Abstract Microcystins are small hepatotoxic peptides pro- duced by a number of cyanobacteria. They are synthesized non-ribosomally by multifunctional enzyme complex syn- thetases encoded by the mcy genes. Primers deduced from mcy genes were designed to discriminate between toxic microcystin-producing strains and non-toxic strains. Thus, PCR-mediated detection of mcy genes could be a simple and efficient means to identify potentially harmful geno- types among cyanobacterial populations in bodies of wa- ter. We surveyed the distribution of the mcyB gene in dif- ferent Microcystis strains isolated from Chinese bodies of water and confirmed that PCR can be reliably used to identify toxic strains. By omitting any DNA purification steps, the modified PCR protocol can greatly simplify the process. Cyanobacterial cells enriched from cultures, field samples, or even sediment samples could be used in the PCR assay. This method proved sensitive enough to detect mcyB genes in samples with less than 2,000 Microcystis cells per ml. Its accuracy, specificity and applicability were confirmed by sequencing selected DNA amplicons, as well as by HPLC, ELISA and mouse bioassay as con- trols for toxin production of every strain used. Keywords Cyanobacteria · Microcystis · Microcystin · Toxin · Peptide synthetase · Whole-cell PCR Introduction In eutrophic water habitats, the proliferation of cyanobac- teria results in the formation of water blooms, a world- wide phenomenon that causes the poisoning of animals. Most bloom-forming cyanobacteria are known to synthe- size a variety of toxins. Among the cyanotoxins is a fam- ily of cyclic heptapeptides called microcystins which are potent hepatotoxins and liver tumor promoters (Car- michael 1996; Sivonen, 1996). The most common produc- ers of microcystins are various Microcystis species (Car- michael 1996; Sivonen, 1996). These species often form a heavy bloom on water surface of lakes or reservoirs. They are also abundant in the sediment of lakes and reservoirs throughout the winter. These overwintering colonies may provide the inoculum for the next bloom (Noriko et al. 1984; Preston and Stewart 1980). Bodies of water that are used for recreational purposes and/or as the source of drinking water should thus be regularly controlled for the presence of toxic cyanobacteria. The majority of Microcystis aeruginosa isolates are toxic and synthesize microcystins. Only toxic isolates contain the genes for the enzymes involved in microcystin biosynthesis (Dittmann et al. 1999; Meissner et al. 1996; Neilan et al. 1999). Microcystins are synthesized nonribo- somally by the large modular multifunctional enzyme complexes known as peptide synthetases encoded by the mcy (microcystin synthetase) gene cluster (Dittmann et al. 1999; Tillett et al. 2000; Nishizawa et al. 1999, 2000). Amplification of mcy genes by PCR from DNA isolated from axenic cultures and field samples has proven to be a sensitive means to differentiate between microcystin-pro- ducing hepatotoxic and non-hepatotoxic Microcystis strains (Dittmann et al. 1999; Meissner et al. 1996; Neilan et al. 1999). Two pairs of oligonucleotide primers, TOX1P/ TOX1 M and TOX2P/TOX2 M, were designed to detect and characterize microcystin-producing and non-toxic cyanobacteria species by specifically amplifying frag- ments of the mcyB gene (Dittmann et al. 1999). These PCR-based gene detection procedures established a corre- Hui Pan · Lirong Song · Yongding Liu · Thomas Börner Detection of hepatotoxic Microcystis strains by PCR with intact cells from both culture and environmental samples Received: 21 September 2001 / Revised: 25 June 2002 / Accepted: 1 July 2002 / Published online: 27 August 2002 ORIGINAL PAPER H. Pan · L. Song (✉) · Y. Liu Department of Phycology, Institute of Hydrobiology, The Chinese Academy of Sciences, Luojiashan, Wuhan 430072, P. R. China e-mail: lrsong@ihb.ac.cn, Tel.: +86-27-87647715, Fax: +86-27-87647715 T. Börner Institute for Biology, Humboldt University, Chausseestrasse 117, 10115 Berlin, Germany Arch Microbiol (2002) 178 : 421–427 DOI 10.1007/s00203-002-0464-9 © Springer-Verlag 2002