Cells of Tetraspora sp. CU2551 were further examined for H2 production under the combination of positive parameters. The production was observed when cells were incubated under the increase of light intensity (Figure 3.16). As the result indicated in section 3.4.2.6 that Tetraspora sp. grown in the presence of 0.5 mM β-mercaptoethanol produced biohydrogen in double rate of production, the increase pattern was observed when low light was applied to the culture ranging from 0 to about 5 μE/m2s. After light intensity was higher than 7 μE/m2s, the production from TAP+β cells (▲) reached the maximum capacity yielding about 0.28 μmolH2 (mg DW)-1 h-1. This is in contrast to cells grown in normal TAP medium (●) in which the production increased when high ligh was applied up to 39 μE/m2s