Molecular characterization of a novel isolate of Candida tropicalis for enhanced lipid production.

AIM: To characterize a new isolate of Candida tropicalis for its enhanced storage lipid accumulation with respect to lipid composition, fatty acid profile and transcriptional regulation of four key genes involved in lipid productivity using different carbon sources. METHODS AND RESULTS: Upon growing C. tropicalis on various carbon substrates, glucose was found to be the best followed by xylose for the production of both biomass and storage lipid. On glucose (100 g l(-1)) medium having specific nitrogen stress (C:N 150 : 1), the yeast was capable of yielding about 58% lipid content of its dry biomass, and neutral lipid accounted for about 75% of the total lipid. Fatty acid profiles revealed that the glucose contributed to the highest yield of total fatty acids, maximum proportion of saturated fatty acids and a significant amount of oleic acid. The enhanced lipid production with specific fatty acid profile correlated with the strong upregulation of acetyl Co-A carboxylase, stearoyl-ACP desaturase and diacylglycerol acyltransferase genes, but not the malic enzyme gene. CONCLUSIONS: Together, the results documented the differential regulation of four genes of lipid biosynthesis in the newly isolated C. tropicalis oleaginous strain by various carbon sources. SIGNIFICANCE AND IMPACT OF THE STUDY: We report here on optimization of the carbon substrate for improved lipid yield and transcriptional regulation of lipid biosynthetic genes in C. tropicalis. Our study paves the way for further enhancement of lipid production by metabolic engineering in this organism, which has potential to be the lipid feedstock as a cocoa-butter substitute.

Cloning and functional expression of an acyl-ACP thioesterase FatB type from Diploknema (Madhuca) butyracea seeds in Escherichia coli.

A cDNA of fatty acyl-acyl carrier protein (ACP) thioesterase (Fat) from developing seed of Madhuca butyracea has been cloned. The deduced amino acid sequence of the cDNA corresponding to the mature polypeptide showed 30-40% and 60-75% identity to the reported FatA and FatB class of plant thioesterases, respectively. This gene, MbFatB, is present as a single copy in M. butyracea genome and the MbFatB protein was detected clearly in seed tissues of this plant but not in that of Indian mustard (Brassica juncea). Heterologous expression of the MbFatB gene driven by different promoters in E. coli wild type and fatty acid beta-oxidation mutant (fadD88) strains resulted production of the recombinant protein with various fusion tags either as biologically inactive (insoluble) or functionally active forms. Expression of functionally active recombinant MbFatB in E. coli affected bacterial growth and cell morphology as well as changed the fatty acid profiles of the membrane lipid and the culture supernatant. Alteration of the fatty acid composition was directed predominantly towards palmitate and to a lesser extent myristate and oleate due to acyl chain termination activity of plant thioesterase in bacteria. Thus, this new MbFatB gene isolated from a non-traditional oil-seed tree can be used in future for transgenic development of oil-seed Brassica, a widely cultivated crop that expresses predominantly oleoyl-ACP thioesterase (FatA) in its seed tissue and has high amount of unwanted erucic acid in edible oil in order to alter the fatty acid profile in a desirable way.

Glyoxalase II from A. thaliana requires Zn(II) for catalytic activity.

Cytosolic glyoxalase II from Arabidopsis thaliana, GLX2-2, was overexpressed and purified to homogeneity using Q-sepharose chromatography. MALDI-TOF mass spectrometry studies indicated a molecular weight of 28 767 Da. Using steady-state kinetics studies, the purified enzyme exhibited a Km of 660 +/- 100 microM and a kcat of 484 +/- 92 s(-1) at 37 degrees C. Metal analyses demonstrated that the enzyme binds 2.1 +/- 0.5 moles of Zn(II) per monomer; the binding of Zn(II) is essential for enzyme viability and activity. Sequence comparison of glyoxalase II enzymes from human, A. thaliana, and yeast and the metallo-beta-lactamases reveal that all metal binding ligands of the metallo-beta-lactamases are conserved in glyoxalase II enzymes, suggesting that all glyoxalase II enzymes are Zn(II) metalloenzymes. These results and their implications are discussed in light of previous studies on glyoxalase II, and an active site for the glyoxalase II enzymes is proposed.

Acyl carrier protein of Azospirillum brasilense: properties of the purified protein and sequencing of the corresponding gene, acpP.

Acyl carrier protein (ACP) plays a crucial role in bacterial fatty acid synthesis. Cloning genes encoding ACPs from Gram-negative bacteria in Escherichia coli is difficult due to adverse effects of the cloned gene on host cell viability, and we were unsuccessful in cloning the full length ACP gene (acpP) from Azospirillum brasilense using conventional methods. Therefore, ACP from A. brasilense was purified to homogeneity and a part of the acpP gene was cloned using the polymerase chain reaction (PCR) technique with two primers, one designed from the N-terminal amino acid sequence of the purified ACP and the other from the highly conserved amino acid sequence of bacterial ACPs. The nucleotide sequence of the gene was obtained by cloning and sequencing inverse PCR products containing the acpP region generated by two oppositely oriented internal primers designed from the partial acpP gene sequence using restriction-enzyme-digested, self-circularized chromosomal DNA fragments as templates. Characterization of the purified ACP and analysis of the derived amino acid sequence of the acpP gene of A. brasilense revealed that: (a) the mature ACP, composed of 78 amino acids, is a highly expressed protein (about 2.0-3.0 x 10(4) molecules per cell), (b) compared to E. coli ACP, it has a more compact structure and contains significantly more hydrophobic amino acid residues and (c) the potential mRNA sequence of the ACP gene has some structural features typical of a stable mRNA.

Molecular characterization of glyoxalase II from Arabidopsis thaliana.

Glyoxalase II is part of the glutathione-dependent glyoxalase detoxification system. In addition to its role in the detoxification of cytotoxic 2-oxo-aldehydes, specifically methylglyoxal, it has been suggested that the glyoxalase system may also play a role in controlling cell differentiation and proliferation. During the analysis of a T-DNA-tagged mutant of Arabidopsis we identified the gene for a glyoxalase II isozyme (GLY1) that appears to be mitochondrially localized. The cDNA encoding a glyoxalase II cytoplasmic isozyme (GLY2) was also isolated and characterized. Southern blot and sequence analyses indicate that glyoxalase II proteins are encoded by at least two multigene families in Arabidopsis. Escherichia coli cells expressing either GLY1 or GLY2 exhibit increased glyoxalase II activity, confirming that they do, in fact, encode glyoxalase II proteins. Northern analysis shows that the two genes are differentially expressed. Transcripts for the mitochondrial isozyme are most abundant in roots, while those for the cytoplasmic isozyme are highest in flower buds. The identification of glyoxalase II isozymes that are differentially expressed suggests that they may play different roles in the cell.