An increasing body of evidence suggests that microorganisms are far more sensitive to heavy metal stress than soil animals or plants growing on the same soils. Not surprisingly, most studies of heavy metal toxicity to soil microorganisms have concentrated on effects where loss of microbial function can be observed and yet such studies may mask underlying effects on biodiversity within microbial populations and communities. The types of evidence which are available for determining critical metal concentrations or loadings for microbial processes and populations in agricultural soil are assessed, particularly in relation to the agricultural use of sewage sludge. Much of the confusion in deriving critical toxic concentrations of heavy metals in soils arises from comparison of experimental results based on short-term laboratory ecotoxicological studies with results from monitoring of long-term exposures of microbial populations to heavy metals in field experiments. The laboratory studies in effect measure responses to immediate, acute toxicity (disturbance) whereas the monitoring of field experiments measures responses to long-term chronic toxicity (stress) which accumulates gradually. Laboratory ecotoxicological studies are the most easily conducted and by far the most numerous, but are difficult to extrapolate meaningfully to toxic effects likely to occur in the field. Using evidence primarily derived from long-term field experiments, a hypothesis is formulated to explain how microorganisms may become affected by gradually increasing soil metal concentrations and this is discussed in relation to defining "safe" or "critical" soil metal loadings for soil protection.

Growth curves for a selection of pertinent microorganisms in ricotta and ricotta-filled ravioli were analyzed in terms of Gompertz's model. The growth of Enterobacteriaceae, molds and yeasts and psychrotrophic microorganisms during storage at 0, 4, 8 and 10C was determined. Lag phase duration and specific growth rate were inversely related. The activation energies from an Arrhenius-type equation were calculated for the microorganisms under study. For ricotta samples, molds and yeasts were the most sensitive organisms showing E(mu) values of 74.60 KJoule/mol while Enterobacteriaceae and psychrotrophic microorganisms had E(mu) values of 24.30 and 25.70 KJoule/mol, respectively. For ricotta-filled ravioli samples, the three microorganisms showed activation energies in the range of 31.47-32.99 KJoule/mol; hence the temperature dependence of their growth rates was comparable. Results allow to predict microbial growth of different microorganisms in ricotta and ricotta-filled ravioli when exposed to different storage temperatures.

Environmental release of beneficial microorganisms, including genetically engineered ones, is a matter of concern in the field of bioremediation and improvement of crop production. Factors affecting survival and death of the microorganisms introduced into the environment, such as soil ecosystem, must be clarified to obtain effectively and safely the expected function of the microorganisms. Generally, microorganisms introduced into soil environment decrease in number with time, the decrease is mainly caused by the predatory activity of soil protozoa. Indigenous soil microorganisms survive for a long period in the microhabitats where they are protected against the attack of grazing protozoa. The artificial microhabitats, such as Microporous Glass and bentonite, offer protective microhabitats for the bacterium and are useful to increase the survival of bacterial inocula into soil. The pre-culture condition of bacterial inocula also affects their survival in soil. Starvation treatment of the bacterial cell s prior to inoculation improves their survival. This information must be considered when utilizing beneficial microorganisms in soil environments

In Ago Bay, Mie Prefecture, red tides of the harmful dinoflagellate Heterocapsa circularisquama have recurrently occurred since 1992 and have caused mass mortality of pearl oysters (to do substantial damage to pearl industry). Studies on kill microorganisms against H. circularisquama were carried out for water samples collected in Ago Bay in summer using the newly developed microplate MPN method. A comparison was made on the numbers of killer microorganisms against Chattonella antiqua, Heterosigma akashiwo, gymnodinium mikimotoi, and H. circularisquama using a water sample collected on 16 August 1994, when a red tide of H. circularisquama was observed. The water sample contained H. circularisquama at a density of about 8000 cells.ml(-1). Killer microorganisms against all the four algal species were scarce (1.ml(-1)). Temporal fluctuations of algicidal microorganisms against H. circularisquama and C. antiqua (Raphidophyceae) were investigated during the summer of 1995 to elucidate effects of those microorganisms on H. circularisquama red tides. Killer microorganisms against H. circularisquama were scarce (1.ml(-1)) during the summer of 1995, although vegetative cells of H. circularisquama appeared at rather high density (1493 cells.ml(-1)).(Stn. K3W). Killer microorganisms against C. antiqua were also scarce (maximum 1.52.ml(-1)). Red tides of H. circularisquama tend to last 1 month or more. It is suggested that the scarcity of killer microorganisms against H. circularisquama in the coastal seas such as Ago Bay presumably contribute to maintain red tides of this species for rather long period

