Microorganisms, which are always present in the root region of plants growing in soil, carry out there a range of activities of great relevance for plant growth and nutrition. This paper reviews: a. the concept of rhizosphere; b. the population dynamic in soil; c. microbial interactions; d. the plant-microorganisms systems; e. quali and quantitative aspects of microbial substrates in the rhizosphere; f. action mechanisms which account for the plant growth enhancement by soil microorganisms

One of the most important environmental parameters which affect the growth, biochemical activities and death of microorganisms in foods is water activity (aw). By appropriate adjustment of aw in the food system the food scientist can secure its extended preservation and minimize the possibility of a food-borne disease problem. This paper deals with the following subjects with respect to aw: the effect of aw on the growth and the biochemical activities of microorganisms; the parameters which affect the water requirement of microorganisms; the effect of aw on the survival of microorganisms at low and high temperature; the technology of aw adjustment in foods and its food safety implications and finally a discussion of some recent developments, trends and problems in the application of the aw principle in food preservation.

Changes in number and types of microorganisms in fermenting wild rice were studied. The effect of various microorganisms on keeping quality of wild rice during fermentation and on flavor of wild rice was also determined. Addition of microbial cultures and/or nutrient solutions did not increase the storage life of fermenting wild rice held at 21 or 5°C. Refrigeration of rice greatly increased the effective keeping time of the unprocessed grain. Periodic addition of a 0.1% (w/v) (NH4)2SO4 solution apparently decreased the acceptable storage life of refrigerated (5°C) rice. Although unprocessed rice could not be kept beyond 10–14 d at 21 °C without obvious changes in organoleptic quality, rice stored at 5°C remained acceptable for 7 weeks. Steaming wild rice for 15 min before fermentation generally caused a marked reduction in microbial load during the first few days of storage. Rice inoculated with Streptomyces sp. in a circulating nutrient medium to produce an “earthy” flavor was rapidly spoiled by microorganisms indigenous to rice. Cultures of Pseudomonas perolens and Pseudomonas taetrolens inoculated into rice stored at 5°C gave only mild methoxylated-pyrazine (green-earthy) flavors to resulting processed rice. In most treatments, bacteria and molds generally increased during the first week of fermentation, maintained a rather constant number for most of the remainder of the fermentation, and often decreased near the end of storage. Gram-negative, rod-shaped bacteria were the microorganisms most commonly isolated from fermenting wild rice. Many psychrotrophic bacteria were isolated from refrigerated (5°C) rice. Low-temperature storage greatly increased the keeping quality of rice, but unacceptable organoleptic changes eventually occurred at this temperature. Many bacteria isolated from wild rice were facultatively anaerobic Enterobacteriaceae. Although rice contained large populations of various types of microorganisms, the potentially hazardous Bacillus cereus and Pseudomonas aeruginosa were not found.

The disinfection effects of sunlight and predacious microorganisms on enteric bacteria of Escherichia coli and Proteus vulgaris were examined in sewage water at 22 to 26 C. The test organisms were disinfected by 4 to 5 logs during 6-hour a day exposure to sunlight for seven days. The effect was proportional to the light intensity and was proven to be due to the action of the visible light of short wavelength which can transmit the soft glass of a flask, not the ultraviolet light which cannot transmit the flask glass. The predacious microorganisms decreased the test organisms by about 3 to 4 logs during 7 days. The complex actions of sunlight and predacious microorganisms were variable depending upon the test organisms, but the total effects of those environmental factors were yet completely understood

The "fish reservoirs" of the Arcachon Basin (France) are artificial ponds created in lagoonal marshes. Opportunistic populations of microorganisms and of meiofauna increase the tendency to create dystrophic crisis. Fry stocking of soles (Solea vulgaris ) into the fish ponds have been made to estimate the influence of the predatory activity and bioturbation on the food web. For 10 soles/m super(2), the abundance of opportunistic populations of meiofauna decreases and this result indicates a modification in competitive interactions contributing to a better spatial heterogeneity in the ecosystem. These results could be used in aquaculture ponds to regulate opportunistic microorganisms and meiofauna.