Microbial cells bacteria

Single cell protein, normally called simply SCP, is the term used to describe microbial cells, or proteins from them, which are used as food (food for humans) or feed (food for farm animals or fish). Although the term micro-organisms covers viruses, bacteria, fungi, algae and protozoa, viruses and protozoa are not considered suitable for SCP production. 

Micro-organisms are rich in protein. Microbial cells can contain as much protein as conventional foods. Bacteria can contain 60-65% (as a % of dry weight) protein whereas fungi and algae contain about 40%. In addition, microbial cells can be a rich source of fibre, unsaturated fats, minerals and vitamins. They are low in saturated fats and sodium. 

There is another fundamental difference between folate utilization in microbial and mammalian cells. Bacteria and protozoa are unable to take up exogenous folate and must synthesize it themselves. This is carried out in a series of reactions involving first the synthesis of dihydropteroic acid from one molecule each of pteridine and p-aminobenzoic acid (PABA). Glutamic acid is then added to form DHF which is reduced by DHFR to THF. Mammalian cells do not make their own DHF, instead they take it up firm dietary nutrients and convert it to THF using DHFR. 

Microbial cells transported with the stream of fluid above the surface interact with conditioning films. Immediately after attachment, microorganisms initiate production of slimy adhesive substances, predominantly exopolysaccharides (EPS) that assist the formation of microcolonies and microbial films. EPS create bridges for microbial cells to the substratum and permit negatively charged bacteria to adhere to both negatively and positively charged surfaces. EPS may also control interfacial chemistry at the mineral/biofilm interface. 

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... 

Macro- and micronutrients should be provided as needed. Soils usually contain sufficient levels of micronutrients, but very often there is a lack of nitrogen and phosphorus. The addition of N and P is particularly important during the initial stages of treatment, in order to stimulate the growth of indigenous bacteria. After the initial development of a critical microbial mass, N and P are constantly recycled due to the lysis of dead microbial cells.9... 

The sol-gel-entrapped microbial cells have shown excellent tolerance to different alcohols [99], The immobilized E. coli cells followed the Michaelis-Menten equation when quantified with the (3-glucosidase activity via the hydrolysis of 4-nitrophenyl-(3-D-galactopyranosdie [142], The sol-gel matrices doped with gelatin prevented the cell lysis, which usually occurs during the initial gelation process [143], Microorganisms are now widely used in the biosorption of different pollutants and toxicants. Bacillus sphaericus JG-A12 isolated from uranium mining water has been entrapped in aqueous silica nanosol for the accumulation of copper and uranium [144], Premkumar et al. [145] immobilized recombinant luminous bacteria into TEOS sol-gel to study the effect of sol-gel conditions on the cell response (luminescence). The entrapped and free cells showed almost the same intensity of luminescence (little lower), but the entrapped cells were more stable than the free cells (4 weeks at 4°C). This kind of stable cell could be employed in biosensors in the near future. 

Lebeau et al. (2002) investigated the sorption of cadmium by viable microbial cells that were free or immobilized in alginate beads by incubating the bacteria in a liquid soil extract medium at pH 5 7 and Cd concentrations of 1 to 10 mg L-1. The percentage of Cd biosorbed reached a maximum (69%) at low Cd concentrations and neutral pH. Thus, the effectiveness of bacteria, inoculated into metal-contaminated soils, would largely depend on the concentration of the metal and its distribution between the biomass and the medium. 

Environmental chemicals occur as pure liquid or solid compounds, dissolved in water or in nonaqueous liquids, volatilised in gases, dissolved in solids (absorbed) or bound to interfaces (adsorbed). Figure 5 gives a schematic view of the different physical states at which substrates are taken up by microbial cells. There is a consensus that water-dissolved chemicals are available to microbes. This is obvious for readily soluble chemicals, but there is also clear evidence for microbial uptake of the small dissolved fractions of poorly water soluble compounds. Rogoff already had shown in 1962 that bacteria take up phenanthrene from aqueous solution [55], In the intervening time many other researchers have made the same observation with various combinations of microorganisms and poorly soluble compounds [14,56,57]. 

Highly halogenated organic compounds such as polychlorinated biphenyls and perchloroethylene appear to be too highly oxidised and low in energy content to serve as sources of electrons and energy for microbial metabolism. Bacteria are more likely to use them as electron acceptors in cell-membrane-based respiration processes [154]. The environmental fate of halogenated polymers such as polyvinylchloride or Teflon may depend on the question of whether it will be appropriate to sustain de-halorespiration processes. 

In some undisturbed subsurface systems, an equilibrium is established. Bacteria have acclimated to food sources, water availability, and electron acceptor types. The number and variety of microbial cells are balanced in this system. If the system is aerobic, the microbial activity continues at the rate of oxygen resupply. If the system is anaerobic, the rate of activity cannot exceed the accessibility of alternate electron acceptors. Generally, the subsurface (lower than the plant root zone) is relatively deficient in available carbon and electron acceptors. Under these normal semi-equilibrium conditions, a soil or aquifer system can consume organic materials within a reasonable range. When a chemical release is introduced into a well-established soil system, the system must change to react to this new energy source. The bacterial balance readjusts, in an effort to acclimate to the new carbon source. 

Most of the antibiotics commercially available nowadays are derivatives of natural compounds produced by bacteria or fungi. It is widely accepted that in nature these secondary metabolites can act as weapons for microbial cell defence, inhibiting the growth of competitors. However, it seems that antibiotics have, in nature, more sophisticated and complex functions [1-3]. Many environmental bacteria can not only cope with natural antimicrobial substances but also benefit from their presence. For instance, the use of antibiotics by bacteria as biochemical signals, modulators of metabolic activity or even carbon sources has been demonstrated [1, 2, 4]. In other cases, antibiotics can be tolerated because they have structures similar to the natural substrates of bacterial housekeeping enzymes and thus are inactivated, leading to a natural form of resistance [2]. These are just some... 

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