A DIALOG IN THE WATER BODY - INTERACTION BETWEEN BACTERIA AND MICROCYSTIS SP

Gad Weiss ¹ Dimitry Kovalerchick ² Judy Lieman-Hurwitz ¹ Omer Murik ¹ Shmuel Carmeli ² Assaf Sukenik ³ Aaron Kaplan ¹

¹Plants and Environmental sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
²Raymond and Beverly Sackler School of Chemistry and Faculty of Exact Sciences, Tel-Aviv University, Tel-Aviv, Israel
³The Yigal Allon Kinneret Limnological Laboratory, Israel Oceanographic and Limnological Research, Migdal, Israel

Intensification of toxic cyanobacterial blooms, mainly Microcystis sp., in freshwater bodies is a serious threat to the drinking water quality worldwide, a matter of growing concern. The natural role of secondary metabolites, such as toxic microcystins and others in inter-and intra-species communication in the aquatic ecosystem is emerging.

From Microcystis sp. colonies collected in various locations we isolated the bacterium Aeromonas veronii, a fish parasite. When grown in mixed cultures, A. veronii inhibits the growth of Microcystis sp. The potency and duration were significantly increased when A. veronii was pre-exposed to Microcystis sp., by growing it in a medium prepared from a filtrate of stationary Microcystis sp. culture.

From the A. veronii extract, we produced an active fraction, in which one of the materials present was identified as lumichrome by NMR analysis. Testing the activity of lumichrome against Microcystis sp. showed inhibition in concentration levels as low as 10^-6mg/ml (4.1 nM). A mutation in a key component of lumichrome biosynthetic pathway impaired A. veronii potency against Microcystis sp.

On the other hand, Aeromonas growth in response to conditioned medium expressed in longer lag, followed by a rapid burst in growth rate. The intensity of the burst was dose-dependent.

These results suggest a complex dialog between Microcystis and Aeromonas, mediated by secondary metabolites. Our study set the stage towards control of toxic Microcystis blooms taking advantage of the chemical languages used in the interspecies communication.