Microbial population cells

Viable count Measurement of the concentration of live cells in a microbial population. 

Any bacterial species living in a mixed microbial population, such as that of the rhizosphere, may encounter not only the molecular signal produced by a cell of the. same species but also molecular signals produced by cells of different species. The situation is made more complex by the presence of plant molecular signals, and by the fact that the same AHL molecule can be used to regulate the... 

M. C. Hawes, Living plant cells released from the root cap a regulator of microbial populations in the rhizosphere The Rhizosphere and Plant Growth (D, L. Keister and P. B. Creagan, eds.), Kluwer Academic Publishers. Dordrecht, 1991, p. 51. 

The main obstacles to increasing our knowledge in this field are methodological (103). Microbial cell enumeration techniques and identification procedures are often difficult or tedious, and the collection of relevant samples or the simulation of natural conditions in the laboratory can be problematical. However, the development of molecular approaches for the study of microbial populations can contribute to solving these problems. Considering the vast array of techniques used and presented in the literature, only a selection of these methods is discussed in this review. 

All cell culture-based methodologies are essentially limited when studying whole microbial populations, since the dominant proportion of microbial biomass of soil, rhizosphere and rhizoplane, and other environments cannot be cultured on standard laboratory media (114). To obtain information on the composition and activity of the nonculturable fraction and to aid the study of the culturable fraction, direct detection methods are needed. 

Methods of DNA manipulation now make it possible to insert DNA into prokaryotic, eukaryotic, or viral hosts, creating versatile marker systems that allow as- sessment of the survival and spread of strains, studies on gene transfer, and determinations of cell activity. A potential marker gene must be absent from the strain used in the study, and either absent or in sufficiently low abundance in the microbial population under study to allow detection of marked cells at an appropriate level. 

The air that we breathe is full of microbial cells and spores of bacteria and fungi. Because they are extremely light they are readily are carried by wind currents. In hot weather soil, a rich source of all types of microbes, turns to dust and increases the airborne microbial population... 

Darvey, H. M. Kell, D. B. Flow cytometry and cell sorting of heterogenous microbial populations the importance of single cell analysis. Microbiol. Rev. 1997, 60, 641-696. 

Based on the previous publications, azo dye can be reduced by azoreductase-catalyzed reduction under anaerobic conditions. But still there is a speculation whether bacterial flavin reductases are responsible for the azo reductase activity observed with bacterial cell extracts. In a published report, it is reported that flavin reductases are indeed able to act as azo reductases [24]. Bacteria produce extracellular oxidative enzymes, which are relatively nonspecific enzymes catalyzing the oxidation of a variety of dyes. It was reported that so many diverse groups of bacteria play a role in decolorization. It has been also reported that mixed microbial community could reduce various azo dyes, and members of the y-proteabacteria and sulfate reducing bacteria (SRB) were found to be prominent members of mixed bacterial population by using molecular methods to determine the microbial population dynamics [1],... 

The principal controls on the microbial reaction rate in our example, then, are biomass and thermodynamic drive (Fig. 33.2). Initially, in the presence of abundant lactate and arsenate, the rate is controlled by the size of the microbial population available to catalyze lactate oxidation. As the population increases, so does reaction rate. Later, as reactants are consumed and products accumulate, the reaction approaches the point at which the energy liberated by its progress is balanced by that needed in the cell to synthesize ATR Reaction rate is governed now by the energy available to drive forward the cellular metabolism, this energy represented by the thermodynamic potential factor Ft over the course of the experiment, the kinetic factors Fd and Fa play minor roles. 

The temperature in a sewer depends on a number of different conditions, e.g., climate, source of wastewater and system characteristics. The microbial community developed in a sewer is typically subject to annual temperature variations and, to some extent, a daily variability. Different microbial systems may be developed under different temperature conditions, and process rates relevant for the microorganisms vary considerably with temperature. Long-term variations may affect which microbial population will develop in a sewer, whereas short-term variations have impacts on microbial processes in the cell itself as well as on the diffusion rate of substrates. 

The diversity of functions within a microbial population is important for the multiple functions of a soil. The functional diversity of microbial communities has been found to be very sensitive to environmental changes (Zak et al. 1994 Kandeler et al. 1996,1999). However, the methods used mainly indicate the potential in vitro functionality. Functional diversity of microbial populations in soil may be determined by either expression of different enzymes (carbon utilization patterns, extracellular enzyme patterns) or diversity of nucleic acids (mRNA, rRNA) within cells, the latter also reflecting the specific enzymatic processes operating in the cells. Indicators of functional diversity are also indicators of microbial activity and thereby integrate diversity and function. 

High hydrostatic pressure (HHP) processes have been used mainly for sauces or seafood and proven effective at reducing microbial populations without adverse effects on product quality (Considine et al., 2008 Brinez et al., 2006). HHP treatment causes bacterial inactivation by damaging the cell membrane, which affects membrane permeability and intracellular enzyme inactivation and possibly ruptures the plant cell wall (Kniel et al.,... 

The actual number of cells or percentage of microbial population that will be killed by an absorbed radiation dose depends also on various factors such as the inherent resistance of the particular organism, the growth stage, as well as environmental factors such as tem-... 

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