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5.4: The Ability to Compete for Nutrients - Biology


Learning Objectives

  • State why the ability to compete for iron and other nutrients is important for bacteria to cause disease and describe briefly three ways bacteria may accomplish this as part of their pathogenicity.

Often the ability to be pathogenic is directly related to the bacterium's ability to compete successfully with host tissue and normal flora for limited nutrients. One reason the generation time of bacteria growing in the body is substantially slower than in lab culture is because essential nutrients are limited. In fact this is a major reason why the overwhelming majority of bacteria found in nature are not harmful to humans.

To be pathogenic, a bacterium must be able to multiply in host tissue. The more rapid the rate of replication, the more likely infection may be established. Pathogens, therefore, are able to compete successfully for limited nutrients in the body. Generally bacteria compete for nutrients by synthesizing specific transport systems or cell wall components capable of binding limiting substrates and transporting them into the cell. A good example of this is the ability of bacteria to compete for iron.

As we will see later in Unit 5 under innate immunity, the body makes considerable metabolic adjustment during infection to deprive microorganisms of iron. Iron is essential for both bacterial growth and human cell growth. Bacteria synthesize iron chelators - compounds capable of binding iron - called siderophores. Many siderophores are excreted by the bacterium into the environment, bind free iron, and then re-enter the cell and release the iron. Other siderophores are found on the cell wall where they bind iron and transport it into the bacterium.

Meanwhile, the body produces iron chelators of its own (transferrin, lactoferrin, ferritin, and hemin) so the concentration of free iron is very low. The ability of bacterial iron chelators to compete successfully with the body's iron chelators as well as those of normal flora may be essential to pathogenic bacteria. In addition to their own siderophores, some bacteria:

  1. Produce receptors for siderophores of other bacteria in this way take iron from other bacteria.
  2. Are able to bind human transferrin, lactoferrin, ferritin, and hemin and use that as their iron source. For example, Neisseria gonorrhoeae, Neisseria meningitidis, and Haemophilus influenzae are able to use iron bound to human transferrin and lactoferrin for their iron needs, while pathogenic Yersinia species are able to use transferrin and hemin as iron sources.
  3. Produce proteases that degrade human lactoferrin, transferrin, or heme to release the bound iron for capture by bacterial siderophores.
  4. Do not use iron as a cofactor. Borrelia burgdorferi instead uses manganese as a cofactor.
  5. Are able to produce exotoxins that kill host cells only when iron concentrations are low. In this way the bacteria can gain access to the iron that was in those cells.

Staphylococcus aureus, on the other hand, produces surface adhesins that bind to extracellular matrix proteins and polysaccharides surrounding host cell tissue, including fibronectin, collagen, laminin, hyaluronic acid, and elastin. S. aureus proteases and hyaluronidase then dissolve these components of the extracellular matrix providing food for the bacteria and enabling the bacteria to spread.


Postharvest biological control of blue mold of apple by Pseudomonas fluorescens during commercial storage and potential modes of action

Three P. fluorescens isolates inhibited P. expansum in vitro and in vivo.

Volatiles from P. fluorescens isolates completely inhibited spore germination.

Two P. fluorescens isolates showed potential for synthesis of phenazine.

Three P. fluorescens isolates colonized fungal hyphae in vitro and in apple wounds.


