15  US 9,834,531 B2  16  aldonic acids, and uronic acids. These three kinds of sugar  acids are subject subsequently to bio-transformation into a  keto-acid intermediate that in some species can cyclize to  form a mono or disubstituted furanic molecule (i.e., a furanic  precursor or body) (e.g., furan dicarboxylic acid (FDCA),  formyl furan carboxylic acid (FFCA) hydroxymethyl furan  carboxylic acid (HMFA) from hexoses, furoic acid (FA)  from pentoses). As used herein, the terms "bio-transforma- tion," "bio-transforming," or "bio-transform" refers to a  process by which a starting material is chemically modified  or converted into a desired product by means of using a  catalyst derived from a biological source ( e.g., free or  supported enzymes, or whole cells). As used herein, the term  "keto-acid intermediate" refers to an organic molecule that  has a methylene (methane-diyl) carbon atom adjacent to a  ketone functional group. The term "furanic molecule" as  used herein refers to is an organic molecule having a  5-carbon heterocycle.  The aldose sugar can be converted to a sugar acid accord› ing to an oxidative operation using either a chemical means,  such as either nitric acid or a noble metallic catalyst, or a  biological means (i.e., a biological organism or bio-trans› formation). The sugar acid is bio-transformed to a keto-acid  intermediate using one or more enzymes selected from an  enolase superfamily. For example, the enzyme ( dehydratase)  can be at least: a glucarate dehydratase, gluconate dehy› dratase, altronate dehydratase, or a mixture thereof.  In particular embodiments, one may use biological organ- isms that can be identified for their enzymatic functionality.  For instance, one can identify glucarate dehydratase  homologs using BLAST (Basic Local Aligmnent Search  Tool). Enzymes that can catalyze the dehydration of glu- carate can be identified from ascomycetes ( e.g.,  fusarium,  Aspergillus, verricillium),  protea-bacteria (e.g.,  E. coli sal- monella, Burkholderia, Rhizobium, Agrobacterium, Actino- bacteria),  or high G+C rich organisms ( e.g.,  Streptomyces.  Rhodococcus, Arthrobacter, Acidobacteria  ).  In another  example, gluconate dehydratase homologs can be identified  using BLAST. Particular enzymes that can catalyze the  dehydration of gluconate can be selected from archea ( e.g.,  Thermoproteus tenax, Sulfolobus solfataricus),  halophiles  (e.g.,  Halarchaeum acidiphilum),  or bacteria (e.g.,  Strepto- myces, Norcardia, Pseudomonas, Salmonella, Klebsiella,  Burkholderia).  This should not be considered an exhaustive  listing. Other organisms that can provide similar dehy- dratase function should also be considered within the scope  of the present system.  The pH value of a solution containing keto-acid interme- diates and/or furanic bodies is adjusted to a pH of less than  5. According to an embodiment, one can convert the aldonic,  aldaric, and uronic acids to furanic esters (e.g., hydroxym› ethyl furoic methyl ester, 2,5-furandicarboxylic dimethyl  ester (FDME), or 5-formyl furan carboxylic methyl ester) or  other species, which can be used as precursors for polymers  or other uses.  In accord with the present invention, hexoses include:  allose, altrose, glucose, mamiose, gulose, idose, galactose,  and talose. Pentoses include: ribose, arabinose, xylose, and  lyxose. Hence, the particular a) aldaric acids, b) aldonic  acids, or c) uronic acids of the hexose or pentose sugars can  include respectively: a) hexose-derived: allaric acid, altraric  acid, glucaric acid, galactaric acid, mannaric acid, gularic  acid, idaric acid, and talaric acid; pentose-derived: xylaric  acid, lyxaric acid, arabinaric acid, and ribaric acid; b)  hexose-derived: allonic acid, altronic acid, gluconic acid,  galactonic acid, mannonic acid, gulonic acid, idonic acid,  and talonic acid; pentose-derived: xylonic acid, lyxonic acid,  arabonic acid, and ribonic acid; and c) hexose-derived:  alluronic acid, altruronic acid, glucuronic acid, galacturonic  acid, mamiuronic acid, guluronic acid, iduronic acid, and  taluronic acid; pentose-derived: xyluronic acid, lyxuronic  acid, araburonic acid, and riburonic acid.  Scheme 1,-Hexoses.  OH  OH  HO~O  4  ------- y  OH  OH  OH  Aldonic acid  OH  OH  0  OH  OH  HO~O  2  HO)yyyo  5  ------- ------- OH  OH  OH  OH  OH  hexose  Aldaric acid  ~  0  OH  OH  HO~O  6  ------- OH  OH  Uronic acid 