TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Method: Method for producing a fatty aldehyde, involves:(1) method (A): expressing in a host cell a gene encoding a polypeptide comprising an amino acid sequence having greater than or equal to 80% sequence identity to an amino acid sequence selected from 42 amino acid sequences (S1) of fatty aldehyde biosynthetic enzymes as given in the specification e.g. nicotinamide adenine dinucleotide (NAD) dependent epimerase/dehydratase having a defined amino acid sequence containing 1168 amino acids (SEQ ID NO: 20) as given in the specification; fatty acid coenzyme A (CoA) ligase having a defined amino acid sequence containing 1173 amino acids (SEQ ID NO: 22) as given in the specification; fatty acid CoA ligase having a defined amino acid sequence containing 1183 amino acids (SEQ ID NO: 30) as given in the specification; NAD dependent epimerase/dehydratase having a defined amino acid sequence containing 1168 amino acids (SEQ ID NO: 32) as given in the specification; fatty acid CoA ligase having a defined amino acid sequence containing 1168 amino acids (SEQ ID NO: 40) as given in the specification; fatty acid CoA ligase having a defined amino acid sequence containing 1299 amino acids (SEQ ID NO: 42) as given in the specification; fatty aldehyde biosynthetic enzyme having a defined amino acid sequence containing 1173 amino acids (SEQ ID NO: 50) as given in the specification; thioester reductase domain having a defined amino acid sequence containing 1174 amino acids (SEQ ID NO: 52) as given in the specification; fatty acid CoA ligase having a defined amino acid sequence containing 1184 amino acids (SEQ ID NO: 60) as given in the specification; or fatty acid CoA ligase having a defined amino acid sequence containing 1183 amino acids (SEQ ID NO: 62) as given in the specification; and isolating the fatty aldehyde from the host cell;(2) method (B): expressing in a host cell a gene encoding a polypeptide comprising an amino acid sequence having greater than or equal to 80% sequence identity to an amino acid sequence (S2) of ATP/nicotinamide adenine dinucleotide hydrogen phosphate (NADPH) dependent carboxylic acid reductase having a defined amino acid sequence containing 1174 amino acids (SEQ ID NO: 16) as given in the specification, and a gene encoding a recombinant fatty acid synthase; and isolating the fatty aldehyde from the host cell;(3) method (C): expressing in a host cell a gene encoding a polypeptide comprising the amino acid sequence (S3) of (SEQ ID NO: 16), or its variant; and isolating the fatty aldehyde from the host cell, where the host cell is genetically engineered to express an attenuated level of a fatty acid degradation enzyme relative to a wild type host cell;(4) method (D): expressing in a host cell a recombinant vector comprising a nucleotide sequence having greater than or equal to 80% sequence identity to a nucleotide sequence selected from 42 nucleotide sequences (S1') of fatty aldehyde biosynthetic enzymes as given in the specification e.g. NAD dependent epimerase/dehydratase having a defined nucleotide sequence containing 3507 base pairs (SEQ ID NO: 19) as given in the specification; fatty acid CoA ligase having a defined nucleotide sequence containing 3522 base pairs (SEQ ID NO: 21) as given in the specification; fatty acid CoA ligase having a defined nucleotide sequence containing 3523 base pairs (SEQ ID NO: 29) as given in the specification; NAD dependent epimerase/dehydratase having a defined nucleotide sequence containing 3507 base pairs (SEQ ID NO: 31) as given in the specification; fatty acid CoA ligase having a defined nucleotide sequence containing 3507 base pairs (SEQ ID NO: 39) as given in the specification; fatty acid CoA ligase having a defined nucleotide sequence containing 3489 base pairs (SEQ ID NO: 41) as given in the specification; fatty aldehyde biosynthetic enzyme having a defined nucleotide sequence containing 3522 base pairs (SEQ ID NO: 49) as given in the specification; thioester reductase domain having a defined nucleotide sequence containing 3525 base pairs (SEQ ID NO: 51) as given in the specification; fatty acid CoA ligase having a defined nucleotide sequence containing 3555 base pairs (SEQ ID NO: 59) as given in the specification; or fatty acid CoA ligase having a defined nucleotide sequence containing 3552 base pairs (SEQ ID NO: 61) as given in the specification; and isolating the fatty aldehyde from the host cell;(5) method (E): expressing in a host cell a recombinant vector comprising a nucleotide sequence (S2') having greater than or equal to 80% sequence identity to a sequence of ATP/NADPH dependent carboxylic acid reductase having a defined nucleotide sequence containing 3525 base pairs (SEQ ID NO: 15) as given in the specification, and a recombinant fatty acid synthase; and isolating