Study on the Strategies for L-isoleucine Fermentation by Brevibacterium Lactofermentum

Posted on June 17, 2012 | Category :Chemistry | Comments Off
Title Study on the Strategies for L-isoleucine Fermentation by Brevibacterium Lactofermentum
Abstract

L-isoleucine (Ile) is one of the three branched chain amino acids that are essential to human. It is one of the important amino acids to synthesize some hormones and enzymes [1]. Ile can enhance the protein integration and inhibit the protein from degradation [2, 3]. Ile also plays a very important role in human life. Ile has been widely used as addictive in biological medicine, structuring project, photochemistry, electrochemistry, food industry and cosmetics [4-6]. It is also be used as feed addictive [7] and added to functional beverage [8].In this paper, the Brevibacterium lactofermentation strain was used to produce L-isoleucine. A series of feasible approaches or strategies were carried out to achieve high product concentration, high yield and high productivity of isoleucine in the optimization of B.lactofermentation cultivation processes, including:1. The effect of dissolved oxygen and pH on L-isoleucine production by Brevibacterium lactofermentation was investigated in batch fermentation process, a two-stage agitation speed control strategy was developed, in which the agitation speed was controlled at 700 r/min in the first 12 h to achieve a DO level of up to 35%, and then switched to 600 r/min after 12 h to maintain a DO level at 15–20%. A relative high productivity(0.094 g/g) and glucose consumption velocity(4.76 g/L-1·h-1) were gained, the high isoleucine production(23.3 g/L) was achieved in a relative short time(56 h), which was increased by 11.6% compared to the single agitation speed, and the isoleucine productivity respectively increased by 83.6%、28.7%、44.9%、35.7%. In order to make sure whether the combination of DO and pH control can boost the production by a mutual effect, different control modes were conducted, based on the data obtained from the two-stage agitation speed control strategy and the analysis of kinetics parameters at different pH values. The results showed that the mode of combining two-stage DO with constant pH7.2 control strategy was the optimal, the isoleucine production reached 23.9 g/L.2. Under different initial concentrations of glucose, the cell growth and the isoleucine production were difference: the higher the initial concentration of glucose (140 g/L) may eventually enhance the duration of cell growth, but isoleucine reduced the yield of glucose (0.131 g/g); the lower the initial concentration of glucose (100 g/L) can improve the isoleucine yield (0.148 g / L); through fed-batch fermentation with an appropriate complement of glucose (60 g/L) maybe improve cell concentration (OD562 was 1.273), and increase isoleucine production (23 g/L). However, too high and too low amount of glucose were not good for isoleucine synthesis. A constant flow rate can effectively control bacterial concentration to avoid excessive cell growth so that eventually improve isoleucine production (24.5 g/L) and higher yield (0.154 g/g). On the basis of the above analysis, a constant flow strategy was carried out: when the residual glucose concentration was less than 15 g/L, the constant flow rate of 3.3 g?L-1?h-1 was controlled to the end of fermentation. 3. The effect of temperature, varied from 26℃to 34℃, on production of isoleucine was investigated. Based on kinetic parameters analysis, a temperature-shifting strategy was proposed, in which, at 0-12 h, culture was performed at 31℃to obtain a high specific cell growth rate, and 12 h later, the temperature was decreased step by step from 31℃to 28℃to keep a high isoleucine production rate, and then switched temperature to 26℃until the end. A high concentration (27.7 g/L), yield (0.78 g/g) and productivity (0.475 g/(L h)) of isoleucine were achieved by applying this strategy, which were 11.3%、21.9% and 18.8% higher than batch fermentation with constant temperature 31℃, respectively. Studied on the isoleucine biosynthesis metabolic flux under different temperature, with too low temperature, the metabolic flux to TCA cycle would reduce while the metabolic flux to by-products would increase. With the increasing of temperature, the metabolic flux to TCA cycle will increase while the metabolic flux to by-products would decrease. But too high DO, the metabolic flux to isoleucine would be few as the metabolic flux to TCA cycle was abundant. The three-stage temperature control strategy can led more carbon flow to the EMP and TCA cycle which would increase metabolic flux to isoleucine and improve the isoleucine production (increased by 11.3 %).

Category Chemistry
Subject agitation speed, B.lactofermentation, Isoleucine, metabolic flux, pH, Temperature,
FileType PDF
Pages 154
Price US$48.00
Buy Now
Download
Contact E-Mail:bpaper@live.com
TEL:9-358-716-819A
FAQ How to get this paper's electronic documents?
1, Click the "Buy Now" button to complete the online payment
2, Download the paper's electronic document from the successful payment return page/Or the system will send this paper's electronic document to your E-Mail within 24 hours
Favorite ADD TO FAVORITE
Version zh-cn
» Tags: , , , , ,

Comments are closed.