Aquatic Chemical Ecology

Induction of cell filamentation in freshwater bacteria as a defense mechanism against bacterivorous protists, and characterization of potential signaling compounds

Thread-like bacterial morphotypes temporarily constitute a large fraction of biomass in lakes of different trophic state. It is assumed that this phenotype provides protection from predation by heterotrophic flagellated protists. Some bacterial species in freshwaters, e.g. Flectobacillus major, are able to form both small, rod-shaped and filamentous cells, but it is unclear if this is due to phenotypic plasticity, or if the accumulation of thread-like morphotypes resembles genotypic diversification. Currently, two mechanisms are discussed how filament-formation is induced in bacteria related to F. major: On the one hand, it has been suggested that the thread-like morphotype may be a consequence of enhanced growth rates, potentially fuelled by excretion of organic carbon by the protistan predator. By contrast, other evidence suggests that filament formation in a F. cf. major strain was caused by a chemical cue (kairomone) that is released during flagellate grazing.

Key words: Predator-prey interactions, Ochromonas, Flectobacillus, allelochemicals

Grazer toxins and protease inhibitors in the cyanobacterium Planktothrix rubescens and their role in the plankton community

Cyanobacterial blooms are common phenomena in brackish and freshwater ecosystems of temperate, subtropical and tropical regions. Planktothrix rubescens dominates the phytoplankton community in Lake Zürich throughout the year and is concentrated in a dense layer at a depth of 10 m in the second part of the year. Cyanobacterial blooms represent a health hazard due to their potent neuro- and hepatotoxins. Experimental work has shown that these compounds actively control the grazing of zooplankton. The structures of several toxins in natural populations and laboratory cultures of Planktothrix rubescens were determined by HPLC, GC-MS and NMR-spectrometry. Bioassay-guided fractionations were initiated to trace both the toxic compounds and protease inhibitors responsible for the effects on grazers. Extensive work has been done to obtain high purity compounds in order to determine their physical properties necessary for quantitative ecological work to be conducted in microcosms. Protein phosphatase and protease assays have been conducted to compair the inhibitory activity of different depsipetides of cyanobacterial origin.

 Key words: Cyanobacterial bloom, toxins, Planktothrix, Microcystis, microcystins, bioassay-guided fractionations, depsipeptides

Education and Research

2006-Present Postdoctoral Fellow (Prof. J. Pernthaler; Limnological Station, University of Zürich)
Induction of cell filamentation in freshwater bacteria as a defense mechanism against bacterivorous protists, and characterization of potential signalling compounds

2008 Visiting Researcher (Prof. Karel Šimek; Biology Centre of the Academy of Sciences of the Czech Republic, Institute of Hydrobiology, České Budĕjovice, Czech Republic) 

2003-2006 Postdoctoral Fellow (Prof. F. Jüttner; Limnological Station, University of Zürich)
Isolation, characterisation, and structure elucidation of bioactive compounds of cyanobacteria.

1998-2003 Dr. sc. nat. (Prof. F. Jüttner; Limnological Station, University of Zürich)
Enzyme-inhibitory and grazer-toxic effects of cyclic peptides from Planktothrix rubescens.

1998 Internship (Prof. W. Stöcker; Institute of Zoophysiology, University of Münster)
Bacterial expression of recombinant proteins and their purification, renaturation and characterisation.

1994-1996 Basic Studies in Medical Science at the University of Münster

1992-1998 Dipl. Biol. (Prof. R.J. Paul; Institute of Zoophysiology, University of Münster)
Respiration physiology of marine copepods.

Patents

Blom JF and Gademann K. 2005. Heterocyclic compounds and their use as antifouling agents. Patent # EP1783128A1

Book Chapter

Blom JF, Hoeger SJ, Jüttner F. 2010. Characterization of bioactive cyclic oligopeptides of freshwater cyanobacteria (microcystins, cyanopeptolins, cyclamides). SN Bagchi, D Kleiner, P Mohanty (Eds) Protocols on Algal and Cyanobacterial Research. Narosa Publishing, New Delhi, India

List of publications

Blom JF, Robinson JA, Jüttner F. 2001. High grazer toxicity of [D-Asp3,(E)-Dhb7]microcystin-RR of Planktothrix rubescens as compared to different microcystins. Toxicon. 39, 1923-32. download (,151823KB)

