Cyanobacteria-cyanophage Interactions in Continuous Culture

When the filamentous Plectonema boryanum 594 or the unicellular Aphanothece stagnina were grown in chemostats with phages LPP-DUN1 and Aph-1, respectively, an initial series of reciprocal oscillations in cyanobacterial and phage numbers occurred; their magnitudes decreased successively until an equilibrium population of cyanobacteria and virus was established in each system. Evolution of the protagonists occurred as the interactions proceeded. Most of the A. stagnina population appeared resistant to Aph-1 at the end of the experiment. Two types of resistant P. boryanum , designated PR1 and PR2, were isolated. PR1 was resistant to wild-type LPP-DUN1 but susceptible to a mutant phage; PR2 was unaffected by the phage. The sequence of appearance and interaction of mutant phage and P. boryanum accounted for the initial fluctuations in population numbers, and the coexistence of host and pathogen in the climax population. Plectonema boryanum PR2 grew more slowly than wild-type, or PR1 and competed poorly with them in the absence of phage. The ecological implications of the results are discussed.     

Expressed sequence tags from the flower pathogen Claviceps purpurea

The ascomycete Claviceps purpurea (ergot) is a biotrophic flower pathogen of rye and other grasses. The deleterious toxic effects of infected rye seeds on humans and grazing animals have been known since the Middle Ages. To gain further insight into the molecular basis of this disease, we generated about 10 000 expressed sequence tags (ESTs)—about 25% originating from axenic fungal culture and about 75% from tissues collected 6–20 days after infection of rye spikes. The pattern of axenic vs. in planta gene expression was compared. About 200 putative plant genes were identified within the in planta library. A high percentage of these were predicted to function in plant defence against the ergot fungus and other pathogens, for example pathogenesis-related proteins. Potential fungal pathogenicity and virulence genes were found via comparison with the pathogen–host interaction database (PHI-base; http://www.phi-base.org ) and with genes known to be highly expressed in the haustoria of the bean rust fungus. Comparative analysis of Claviceps and two other fungal flower pathogens (necrotrophic Fusarium graminearum and biotrophic Ustilago maydis ) highlighted similarities and differences in their lifestyles, for example all three fungi have signalling components and cell wall-degrading enzymes in their arsenal. In summary, the analysis of axenic and in planta ESTs yielded a collection of candidate genes to be evaluated for functional roles in this plant–microbe interaction.