UVB radiation as a potential selective factor favoring microcystin producing bloom forming Cyanobacteria

PLoS One. 2013 Sep 13;8(9):e73919. doi: 10.1371/journal.pone.0073919. eCollection 2013.

Abstract

Due to the stratospheric ozone depletion, several organisms will become exposed to increased biologically active UVB (280-320 nm) radiation, not only at polar but also at temperate and tropical latitudes. Bloom forming cyanobacteria are exposed to UVB radiation on a mass scale, particularly during the surface bloom and scum formation that can persist for long periods of time. All buoyant species of cyanobacteria are at least periodically exposed to higher irradiation during their vertical migration to the surface that usually occurs several times a day. The aim of this study is to assess the influence on cyanobacteria of UVB radiation at realistic environmental intensities. The effects of two UVB intensities of 0.5 and 0.99 W/m(2) in up to 0.5 cm water depth were studied in vitro on Microcystis aeruginosa strains, two microcystin producing and one non-producing. After UVB exposure their ability to proliferate was estimated by cell counting, while cell fitness and integrity were evaluated using light microscopy, autofluorescence and immunofluorescence. Gene damage was assessed by TUNEL assay and SYBR Green staining of the nucleoide area. We conclude that UVB exposure causes damage to the genetic material, cytoskeletal elements, higher sedimentation rates and consequent cell death. In contrast to microcystin producers (PCC7806 and FACHB905), the microcystin non-producing strain PCC7005 is more susceptible to the deleterious effects of radiation, with weak recovery ability. The ecological relevance of the results is discussed using data from eleven years' continuous UVB radiation measurements within the area of Ljubljana city (Slovenia, Central Europe). Our results suggest that increased solar radiation in temperate latitudes can have its strongest effect during cyanobacterial bloom formation in spring and early summer. UVB radiation in this period may significantly influence strain composition of cyanobacterial blooms in favor of microcystin producers.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Toxins / biosynthesis*
  • Benzothiazoles
  • Diamines
  • Fresh Water / microbiology
  • Microbial Viability / radiation effects
  • Microcystins / biosynthesis*
  • Microcystins / metabolism
  • Microcystis / growth & development
  • Microcystis / metabolism
  • Microcystis / radiation effects*
  • Microscopy, Fluorescence
  • Organic Chemicals
  • Photoperiod
  • Quinolines
  • Species Specificity
  • Ultraviolet Rays
  • Water Microbiology*

Substances

  • Bacterial Toxins
  • Benzothiazoles
  • Diamines
  • Microcystins
  • Organic Chemicals
  • Quinolines
  • SYBR Green I
  • microcystin

Grants and funding

The work was supported by Slovenian Research Agency (http://www.arrs.gov.si/en/dobrodoslica.asp), Research Program P1-0245ARRS: Ecotoxicology, Toxicogenomics and Carcinogenesis - (BS salary,reagents, materials, analysis tools), and Ministry of Defence Administration for Civil Protection and Dosaster Relief (Contract No URSZR 4300-1117/2009-1) “Cyanobacterial toxins in surface waters,” which co-financed the Laminar Flow Cabinet. Chinese grants from the Natural Science Foundation of China-Yunnan Project (U0833604) (http://www.nsfc.gov.cn/e_nsfc/desktop/zn/0101.htm) and ‘973’ Program (2008CB418000) funded the nine-month stay of Ding Yi at the National Institute of Biology in Ljubljana. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.