J. Gen. Appl. Microbiol., 48, 211–222 (2002)

Dense microbial mats and/or streamers of various colors (white, yellow, pink, purple, orange, red, green, etc.) develop in neutral or alkaline hot springs as follows: The color is determined by interaction between microbes in hot springs and physicochemical factors such as temperature, pH, sulfur and light (Brock, 1978; Castenholz, 1988; Hanada et al., 1995; Hiraishi et al., 1999; Jørgensen and Nelson, 1988; Pierson, 1994; Skirnisdottir et al., 2000). Among them, in situ temperature, sulfide and light can be some of the key factors in developing microbial community structure. For instance, Aquificales-like organisms dominated within white or yellow sulfurturf mats, consisting mainly of microorganisms and sulfur compounds, in sulfide-rich hot springs with sulfide concentrations over 0.091 mM and temperature ranging from 52–72°C (Skirnisdottir et al., 2000; Yamamoto et al., 1998). On the other hand, orange or yellow Chloroflexus mats were formed in the sulfide-poor hot spring with sulfide concentrations less than 0.030 mM at 65–70°C (Skirnisdottir et al., 2000). Phylogenetic characterization of microbial mats and streamers from a Japanese alkaline hot spring with a thermal gradient