Provided herein is a transgenic bacteria engineered to accumulate carbohydrates, for example disaccharides. Also provided is a photobioreactor for cultivating photosynthetic microorganisms comprising a non-gelatinous, solid cultivation support suitable for providing nutrients and moisture to photosynthetic microorganisms and a physical barrier covering at least a portion of the surface of the cultivation support. Devices for the large scale and continuous cultivation of photosynthetic microorganisms incorporating photobioreactors and methods of use are disclosed. Also disclosed are methods of producing fermentable sugar from photosynthetic microorganisms using a photobioreactor of the invention.