Stephen Giovannoni教授为5123导航“郑重”杰出访问学者，是海洋微生物生态学领域的国际知名专家。
1984年博士毕业4年后供职俄勒冈州立大学微生物系至今，现为该校特聘教授，同时任百慕大海洋科学研究所兼职教授，美国微生物学会理事会提名委员，知名期刊Annual Reviews of Marine Science (创刊主编)、MBio主编，ISMEJ、Environmental Microbiology副主编。2000-2004年，曾任俄勒冈州立大学分子与细胞生物学项目（Molecular and Cellular Bioglogy Program）主任。
致力于海洋细菌的分离培养和基因组学研究，发明细菌高通量培养技术，成功分离培养上千株海洋细菌，如最为轰动效应的SAR11细菌，同时也是国际上在海洋生态领域运用蛋白质组学和代谢组学的领军人物，树立了SAR11细菌研究领域的权威。至今已发同行评议的论文140余篇，其中20余篇发表在著名期刊Nature、Science和PNAS上。由于其杰出贡献，2012年获美国微生物学会J. Roger Proter奖、国际微生物生态学会Jim Tiedje奖。
Prof. Giovannoni’s personal webpage:http://microbiology.science.oregonstate.edu/dr-stephen-giovannoni
Abstract:
The simplest free-living chemoheterotrophic bacteria known are the SAR11 clade of alphaproteobacteria. Paradoxically, with genome sizes of only 1.2-1.5 Mbp they oxidize 5-20% of all carbon fixed each day on Earth. Recently it has been recognized that small genome size is a common feature of uncultured bacteria from many environments. Small genomes raise questions about the strategies used by chemoheterotrophic cells to interact with complex organic matter. Small cells and genomes have been attributed to selection that favors minimization of cell size and complexity in nutrient-limited systems to reduce the resources required for replication, a process known asstreamlining. Regardless of the cause of genome reduction, lost coding potential eventually dictates loss of function, raising the questions, what genome features are expendable, and how do cells become highly successful with a minimal genomic repertoire? One consequence of reductive evolution in streamlined organisms is atypical patterns of prototrophy, for example the recent discovery of a requirement for the thiamin precursor 4-amino-5-hydroxymethyl-2-methylpyrimidine in some plankton taxa. Examples such as this fit within the framework of the Black Queen Hypothesis, which describes genome reduction that results in reliance on community goods and increased community connectivity. Other examples of genome reduction include losses of regulatory functions, or replacement with simpler regulatory systems, and increased metabolic integration. In one such case, in the orderPelagibacterales, the PIIsystem for regulating responses to N limitation has been replaced with a simpler system composed of fewer genes. Both the absence of common regulatory systems and atypical patterns of prototrophy have been linked to difficulty in culturingPelagibacterales, lending credibility to the idea that streamlining might broadly explain the phenomenon of the uncultured microbial majority. The success of streamlined osmotrophic bacterioplankton suggests that they successfully compete for labile organic matter and capture a large share of this resource, but an alternative theory postulates they are not good resource competitors and instead prosper by avoiding predation. The answers to these complex questions hinge on translating gene frequencies into trait based ecological models that reflect the systems biology of cells.
