Overcoming Obstacles to Evolution Education: Why Bother Teaching Evolution in High School?

Evolution is a foundational organizing principle of the life sciences, and yet people still argue that it should be taught only in college, urging that it’s not necessary, too controversial, or too difficult to teach evolution in high school. Faced with such arguments, teachers and administrators need to have responses. Moreover, they need to teach evolution so that the coverage of evolution in the K-12 curriculum reflects its central place in biology.     

The complete genome sequence of Fibrobacter succinogenes S85 reveals a cellulolytic and metabolic specialist

Fibrobacter succinogenes is an important member of the rumen microbial community that converts plant biomass into nutrients usable by its host. This bacterium, which is also one of only two cultivated species in its phylum, is an efficient and prolific degrader of cellulose. Specifically, it has a particularly high activity against crystalline cellulose that requires close physical contact with this substrate. However, unlike other known cellulolytic microbes, it does not degrade cellulose using a cellulosome or by producing high extracellular titers of cellulase enzymes. To better understand the biology of F. succinogenes, we sequenced the genome of the type strain S85 to completion. A total of 3,085 open reading frames were predicted from its 3.84 Mbp genome. Analysis of sequences predicted to encode for carbohydrate-degrading enzymes revealed an unusually high number of genes that were classified into 49 different families of glycoside hydrolases, carbohydrate binding modules (CBMs), carbohydrate esterases, and polysaccharide lyases. Of the 31 identified cellulases, none contain CBMs in families 1, 2, and 3, typically associated with crystalline cellulose degradation. Polysaccharide hydrolysis and utilization assays showed that F. succinogenes was able to hydrolyze a number of polysaccharides, but could only utilize the hydrolytic products of cellulose. This suggests that F. succinogenes uses its array of hemicellulose-degrading enzymes to remove hemicelluloses to gain access to cellulose. This is reflected in its genome, as F. succinogenes lacks many of the genes necessary to transport and metabolize the hydrolytic products of non-cellulose polysaccharides. The F. succinogenes genome reveals a bacterium that specializes in cellulose as its sole energy source, and provides insight into a novel strategy for cellulose degradation.     

Transposition is modulated by a diverse set of host factors in Escherichia coli and is stimulated by nutritional stress

The role of host factors in regulating bacterial transposition has never been comprehensively addressed, despite the potential consequences of transposition. Here, we describe a screen for host factors that influence transposition of IS903, and the effect of these mutations on two additional transposons, Tn10 and Tn552. Over 20,000 independent insertion mutants were screened in two strains of Escherichia coli; from these we isolated over 100 mutants that altered IS903 transposition. These included mutations that increased or decreased the extent of transposition and also altered the timing of transposition during colony growth. The large number of gene products affecting transposition, and their diverse functions, indicate that the overall process of transposition is modulated at many different steps and by a range of processes. Previous work has suggested that transposition is triggered by cellular stress. We describe two independent mutations that are in a gene required for fermentative metabolism during anaerobic growth, and that cause transposition to occur earlier than normal during colony development. The ability to suppress this phenotype by the addition of fumarate therefore provides direct evidence that transposition occurs in response to nutritional stress. Other mutations that altered transposition disrupted genes normally associated with DNA metabolism, intermediary metabolism, transport, cellular redox, protein folding and proteolysis and together these define a network of host proteins that could potentially allow readout of the cell's environmental and nutritional status. In summary, this work identifies a collection of proteins that allow the host to modulate transposition in response to cell stress.