Viral Infection of the Cyanobacterium Cylindrospermopsis raciborskii

Abstract

Viruses play an integral role in the recycling of nutrients and organic carbon through microbial food webs and are a significant cause of bacterial mortality. The aim of this study was to determine whether cyanophage (viruses specific to cyanobacteria) could exert a controlling influence on the potentially toxic cyanobacterium Cylindrospermopsis raciborskii (host) abundance. C. raciborskii was isolated from Lake Samsonvale Brisbane, Queensland, and cultured in a modified Jaworski growth medium from which nitrogen was removed. After sonication and filtration, the water sample containing the natural viral population was incubated with C. raciborskii and grown under optimal light and temperature. Within seven days, the host's abundance decreased by 86% and viral numbers had doubled. The cyanophage replication time was 9 hours, with an average burst size of 33 viral particles per host cell. Transmission Electron Microscopy morphologically identified for the first time, a cyanophage specific to C. raciborskii as having long non-contractile tail and a capsid diameter of 70nm belonging to the Siphoviridae family of viruses which we have called cyanophage Cr-LS. The result of this study shows that cyanophage can control the abundance of C. raciborskii in freshwater aquatic ecosystems and ultimately change the structural dynamics of the microbial population in Lake Samsonvale.