Bacterial Host Strains Research Articles

Factors in the physical and biological environment affecting nodulation and nitrogen fixation by legumes

The effects of root temperature on the four main stages of nodule formation and function are reviewed. Compared with results obtained under optimal conditions, lower root temperatures retard root hair infection more than they affect nodule initiation, nodule development (including bacteroid tissue development and degeneration), or nitrogen assimilation. Higher root temperatures upset the formation of bacteroid tissue and hasten its degeneration. Tropical and subtropical legumes have higher minimum temperatures for nodule formation than temperate species. Low and high shoot temperatures affect nodulation and nitrogen fixation, but the effect is less severe than that of similar root temperatures. Various approaches to minimise adverse environmental effects are considered. These include the selection of appropriate biological material (both host plants and bacterial strains) for the prevailing conditions, and the adoption of management practices designed to utilise the environment or to minimise its adverse effects. The importance of increase in bacteroid volume in relation to increase in rate of nitrogen fixation is considered, and the concept of compensation in nodule production and activity is examined. The limited information on defoliation effects on the nodulation of both temperate and tropical legumes is reviewed and aspects requiring examination are discussed.

Inactivation and repair of polyvalent Staphylococcus phages after U.V.- or gamma-irradiation or acridine orange treatment.

SummaryThe influence was studied of changes of the bacterial host strain on the course of inactivation of Staphylococcus phages A/5 and ϕ131 after u.v.-irradiation, gamma-irradiation and photodynamic inactivation by AO. Effectiveness of phage plating was alike on all the host strains used. An influence of the various bacterial host strains on the survival of inactivated phages was found for u.v.-irradiated phages only. The bacterial host strains could be divided into strain groups having a favourable effect on the inactivation course of u.v.-irradiated phages, i.e. increasing the number of surviving phage particles, and into bacterial strains which may further reduce the survival of inactivated phage particles. The possible presence of repair mechanism in Staphylococcus bacterial cells is discussed.