Cell hydration as the primary factor in carcinogenesis: A unifying concept

The paper discusses the unifying concept that cell hydration is the primary factor in the mechanism of carcinogenesis. The concept includes the following hypotheses: (1) Increased cell hydration causes cancer not only by promoting cell division and oncogene expression, but also by inactivating genes inducing cell differentiation, and by preventing apoptosis. Conversely, factors that reduce cell hydration prevent cancer by inhibiting cell division and oncogene expression, while activating genes inducing cell differentiation, and by promoting apoptosis. The unique ability of cell hydration to have these opposite effects on cell behavior and gene expression can account for its postulated role as the primary factor in both the promotion and prevention of cancer. (2) A progressive increase in cell hydration, induced by successive mutations and/or epigenetic changes, is the basic mechanism of multi-step carcinogenesis, the degree of malignancy increasing with the degree of cell hydration. (3) The increased hydration of cancer cells accelerates their respiration rate, thereby enhancing their ability to compete for nutrients with their normal counterparts. This effect may play a major role in promoting tumor growth and in the postulated mechanism of multi-step carcinogenesis. (4) Increased cell hydration is also proposed as an alternative or additional explanation of the carcinogenetic effect of inflammatory agents and of hormones. A survey of the literature provides evidence consistent with these hypotheses, but suggestions are included for further investigations to test their validity and their implications. From a clinical perspective, the abnormally high water content of cancer cells permits the use of microwave technology for tumor detection and treatment. Also of considerable therapeutic significance is the increased sensitivity if cancer cells to desiccation, postulated to result from genetic changes induced by increased hydration. This may well be the achilles heel of cancer, and recent investigations indicate that it may be exploited very effectively in the treatment of the disease. In conclusion, I suggest that the need for studies on the molecular biology of cancer to be supplemented by more information on environmental effects on gene expression and on the biochemical and physiological factors that mediate genetic effects at the cellular level. This approach might also be used to assess the validity of the postulated role of cell hydration as a factor of particular significance.


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Plant relationships with other organisms

While plants have ready access to carbon (carbon dioxide) and water (except in dry climates or during drought), they msut extract minerals and ions from the soil. Often nitrogen is most limiting for plant growth while it comprises approximately 80% of the atmosphere, gaseous nitrogen is chemically stable and not biologically available to plants. Many plants have evolved mutualistic relationships with microorganisms, such as specific species of bacteria and fungi, to enhance their ability to acquire nitrogen and other nutrients from the soil. This relationship improves the nutrition of both the plant and the microbe.

Though the atmosphere is 80% nitrogen, nitrogen in its gaseous form is unavailable to most organisms. Only a few species of bacteria are able to “fix” nitrogen, and all biologically-available nitrogen comes from the activities of these bacteria. Plants are able to utilize nitrogen from nitrogen-fixing bacteria or from nitrogen releaed by decomposers such as fungi. By Cicle_del_nitrogen_de.svg: *Cicle_del_nitrogen_ca.svg: Johann Dréo (User:Nojhan), traduction de Joanjoc d’après Image:Cycle azote fr.svg.derivative work: Burkhard (talk)Nitrogen_Cycle.jpg: Environmental Protection Agencyderivative work: Raeky (talk) – Cicle_del_nitrogen_de.svgNitrogen_Cycle.jpg, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=7905386


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Fat Intake & Athletes

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Competition as a Regulator

When two organisms or populations compete with each other, whether it be directly or indirectly, one of several outcomes can be expected. In extreme cases one population (or individual) out-competes the other and the ‘losing’ organism becomes extinct from the area. If, however, the competition event is spread over time and the losing animal has time to respond and recover, they may relocate to another geographic area (emigrate). If the losing organism is not displaced, it may change its behavior or requirements to utilize different resources so that it is no longer in competition with its opponent.
Intraspecific competition can serve as a regulator for population size. If a particular source of prey, or abiotic habitat feature is not readily available, then competition for the ones that are will be heavy. If the requirements are scarce enough, this will cause the population to remain stable, or decrease. If resources are readily available, then competition will be low and a population may increase.


Plant-Animal Interactions

III.A.2. Benefits to Plants—What Motivates Ants?

Ants can benefit plants in three ways. First, they may patrol the plant and discourage or repel would-be herbivores. They also prune neighboring plants, thereby reducing plant competition for their host. Finally, some ants feed their host plant (myrmecotrophy).

Ants have frequently been observed killing and removing insect herbivores, and numerous experiments demonstrate the efficacy of this defense. For example, Fonseca observed four times as many herbivores on Tachigali myrmecophila plants from which he removed Pseudomyrmex concolor ants as on plants with intact ant colonies. Further, the daily rate of herbivory was about 10 times lower when ants were present, resulting in experimental plants without ants exhibiting about twice as much cumulative herbivore damage during the 18-month experiment. Leaf longevity was also substantially higher on plants with ants. It is interesting to note that these ants do not eat the herbivores they kill. Instead, they feed exclusively on catenococcid insects they tend inside the domatium, which is the hollow rachis of the compound leaf.

