Avaliação da influência do estresse salino e luminoso na produção de carotenoides por Micrococcus luteus

Abstract

Carotenoids are pigments derived from terpenoids, can have yellowish to reddish tones, found in plants and microorganisms. In bacteria they are secondary metabolites that may have a photo-oxidative protection function. Among them, previous studies point out the potential of the bacterium Micrococcus luteus regarding the accumulation of sarcinaxanthin, a 50-carbon carotenoid. These compounds have been highlighted due to their antimicrobial and antioxidant properties, protection against UV radiation, and health benefits related to the prevention of cardiovascular diseases and Alzheimer's disease. Thus, due to this diversity of application, the present work aimed to evaluate the influence of salt and light stress associated and disassociated on the production of carotenoids from M. luteus bacteria. The experiments were performed in 125 mL Erlenmeyers flasks with 50 mL of soy triptone broth with sucrose and potassium nitrate at 35 °C, pH 7.00 and 150 rpm, with sufficient inoculum volume for optical density of 0.1. The experimental conditions were no salt without light, no salt with light, salt without light, salt with light, and salt with blue light. The latter condition was evaluated by packing the flasks with blue cellophane paper. For the no-light condition, the flasks were covered with kraft paper. For the light supply, three 20 W led lamps were attached to the surface of the orbital shaker. The samples were removed at different times up to 40 h and centrifuged. The supernatant was separated to measure the pH of the samples, the pellets were resuspended in 10 mL of methanol for carotenoid extraction, and then resuspended in water again for determination of cell biomass. According to the results, there was a decrease in the pH of all experiments evaluated, going from 7.0 (initial pH) to values between 5.0 and 5.5 at the end of the culture, which showed that the salt and light did not influence the pH. Similar behavior was observed in biomass production, as the different experiments presented a similar growth curve, thus the different treatments also did not influence this parameter. Regarding pigment production, it was verified that the presence of salt did not interfere positively in the production, different from the light, because the highest productivities occurred in the conditions with light. In relation to the blue light condition, an increase in productivity was observed, but it was not very expressive, corresponding to a value of 13.78 % in relation to the visible light condition. It is concluded from this previous study that the bacterium M. luteus has a great carotenoid producing potential when submitted to light stress conditions and that the presence of salt did not influence such production. Further studies are necessary to evaluate other extracting solvents, as well as other light stains aiming to optimize carotenoid production.