Zongjie Hao

Simulated microgravity alters growth and microcystin production in Microcystis aeruginosa (cyanophyta)

Recent researches indicated that microgravity can increase pathogenic bacteria virulence. We presumed that microgravity might affect the toxin production of toxic cyanobacteria too. Microcystis aeruginosa PCC7806 was chosen as the model organism to investigate the effects of simulated microgravity (SMG) on the growth and toxin production of toxic cyanobacteria. SMG could inhibit the growth of M. aeruginosa, which resulted in decreased cell number and lower specific growth rate after 20-day treatment. M. aeruginosa sensed the reduced gravity very quickly and immediately up-regulated its microcystin (MC) synthesis and exudation in 2 days. Subsequently, the intracellular MC content fell back since the 8(th) day and was stable around the initial level in the following days, suggesting a quick adaptation to the reduced gravity. SMG had negative effects on the photochemical system and the absorption of phosphorus in most time. However, the photosynthetic pigment concentrations and nitrogen absorption used to be transitorily stimulated upwards by SMG. It was assumed that SMG inhibited cell growth by interfering its photosynthesis and phosphorus uptake, while the enhanced MC production was related with pigment and nitrogen metabolisms. This study reveals that SMG is a novel environmental signal which inhibits growth and enhances MC production of M. aeruginosa.

Raman Spectroscopic Analysis of a Desert Cyanobacterium Nostoc sp. in Response to UVB Radiation

Cyanobacteria are capable of tolerating environmental extremes. To survive in extreme environments, cyanobacteria have developed the capability to adapt to a variety of stresses. For example, cyanobacteria have adopted a number of strategies with which to survive UV stress, including expression of UV-screening pigments and antioxidant systems. We have previously shown that several antioxidants are significantly expressed in Nostoc sp. by UVB irradiation. We report here that the content of UV-responsive biomarkers such as β-carotene and scytonemin can be easily detected by Fourier transform Raman spectroscopy with use of a small sample size and that the content of β-carotene is dependant on the UVB intensity and exposure time. Our results indicate that Raman spectroscopy may be a helpful tool to analyze UV-protective molecules of cyanobacterium in astrobiological studies without access to large sample sizes and complicated extractions, which are needed by other analytical techniques such as high-performance liquid chromatography and mass spectrometry.