Arpita Agrawal

Rice University, Houston, TX, United States

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Publications (3)15.57 Total impact

  • Mai Li, Xiujun Zhang, Arpita Agrawal, Ka-Yiu San
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    ABSTRACT: Microbial biosynthesis of fatty acid like chemicals from renewable carbon sources has attracted significant attention in recent years. Free fatty acids can be used as precursors for the production of fuels or chemicals. Wild type E. coli strains produce fatty acids mainly for the biosynthesis of lipids and cell membranes and do not accumulate free fatty acids as intermediates in lipid biosynthesis. However, free fatty acids can be produced by breaking the fatty acid elongation through the overexpression of an acyl-ACP thioesterase. Since acetyl-CoA might be an important factor for fatty acid synthesis (acetate formation pathways are the main competitive pathways in consuming acetyl-CoA or pyruvate, a precursor of acetyl-CoA), and the long chain fatty acid CoA-ligase (FadD) plays a pivotal role in the transport and activation of exogenous fatty acids prior to their subsequent degradation, we examined the composition and the secretion of the free fatty acids in four different strains including the wild type MG1655, a mutant strain with inactivation of the fatty acid beta-oxidation pathway (fadD mutant (ML103)), and mutant strains with inactivation of the two major acetate production pathways (an ack-pta (acetate kinase/phosphotransacetylase), poxB (pyruvate oxidase) double mutant (ML112)) and a fadD, ack-pta, poxB triple mutant (ML115). The engineered E. coli cells expressing acyl-ACP thioesterase with glucose yield is higher than 40% of theoretical yield. Compared to MG1655(pXZ18) and ML103(pXZ18), acetate forming pathway deletion strains such as ML112(pXZ18) and ML115(pXZ18) produced similar quantity of total free fatty acids, which indicated that acetyl-CoA availability does not appear to be limiting factor for fatty acid production in these strains. However, these strains did show significant differences in the composition of free fatty acids. Different from MG1655(pXZ18) and ML103(pXZ18), acetate formation pathway deletion strains such as ML112(pXZ18) and ML115(pXZ18) produced similar level of C14, C16:1 and C16 free fatty acids, and the free fatty acid compositions of both strains did not change significantly with time. In addition, the strains bearing the fadD mutation showed significant differences in the quantities of free fatty acids found in the broth. Finally, we examined two potential screening methods for selecting and isolating high free fatty acids producing cells.
    Metabolic Engineering 03/2012; 14(4):380-7. · 6.86 Impact Factor
  • Xiujun Zhang, Arpita Agrawal, Ka-Yiu San
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    ABSTRACT: The microbial biosynthesis of free fatty acid, which can be used as precursors for the production of fuels or chemicals from renewable carbon sources, has attracted significant attention in recent years. Free fatty acids can be produced by introducing an acyl-carrier protein (ACP) thioesterase (TE) gene into Escherichia coli. The first committed step of fatty acid biosynthesis is the conversion of acetyl-CoA to malonyl-CoA by an adenosine triphosphate (ATP)-dependent acetyl-CoA carboxylase followed by the conversion of malonyl-CoA to malonyl-ACP through the enzyme malonyl CoA-acyl carrier protein transacylase (MCT; FabD). The E. coli fabD gene encoding MCT has been cloned and studied. However, the effect of FabD overexpression in a fatty acid overproducing strain has not been examined. In this study, we examined the effect of FabD overexpression in a fatty acid overproducing strain carrying an acyl-ACP TE. Specifically, the effect of overexpressing a fabD gene from four different organisms on fatty acid production was compared. The strains carrying a fabD gene from E. coli, Streptomyces avermitilis MA-4680, or Streptomyces coelicolor A3(2) improved the free fatty acid production; these three strains produced more free fatty acids, about 11% more, than the control strain. The strain carrying a fabD gene from Clostridium acetobutylicum ATCC 824, however, produced similar quantities of free fatty acids as the control strain. In addition, the three FabD overexpressed strains also have higher fatty acid/glucose yields. The results suggested that FabD overexpression can be used to improve free fatty acid production by increasing the malonyl-ACP availability.
    Biotechnology Progress 01/2012; 28(1):60-5. · 1.85 Impact Factor
  • Xiujun Zhang, Mai Li, Arpita Agrawal, Ka-Yiu San
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    ABSTRACT: Microbial biosynthesis of fatty acid-like chemicals from renewable carbon sources has attracted significant attention in recent years. Free fatty acids can be used as precursors for the production of fuels or chemicals. Free fatty acids can be produced by introducing an acyl-acyl carrier protein thioesterase gene into Escherichia coli. The presence of the acyl-ACP thioesterase will break the fatty acid elongation cycle and release free fatty acid. Depending on their sequence similarity and substrate specificity, class FatA thioesterase is active on unsaturated acyl-ACPs and class FatB prefers saturated acyl group. Different acyl-ACP thioesterases have different degrees of chain length specificity. Although some of these enzymes have been characterized from a number of sources, information on their ability to produce free fatty acid in microbial cells has not been extensively examined until recently. In this study, we examined the effect of the overexpression of acyl-ACP thioesterase genes from Diploknema butyracea, Gossypium hirsutum, Ricinus communis and Jatropha curcas on free fatty acid production. In particular, we are interested in studying the effect of different acyl-ACP thioesterase on the quantities and compositions of free fatty acid produced by an E. coli strain ML103 carrying these constructs. It is shown that the accumulation of free fatty acid depends on the acyl-ACP thioesterase used. The strain carrying the acyl-ACP thioesterase gene from D. butyracea produced approximately 0.2g/L of free fatty acid while the strains carrying the acyl-ACP thioesterase genes from R. communis and J. curcas produced the most free fatty acid at a high level of more than 2.0 g/L at 48 h. These two strains accumulated three major straight chain free fatty acids, C14, C16:1 and C16 at levels about 40%, 35% and 20%, respectively.
    Metabolic Engineering 11/2011; 13(6):713-22. · 6.86 Impact Factor

Publication Stats

52 Citations
15.57 Total Impact Points

Institutions

  • 2011–2012
    • Rice University
      • Department of Bioengineering
      Houston, TX, United States