Blom JF, Bister B, Bischoff, D, Nicholson, G, Jung, G, Süssmuth, RD, Jüttner F. 2003. Oscillapeptin J, a new grazer toxin of the freshwater cyanobacterium Planktothrix rubescens. J Nat Prod 66, 431-434 (selected as ‘Hot Article’ by the American Chemical Society in April 2003 in the ‘Environmental Month’ feature). download (,56257KB)

Von Elert E, Oberer L, Merkel P, Huhn T, Blom JF. 2005. Cyanopeptolin 954, a chlorine-containing chymotrypsin inhibitor of Microcystis aeruginosa NIVA Cya 43. J Nat Prod, 68, 1324-1327. download (,79432KB)

Blom JF, Juttner F. 2005. High crustacean toxicity of microcystin congeners does not correlate with high protein phosphatase inhibitory activity. Toxicon. 46, 465-470. download (,151823KB)

Blom JF, Brütsch, T, Barbaras D, Bethuel Y, Locher HH, Hubschwerlen C, Gademann K . 2006. Potent algicides based on the cyanobacterial alkaloid nostocarboline. Org Lett. 8, 737-740. download (,68766KB)

Blom JF, Baumann HI, Codd GA, Jüttner F. 2006. Sensitivity and adaptation of aquatic organisms to oscillapeptin J and [D-Asp3,Dhb7]microcystin-RR. Arch. Hydrobiol. 167, 547-559. download (,675916KB)

Hoeger SJ, Schmid D, Blom JF, Ernst B, Dietrich DR. 2007. Analytical and functional characterization of microcystins [Asp3]MC-RR and [Asp3,Dhb7]MC-RR: Consequences for Risk Assessment? Environ. Sci. Technol. 41, 2609-2616. download (,378581KB)

Christiansen G, Yoshida WY, Blom JF, Portmann C, Gademann K, Hemscheidt T, Kurmayer R. 2008. Isolation and Structure Determination of Two Microcystins and Sequence Comparison of the McyABC Adenylation Domains in Planktothrix Species. J Nat Prod 71, 1881-1886. download (,172922KB)

Portmann C, Blom JF, Gademann K, Jüttner F. 2008. Aerucyclamides A and B: Isolation and Synthesis of Toxic Ribosomal Heterocyclic Peptides from the Cyanobacterium Microcystis aeruginosa PCC 7806. J Nat Prod 71, 1193-1196. download (,90878KB)

Portmann C, Blom JF, Kaiser M, Brun R, Jüttner F, Gademann K. 2008. Isolation of Aerucyclamides C and D and Structure Revision of Microcyclamide 7806A: Heterocyclic Ribosomal Peptides from Microcystis aeruginosa PCC 7806 and Their Antiparasite Evaluation. J Nat Prod 71, 1891-1896. download (,165879KB)

Schmidt S, Blom JF, Pernthaler J, Berg G, Baldwin A, Mahenthiralingam E, Eberl L. 2009. Production of the antifungal compound pyrrolnitrin is quorum sensing-regulated in members of the Burkholderia cepacia complex. Environ. Microbiol. 11, 1422-1437. download (,500234KB)

Portmann C, Blom JF, Kaiser M, Brun R, Jüttner F, Gademann K. 2009. New plasmodial natural products from cyanobacteria: linking their ecological role to their therapeutic potential. Planta Med. 75, 886 . download (,5857KB)

Blom JF, Pernthaler J. 2010. Antibiotic effects of three strains of chrysophytes (Ochromonas, Poterioochromonas) on freshwater bacterial isolates. FEMS Microbiol. Ecol. 71, 281-290. download (,374654KB)

Blom JF, Horňák K, Šimek K, Pernthaler P. 2010. Aggregate formation in a freshwater bacterial strain induced by growth state and conspecific chemical cues. Environ Microbiol. download (,529999KB)

Gademann K, Portmann C, Blom JF, Zeder M, Jüttner F. 2010. Multiple toxin production in the cyanobacterium Microcystis: Isolation of the toxic protease inhibitor cyanopeptolin 1020. J Nat Prod. download (,2596984KB)