Studies on the ecology of West Australian actinomycetes: Factors which influence the diversity and types of actionomycetes in Australian soils

A statistical technique has been employed to study the effects of various environmental factors in altering the actinomycete populations of soils located in the western part of Australia. Over 12,000 actinomycetes obtained at 28 different locations were included in the evaluation. Among factors that had a significant influence were the geographic area at which the sample was taken, the nature of plant rhizosphere, and a rainstorm. Seasonal changes in population did occur, but there was considerable stability of population with time. Although marked differences occurred in types of actinomycetes present among different geographic locations, multiple samples taken within a location at distances of 30 cm or greater showed marked similarity in populations. There were varied degrees of diversity among the populations studied. The population that developed after a rainstorm was low in diversity, whereas the populations of root rhizospheres were as diverse as those of plant-free soil-litter areas. In assessing the ecology of soil actinomycetes, it is important to consider the degree of change in population induced by an environmental factor and also its effect on diversity, since the effects may be complementary or may be opposite in nature.     

Dynamics of erabutoxin b as studied by nuclear magnetic resonance. Relaxation studies of methyl proton resonances

Longitudinal and transverse relaxation times were measured for well-resolved and assigned methyl proton resonances of erabutoxin b at 270 MHz, 300 MHz and 500 MHz. Both longitudinal and transverse magnetization decay curves are non-exponential due to cross-relaxation and cross-correlation effects. The longitudinal and transverse relaxation rates were obtained from the initial slope of both magnetization decay curves. The correlation times for the isotropic tumbling motion of the protein were determined to be 2.82 ns at 300 K and 1.62 ns at 330 K from the analysis of the relaxation data of some alpha protons. Using these values, the relaxation data of methyl protons were fitted to various theoretical models. Most of the methyl resonances could be fitted well to a model which allowed methyl rotation (in the range 0.01-0.05 ns) and an external contribution from protons assumed to be in positions derived from X-ray coordinates. The data for a few methyl groups, however, could not be fitted in this way. For these a smaller number of external protons than predicted by the X-ray coordinates was assumed. Additionally, a larger amplitude motion had to be introduced into the model for particular residues. This additional motion requires concerted protein motion close to these residues, since the X-ray structure suggests that steric hindrance would prevent local motion. These results are consistent with the idea of a flexible and dynamic structure for proteins.     

Pulmonary Thromboembolism Presenting as Asthma

When a patient presents with wheezing, pulmonary embolism is not usually considered as a possible cause. However, undoubtedly bronchoconstriction can be caused by pulmonary emboli and occasionally wheezing may be so obvious as to suggest a diagnosis of bronchial asthma. Eleven cases are reported in which wheezing was attributable to recurrent pulmonary emboli and one in which it was a clamant feature after a single embolic incident.