The effects of ultraviolet radiation on photosynthetic performance, growth and sunscreen compounds in aeroterrestrial biofilm algae isolated from building facades

Abstract

The effects of artificial ultraviolet radiation [UVR; 8 W m(-2) ultraviolet-A (UVA), 0.4 W m(-2) ultraviolet-B (UVB)] on photosynthetic performance, growth and the capability to synthesise mycosporine-like amino acids (MAAs) was investigated in the aeroterrestrial green algae Stichococcus sp. and Chlorella luteoviridis forming biofilms on building facades, and compared with the responses of two green algae, from soil (Myrmecia incisa) and brackish water (Desmodesmus subspicatus). All species exhibited decreasing quantum efficiency (Fv/Fm) after 1-3 days exposure to UVR. After 8-12 days treatment, however, all aeroterrestrial isolates exhibited full recovery under UVA and UVA/B. In contrast, D. subspicatus showed only 80% recovery after treatment with UVB. While Stichococcus sp. and C. luteoviridis exhibited a broad tolerance in growth under all radiation conditions tested, M. incisa showed a significant decrease in growth rate after exposure to UVA and UVA/B. Similarly D. subspicatus grew with a reduced rate under UVA, but UVA/B led to full inhibition. Using HPLC, an UV-absorbing MAA (324 nm-MAA) was identified in Stichococcus sp. and C. luteoviridis. While M. incisa contained a specific 322 nm-MAA, D. subspicatus lacked any trace of such compounds. UV-exposure experiments indicated that all MAA-containing species are capable of synthesizing and accumulating these compounds, thus supporting their function as an UV-sunscreen. All data well explain the conspicuous ecological success of aeroterrestrial green algae in biofilms on facades. Biosynthesis and accumulation of MAAs under UVR seem to result in a reduced UV-sensitivity of growth and photosynthesis, which consequently may enhance survival in the environmentally harsh habitat.

Isolate-specific effects of ultraviolet radiation on photosynthesis, growth and mycosporine-like amino acids in the microbial mat-forming cyanobacterium Microcoleus chthonoplastes

“…The PAR + UV-A treatment signiWcantly reduced growth rate in Desmodesmus subspicatus, while the addition of UV-B was accompanied by a complete inhibition of growth ). In the present study, no substantial growth was observed in all isolates of M. chthonoplastes exposed to PA and PAB, although the irradiances were similar to those used by Karsten et al (2007). Under PA treatment, where slight bleaching of Wlaments was observed, pigments (Chl a and phycobilins) could have been slightly degraded resulting in a lower autoXuorescence per cell.…”

“…Organisms of 1 to <10 m cell size (M. chthonoplastes cells diameter = 2.6-6.9 m; Karsten and Garcia-Pichel 1996) using UV sunscreens as photoprotective mechanisms can gain considerable physiological beneWts but at the expense of high energetic investment and sometimes with restricted eYciency (Garcia-Pichel 1994). A signiWcant positive correlation between growth rate and MAAs accumulation among diVerent species of aeroterrestrial bioWlm algae was reported by Karsten et al (2007). On the other hand, strain-speciWc physiological responses (pigment, Fv/ Fm and growth) in UVR-exposed Nodularia spumigena were not related to MAAs accumulation (WulV et al 2007).…”

Ecophysiological performance of an urban strain of the aeroterrestrial green algaKlebsormidiumsp. (Klebsormidiales, Klebsormidiophyceae)

“…Compared with the aquatic environment, aeroterrestrial green algae are exposed to harsher environmental conditions, such as diurnally and seasonally high insolation, strong temperature fluctuations and restricted water availability (Karsten et al, 2007a(Karsten et al, , 2007b. Extensive exposure to the atmosphere results in dehydration, which strongly affects photosynthesis and growth.…”

Physiological, biochemical, and ultrastructural responses of the green macroalga Urospora penicilliformis from Arctic Spitsbergen to UV radiation

“…A presumptive UV-absorbing compound with strong absorption below 300 nm was detected in methanol extracts of Ulva pertusa Kjellman (Ulvophyceae; Han and Han 2005). Another UVabsorbing compound identified as 324-nm mycosporinelike amino acid (MAA) was described in Prasiola crispa (Lightfoot) Kützing and occurs only in numerous green algal members of the Trebouxiophyceae (Karsten et al 2005(Karsten et al , 2007. The absence of this compound in members of the Ulvophyceae and Chlorophyceae suggests a phylogenetic pattern in MAA synthesis.…”