Extremophile cyanobacteria: in vitro production of protective compounds against UVB radiation

Abstract

The Andean Altiplano-Puna is a sedimentary volcanic plateau at an average altitude of 4000 m located between latitudes 13°and 27° south. Solar irradiance is 165% higher than that at the level of the sea with instant flow of UV-B that reaches 17 Wm2,low nutrient concentration particularly phosphorous; presence of heavy metals and arsenic and broad fluctuation of thetemperature of the air, ranging from 20 °C during the day to -10 ° C at night. Even though these conditions are highly limiting,previous results from our laboratory have described the microbial diversity of different lakes, mats and crust of the altiplanoand revealed an unexpectedly diverse microbial community, including several genera of cyanobacteria. Cyanobacteria isolatedfrom extreme conditions like Andean microbial mats and crust could produce mycosporine-like amino acids (MAAs) as amitigation strategy to reduce the damaging effect of ultraviolet radiation. In order to probe the production of MAAs from thesecyanobacteria, the analysis of the methanolic extract by spectrophotometry was used as a rapid method to know the presenceor absence of these compounds. Different strains of cyanobacteria were placed in quartz tubes and exposed to UVB radiationfor 4 and 24 hours. Then the culture was centrifuged at 10000 rpm during 10 min, and 0,15 g of biomass were placed in tubeswith 15 ml of methanol during 24 h in dark. Methanolic extract was analyzed in a spectrophotometer by scanning from 250nm to 750 nm. Also, the methanolic extract was analyzed with high performance liquid chromatographic (HPLC), using WatersAlliance 2695e - Waters PDA 2998 Detector - Empower 2 Software, Column: Gemini C18-5u-4.6 x 250 mm and the mobilephase: 0.1% acetic acid in methanol 2.5%. The cyanobacteria that showed presence of MAAs were cultivated in differentconditions in order to determine the most convenient: condition 1: light 24 h, without shaking and room temperature; condition2: light:dark 12:12 h, without shaking and 28°C; condition 3: light:dark 12:12 h, without shaking but bubbling air into thereactor and 28° C. The strain GTAR 001, Anabaena sp., showed the most significant peak of absorbance at 334 nm when wasexposed for 24 h to UVB. The MAAs reported for cyanobacteria have peaks between 310 and 360 nm and the peak of 334 nmcorresponds to Shinorine. On the other hand, the strain GTAR 001 produced significantly more biomass with condition 3 andin a shorter period. These preliminary results agree with the MAAs reported for Anabaena sp. isolated from rice paddy fieldand hyper saline pond/marine habitat. It will be necessary to analyze this compound with liquid chromatography coupled withtandem mass spectrometry for the final determination.