Ants are also effective deterrents of mammalian herbivory. For example, the African myrmecophyte Acacia drepanolobium, possesses two kinds of thorns. The swollen thorns are domatia in which Crematogaster ants live and rear their broods. Stapley has shown that the unswollen thorns slow plant damage by browsing mammals, but that browsers may compensate by feeding longer. Ants were far more effective defenses. When a browsing mammal encountered and was stung by ants, it stopped feeding immediately and could not be induced to feed further on that tree.

A second benefit that patrolling ants may provide is in competition with neighboring plants. Ants will prune vines (lianas) and branches of neighboring trees, effectively preventing their host tree from being overgrown. The result of this vigilance is that the host tree occupies a dramatically open cylinder of space amid otherwise densely packed tree canopies. Although such pruning of neighbors clearly benefits the host tree, it also benefits the ant colony by reducing the number of directions from which it may be attacked by competing or predatory ants.

In certain circumstances, ants may harm their own host by pruning it rather than its neighbors. For example, Stanton and colleagues discovered a situation in which Crematogaster nigriceps so severely prunes its host tree, Acacia drepanolobium, that the tree cannot flower and is sterilized. In the habitat studied, four species of ants compete strongly for hosts, and C. nigriceps fares poorly in the violent conflicts over nest space. Instead of pruning neighboring trees, C. nigriceps prunes its own tree, apparently because it cannot prune neighboring trees occupied by competitively dominant ants. Indeed, careful observation of a large number of trees occupied by C. nigriceps revealed that these trees were always pruned in such a way as to avoid canopy contact with adjacent trees occupied by competing ant colonies. Canopy pruning of its own tree appears to be a defensive response by a C. nigriceps colony to competition with dominant ants that prevent it from pruning their trees.


About the book

Description

Advances in Physiological Sciences, Volume 12: Nutrition, Digestion, Metabolism covers the proceedings of the 28th International Congress of Physiological Sciences, held in Budapest in 1980, which mainly focuses on human nutrition, digestion, and metabolism. This compilation is divided into eight parts. This text first gives an introduction to vitamins and trace elements, including its role, effects, and influences on human biological processes. This book then explains the role of cyclic nucleotides in stimulus—secretion coupling of exocrine glands and the physiological components of the gastric mucosal barrier, along with their role in mucosal defense. Motility in control of gastric emptying intestinal polypeptides and peptidergic nerves and molecular changes during metabolic processes of gastrointestinal peptide hormones are also tackled. This text also introduces the factors involved in the integrated mechanism of intestinal absorption. This book concludes by explaining the lipoprotein metabolism, apolipoproteins, and lipid constituents. This publication will be invaluable to those in the field of physiological sciences interested specifically in studying human nutrition, digestion, and metabolism.

Advances in Physiological Sciences, Volume 12: Nutrition, Digestion, Metabolism covers the proceedings of the 28th International Congress of Physiological Sciences, held in Budapest in 1980, which mainly focuses on human nutrition, digestion, and metabolism. This compilation is divided into eight parts. This text first gives an introduction to vitamins and trace elements, including its role, effects, and influences on human biological processes. This book then explains the role of cyclic nucleotides in stimulus—secretion coupling of exocrine glands and the physiological components of the gastric mucosal barrier, along with their role in mucosal defense. Motility in control of gastric emptying intestinal polypeptides and peptidergic nerves and molecular changes during metabolic processes of gastrointestinal peptide hormones are also tackled. This text also introduces the factors involved in the integrated mechanism of intestinal absorption. This book concludes by explaining the lipoprotein metabolism, apolipoproteins, and lipid constituents. This publication will be invaluable to those in the field of physiological sciences interested specifically in studying human nutrition, digestion, and metabolism.


5.4: The Ability to Compete for Nutrients - Biology

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