To study the mechanism of light color on a sea urchin (Tripneustes gratilla), blue light (B, λ450nm), yellow light (Y, λ585-590nm), red light (R, λ640nm), green light (G, λ510nm), white light (W, λ400-780nm) and darkness groups (H) were set up in a seawater recirculating aquaculture system. Six different LED light color treatment groups with a photoperiod of 12 L:12 D were tested for 30 d to investigate the effects of different light colors on the feeding, growth and enzyme activities of T. gratilla (142.45±4.36 g). We found that varying LED light colors significantly impacts the feeding, growth, and enzyme activity of T. gratilla. Notably, the sea urchins in group B exhibited better growth with a weight gain rate of 39.26%, while those in group R demonstrated poorer growth with a weight gain rate of only 26%. The feeding differed significantly (P<0.01) between groups B and R, with group B consuming the highest daily intake (6.03±1.69 g) and group R consuming the lowest (4.54±1.26 g). Throughout the three phases, there was no significant change in the viability of the AMS (P>0.05). Conversely, pepsin viability significantly increased (P<0.01) in group B. LPS viability remained consistently at the lowest level, with no notable differences in group W from those observed in group B. In group R, both AMS and pepsin viability remained lower, whereas lipase viability was noticeably higher in each phase compared to group B (P<0.01). Regarding antioxidant enzymes, group R exhibited a trend of initially increasing and then decreasing CAT, SOD, and GSH-PX activities, particularly during the third stage (15-30 d), with a significant decrease observed in antioxidant enzyme activities (P<0.01). The outcomes suggest that blue light positively affects the growth, feeding, digestion, and antioxidant capacity of T. gratilla in comparison to other light environments, whereas the red light has an inhibitory impact.

Understanding the energy metabolism and its regulation is one of the clues to metabolic engineering of stress-resistant lignocellulose-converting microbial strains, including also the promising ethanologen Zymomonas mobilis. Z. mobilis is an obligately fermentative, facultatively anaerobic bacterium, carrying an active respiratory chain with a low energy-coupling efficiency. Its respiration does not supply energy to aerobically growing culture on sugary media, yet oxidative phosphorylation has been demonstrated in non-growing cells with ethanol. In the present work we show that in respiring, non-growing Z. mobilis cells, receiving regular small amounts of ethanol, oxidative phosphorylation significantly contributes to the maintenance of their viability. Accordingly, no improvement of viability is seen in the NADH dehydrogenase (ndh)-deficient respiratory mutant, unable to oxidize ethanol. The ethanol effect is hampered also by the protonophoric uncoupler CCCP, or the inhibitor of ATP synthase, DCCD. At higher concentrations (6% v/v) ethanol causes stress that slows down culture growth. By monitoring the activity of several respiratory gene promoters in aerobically growing culture under ethanol stress with the green fluorescent protein reporter system, we demonstrate downregulation of these promoters, in particular the ndh promoter. We speculate that the decrease of the respiratory chain activity mitigates the production of reactive oxygen species.