PNG2001

Microbial loop and nutrient cycling: 

Microbial loop and nutrient cycling David Stopar October, 2001 Nova Gorica International Short-Course Series Bioremediation and Phytoremediation of Organics and Nutrients University of Ljubljana Biotechnical faculty Vecna pot 111, SI-1000 Ljubljana, Slovenia

Microbial loop: 

Microbial loop

Why bacteria die?: 

Why bacteria die? predation lethal environment starvation disease (phages) programmed cell death

Vibrio gazogenes organic carbon sources: 

Vibrio gazogenes organic carbon sources Sugars glucose D-fructose D-mannose maltose D-xylose sucrose trehalose L-arabinose D-galactose D-ribose

Vibrio lysate as a source of organic carbon for a bacterial community: 

Vibrio lysate as a source of organic carbon for a bacterial community Natural bacterial community is able to grow on bacterial lysate

Slide7: 

Why bacteria die? starvation disease (phages) programmed cell death predation lethal environment

Slide8: 

Phage life cycle

Phage abundances: 

Phage abundances phages are probably the most abundant living entities in the ecosystem sea water 106 - 108/ml fresh water 106 - 108/ml sediments 108 - 109/g soil ND

Slide10: 

phages mediate horizontal gene exchange phages mediate community structure phages influence the flow of energy and carbon Phage role in the ecosystem

Impact of lysogenic viruses on nutrient cycling: 

Impact of lysogenic viruses on nutrient cycling OD660 = 0.5 t (min) control mitomycin C Bacteriophage induction experiment

In vitro phage induction from bacterial isolates: 

In vitro phage induction from bacterial isolates 75 % of all tested strains were lysogenic 51 % of all tested strains were polylysogenic

In situ induction of phages from a sea water samples: 

In situ induction of phages from a sea water samples

Impact of lytic viruses on nutrient cycling: 

Impact of lytic viruses on nutrient cycling

Simulating phage production with and withoutmean free time simplification: 

Simulating phage production with and without mean free time simplification

Phage growth as a function of host density:theoretical versus experimental: 

Phage growth as a function of host density: theoretical versus experimental  host density o phage titer  exponential decay  MFT function  MFT function, Eqn2

Impact of host density on phage latent-period optima: 

Impact of host density on phage latent-period optima

Impact of host quality on latent period optima: 

Impact of host quality on latent period optima  high quality host, control  E-varied  k-varied  R-varied  E + R + k varied

Slide19: 

Why bacteria die? starvation disease (phages) programmed cell death predation lethal environment

What is the benefit for unicellular organism of committing a suicide?: 

What is the benefit for unicellular organism of committing a suicide? no obvious reason unless we consider a unicellular organism as being part of a complex microbial community better use of resources reduced mutation rate (elimination of DNA damaged cells) reducing the impact of infection by pathogens lowering the probability of take over mutants facilitating genetic exchange

Population of Vibrio committing a suicide after entering a stationary phase : 

Population of Vibrio committing a suicide after entering a stationary phase At high cell density in a rich medium a sub population of cells commit suicide. In the lysate viruses are present. At low host density cell in a poor medium there are no viruses present. PYE 5 PYE 2

Survival of rare cells in a population: 

Survival of rare cells in a population sensitivity of the whole population to a programme cell death could eliminate the whole clonal population (a contraproductive strategy) experimentally it is known that the entire population is not sensitive to the external damaging effect (i.e. UV, antbiotics) a random variation of regulator molecules can induce or prevent a suicide program

Survival of rare cells after induction with mitomycin C: 

Survival of rare cells after induction with mitomycin C rich growth conditions poor growth conditions

Pheromones and quorum sensing(a coordinated response to stress environment): 

Pheromones and quorum sensing (a coordinated response to stress environment) cell producing pheromone

Slide25: 

Genetic competence in Bacillus subtilis develops during stationary phase, when 1-10% cells become competent and ready to uptake foreign DNA genetic competence is under nutritional control and cell density control i.e. quorum sensing it is cell last chance to avoid sporulation

Slide26: 

Quorum sensing players in Bacillus subtilis

Pheromone comX specificity test: 

Pheromone comX specificity test producer strain

Slide28: 

Quorum-sensing specificities * Strains are grouped according to phylogenetic relationship

Slide29: 

ComX(s) purification and characterization srfA-lacZ 1- comQ and comX cloning and expression in E. coli 2- Purification by reverse phase chromatography

Slide30: 

ComX(s) characteristics Modification masses are consistent with farnesylation or geranylation of com X in addition ComQ resembles a farnesyl-geranyl transferase

Slide31: 

Why bacteria die? predation lethal environment starvation disease (phages) programmed cell death

Slide32: 

Bacterial and viral loop facilitate nutrient cycling

Slide33: 

Acknowledgements Ivan Mahne Ines Mandič-Mulec Kaja Gnezda Aleša Černe Andrej Žagar Duško Odič Dave Dubnaw, New York University, USA Valentina Turk, National Institute of Biology, SI Mateja Poljšak-Prijatelj, Institute of Microbiology and Immunology, SI Stephen T. Abedon, Ohio State University, USA