The Paradox of the Viroplankton: High Viral Abundance and Resistance to Infection

鲍尔病毒是浮游生物中数量最多的组成部分，通常比原核生物和真核生物多十倍。在大多数水生系统中，细菌和病毒之间存在一种稳定的状态，而细菌或蓝藻宿主群体不会崩溃。因为噬菌体的感染性在地表水中腐烂得相对较快，所以必须同样迅速地重新供应新的噬菌体。然而，蓝藻(也许还有异养细菌)在很大程度上对噬菌体感染具有抵抗力。在有抗药性的宿主群体存在的情况下，如何才能持续生产噬菌体？在这个项目中检验的假设是，浮游细菌在高病毒丰度存在的情况下仍然存在，因为裂解噬菌体已经选择了对感染具有抵抗力的群落。另外，浮游细菌(包括蓝藻)由于溶原性和假溶原性所产生的同源免疫而持续存在高病毒丰度。为了验证这些假设，该项目将致力于以下目标：1.利用培养中的分离株确定裂解、假溶源和溶源存在模式之间的关系。2.确定在自然微生物种群中是否发生了溶源和裂解存在之间的转变，如坦帕湾的微生物种群。3.确定海洋聚球菌分离株中溶原性的流行情况。我们将通过丝裂霉素C和/或紫外线暴露来检测一系列含有藻红蛋白和非PE的菌株以及我们从墨西哥湾分离的菌株是否存在原噬菌体，并将使用这些菌株来了解蓝藻中溶原性的过程。4.确定溶原性或假溶原性是聚球藻自然种群的耐药机制。这项研究的结果可能会极大地改变我们对微生物循环中病毒的理解，从永远攻击宿主的裂解实体到高度进化的共生关系的共同参与者，这种共生关系可能会因环境提示而从毒力转换为温带存在。

9811319PaulViruses are the most numerous component of the plankton, often ten-fold more abundant than their procaryotic and eucaryotic counterparts. In most aquatic systems, a steady state exists between bacteria and viruses without collapse of the bacterial or cyanobacterial host populations. Because the infectivity of phages decays relatively quickly in surface waters, there must be an equally rapid re--supply of new phages. However, the cyanobacteria (and perhaps the heterotrophic bacteria) are largely resistant to phage infection. How can there be constant phage production in the presence of a resistant host population? The hypothesis tested in this project is that bacterioplanlkon persist in the presence of high viral abundance because lytic phages have selected for a community that is resistant to infection. Alternatively, bacterioplankton (including cyanobacteria) persist in the presence of high viral abundance because of homo-immunity conferred by lysogeny and pseudolysogeny. To test these hypotheses, the project will work toward the following objectives: 1. To determine the relationship between lytic, pseudolysogenic, and lysogenic modes of existence using isolates in culture. 2. To determine if the transition between lysogeny and lytic existence occurs in natural microbial populations such as those occurring in Tampa Bay. 3. To determine the prevalence of lysogeny amongst marine Synechococcus isolates. We will examine a series of phycoerythrin containing and non-PE containing strains from culture collections as well as our own isolates from the Gulf of Mexico for the presence of prophage by mitomycin C and/or UVC exposure, and will use these strains to understand the process of lysogeny in cyanobacteria. 4. To determine if lysogeny or pseudolysogeny is the mechanism of resistance in natural Populations of Synechococcus. The results obtained from this study may substantially alter our understanding of viruses in the Microbial Loop, from lytic entities that perpetually attack their hosts to co-participants in a highly evolved symbiosis that may switch from virulence to temperate existence in response to environmental cues.