Light is one of the most important energy sources and signals providing critical information to biological systems. The photoreceptor rhodopsin, which possesses retinal chromophore (vitamin A aldehyde) surrounded by seven transmembrane alpha-helices, is widely dispersed in prokaryotes and in eukaryotes. Although rhodopsin molecules work as distinctly different photoreceptors, they can be divided according to their two basic functions such as light-energy conversion and light-signal transduction. Thus rhodopsin molecules have great potential for controlling cellular activity by light. Indeed, a light-energy converter channel rhodopsin is used to control neural activity. From 2001, we have been working on various microbial sensory rhodopsins functioning as light-signal converters. In this review, we will introduce rhodopsin molecules from microbes, and will describe artificial and light-dependent protein expression system in Escherichia coli using Anabeana sensory rhodopsin (ASR). The newly developed tools would be widely useful for life scientists.