Changes in the heat resistance of Salmonella typhimurium during heating at rising temperatures

The heat resistance of Salmonella typhimurium , measured as survival following a standard heat challenge at 55°C for 25 min, increased progressively as cells were heated up at linearly rising temperatures. The amount by which heat resistance increased depended on the rate of temperature rise; the slower the temperature rise, the greater the increase in resistance.     

Body size but not colony size increases with altitude in the holarctic ant,Leptothorax acervorum

1. Bergmann's rule states that organisms inhabiting colder environments show an increase in body size or mass in comparison to their conspecifics living in warmer climates. Although originally proposed for homoeothermic vertebrates, this rule was later extended to ectotherms. In social insects, only a few studies have tested this rule and the results were ambiguous. Here, ‘body size’ can be considered at two different levels (the size of the individual workers or the size of the colony). 2. In this study, data from 53 nests collected along altitudinal gradients in the Alps were used to test the hypotheses that the worker body size and colony size of the ant Leptothorax acervorum increase with increasing altitude and therefore follow Bergmann's rule. 3. The results show that the body size of workers but not the colony size increases with altitude. Whether this pattern is driven by starvation resistance or other mechanisms remains to be investigated.     

The use of vesicular-arbuscular mycorrhizal roots grown by the nutrient film technique as inoculum for field sites

Bean roots grown by the nutrient film technique and infected with vesicular-arbuscular mycorrhizal fungi were successfully used as inoculum for red clover growing in an unsterile field site. The endophyte introduced with the roots became well established in the presence of indigenous mycorrhizal fungi.     

Effect of Hyper-Osmotic Stress On Alanine Content of Leishmania Major Promastigotes

ABSTRACT Earlier studies showed that Leishmania major promastigotes are sensitive to osmotic conditions. A reduction in osmolality caused the cells to shorten and to rapidly release most of their large internal pool of alanine. In this study some effects of hyper-osmotic stress were examined. an increase in osmolality of the culture medium from 308 to 625 mOsm/kg caused only a small decrease in growth rate. When cells grown in the usual culture medium (308 mOsm/kg) were washed, resuspended in iso-osmotic buffer, and subjected to acute hyper-osmotic stress by addition of mannitol, the alanine content increased even in the absence of exogenous substrate. Promastigotes, depleted of alanine by a 5-min exposure to hypo-osmotic conditions, also synthesized alanine when resuspended in iso-osmotic buffer. Washed cells resuspended in iso-osmotic buffer consume their internal pool of alanine under aerobic conditions, Rates of consumption decreased on addition of mannitol, becoming zero at about 440 mOsm/kg. At higher osmolalities, alanine synthesis occurred. to estimate whether proteolysis could account for alanine synthesis in the absence of exogenous substrate, cells that had been grown with [1-¹⁴C]leucine were washed and resuspended under hypo-, iso-, and hyper-osmotic conditions and the amounts of ¹⁴CO₂ and ¹⁴C-labelled peptides released in 1 h were measured. Little proteolysis occurred under these conditions, but the possibility that proteolysis was the source of the alanine increase, observed in response to hyper-osmotic stress, cannot be ruled out.     

Metabolism of α-Glyceryl Ethers by Crithidia fasciculata. I. Study of the In Vivo Degradation of Exogenous Chimyl and Batyl Alcohols1

ABSTRACT. [¹⁴C]chimyl and [³H]batyl alcohols were added to Crithidia fasciculata cultures during the mid-log phase of cell growth, and the lipid extracts of the cells were analyzed for degradation products. C. fasciculata cells were able to take up exogenous glyceryl ethers, and in amounts as high as the endogenous lipid content. The glyceryl ether taken up by the cells was incorporated into lipids either prior to the ether bond cleavage or after degradation to fatty acid. The extent of degradation and the degree of incorporation of degradation products into cellular lipid were higher for chimyl than for batyl alcohol. Batyl alcohol was not metabolized efficiently, leading to the formation of large intracellular pools of free substrate. One product of glyceryl ether degradation was identified as alkyl-dihydroxy acetone, and was detected inside and outside of the cells. The data strongly suggest that this product is the first stable intermediate in the degradation process and indicate that the extracellular formation of alkyl-dihydroxy acetone is due to the action of exocnzyme; ecteted by the cells. The constant detection of alk I cnyl glycerol among the degradation products indicates the existence of a second mechantsm in C. fasciculata for converting the alkyl-to alkenyl-glycerol.