EFFECT OF STRESS CONDITIONS ON C/N METABOLISM IN TWO M. aeruginosa TOXIGENIC STRAINS

KOLMAN, MARÍA DE LOS ÁNGELES; CAINZOS, MAXIMILIANO; MARTIN, MARÍA VICTORIA; SALERNO, GRACIELA

Florianópolis

Congreso; The 17th International coference on Harmful Algae Brazil 2016; 2016

ICHA

Cyanobacteria are oxygenic photosynthetic organisms found in a diverse range of habitats that play a key role in the biogeochemical carbon/nitrogen (C/N) cycle. Light can be harmful to photosynthetic organisms despite its essential role in photosynthesis. When the amount of light energy absorbed by light-harvesting systems exceeds the limit of energy consumption by different cellular processes, the energy excess produces reactive oxygen species (ROS) leading to a severe photodamage to cellular components.Microcystis strains produce blooms and are also able to synthesize microcystins, powerful hepatotoxins. It has been reported that M. aeruginosa are responsible for over 60% of bloom poisoning cases in the world. Recently, it has been reported an increased expression of genes encoding proteins related to microcystin synthesis (mcy genes) under stress conditions as high light. Furthermore, it was shown that microcystins bind to some proteins (such as those related to C/N metabolisms) giving them stability during oxidative stress, a fairly common condition in a bloom or massive proliferation. Recent genomic and proteomic studies comparing toxigenic and non-toxigenic Microcystis strains showed that nine proteins, involved in C and N metabolisms and in redox balance, exhibit differential expression. In the present work, we analyzed by RT-PCR the expression of genes involved in C fixation and C/N relationship regulation and in microcystin synthesis, in two M. aeruginosa strains (a model and a native strain), under different light conditions. On other hand, we performed a quantification of total microcystin, glycogen and cyanophycin (C and N storage compounds, respectively) contents.Our results show that the two toxigenic strains analyzed differ in the expression of genes related to C metabolism and microcystin synthesis. However, no change was detected in the expression of genes involved in N metabolism in cells under a high light condition compared to control growth condition. Besides, glycogen and cyanophycin contents differ between the two strains. Also, the total microcystin content was not affected by the treatment in both strains. The data presented support that toxigenic Microcystis strains have different responses to stresses which may be ascribed to different strategies to deal with them.