Several Physiological And Ecological Characters Of Freshwater Cyanophage

Investigation in details on a freshwater cyanophage isolated in China infecting Plectonema and Phormidium is presented in this thesis. Under Trasmission Electronic Microscope (TEM), the cyanophage showed a bacteria-phage shape with head diameter at 52nm and short tail (almost invisible). Several methods for measuring the lysing cycle and burst size of the cyanophage were tested. It was established that cell counting method was more convenient and exact for confirming the lysing cycle. Burst size obtained by 1 PFU infecting was reliable. More studies were conducted on both the physiology and ecology of the cyanophage.Results involved in the physiological characters are as below: the cycle of lysing Plectonema at 28 癈 was 4hrs, including 3hrs of patent period and Ihr of lysing period. The burst size of the cyanophage was ca. 200 PFU ?Cell"1. The rate of adsorption to host was markedly higher under light condition than that under dark condition (P=0.02), and light was necessary for infection. Moreover, the adsorption rate was affected by the growth of host: it became greater along with the host growth and reached the maxium at stable stage. During infection, the photosynthetic oxygen releasing rate decreased drastically. The activity of cyanophage changed under different temperatures: 100% activity remained at 40癈 for lOmin, more than 75% at 50癈 for Imin, 60% at 50癈for lOmin, 15% at 60癈 for Imin and less than 1% at 60癈 for lOmin. It was also indicated that the enlargement of plaque related to the growth of host, i.e, the more rapid the growth, the more notable the enlargement of the plaque.Preliminary studies on the ecological characters of freshwater cyanophage were carried out under both field condition and culturing system. The field investigation result showed that 6 in 19 water samples contained cyanophages lysing plectonema and the lysis phenomenon were readily observed without concentrating the water. Thus it could be presumed that there was a widespread distribution and a high infectivity of cyanophage in nature. Under mixed culturing conditions, it was observed that bacterial number rapidly incre;ised soon after the lysing of hostcells. On the contrary, while the non-host cyanobacterium( i.e. Anabaena flos-aquae) was incubated in the mix culturing system, the breeding of the bacteria could be inhibited. It may be suggested from the result above that cyanophage could bring about the changes in microorganism populations.