Plasmids and Rickettsial Evolution: Insight from Rickettsia felis

BACKGROUND: The genome sequence of Rickettsia felis revealed a number of rickettsial genetic anomalies that likely contribute not only to a large genome size relative to other rickettsiae, but also to phenotypic oddities that have confounded the categorization of R. felis as either typhus group (TG) or spotted fever group (SFG) rickettsiae. Most intriguing was the first report from rickettsiae of a conjugative plasmid (pRF) that contains 68 putative open reading frames, several of which are predicted to encode proteins with high similarity to conjugative machinery in other plasmid-containing bacteria. METHODOLOGY/PRINCIPAL FINDINGS: Using phylogeny estimation, we determined the mode of inheritance of pRF genes relative to conserved rickettsial chromosomal genes. Phylogenies of chromosomal genes were in agreement with other published rickettsial trees. However, phylogenies including pRF genes yielded different topologies and suggest a close relationship between pRF and ancestral group (AG) rickettsiae, including the recently completed genome of R. bellii str. RML369-C. This relatedness is further supported by the distribution of pRF genes across other rickettsiae, as 10 pRF genes (or inactive derivatives) also occur in AG (but not SFG) rickettsiae, with five of these genes characteristic of typical plasmids. Detailed characterization of pRF genes resulted in two novel findings: the identification of oriV and replication termination regions, and the likelihood that a second proposed plasmid, pRFδ, is an artifact of the original genome assembly. CONCLUSION/SIGNIFICANCE: Altogether, we propose a new rickettsial classification scheme with the addition of a fourth lineage, transitional group (TRG) rickettsiae, that is unique from TG and SFG rickettsiae and harbors genes from possible exchanges with AG rickettsiae via conjugation. We offer insight into the evolution of a plastic plasmid system in rickettsiae, including the role plasmids may have played in the acquirement of virulence traits in pathogenic strains, and the likely origin of plasmids within the rickettsial tree

Seasonal variation at four loci in a continuously breeding population of Danaus plexippus L.

Temporal genetic variation in a continuously breeding population of monarch butterflies, Danaus plexippus, was assessed by sampling two milkweed patch sites for about 2 years. Variation was determined at four loci; Pgm, Pgi, Idh and Hbdh. Large changes in heterozygote and allele frequencies where observed between sample dates and between dates grouped into three 'seasons' (early summer, late summer, and winter). Both sites showed similar changes, but the question of 'seasonality' will require a longer period of study

Anionic transporters and channels in pancreatic islet cells

After a brief description of the so-called consensus hypothesis for the mechanism of stimulus-secretion coupling in the process of glucose-induced insulin release, the present chapter, which deals with anionic transporters and channels in pancreatic islet cells, concerns mainly a second modality for the control of insulin secretion by the hexose. In such a perspective, it draws attention to the NBCe1 Na+/HCO3−cotransporters, the volume-regulated anion channel hypothesis, the experimental model of extracellular hypotonicity, the possible role of NAD(P)H oxidase-derived H2O2 in the activation of volume-regulated anion channels in β-cells exposed to a hypotonic medium, the identity of the anions concerned by the volume-regulated anion channel hypothesis, the expression and function of anoctamin 1 in rodent and human pancreatic islet cells, the possible role of bicarbonate-activated soluble adenylyl cyclase, the identity and role of aquaporins in insulin-producing cells, and a proposed role for volume-regulated anion channels in glucagon secretion.SCOPUS: ch.binfo:eu-repo/semantics/publishe