Efeito do balanço pH/carbono inorgânico em parâmetros ecofisiológicos de Cylindrospermopsis raciborskii (Cyanobacteria) sob condições experimentais

Abstract

Cylindrospermopsis raciborskii (Wolozynska) Seenayya & Subba Raju is a cosmopolitan diazotrophic and potentially toxic specie considered as invasive in different latitudes. Its capacity of occupying several niches is a feature which is linked to its physiological traits, which allow it to have wide ecological amplitude to several environmental parameters. However, in laboratory conditions that specie might show some growth limitations related to pH, temperature and nutrients. In this scenario, this work aimed to investigate the effect of pH and source of inorganic carbon in growth-related parameters of C. raciborskii. The strain ITEP-A1 (saxitoxin-producing) was cultured in ASM-1 medium and maintained under controlled conditions. Experiments were worked out in 2L erlenmeyers filled with 1.5 L culture medium in different pH ranges and inorganic carbon availability, with/without CO2 enriched-air bubbling. Cyanobacterial growth, morphological traces, biomass acquisition, temperature, pH, conductivity, alkalinity and total inorganic carbon dissolved were analyzed. Results were compared using repeated-measures ANOVA and ANOVA one way with Tukey’s test post hoc (p<0.05). Graphics and statistical analysis were performed in Statistica 7.0 and R i386 3.1.2, respectively. C. raciborskii ITEP-A1 showed better growth rate and biomass under alkaline pH (> 8.0) (P<0,05) in both aeration conditions. pH, alkalinity and inorganic carbon showed an increasing trend throughout the experiment under pH free. At the pH condition > 8.0 with aeration the bicarbonate ion (HCO3-) was the main source of inorganic carbon available to the photosynthetic process, which favored C. raciborskii growth. These results can be extrapolated to a global scale, and suggested as factors that have favored the distribution and expansion of this cyanobacterium to other latitudes.