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International Symposium on Photosynthetic Prokaryotes Meeting Report

by Bas Ibelings (Institute for Inland Water Management, Arnhern)

From an ecologists point of view this well organised symposium took a while to gain momentum. The first time I was treated to the phrase "it's function in the natural environment" was well into the third day of the meeting (in Fritz Jüttner's presentation about nostocyclamide, a compound that inhibits growth of other cyanobacteria). Yet, did all of the structures and processes we study not evolve in the natural environment, and is it not in the natural environment that they all have their function? The meeting really came to life with the change to the second poster session - many interesting posters.

Initially I was displeased that even the historic overviews preceded the ecology session on the last day. The presentation by Noel Carr (U. Warwick), however, turned out to be one of the highlights of the meeting for me. Some of his messages were well worth our attention: e.g. the need for a tighter integration of biochemistry and ecology; or the observation that disruption of a gene often does not have any obvious effects: metabolism does not work as a Swiss watch, but has many alternative pathways; or the remark that we saw many beautiful facts but too little speculation during the meeting. I have been attracted to the ISPP meetings by the combination of a specialised subject (phototrophic prokaryotes), with a wide range of presentations, from bioenergetics or molecular biology to the worlds lakes and oceans. I would applaud a restoration of this integrated approach in the next meeting.

The harmful effects of toxic cyanobacteria help to keep alive the interest of water management and funding agencies in our favourite organisms. Reports in the press cause concern among the public during periods of warm stable weather ("Blue-green algae: one sip will kill you!" - Dutch press, "Queen's swans poisoned by outbreak of algae!"- U.K. press). Geoff Codd (U. Dundee) gave an overview of the occurrence and significance of cyanobacterial toxins, recognition of which has been limited by in part by inadequate detection methods. A sensitive detection method for the widely occurring microcystins is the Protein Phosphatase Inhibition Assay. It is insufficient however to focus solely on these microcystins, as other toxins, e.g. nostocyclin, are also important. Codd finished his presentation with the recommendation that it is necessary to rationalise water management with respect to these toxins and to try to understand their natural function and evolution.

Steven Bell and others at U. Dundee investigated the phenomenon of fish kills, which are often associated with the occurrence of toxic cyanobacteria. Exposure of rainbow-trout to aqueous solutions of hepatotoxins resulted in sub-clinical liver damage. Radioactivity of 14C-labelled microcystin was detected in liver tissue, although microcystins did not show up in HPLC analysis.

Elke Dittmann (Humboldt U.) reported cloning a peptide synthetase gene cluster that is responsible for hepatotoxin biosynthesis in Microcystis aeruginosa. The genes may prove useful in the study of toxin expression and in new DNA-based detection methods. She also created mic- mutants that may offer the first glimpse into the role of microcystins in cyanobacterial physiology.

Biodiversity is another topic that in some ways spans the gap between science and politics. Ferran Garcia-Pichel presented an interesting poster about the interrelations between productivity, stability and diversity of ecosystems. He used cyanobacterial communities as a model system and quantified productivity (using microsensors and benthic flux chambers), stability against environmental change and diversity (using PCR-amplified 16S rRNA sequences and denaturing gradient gel electrophoresis). Stability was calculated from measurements of productivity and diversity before and after environmental disturbance. Productivity turned out to be only a weak function of diversity, but stability was found to be a strongly dependent on diversity.

Paul Hayes is interested in the genetic diversity of Nodularia populations in the Baltic. His poster discussed one of the worries that many plankton-ecologists share: how representative are the cultures that we use in the lab of the diversity of the natural system? To quantify and compare the diversity of natural and cultured Nodularia, he amplified an intergenic spacer within the cpc operon (encoding phycocyanin) from individual trichomes, both from clonal isolates and from natural populations. Sequence analysis showed three allelic variants of this region from cultured Nodularia, and only two from Nodularia taken directly from the natural environment.