T Panda

Enzyme kinetics data play a vital role in the design of reactors and control of processes. In the present study, kinetic studies on pectinases were carried out. Partially purified polymethylgalacturonase (PMG) and polygalacturonase (PG) were the two pectinases studied. The plot of initial rate vs. initial substrate concentration did not follow the conventional Michaelis-Menten kinetics, but substrate inhibition was observed. For PMG, maximum rate was attained at an initial pectin concentration of 3 g/l, whereas maximum rate was attained when the initial substrate concentration of 2.5 g/l of polygalacturonic acid for PG I and PG II. The kinetic data were fitted to five different kinetic models to explain the substrate inhibition effect. Among the five models tested, the combined mechanism of protective diffusion limitation of both high and inhibitory substrate concentrations (semi-empirical model) explained the inhibition data with 96-99% confidence interval.

Metal nanoparticles have gained considerable attention as versatile nanomaterials due to their size- and shape- dependent electrical, electronic, optical, and catalytic properties. Various physical and chemical approaches have been investigated for synthesizing metal nanoparticles, specifically gold nanoparticles due to their biocompatibility, antioxidant potentials, catalytic activity, and other promising characteristics. As the chemical based approaches have led to questions on toxicity, plant-based sources and microorganisms like bacteria, fungi and algae have been evaluated for synthesizing metal nanoparticles. Gold nanoparticles derived from biological sources are expected to have different properties than those derived from chemical sources, allowing for a wider range of applications. This review provides an overview of the myriad of sources explored for the synthesis of gold nanoparticles which have found useful applications in several fields. The general approach for synthesizing gold nanoparticles is provided followed by the major applications in specific fields namely medicine, biology, electrochemistry and catalysis. Additionally, the possible challenges and future prospects of biosynthesis of nanoparticles have been highlighted. This work could provide an update on the recent advances in the applications of biogenic nanoparticles for future developments.

The Plackett-Burman experimental design was employed to evaluate the relative importance of medium constituents of each medium for enhanced griseofulvin production by Penicillium griseofulvum MTCC 1898 and Penicillium griseofulvum MTCC 2004. It was found that the medium constituents, sucrose, K2HPO4, NaNO3, and FeSO4.7H2O, significantly influenced the griseofulvin production by Penicillium griseofulvum MTCC 1898. In the case of Penicillium griseofulvum MTCC 2004, lactose, glucose, and MnSO4·H2O significantly influenced the griseofulvin production.

Chitin, a homopolymer of N-acetylglucosamine, is obtained from a variety of sources. They form the structural component of fungal cell wall and plants. They are commercially obtained from shrimp and crab shell waste from the fishing industry. Recent advances in understanding the structure and properties of chitin and its derivatives has opened a lot of new avenues for its applications. Improvements in the properties of chitin for a particular application can be easily brought about by chemical modifications. The applicability of chitin in many areas and its easy manipulation has resulted in a considerable amount of research being done on the possible applications of chitinase.

The synthesis of pectinase is investigated using six species of Aspergillus, with five media differing either in their carbon sources or level of carbon source(s). Five of the six species used, synthesized appreciable amounts of pectinase in the media containing sugars. Pectinase synthesis was highest for A. niger, NCIM 548, with all the sugar containing media. A. foetidus, NCIM 510, was the only one among the organisms studied, that responded well to the medium containing pectin in the absence of additional sugars supplied in the medium. © 1995 Springer-Verlag.

In order to convert cellulosic material to ethanol by single step process a chemofusion method has been followed between protoplasts of Trichoderma reesei, QM 9414, and the spheroplasts of Saccharomyces cerevisiae, NCIM 3288, in the author's laboratory. The fusion was a success and it was observed that endoglucanase was the key enzyme in the success of the fusion. In the present study, characterization of the fusants based on the endoglucanase synthesis, its localization and the distribution in the cells are described and compared with that of Trichoderma reesei, QM 9414, (wild type).

The addition of varying concentrations of precursor gold salt to different cellular fractions of Fusarium oxysporum, viz., the culture filtrate and the intracellular extract obtained in the growing and resting phase of the cells had a profound influence on the size, shape, and state of aggregation of the nanoparticles. Multiply-twinned nanoparticles were obtained when the culture filtrate was used for synthesizing nanoparticles while mostly irregular shapes were obtained with the intracellular extract. The time taken for the formation of gold nanoparticles in the culture filtrate of resting cells was very less (<30 min) while it took more than 8 h when the intracellular extract was used for synthesis of nanoparticles. There was a reduction in size of the nanoparticles with decreasing concentration of the gold salt from 1 mM to 0.05 mM. With the intracellular extract, the initial rate of increase in surface plasmon absorption maximum was linearly proportional to the initial concentration of the gold salt used. Gold nanoparticles were also obtained with the heat-inactivated culture filtrate which suggests alternatively the role of peptides and amino acids besides proteins in reducing and/or stabilizing the nanoparticles. Copyright © 2014 American Scientific Publishers.

Motile bacteria respond to changing chemical environment by moving towards or away from a particular location. Bacterial migration under chemical gradient is one of the most studied areas in biomedical field. In this work we looked into how bacterial cells respond to sudden change in the microfluidic chemical environment. E.coli DH5α cells were subjected to an attractant gradient (0.1 mM sorbitol - attractant to E.coli cells) and after 120 min the same cells were exposed to an inhibitor (0.1 mM NiSO4) gradient in the same microfluidic device. Our studies revealed that when the E.coli DH5α cells were exposed to 0.1 mM sorbitol, they showed faster chemotaxis towards the attractant (0.1 mM sorbitol) and achieved steady state by 60 min. When we replaced 0.1 mM sorbitol with 0.1 mM NiSO4 in the device we found that that the E.coli DH5α cells started responding to change in chemical environment within 10 min and achieved steady state at the end of 60 min. This shows that the bacterial cells respond to change in local chemical environment is within few minutes.

Whole cells of Zymomonas mobilis, immobilised on pectin beads, were stablised by curing in a mixture of 0.2 M CaCl2 · 2H2O and Na2B4O7 · 10H2O for 24 h at 4°C. Ethanol fermentation was studied using different glucose concentrations (50-200 g/litre) by these immobilised beads. The kinetics of this process was studied in a glucose step-feeding system with different total glucose concentrations (150 and 200 g/litre) in a specially designed shake flask. Immobilised whole cells were also used for ethanol fermentation in an expanded bed bioreactor and its performance characteristics were compared with those of a regular batch mechanically stirred tank bioreactor. Fermentation rates and ethanol yields were higher in the expanded bed bioreactor system than in the batch mechanically agitated stirred tank bioreactor. The stabilised pectin beads were damaged less in the expanded bioreactor than in the regular batch stirred tank reactor. Copyright © 1996 Elsevier Science Ltd. All rights reserved.