Selection of nitrogen-fixing deficient Burkholderia vietnamiensis strains by cystic fibrosis patients: involvement of nif gene deletions and auxotrophic mutations

Burkholderia vietnamiensis is the third most prevalent species of the Burkholderia cepacia complex (Bcc) found in cystic fibrosis (CF) patients. Its ability at fixing nitrogen makes it one of the main Bcc species showing strong filiations with environmental reservoirs. In this study, 83% (29 over 35) of the B. vietnamiensis CF isolates and 100% of the environmental ones (over 29) were found expressing the dinitrogenase complex (encoded by the nif cluster) which is essential in N 2 fixation. Among the deficient strains, two were found growing with ammonium chloride suggesting that they were defective in N 2 fixation, and four with amino acids supplements suggesting that they were harbouring auxotrophic mutations. To get insights about the genetic events that led to the emergence of the N 2 -fixing defective strains, a genetic analysis of B. vietnamiensis nitrogen-fixing property was undertaken. A 40-kb-long nif cluster and nif regulatory genes were identified within the B. vietnamiensis strain G4 genome sequence, and analysed. Transposon mutagenesis and nifH genetic marker exchanges showed the nif cluster and several other genes like gltB (encoding a subunit of the glutamate synthase) to play a key role in B. vietnamiensis ability at growing in nitrogen-free media. nif cluster DNA probings of restricted genomic DNA blots showed a full deletion of the nif cluster for one of the N 2 -fixing defective strain while the other one showed a genetic organization similar to the one of the G4 strain. For 17% of B. vietnamiensis clinical strains, CF lungs appeared to have favoured the selection of mutations or deletions leading to N 2 -fixing deficiencies.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75167/1/j.1462-2920.2007.01240.x.pd

A volumetric comparison of the insular cortex and its subregions in primates

The neuronal composition of the insula in primates displays a gradient, transitioning from granular neocortex in the posterior-dorsal insula to agranular neocortex in the anterior-ventral insula with an intermediate zone of dysgranularity. Additionally, apes and humans exhibit a distinctive subdomain in the agranular insula, the frontoinsular cortex (FI), defined by the presence of clusters of von Economo neurons (VENs). Studies in humans indicate that the ventral anterior insula, including agranular insular cortex and FI, is involved in social awareness, and that the posterodorsal insula, including granular and dysgranular cortices, produces an internal representation of the body's homeostatic state. We examined the volumes of these cytoarchitectural areas of insular cortex in 30 primate species, including the volume of FI in apes and humans. Results indicate that the whole insula scales hyperallometrically (exponent = 1.13) relative to total brain mass, and the agranular insula (including FI) scales against total brain mass with even greater positive allometry (exponent = 1.23), providing a potential neural basis for enhancement of social cognition in association with increased brain size. The relative volumes of the subdivisions of the insular cortex, after controlling for total brain volume, are not correlated with species typical social group size. Although its size is predicted by primate-wide allometric scaling patterns, we found that the absolute volume of the left and right agranular insula and left FI are among the most differentially expanded of the human cerebral cortex compared to our closest living relative, the chimpanzee