Oxidative state in idiophase links reactive oxygen species (ROS) and lovastatin biosynthesis: differences and similarities in submerged- and solid-state fermentations.

The present work was focused on finding a relationship between reactive oxygen species (ROS) and lovastatin biosynthesis (secondary metabolism) in Aspergillus terreus. In addition, an effort was made to find differences in accumulation and control of ROS in submerged (SmF) and solid-state fermentation (SSF), which could help explain higher metabolite production in the latter. sod1 expression, ROS content, and redox balance kinetics were measured during SmF and SSF. Results showed that A. terreus sod1 gene (oxidative stress defence enzyme) was intensely expressed during rapid growth phase (trophophase) of lovastatin fermentations. This high expression decreased abruptly, just before the onset of production (idiophase). However, ROS measurements detected high concentrations only in idiophase, suggesting a link between ROS and lovastatin biosynthesis. Apparently sod1 down regulation promotes the rise of ROS during idiophase. This oxidative state in idiophase was further supported by a high redox balance observed in trophophase that changed to a low value in idiophase (around six-fold lower). The patterns of ROS accumulation, sod1 expression, and redox balance behaviour were similar in SmF and SSF. However, sod1 expression and ROS concentration (ten-fold), were higher in SmF. Our results indicate a link between ROS and lovastatin biosynthesis. Also, showed differences of physiology in SSF that yield lower but more steady ROS concentrations, which could be associated to higher lovastatin production.