Abstract: Methods and procedures for designing and constructing microbes with the ability to harvest light energy are described. In certain embodiments, these methods and procedures are used to construct a photosynthetic yeast based on proteorhodopsin (PR) expression. Proteorhodopsin is a light powered proton pump used by some ocean bacteria to scavenge light energy. By illuminating single yeast cells expressing PR, controlled amounts of energy can be delivered to these cells. A light-harvesting yeast is a unique bioenergetics research platform for investigating the interplay of biofuel production, cellular ATP levels, and the proton-motive-force (pmf). Also, a strain of yeast with light-boosted biomass to biofuel conversion efficiency possesses direct industrial and commercial utility.