quality for nitrogen limited and enriched condition were generated using Illumina NextSeq500. Trinity analysis and clustered transcripts annotation of the reads produced 17,611 unigenes, out of which 14,157 could be annotated. Gene Ontology term analysis generated 44.92% cellular component terms, 39.81% molecular function terms and 15.24% biological process terms. The most over represented pathways in general were translation, carbohydrate metabolism, amino acid metabolism, general metabolism, folding, sorting, degradation followed by transport and catabolism, nucleotide metabolism, replication and repair, transcription and lipid metabolism. A total of 4256 Single Sequence Repeats were identified. Differential gene expression analysis detected 996 P-significant transcripts to reveal transmembrane transport, lipid homeostasis, fatty acid catabolism and translation as the enriched terms which could be essential for Papiliotrema laurentii strain RY1 to adapt during nitrogen deprivation. Transcriptome data was validated by quantitative real-time PCR analysis of twelve transcripts. To the best of our knowledge, this is the first report of Papiliotrema laurentii strain RY1 transcriptome which would play a pivotal role in understanding the biochemistry of the yeast under acute nitrogen stress and this study would be encouraging to initiate extensive investigations into this Papiliotrema system.