The present paper deals with effects of different quantities of sewage mud, worm casting and NPK-fertilizer on the number of aminoautotrophs, aminoheterotrophs, nitrifiers and nitrogenbacters in soil sown with potatoes. Systems of fertilizing influenced the number of almost all of the examined groups of microorganisms. The highest number of almost all of them was found in the variant fertilized with worm casting compared with mineral fertilizer, introduction of sewage mud caused greater increase in the number of microorganisms. With increase in the quantity of sewage mud, the number of all examined groups of microorganisms became higher. The number of the examined microorganisms was highest in soil with a depth from 10 to 20 cm, at the end of potato vegetation; the lowest number was found in soil with a depth from 0 to 10 cm at the beginning of potato vegetation.

A new model describing microbial growth in soil and considering carbon and nitrogen turn-over is proposed. The approach we present modifies the classical equations for microbial growth by the introduction of a new state variable (r), which determines the microbial activity. The activity factor in turn controls microbial growth and death rates as well as the decomposition rate of insoluble organic matter and the immobilization rate of mineral N. The N-to-C ratios of microbial biomass are flexible dependent on the availability of N. The efficiency of microbial biosynthesis and maintenance respiration are controlled by the N-to-C ratio and activity state of the biomass. The behaviour of the model is investigated for conditions of batch and continuous input of substrate at different amounts of microbial activity and C and N in the soil. The proposed model structure is capable of reproducing such features of microbial turnover in soil as a transition of microbial population from an active to a dominant state in the case of C or N limitation, priming action on the decomposition of insoluble soil organic matter, and the reduced efficiency of microbial biosynthesis in the case of a N deficit.

Different procedures for the release of microorganisms from soils were tested. The extraction efficiency was evaluated by combining biochemical activities (fluorescein diacetate hydrolysis, dehydrogenase activity and dimethylsulfoxide reduction) and cell counting. In contrast to the counting methods these activities have the advantage that there is no interference from the soil matrix or from the clay and silt in the extracts. We determined the distribution of activities and cell counts among the successive extracts and the soil residue of a three-step and a five-step extraction procedure. Centrifugation at 600 x g, used in order to separate soil particles, causes a significant proportion of the bacteria and nearly all fungi to enter the sediment. The influence of relative centrifugal forces <600 x g on the recording of microorganisms was investigated in detail. g-Values greater than or equal to 200 lead to unacceptable losses of microorganisms. Because the satisfactory separation of microorganisms and clay or silt is not possible, a compromise between removing the soil particles and quantifying the microorganisms is necessary. We recommend the one-step extraction of the soil by shaking and ultrasonication with subsequent centrifugation at less than or equal to 100 x g. This results in extracts containing about 50% of the biochemical activities and 45% of the cell counts of the soils. This method thus corresponds in its extraction efficiency to a conventional three-step extraction, but is much simpler to carry out.

Contamination of microorganisms and borax was determinated for 9 samples from 2 markets, Yauwarat and Bangkae markets. Seven samples were found to contain the total amount of microorganisms more than the standard of Department of Medical Science. By the standard, the microorganisms should be found less than 1x10**(6) colonies/gram. Coliform bacteria and E.coli, the index of productivity hygiene, were found to excess the limit of quality standard index which should be less than 2.2 colonies/gram. Staphylococcus aureus, Salmonella spp. and Vibrio parahaemolyticus, food poisoning microorganisms, were determinated. S. aureus was found in 9 samples less than the limitation 1x10**(4) colonies/gram. On the other hand, Salmonella spp. was found in only 2 samples. According to the quality index, Salmonella spp. must not be found. V. parahaemolyticus was found in 3 samples which have excess 3 colonies/gram whereas it must be found less than 3 colonies/gram. In addition, borax, i.e. a firming and crisping agent, was not found in all samples.