Symbionts often exhibit significant reductions in genome complexity while pathogens often exhibit increased complexity through acquisition and diversification of virulence determinants. A few organisms have evolved complex life cycles in which they interact as symbionts with one host and pathogens with another. How the predicted and opposing influences of symbiosis and pathogenesis affect genome evolution in such instances, however, is unclear. The Polydnaviridae is a family of double-stranded (ds) DNA viruses associated with parasitoid wasps that parasitize other insects. Polydnaviruses (PDVs) only replicate in wasps but infect and cause severe disease in parasitized hosts. This disease is essential for survival of the parasitoid's offspring. Thus, a true mutualism exists between PDVs and wasps as viral transmission depends on parasitoid survival and parasitoid survival depends on viral infection of the wasp's host. To investigate how life cycle and ancestry affect PDVs, we compared the genomes of Campoletis sonorensis ichnovirus (CsIV) and Microplitis demolitor bracovirus (MdBV). CsIV and MdBV have no direct common ancestor, yet their encapsidated genomes share several features including segmentation, diversification of virulence genes into families, and the absence of genes required for replication. In contrast, CsIV and MdBV share few genes expressed in parasitized hosts. We conclude that the similar organizational features of PDV genomes reflect their shared life cycle but that PDVs associated with ichneumonid and braconid wasps have likely evolved different strategies to cause disease in the wasp's host and promote parasitoid survival.

The ruminal microbiome of cattle plays an important role not only in animal health and productivity but also in food safety and environment. Microbial profiles of rumen fluid obtained from dairy cows fed on three different fiber/starch diet compositions were characterized. Tagged 16S rRNA gene pyrosequencing and statistical analysis revealed that the dominant ruminal bacteria shared by all three sample groups belonged to phyla Bacteroidetes, Firmicutes, and Proteobacteria. However, the relative abundance of these bacterial groups was markedly affected by diet composition. In animals fed with a high fiber diet, the fibrolytic and cellulolytic bacteria Lachnospiraceae, Ruminococcaceae, and Fibrobacteraceae were found in highest abundance compared with animals fed other diets with lower fiber content. The polysaccharide-degrading Prevotellaceae and Flavobacteriaceae bacteria were most abundant in the rumen of cows fed on diet with the highest starch content. These data highlight the ruminal microbiome's ability to adapt to feed composition and also provide a basis for the development of feed formulation systems designed to improve livestock productivity.

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diminished activity to a lesser degree. The point mutants Y11A, T14A, T22A, and F23A had activity identical or only slightly reduced to that of wild-type PSP. The mutant PSP-(7-23) lacked the entire unstructured domain of PSP and was found to have no plasmatocyte spreading activity. Surprisingly, E1A and N2A had higher activity than wild-type PSP, but F3A had almost no activity. We thus concluded that the lack of activity for PSP-(7-23) was largely due to the critical importance of Phe 3 . To determine whether reductions in activity correlated with alterations in tertiary structure, we compared the C7.19A, R13A, R18A, and F3A mutants to wildtype PSP by NMR spectroscopy. As expected, the simultaneous replacement of Cys 7 and Cys 19 profoundly affected tertiary structure, but the R13A, R18A, and F3A mutants did not differ from wild-type PSP. Collectively, these results indicate that residues in both the unstructured and structured domains of PSP are required for plasmatocyte-spreading activity.

Plasmatocyte-spreading peptide (PSP) is a 23-amino acid cytokine that activates a class of insect immune cells called plasmatocytes. The tertiary structure of PSP consists of an unstructured N terminus (residues 1-6) and a well structured core (residues 7-23). A prior study indicated that deletion of the N terminus from PSP eliminated all biological activity. Alanine substitution of the first three residues (Glu 1 -Asn 2 -Phe 3 ) further indicated that only replacement of Phe 3 resulted in a loss of activity equal to the N-terminal deletion mutant. Here, we characterized structural determinants of the N terminus. Adding a hydroxyl group to the aromatic ring of Phe 3 (making a Tyr) greatly reduced activity, whereas the addition of a fluorine (p-fluoro) did not. Substitutions that changed the chirality or replaced the aromatic ring of Phe 3 with a branched aliphatic chain (making a Val) also greatly decreased activity. The addition of a methylene group to Val (making a Leu) partially restored activity, whereas the removal of a methylene group from Phe (phenyl-Gly) eliminated all activity. These results indicated that a branched carbon chain with a methylene spacer at the third residue is the minimal structural motif required for activity. The deletion of Glu 1 also eliminated activity. Additional experiments identified the charged N-terminal amine and backbone of Glu 1 as key determinants for activity.