Genome sequences of three agrobacterium biovars help elucidate the evolution of multichromosome genomes in bacteria

The family Rhizobiaceae contains plant-associated bacteria with critical roles in ecology and agriculture. Within this family, many Rhizobium and Sinorhizobium strains are nitrogen-fixing plant mutualists, while many strains designated as Agrobacterium are plant pathogens. These contrasting lifestyles are primarily dependent on the transmissible plasmids each strain harbors. Members of the Rhizobiaceae also have diverse genome architectures that include single chromosomes, multiple chromosomes, and plasmids of various sizes. Agrobacterium strains have been divided into three biovars, based on physiological and biochemical properties. The genome of a biovar I strain, A. tumefaciens C58, has been previously sequenced. In this study, the genomes of the biovar II strain A. radiobacter K84, a commercially available biological control strain that inhibits certain pathogenic agrobacteria, and the biovar III strain A. vitis S4, a narrow-host-range strain that infects grapes and invokes a hypersensitive response on nonhost plants, were fully sequenced and annotated. Comparison with other sequenced members of the Alphaproteobacteria provides new data on the evolution of multipartite bacterial genomes. Primary chromosomes show extensive conservation of both gene content and order. In contrast, secondary chromosomes share smaller percentages of genes, and conserved gene order is restricted to short blocks. We propose that secondary chromosomes originated from an ancestral plasmid to which genes have been transferred from a progenitor primary chromosome. Similar patterns are observed in select Beta- and Gammaproteobacteria species. Together, these results define the evolution of chromosome architecture and gene content among the Rhizobiaceae and support a generalized mechanism for second-chromosome formation among bacteria.

How the measurement of residual volume developed after Davy (1800)

H. Davy measured the residual volume of his own lungs in 1800, by inhaling a hydrogen mixture contained in a mercurial air holder. Using the same principle, Nestor Grehant determined the functional residual capacity, and the volume of the dead space, in 1864. Both used a forced breathing method, that was substituted by a prolonged dilution method by D.D. Van Slyke and C.A.L. Binger in 1923. It was in 1941 that G.R. Meneely and M.L. Kaltreider replaced hydrogen with helium. The open circuit nitrogen washout method was proposed by R.E. Darling, A. Cournand and D.W. Richards in 1940, and the body plethysmograph by A.B. DuBois et al. in 1956. So the three methods, still in common use today for measuring the static lung volumes, had been described by the mid-1950s.

Stereological estimation of blood vessel surface and volume densities in human normal and rhinitic nasal mucosa

A technique is proposed for applying well-established stereological methods to study fixed nasal biopsy material to obtain an unbiased estimate of blood vessel surface and volume densities. Biopsies of the nasal mucosa from the anterior 10 mm of an inferior turbinate were obtained from 18 subjects (15 males, 3 females with a mean age of 28.5 years [range: 17-54 years]), ten of whom had perennial allergic rhinitis, and eight control subjects. The mucosal tissue volumes were estimated by water displacement. Zamboni's-fixed cryostat sections (10 microns thick), stained with haematoxylin and eosin, were examined histologically. Computerised images of randomly selected tissue sections were analysed with point-counting and intercept-counting techniques to determine large blood vessel volume and surface densities, respectively. There were no significant differences between the volumes of tissue analysed from the control and rhinitic subjects (p = 0.35). The average volume density of the vessels was similar in the control group (6.17 +/- 1.41%) and the rhinitic group (7.8 +/- 5.59%; p = 0.38), but with a greater variability in the rhinitic group. Surface density estimations were 3.14 +/- 0.74 mm-1 in the control group and 3.10 +/- 1.41 mm-1 in the rhinitic group. Therefore, on average, the volume and surface densities of the cavernous blood vessels in rhinitis were unaltered and there was no evidence of vascular remodelling.

