A Simple Screen to Identify Promoters Conferring High Levels of Phenotypic Noise

Genetically identical populations of unicellular organisms often show marked variation in some phenotypic traits. To investigate the molecular causes and possible biological functions of this phenotypic noise, it would be useful to have a method to identify genes whose expression varies stochastically on a certain time scale. Here, we developed such a method and used it for identifying genes with high levels of phenotypic noise in Salmonella enterica ssp. I serovar Typhimurium (S. Typhimurium). We created a genomic plasmid library fused to a green fluorescent protein (GFP) reporter and subjected replicate populations harboring this library to fluctuating selection for GFP expression using fluorescent-activated cell sorting (FACS). After seven rounds of fluctuating selection, the populations were strongly enriched for promoters that showed a high amount of noise in gene expression. Our results indicate that the activity of some promoters of S. Typhimurium varies on such a short time scale that these promoters can absorb rapid fluctuations in the direction of selection, as imposed during our experiment. The genomic fragments that conferred the highest levels of phenotypic variation were promoters controlling the synthesis of flagella, which are associated with virulence and host–pathogen interactions. This confirms earlier reports that phenotypic noise may play a role in pathogenesis and indicates that these promoters have among the highest levels of noise in the S. Typhimurium genome. This approach can be applied to many other bacterial and eukaryotic systems as a simple method for identifying genes with noisy expression

Contemporary educational argumentation: A multimodal perspective

In contemporary educational contexts there is considerable variation in how argumentation works and what forms and styles it takes. Influencing factors include the educational purpose and task, the level of education, and the discipline or curriculum subject in which it occurs. This paper offers a theoretical framework and a set of multimodal analytical tools which can provide a rich and systematic account of such variation. Using naturalistic data from three different educational sites I illustrate how such a framework reveals the diverse ways in which students use language and other modes of meaning making as they engage in processes of argumentation. In particular, I consider how new technologies have caused shifts in the distribution of meaning across different semiotic modes (such as visual images, space, colour and graphics) and how this impacts upon both argumentation process and product. The educational implications of such changes are also considered