NOVELTY - Producing a fatty aldehyde, involves: expressing in host cell gene encoding polypeptide having amino acid sequence of specified fatty aldehyde biosynthetic enzyme e.g. nicotinamide adenine dinucleotide (NAD) dependent epimerase/dehydratase, fatty acid coenzyme A (CoA) ligase, or thioester reductase; or ATP/nicotinamide adenine dinucleotide hydrogen phosphate (NADPH) dependent carboxylic acid reductase and optionally gene encoding recombinant fatty acid synthase; and isolating the fatty aldehyde from the host cell.    USE - For producing a fatty aldehyde (preferably decanal, dodecanal, myristal, or hexadecal) (claimed), useful as biofuel i.e. fuel and fuel additives. The fatty aldehydes are also useful to produce many specialty chemicals such as polymers, surfactants, plastics, textiles, solvents, adhesives, and personal care additives; as feedstock for subsequent reactions e.g. hydrogenation, or catalytic cracking (e.g. via hydrogenation and/or pyrolysis); and to make other products such as resins, dyes, flavorings, plasticizers, perfumes, pharmaceuticals, preservatives, and disinfectants.    ADVANTAGE - The method provides for synthesis of fatty aldehydes, which are useful as a biofuel i.e. as renewable energy source, as alternative to petrochemical based fuels; by identifying genes that encode fatty aldehyde biosynthetic polypeptides, and using a host cell containing a gene encoding the fatty aldehyde biosynthetic polypeptide. The biologically derived chemicals offer advantages as biofuels over petroleum based fuels. Biologically derived fatty aldehydes provide renewable alternative to petrochemicals, and are superior to petrochemicals because they are produced directly without extensive refining. The yield of the fatty aldehydes produced is 25 to greater than or equal to 2000 mg/L. In the method, the fatty aldehyde is produced by action of enzymes that act as aldehyde-generating, fatty acid reductase (AFAR), which is different from the alcohol-generating fatty acyl-CoA reductases (FAR) of the prior art. The obtaining of aldehydes and other specialty chemicals that can be derived from aldehydes from crude petroleum requires a significant financial investment as well as a great deal of energy; is also inefficient process because frequently long chain hydrocarbons in crude petroleum are cracked to produce smaller monomers; and these monomers are then used as the raw material to manufacture the more complex specialty chemicals. In addition to the problems with exploring, extracting, transporting, and refining petroleum, petroleum is limited and dwindling resource. Also, the burning of petroleum based fuels releases greenhouse gases (e.g. carbon dioxide) and other forms of air pollution (e.g. carbon monoxide, or sulfur dioxide), which increases air pollution and increases global warming. Unlike petrochemicals, biologically derived fatty aldehydes do not need to be refined like crude petroleum to recover raw materials which must then be further processed to make more complex petrochemicals. The fatty aldehydes produced by the method can be relatively immiscible in fermentation broth, as well as in the cytoplasm. Hence, they can be collected in an organic phase either intracellularly or extracellularly. The collection of the products in the organic phase can lessen the impact of the fatty aldehyde on cellular function and can allow the host cell to produce more products. The fatty aldehydes produced by the method have a delta 13C (indicating variations due to isotopic fermentation effects) of at least -15.4, and fraction of modern carbon (fm) 14C (for distinguishing from petroleum based organic products) of greater than or equal to 1.003. The methods can result in the production of homogeneous compounds, where 60 to greater than or equal to 95%of the fatty aldehydes produced have carbon chain lengths that vary by (less than 6, preferably less than 4, especially less than 2)C. These compounds can also be produced with a relatively uniform degree of saturation, and can be directly used. Further, the biologically derived fatty aldehydes can be directly converted from biomass to the desired chemical product.    DETAILED DESCRIPTION - Method for producing a fatty aldehyde involves a method selected from 6 methods as given in the specification e.g.    (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; thioester reductase domain having a defined amino acid sequence containing 1174 amino acids (SEQ ID NO: 52) 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; or    (3) 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; thioester reductase domain having a defined nucleotide sequence containing 3525 base pairs (SEQ ID NO: 51) as given in the specification; and isolating the fatty aldehyde from the host cell.    An INDEPENDENT CLAIM is included for a genetically engineered microorganism (A1) comprising: an exogenous control sequence stably incorporated into the genomic DNA of the microorganism upstream of a polynucleotide comprising a nucleotide sequence having greater than or equal to 70% sequence identity to the nucleotide sequence selected from the fatty aldehyde biosynthetic enzyme sequences (S1'), where the microorganism produces an increased level of a fatty aldehyde relative to a wild-type microorganism.