AME 78:11-23 (2016)  -  DOI: https://doi.org/10.3354/ame01800

ABSTRACT: A lytic virus that infects a European strain of the freshwater filamentous cyano-bacterium Cylindrospermopsis raciborskii was isolated from a lake in the Netherlands and partially characterised. With a genome size of 110 ± 15 kb, an icosahedral capsid of 65 ± 1 nm (n = 22) and a long non-contractile tail of 612 ± 31 nm (n = 15), this dsDNA cyanophage CrV appears to belong to the Siphoviridae family. CrV was highly host specific, not infecting other filamentous cyanobacteria species isolated from the same lake, nor 4 Australian strains of C. raciborskii. The latent period of this cyanophage was 20-24 h. Varying the irradiance affected cyanophage-host interactions: at low light (20 µmol quanta m^-2 s^-1) the latent period was 1.3 times longer compared with at mid light (90 µmol quanta m^-2 s^-1); burst size at mid light was 332 CrV per lysed host cell, at low light it was halved (48%) and at high light (250 µmol quanta m^-2 s^-1) the burst size was further reduced to only 14% of that of mid light. Temperature also affected the virus growth characteristics: the CrV latent period at high temperature (30°C) was reduced to just 11% (compared with a mid temperature of 22°C), but still the burst size increased to 541 CrV per lysed host cell; at low temperature (15°C) the latent period was prolonged 1.3-fold and the burst size was reduced to 43%. Our findings indicate that ecologically relevant environmental factors can affect the extent of viral lysis of C. raciborskii, advancing our understanding of the spread of this invasive cyanobacterium across Europe.

KEY WORDS: Invasive cyanobacteria · Cyanophage · Freshwater · Latent period · Burst size · Temperature · Light