the fatty aldehyde from the host cell; or(6) method (F): expressing in a host cell a recombinant vector comprising a nucleotide sequence (S3') having greater than or equal to 80% sequence identity to the nucleotide sequence of (SEQ ID NO: 15), and isolating the fatty aldehyde from the host cell, where the host cell expresses an attenuated level of a fatty acid degradation enzyme relative to a wild type host cell.The methods (A) and (D) further involve modifying the expression of gene encoding a fatty acid synthase in the host cell, by expressing a gene encoding a thioesterase in the host cell. The method (A) further involves culturing the host cell in the presence of at least one biological substrate for the polypeptide or for a polypeptide encoded by the nucleotide sequence, where the substrate is a fatty acid (preferably 6-26C optionally unsaturated fatty acid; especially decanoate, dodecanoate, myristate, or palmitate). In the method (A), the fatty aldehyde is isolated from the extracellular environment of the host cell; and comprises optionally unsaturated 6-26C fatty aldehyde (preferably decanal, dodecanal, myristal, or hexadecal). Preferred Cell: In the methods (A) and (D), the host cell is genetically engineered to express an attenuated level of a fatty acid degradation enzyme relative to a wild type host cell. The host cell for the method (A) is selected from a mammalian cell, plant cell, insect cell, yeast cell, fungus cell, filamentous fungi cell, and bacterial cell. EXAMPLE - Expression of carboxylic acid reductase (CAR) homologs in E. coli was carried out as follows. Three E. coliexpression plasmids were constructed to express the genes encoding the CAR homologs i.e. probable fatty acid CoA ligase (fadD9), nicotinamide adenine dinucleotide (NAD) dependent epimerase/dehydratase family protein (carA), and NAD dependent epimerase/dehydratase family protein (carb). First, fadD9 was amplified from genomic DNA of Mycobacterium tuberculosis H37Rv using primers fadD9F (catatgtcgatcaacgatcagagactgac (SEQ ID NO: 1)) and FadDR (cctaggtcacagcagcccgagcagtc (SEQ ID NO: 2)). The PCR product was first cloned into PCR-blunt and then released as an NdeI-AvrII (restriction enzyme) fragment. The NdeI-AvrII fragment was then cloned between the NdeI and AvrII sites of pACYCDuet-1 to generate pACYCDuet-l-fadD9. The car A and carB genes were amplified from the genomic DNA of Mycobacterium smegmatis (MC2 155; ATCC 23037D-5)) using primers CARMCaF (catatgacgatcgaaacgcg (SEQ ID NO: 3)) and CARMCaR (cctaggttacagcaatccgagcatct (SEQ ID NO: 4)); or CARMCbF (catatgaccagcgatgttcac (SEQ ID NO: 5)) and CARMCbR (cctaggtcagatcagaccgaactcacg (SEQ ID NO: 6)). Each PCR product was first cloned into PCR-blunt and then released as an NdeI-AvrII fragment. Each of the two fragments was then subcloned between the NdeI and AvrII sites of pACYCDuet-1 to generate pACYCDUET-carA and pACYCDUET-carB. Evaluation of fatty aldehyde production was carried out as follows. Plasmids encoding the CAR homologs (pACYCDUET-fadD9, pACYCDUET-carA, and pACYCDUET-carB) were separately co-transformed into the E. coli strain C41 (DE3, AfadE) (described in PCT/US08/058788) together with pETDuet-1-'tesA (described in PCT/US08/058788). The E. coli transformants were grown in 3 ml of Luria bertani (LB) medium supplemented with carbenicillin (100 mg/L) and chloramphenicol (34 mg/L) at 37 degrees C. After overnight growth, culture (15 ml) was transferred into fresh LB medium (2 ml) supplemented with carbenicillin and chloramphenicol. After 3.5 hours of growth, culture (2 ml) were transferred into a 125 ml flask containing M9 medium (20 ml) with 2% glucose and with carbenicillin and chloramphenicol. When optical density (OD)600 of the culture reached 0.9, isopropyl- beta -D-thiogalactoside (IPTG) (1 mM) was added to each flask. After 20 hours of growth at 37 degrees C, ethyl acetate (20 m, with 1 vol./vol.% of acetic acid) was added to each flask to extract the organic compounds produced during the fermentation. The crude ethyl acetate extract was directly analyzed by gas chromatography/mass spectroscopy (GC/MS). The co-expression of the leaderless 'tesA and any of the three car genes in E. coli resulted in detectable fatty aldehyde production. In one fermentation, LS9001/pACYCDUET carB+ pETDuet-1-'tesA produced an average of 120 mg/L of fatty aldehydes. The retention times were 6.959 minutes for dodecanal, 8.247 minutes for 7-tetradecenal, 8.37 minutes for tetradecanal, 9.433 minutes for 9-hexadecenal, 9.545 minutes for hexadecanal, and 10.945 minutes for 11-octadecenal. The presence of large amounts of fatty aldehydes was consistent with CAR being an aldehyde-generating, fatty acid reductase (AFAR). This mechanism was different from the alcohol-generating fatty acyl-CoA reductases (FAR) e.g. JjFAR, and fatty acyl-CoA reductases, such as Acr1.