ENCYCLOPEDIA OF Espionage, Intelligence, and Security Volume ...

Bacterial Biologybacteria are damaged or have just been recovered fromdeep-freeze storage.After the lag phase, the numbers of living bacteriarapidly increases. Typically, the increase is exponential.That is, the population keeps doubling in number at thesame rate. This is called the log or logarithmic phase ofculture growth, and is the time when the bacteria aregrowing and dividing at their maximum speed.The explosive growth of bacteria cannot continueforever in the closed conditions of a flask of growth medium.Nutrients begin to become depleted, the amount ofoxygen becomes reduced, and the pH changes, and toxicwaste products of metabolic activity begin to accumulate.The bacteria respond to these changes in a variety of waysto do with their structure and activity of genes. Withrespect to bacteria numbers, the increase in the populationstops and the number of living bacteria plateaus. Thisplateau period is called the stationary phase. Here, thenumber of bacteria growing and dividing is equaled by thenumber of bacteria that are dying.Finally, as conditions in the culture continue to deteriorate,the proportion of the population that is dyingbecomes dominant. The number of living bacteria declinessharply over time in what is called the death ordecline phase.Bacteria growing as colonies on a solid growth mediumalso exhibit these growth phases in different regionsof a colony. For example, the bacteria buried in the oldestpart of the colony are often in the stationary or deathphase, while the bacteria at the periphery of the colony arein the actively-dividing lo phase of growth.Culturing of bacteria is possible such that fresh growthmedium can be added at a rate equal to the rate at whichculture is removed. The rate at which the bacteria grow isdependent on the rate of addition of the fresh medium.Bacteria can be tailored to grow relatively slow or fast and,if the set-up is carefully maintained, can be maintained fora long time.Bacterial growth requires the presence of environmentalfactors. For example, if a bacterium uses organiccarbon for energy and structure (chemoheterotrophic bacteria)then sources of carbon are needed. Such sourcesinclude simple sugars (glucose and fructose are two examples).Nitrogen is needed to make amino acids, proteins,lipids and other components. Sulphur and phosphorusare also needed for the manufacture of bacterialcomponents. Other elements, such as potassium, calcium,magnesium, iron, manganese, cobalt and zinc arenecessary for the functioning of enzymes and otherprocesses.Bacterial growth is also often sensitive to temperature.Depending on the species, bacteria exhibit a usuallylimited range in temperatures in which they can growthand reproduce. For example, bacteria known as mesophilesprefer temperatures from 20° – 50° C (68° – 122° F). Outsidethis range, growth and even survival is limited. Otherfactors, which vary depending on species, required forgrowth include oxygen level, pH, osmotic pressure, lightand moisture.The events of growth and division that are apparentfrom measurement of the numbers of living bacteria arethe manifestation of a number of molecular events. At thelevel of the individual bacterium, the process of growthand replication is known as binary division. Binary divisionoccurs in stages. First, the parent bacterium growsand becomes larger. Next, the genetic material inside thebacterium uncoils from the normal helical configurationand replicates. The two copies of the genetic materialmigrate to either end of the bacterium. Then a cross-wallknown as a septum is initiated almost precisely at themiddle of the bacterium. The septum grows inward as aring from the inner surface of the membrane. When theseptum is complete, an inner wall has been formed, whichdivides the parent bacterium into two so-called daughterbacteria. This whole process represents the generation time.Bacterial GeneticsBacteria can exchange genetic material via conjugation.Genetic recombination between bacteria (or protists) occursvia a cytoplasmic bridge between the organisms. Aprimitive form of exchange of genetic material betweenbacteria involving plasmids also can occur. Plasmids aresmall, circular, extrachromosomal DNA molecules thatare capable of replication and are known to be capable oftransferring genes among bacteria. For example, resistanceplasmids carry genes for resistance to antibioticsfrom one bacterium to another, while other plasmids carrygenes that confer pathogenicity. In addition, the transferof genes via bacteriophages—viruses that specificallyparasitize bacteria—also serves as a means of geneticrecombination.Bioengineering uses sophisticated techniques to purposelytransfer DNA from one organism to another inorder to give the second organism new characteristics. Forexample, in a process called transformation, antibioticsusceptible bacteria that are induced to absorb manipulatedplasmids placed in their environment can acquireresistance to that antibiotic substance due to the newgenes they have incorporated. Similarly, in a processcalled transfection, specially constructed viruses are usedto artificially inject bioengineered DNA into bacteria, givinginfected cells some new characteristic.Bacterial adaptation and resistance. Evolution has drivenboth bacterial diversity and bacterial adaptation. Somealterations are reversible, disappearing when the particularpressure is lifted. Other alterations are maintained andcan even be passed on to succeeding generations ofbacteria.The first antibiotic was discovered in 1929. Sincethen, a myriad of naturally occurring and chemically synthesizedantibiotics have been used to control bacteria.82 Encyclopedia of Espionage, Intelligence, and Security