Urinary N tau-methylimidazole acetic acid excretion in respiratory disease

N tau-methylimidazole acetic acid (N tau-MIAA) is the principal urinary metabolite of histamine. The basal urinary excretion rate of N tau-MIAA was determined as 0.117 +/- 0.008 (SE) mg/h, with a renal clearance for N tau-MIAA of 273 +/- 27 ml/min implying active secretion. After subpharmacological infusion of histamine (50 ng.kg-1.min-1 over 2 h) in five volunteers that increased plasma histamine from 0.28 +/- 0.04 to 0.71 +/- 0.15 ng/ml, urinary excretion of N tau-MIAA over 8 h was increased by less than 17% compared with a control saline infusion. Urinary N tau-MIAA excretion in normal controls (273 +/- 14 micrograms/mmol creatinine) was similar to that observed in patients with severe acute asthma (253 +/- 22 micrograms/mmol), antigen-induced bronchoconstriction (269 +/- 21 micrograms/mmol), seasonal allergic rhinitis (304 +/- 31 micrograms/mmol), and clinically stable bronchiectasis (270 +/- 22 micrograms/mmol). In contrast, large increases in metabolite excretion (greater than 7,000 micrograms/mmol creatinine) were observed in a patient with systemic mastocytosis where very high plasma histamine levels were recorded (greater than 500 ng/ml) and marked systemic hemodynamic effects occurred. We conclude that urinary N tau-MIAA will only be increased in pathologies where sustained hyperhistaminemia occurs and that increased local histamine production in the lung or the upper airway does not cause a measurable change in the basal urinary excretion of this metabolite.

Assessment of induced bronchoconstriction in anesthetized cats by the end-inflation occlusion method

Airway occlusion during constant flow inflation allows rapid determination of frequency-dependence of pulmonary resistance by estimating its extreme values: RL,max (zero frequency) and RL,min (high frequency). RL,max represents the maximum resistance value that can be obtained with the prevailing time constant inequalities and stress relaxation, while RL,min represents the resistance that would be obtained in the absence of time constant inequalities and stress relaxation. In 5 anesthetized, tracheostomized, paralyzed, and artificially ventilated cats, RL,min, RL,max, and static pulmonary elastance (EL,st) have been measured following airway occlusion at the end of constant flow tidal inflations. Measurements were made before and during continuous infusion of increasing doses of serotonin (10-100 micrograms/kg/min IV). The development of intrinsic positive end-expiratory pressure (PEEPi) was also assessed. Cats varied greatly in their responsiveness to serotonin, but RL,min, RL,max, and EL,st increased and PEEPi developed in all cats. Increases in RL,max did not always parallel increases in RL,min but were similar to those in EL,st, suggesting that altered viscoelastic properties of the lung contributed to the increases in RL,max. We conclude that time-constant inequalities, changes in the lung periphery, and hyperinflation probably all contribute to the observed increases in RL,max and will influence conventional methods of measuring RL. Measuring RL,min potentially provides a better method for assessing the reduction in caliber of the conducting airways in isolation.

Postural changes in rib cage and abdominal volume-motion coefficients and their effect on the calibration of a respiratory inductance plethysmograph

Volume-motion coefficients were determined for the rib cage and abdomen in normal human subjects in upright, supine, and semirecumbent postures by the isovolume calibration technique of Konno and Mead (J Appl Physiol 1967; 22:407-422, using the respiratory inductive plethysmograph (RIP) to measure displacements of rib cage and abdominal walls. Volume motion coefficients changed systematically with posture; those for the rib cage were smallest in the upright posture, and for the abdomen, greatest in the upright posture. These volume motion coefficients were then used to estimate tidal volume during resting breathing in the different postures, and compared with estimates of tidal volume derived from calibration by the change in posture technique reported by Sackner and coworkers (American Review of Respiratory Disease 1980; 122:867-871). Estimates of tidal volume derived from RIP signals using both calibration techniques were compared with independently measured spirometric volume changes. Errors in tidal volume averaged 6% with the isovolume technique and 9 to 23% with the change in posture technique (depending upon whether the calibrating postures were upright, supine or semirecumbent supine). The larger errors with the change in posture calibration method are attributable to both the change in volume motion coefficients with posture and the change in distribution of tidal volume between rib cage and abdomen compartments with change in posture.