Skeletal muscle glutamine metabolism during sepsis in the rat

1. The effect of sepsis, induced by caecal ligation plus puncture (CLP) or endotoxin injection, on glutamine metabolism was studied in rat skeletal muscle. 2. The concentration of glutamine in muscle was decreased by CLP or after 24 or 48 hr after injection of endotoxin. However, the concentration was increased 3 hr after injection of endotoxin. 3. The plasma glutamine concentration was decreased by CLP, but it was unchanged after injection of endotoxin. 4. The rate of glutamine release from incubated stripped soleus muscles was increased in the muscles removed from animals subjected to CLP or from animals injected with endotoxin. 5. It is concluded that sepsis results in marked changes in skeletal muscle glutamine metabolism, which may be used as an early indicator of the septic state. During sepsis there is likely to be an increased demand for glutamine by the immune system, kidney and intestine. 6. This study provides evidence that during sepsis the rate of release of glutamine from the skeletal muscle per se is increased to a sufficient extent to satisfy this increased requirement.     

Effects of forest disturbance on the structure of ground-foraging ant communities in central Amazonia

This study evaluates biotic responses, using ants as bio-indicators, to relatively recent anthropogenic disturbances to mature forest in central Amazonia. The structure of the ground-foraging ant community was compared in four habitats that represented a gradient of disturbance associated with differences in land use. Ants were collected in undisturbed, mature forest, in an abandoned pasture, in a young regrowth forest (situated in a former pasture area), and in an old regrowth forest (established where mature forest was just cleared and abandoned). More ant species were found in mature and old regrowth forest than in the abandoned pasture. By contrast, ant abundance tended to decrease with forest maturity. Both pasture and young regrowth forest exhibited a distinct ant species composition compared to mature forest, whereas species composition in the old regrowth forest showed greater similarity to that of mature forest. In spite of differences in fallow time between former pasture areas and non-pasture areas, there is evidence that different land-management practices do result in different rates of recovery of the ant forest fauna after land abandonment. In any case, recuperation of the ground-foraging ant fauna appears to be faster than regeneration of the woody-plant community. In this sense, regrowth forests may be valuable for the conservation of ground-foraging ants and perhaps for other components of mature-forest leaf-litter fauna within the context of a fragmented landscape.     

Ants and plant size shape the structure of the arthropod community of Hirtella myrmecophila, an Amazonian ant-plant

Abstract.  1. To investigate the influence of plant size and the presence of resident ants on the arthropod community associated with the ant-plant Hirtella myrmecophila , ants ( Allomerus octoarticulatus ) were experimentally removed from plants of various sizes, with a second group of similar-sized plants remaining as controls. The abundance and diversity of arthropods on these plants were determined at 45-day intervals for 7 months. Collected arthropods were assigned into one of three predetermined groups: herbivores, spiders (mostly web-building spiders), or 'tourists' (mostly non-resident ants, hemipterans, dipterans, or scarabeid beetles).
2. Ant removal had a positive influence on the abundance and diversity of herbivores, but no measurable effects on the abundance and diversity of 'tourists', while the effect on spider abundance was significant only when data from Dipoena sp. nov. were removed from the analysis. While A. octoarticulatus had a negative effect on most spiders, it favoured Dipoena sp. nov., which was found to be a specialist predator of A. octoarticulatus .
3. Plant size positively affected the abundance and diversity of 'tourists' in plants with and without ants, but for herbivores and spiders this effect was dependent on ant treatment. In ant-maintained plants the per-plant abundance of herbivores and spiders was independent of plant size, whereas in ant-removed plants it was not.
4. These results suggest that A. octoarticulatus affects all arthropods found on its host plant, except those presenting an occasional and temporary association with the plant, and that the magnitude of ant effects on the susceptible guilds increases as plant size increases.     

Differences in growth and water relations among Phaseolus vulgaris cultivars in response to induced drought stress

Relatively little ecophysiological research has been conducted to determine the responses to drought of Phaseolus vulgaris. Four bean cultivars (cvs.) from Brazil, A320, Carioca, Ouro Negro and Xodó were submitted to an imposed water deficit in order to evaluate the importance of some adaptive mechanisms of drought resistance through the analysis of growth parameters, water status, gas exchange and indicators of tolerance mechanisms at the cellular level. During the drought treatment, relative growth rates were more reduced for A320 and Xodó than Carioca and Ouro Negro. A320 closed its stomata very rapidly and complete stomatal closure was obtained at Psi(w)=-0.6 MPa, in contrast to the other cvs. where stomata were fully closed only at Psi(w)=-0.9 MPa. Net assimilation rates were closely related to stomatal conductances. Mechanisms at the cellular level appeared to be mostly important for higher tolerance. Carioca and Ouro Negro, when compared to A320 and Xodó, were characterized by having better drought tolerance mechanisms and higher tissue water retention capacity leading to a better growth under water deficits. The leaf dehydration rates of those cvs. were slow whereas those of the drought sensitive cvs. were rapid. The results were confirmed by the electrolyte leakage test and leaf osmotic potential measurements, which indicated higher membrane resistance and osmotic adjustment in the two tolerant cvs. Carioca and Ouro Negro. It appears from this study that despite being cultivated in the same geographical region, the four cvs. of P. vulgaris displayed somewhat different drought adaptive capacities for prolonged drought during the vegetative phase.     

Metabolic engineering of Clostridium acetobutylicum for the industrial production of 1,3-propanediol from glycerol

Clostridium butyricum is to our knowledge the best natural 1,3-propanediol producer from glycerol and the only microorganism identified so far to use a coenzyme B12-independent glycerol dehydratase. However, to develop an economical process of 1,3-propanediol production, it would be necessary to improve the strain by a metabolic engineering approach. Unfortunately, no genetic tools are currently available for C. butyricum and all our efforts to develop them have been so far unsuccessful. To obtain a better "vitamin B12-free" biological process, we developed a metabolic engineering strategy with Clostridium acetobutylicum. The 1,3-propanediol pathway from C. butyricum was introduced on a plasmid in several mutants of C. acetobutylicum altered in product formation. The DG1(pSPD5) recombinant strain was the most efficient strain and was further characterized from a physiological and biotechnological point of view. Chemostat cultures of this strain grown on glucose alone produced only acids (acetate, butyrate and lactate) and a high level of hydrogen. In contrast, when glycerol was metabolized in chemostat culture, 1,3-propanediol became the major product, the specific rate of acid formation decreased and a very low level of hydrogen was observed. In a fed-batch culture, the DG1(pSPD5) strain was able to produce 1,3-propanediol at a higher concentration (1104 mM) and productivity than the natural producer C. butyricum VPI 3266. Furthermore, this strain was also successfully used for very long term continuous production of 1,3-propanediol at high volumetric productivity (3 g L-1 h-1) and titer (788 mM).