Inter-relationships among demographic traits comprising amphipod production and turnover

Hyalella azteca (Amphipoda) were sampled in eight Canadian Shield lakes, and the inter-relationships among life history traits were used to determine the sensitivity of production and turnover rates to demographic variation. Production was positively related to density and negatively related to both mortality and somatic growth. Turnover rates did not vary significantly with respect to any demographic traits. Studies should advance from simply documenting production to instead describing ‘production ecology’ if an understanding of the environmental determinance of population regulation is desired.     

Hydrogen peroxide production and myo‐inositol metabolism as important traits for virulence of Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae is the causative agent of enzootic pneumonia. In our previous work, we reconstructed the metabolic models of this species along with two other mycoplasmas from the respiratory tract of swine: Mycoplasma hyorhinis, considered less pathogenic but which nonetheless causes disease and Mycoplasma flocculare, a commensal bacterium. We identified metabolic differences that partially explained their different levels of pathogenicity. One important trait was the production of hydrogen peroxide from the glycerol metabolism only in the pathogenic species. Another important feature was a pathway for the metabolism of myo‐inositol in M. hyopneumoniae. Here, we tested these traits to understand their relation to the different levels of pathogenicity, comparing not only the species but also pathogenic and attenuated strains of M. hyopneumoniae. Regarding the myo‐inositol metabolism, we show that only M. hyopneumoniae assimilated this carbohydrate and remained viable when myo‐inositol was the primary energy source. Strikingly, only the two pathogenic strains of M. hyopneumoniae produced hydrogen peroxide in complex medium. We also show that this production was dependent on the presence of glycerol. Although further functional tests are needed, we present in this work two interesting metabolic traits of M. hyopneumoniae that might be directly related to its enhanced virulence.     

Degradation of Hyaluronic Acid by Photosensitized Riboflavin In Vitro. Modulation of the Effect by Transition Metals, Radical Quenchers, and Metal Chelators

The effect of photoexcited riboflavin (RF) on the viscosity of hyaluronic acid (HA) solutions has been investigated. UV irradiation of RF causes under aerobic conditions fragmentation of HA and a decrease in the viscosity of its solutions. A decrease of HA viscosity occurs in PO₄-buffered solutions and is accelerated by high pH, Fe²⁺ (but much less so by Fe³⁺), certain metal chelators, and horseradish peroxidase (HRP); it is partially inhibited by catalase and less so by superoxide dismutase (SOD). The reactivity of the system was completely blocked by Tris, ethanol, aspirin, d-manitol, dimethylthiourea (DMTU), dimethylsulfoxide (DMSO), and sodium azide. These results indicate that the most likely chemical species involved in the reaction is the hydroxyl radical. Singlet oxygen (¹0₂) generation is suggested by the ability of NaN₃ and DMSO to completely inhibit the reactivity of the system. These two agents, however, may also interact with OH^√ radical, as well and suppress the reactivity of the system. H₂O₂ and seem also to be produced in significant amounts, because catalase and SOD partially block the reactivity of the system. The effect of HRP may be due to hydrogen subtraction from HA and H₂O₂ reduction to water. Photoexcitation of RF may potentially occur in vitro and in vivo in the organs and tissues that are permeable to light, such as the eye or skin, and damage HA and other cell-matrix components causing inflammation and accelerating aging.  © 1997 Elsevier Science Inc.