NOVELTY - A cyanobacterium comprises a portion of an exogenous cellulose operon sufficient to express bacterial cellulose.    USE - The cyanobacterium is useful for producing cellulose for conversion into ethanol as biofuel (claimed).    ADVANTAGE - The cyanobacterium of the invention can fix CO2 while producing cellulose and reduce atmospheric CO2. The cyanobacterium can produce cellulose without the use of fresh water. The cyanobacterium produces an extracellular sheath digestable by cellulose-degrading enzymes. The cyanobacterium is capable of producing cellulose in saline environments. The cyanobacterium grows at salt concentrations of greater than 4%. The invention provides cellulose having a lower crystallinity than wild-type bacterial cellulose, where the lower crystallinity cellulose is degraded with less energy into glucose than wild-type cellulose and is further converted into ethanol to be used as a biofuel. The cyanobacterium increases the extracellular production of monosaccharides, disaccharides, oligosaccharides or polysaccharides upon exposure to acidic conditions. The extracellular glucose is exuded from cells or released from extracellular polysaccharides by the actions of one or more endogenous secreted glycosyl hydrolases. The viable cells can be returned to the growth medium after glucose harvest for continued production of cells, biomass, cellulose or glucose.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are:    (1) a method of producing cellulose;    (2) a system for manufacturing bacterial cellulose;    (3) a method of producing a photobiomass;    (4) a method of generating carbon credits;    (5) a method for coupled production of cellulose and value added products by growing a photosynthetic cyanobacterium capable of growing in brine, where the cyanobacterium produces non-crystalline cellulose and cellulose II as part of its extracellular sheath and expressing one or more genes in the cyanobacterium that produce one or more pharmaceuticals, vaccines, vitamins, industrial chemicals, proteins, pigments, fatty acids and their derivatives (such as polyhydroxybutyrate), acylglycerols (as precursors for biodiesel), as well as other secondary metabolites;    (6) a method of producing monosaccharides, disaccharides, oligosaccharides or polysaccharides comprising glucose;    (7) a method of fixing carbon into a photobiomass; and    (8) a method of producing sucrose from cyanobacteria;    (9) a method of fixing carbon.