Carbon accumulation in Rhodotorula glutinis induced by nitrogen limitationReport as inadecuate




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Biotechnology for Biofuels

, 7:164

First Online: 09 December 2014Received: 19 May 2014Accepted: 27 October 2014

Abstract

BackgroundOleaginous microorganisms, such as bacterium, yeast and algal species, can represent an alternative oil source for biodiesel production. The composition of their accumulated lipid is similar to the lipid of an oleaginous plant with a predominance of unsaturated fatty acid. Moreover this alternative to conventional biodiesel production does not create competition for land use between food and oleo-chemical industry supplies. Despite this promising potential, development of microbial production processes are at an early stage. Nutritional limited conditions, such as nitrogen limitation, with an excess of carbon substrate is commonly used to induce lipid accumulation metabolism. Nitrogen limitation implies modification of the carbon-to-nitrogen ratio in culture medium, which impacts on carbon flow distribution in the metabolic network.

ResultsThe goal of the present study is to improve our knowledge of carbon flow distribution in oleaginous yeast metabolism by focusing carbon distribution between carbohydrate and lipid pools in order to optimize microbial lipid production. The dynamic effects of limiting nitrogen consumption flux according to carbon flow were studied to trigger lipid accumulation in the oleaginous yeast Rhodotorula glutinis. With a decrease of the specific nitrogen consumption rate from 0.052 Nmol.CmolX.h to 0.003 Nmol.CmolX.h, a short and transitory intracellular carbohydrate accumulation occurred before the lipid accumulation phase. This phenomenon was studied in fed-batch culture under optimal operating conditions, with a mineral medium and using glucose as carbon source. Two different strategies of decreasing nitrogen flow on carbohydrate accumulation were investigated: an instantaneous decrease and a progressive decrease of nitrogen flow.

ConclusionsLipid production performance in these fed-batch culture strategies with R. glutinis were higher than those reported in the previous literature; the catalytic specific lipid production rate was 0.07 Cmollip.CmolX*.h. Experimental results suggested that carbohydrate accumulation was an intrinsic phenomenon connected to the limitation of growth by nitrogen when the nitrogen-to-carbon ratio in the feed flow was lower than 0.045 Nmol.Cmol. Carbohydrate accumulation corresponded to a 440% increase of carbohydrate content. These results suggest that microbial lipid production can be optimized by culture strategy and that carbohydrate accumulation must be taken account for process design.

KeywordsOleaginous yeast Rhodotorula glutinis Carbohydrate accumulation Lipid accumulation C-N ratio Fed-batch culture AbbreviationsDOdissolved oxygen pressure compared to dissolved oxygen pressure with air saturation % sat

iconcentration of compound i mol.L

Μspecific growth rate h

qispecific production or consumption rate of compound i Cmoli.CmolX.h

RQrespiratory quotient m o l C O 2 . reactor volume − 1 . h − 1 . m o l O 2 . reactor volume − 1 . h − 1 − 1 Open image in new window

Electronic supplementary materialThe online version of this article doi:10.1186-s13068-014-0164-0 contains supplementary material, which is available to authorized users.

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Author: Julien Cescut - Luc Fillaudeau - Carole Molina-Jouve - Jean-Louis Uribelarrea

Source: https://link.springer.com/







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