Microbiological control of ticks.

Twelve isolates (9 spore-forming bacteria and 3 fungi) were obtained from a dead adult tick (female) that had failed to lay eggs. There were different internal changes in the tick's eggs, caused by inoculation with these isolates. Such changes differed according to the type of microorganisms under study. However, fungi were more effective than spore-forming bacteria in decreasing hatching percentage of tick's eggs at 28 degrees C. Generally, inoculation with these isolates decreased the longevity of unfed larvae of ticks.

[Degradation and utilization of 2,4-dioxohexahydro-1,3,5-triazine (DHT) by soil microorganisms]. / Abbau und Verwertung von 2,4-Dioxohexahydro-1,3,5-triazin (DHT) durch Bodenmikroorganismen.

The biodegradation and utilization of the antiphytoviral substance 2,4-dioxohexahydro-1,3,5-triazine (DHT) by soil microorganisms was investigated. Mixed cultures of microorganisms deriving from different soils diminish in nutrient broth the content of DHT with increasing duration of culture. Microorganisms from an Egyptian garden soil fully degrade 10(-3) mol/1 DHT in a culture without additional aeration within 28 days. Also in deficient media the mixed microorganisms reduce the amount of DHT, reaching in nitrogen free nutrient solution even a degradation rate up to 12 mg DHT per liter and day. Pure cultures of Rhizobium leguminosarum, Proteus vulgaris, Saccharomyces cerevisiae and especially Agrobacterium radiobacter diminish the content of DHT in nitrogen free media, too. No such effect was detectable in cultures of four other species of soil bacteria. The DHT degradation by the microorganisms is connected with significant cell multiplication, e.g. A. radiobacter in shaking cultures with DHT as sole source of nitrogen shows a typical growth cycle with a lag-phase of 24 hours. The short persistence time of DHT in soils is concluded to be mainly due to biodegradation by microorganisms.

Studies on phosphate-solubilizing bacteria in soil and rhizosphere of different plants. I. Occurrence of bacteria, acid producers, and phosphate dissolvers.

Occurrence of bacteria (total), acid producing and phosphate dissolving micro-organisms in soil, rhizosphere, and rizoplane of Egyptian cotton, peas, or maize during their different growth phases was studied. The rhizosphere effects were generally positive and differed according to type of plant, growth phase of each special plant, and type of micro-organism under study. The high densities of bacteria, acid-producers, and phosphate-dissolvers in the rhizoplane samples suggest the conclusion that roots of the studied plants are colonized with these soil micro-organisms. The role of the micro-organism and the mechanism of the noted colonization is not fully understood yet. However, the presence of high numbers of bacteria in the rhizosphere zones of all plants is undoubtedly important, since they may convert organic and inorganic substances into available plant nutrients. The acidproducing organisms were greatly stimulated in the rhizosphere of all plants. Consequently, the production of acid, especially in alkaline soils such as in Egypt, may directly or indirectly react with insoluble inorganic compounds, converting their nutrient elements into available forms for the growing plants. But not all acid-producers are considered as phosphate-dissolvers. Therefore, the presence of high numbers of phosphate-dissolving bacteria in the rhizophere zones may explain how the growing plants can obtain their requirements in such alkaline soils.

Studies on phosphate-solubilizing bacteria in soil and rhizosphere of different plants. II. Selection of the most efficient phosphate-dissolvers and their morphological grouping.

Two hundred colonies which showed positive reaction on the plates prepared for the phosphate-dissolving bacteria from control soil rhizosphere soils and rhizoplane samples of maize, peas, or cotton were isolated at random. Fifty isolates were selected as the most efficient isolates according to their capability for increasing the amounts of available phosphorus in the media with corresponding decreases in pH values. The percentage of the most efficient isolates differed according to type of plant and location of isolation. Not only the morphological types of the phosphate-dissolving bacteria differed in soil and in rhizosphere, but they also differed in the rhizosphere soil of each special plant. Morphological differences in the isolates from rhizosphere soil and from rhizoplane samples of the same plant were also occurring. The abundance of mycelial-forming bacteria and of aerobic sporeformers in Egyptian soil is important as they are well known to resist adverse conditions, such as high temperature and dryness to which our soils are subjected most time of the year.