Showing papers by "Sathyanarayana N. Gummadi published in 2010"

Asymmetric synthesis of (S)-ethyl-4-chloro-3-hydroxybutanoate using Candida parapsilosis ATCC 7330

Abstract: Asymmetric reduction of ethyl-4-chloro-3-oxobutanoate to (S)-ethyl-4-chloro-3-hydroxybutanoate in aqueous medium by resting cells of Candida parapsilosis ATCC 7330 was optimized. The influence of culture parameters (inoculum size, inoculum age and biocatalyst harvest time) and reaction parameters (co-substrate, resting cell, pH and substrate concentrations) on the asymmetric reduction were studied. It was found that these parameters significantly influenced the rate of the asymmetric reduction. Under the optimum conditions, the final concentration of (S)-ethyl-4-chloro-3-hydroxybutanoate, enantiomeric excess and the isolated yield of (S)-ethyl-4-chloro-3-hydroxybutanoate were 1.38 M (230 g/l), >99 and 95%, respectively. The space time yield was 115 mmol/lh, which is significantly higher than other whole cell biocatalysts reported so far.

Kinetics of growth and caffeine demethylase production of Pseudomonas sp. in bioreactor.

Abstract: The effect of various initial caffeine concentrations on growth and caffeine demethylase production by Pseudomonas sp. was studied in bioreactor. At initial concentration of 6.5 g l−1 caffeine, Pseudomonas sp. showed a maximum specific growth rate of 0.2 h−1, maximum degradation rate of 1.1 g h−1, and caffeine demethylase activity of 18,762 U g CDW−1 (CDW: cell dry weight). Caffeine degradation rate was 25 times higher in bioreactor than in shake flask. For the first time, we show highest degradation of 75 g caffeine (initial concentration 20 g l−1) in 120 h, suggesting that the tested strain has potential for successful bioprocess for caffeine degradation. Growth kinetics showed substrate inhibition phenomenon. Various substrate inhibition models were fitted to the kinetic data, amongst which the double-exponential (R 2 = 0.94), Luong (R 2 = 0.92), and Yano and Koga 2 (R 2 = 0.94) models were found to be the best. The Luedeking–Piret model showed that caffeine demethylase production kinetics was growth related. This is the first report on production of high levels of caffeine demethylase in batch bioreactor with faster degradation rate and high tolerance to caffeine, hence clearly suggesting that Pseudomonas sp. used in this study is a potential biocatalyst for industrial decaffeination.

Enhancement and scale-up of β-(1, 3) glucan production by Agrobacterium sp.

Abstract: Curdlan is a water insoluble polysaccharide composed exclusively of ?-(1, 3) linked glucose residues. Agrobacterium sp. is known to produce extracellular curdlan under nitrogen-limited conditions. The purpose of this study was to investigate the effects of pH, amounts of ammonium, sucrose and trace elements, and time the addition of sucrose, ammonium and uracil on the production of curdlan in a shake flask and to further scale-up the process to a 5 L fermentor. A maximum of 48.7 g L-1 of curdlan was obtained in a shake flask when 150 and 1.4 g L-1 of sucrose and ammonium were used at the initial pH of 6.5. The production was enhanced to 57 g L-1 by adding one third of sucrose and 1 g L-1 of uracil at the 48th h in a fed batch mode. The process was scaled up to a 5 L bioreactor in a batch mode where the oxygen transfer rate was higher (0.192 mg L-1s-1) when compared to that in the shake flask (0.096 mg L-1s-1). Curdlan production was 58 g L-1 in the bioreactor, which was higher than the shake flask under batch conditions (48.7 g L-1). The viscosity average molecular weight of the curdlan produced was found to be 1.4 × 105.