Question

Can sugars other than glucose enter the EMP pathway? How? How does a cell metabolically respond to or act on extracellular polysaccharides found in its environment?

Answer 1

Yes,

The catabolism of sugars other than glucose : Release of glucose from glycogen:

The main storage carbohydrate of animal cells is glycogen, in which chains of glucose molecules linked end-to-end, the C1 position of one glucose being linked to the C4 position of the adjacent one are joined to each other by occasional linkages between a carbon at position 1 on one glucose and a carbon at position 6 on another.

• Fragmentation of other sugars

Other sugars encountered in the diet are likewise transformed into products that are intermediates of central metabolic pathways. Lactose, or milk sugar, is composed of one molecule of galactose linked to one molecule of glucose. Sucrose, the common sugar of cane or beet, is made up of glucose linked to fructose. Both sucrose and lactose are hydrolyzed to glucose and fructose or galactose, respectively.  

• The catabolism of lipids (fats)

Although carbohydrates are the major fuel for most organisms, fatty acids are also a very important energy source. In vertebrates at least half of the oxidative energy used by the liver, kidneys, heart muscle, and resting skeletal muscle is derived from the oxidation of fatty acids. In fasting or hibernating animals or in migrating birds, fat is virtually the sole source of energy.

How does a cell metabolically respond to or act on extracellular polysaccharides found in its environment?

"A biofilm is composed of attached microbial cells encased within a matrix of extracellular polymeric secretions (EPS), which surround and protect cells. The EPS matrix is typically composed of polysaccharides, proteins, lipids, and extracellular DNA". A biofilm forms when one or several bacterial cells suspended in the water attach to a surface.At this point, the cell either detaches again or attaches more firmly by secretion of EPS. As the biofilm develops, different sets of genes are turned on (up-regulated) or off (down-regulated). Therefore bacteria in biofilms express genes differently when compared with similar bacteria as planktonic cells. Some of the genes that are up-regulated are involved in the secretion of EPS. The EPS matrix affords protection to cells and enhances gathering of nutrients through sorption of organics.

The EPS matrix forms the crucial three-dimensional architecture of a biofilm. This allows cells to fix their positions relative to one another, much in the same way that people live in different rooms of a high-rise apartment building. The EPS also forms a confining scaffold to slow diffusive loss and localize extracellular enzymes and extracellular DNA, which is actively secreted by cells as plasmids, or released by lysed cells. The proximity of cells to one another facilitates exchange of plasmids and free DNA, a process that can quickly arm bacteria with the necessary genetic machinery to persist through stresses. Finally, biofilm-forming bacteria use chemical communication, called quorum sensing, to coordinate their metabolism. Bacteria release chemical signals that are sensed by other nearby cells within the biofilm. Thus, groups of bacteria in spatial proximity can coordinate their activities, a process that increases the efficiency and resilience of the community.

Overall, the biofilm state provides a more stable microenvironment for bacteria and other microbial cells. This microenvironment can rapidly adapt to stressors and coordinate activities in response to changes imposed by the environment, other organisms, or both. The species and metabolic diversity that typically develop within a biofilm afford the community greater adaptability and enhanced ecological persistence. These unique characteristics allow biofilms to be present in virtually every corner of natural or engineered environments and, often, to be an integral component of such environments. Some biofilms are found in extremely toxic environments and others act as the workhorse of man-made systems. Below are a few examples of the wide array of e"nvironments" in which biofilms thrive.

Biofilms Found in Nature

• Biofilms in hydrothermal vents

With their steep gradients of pH, temperature, pressure, and metals, deep-sea hydrothermal vents are an excellent example of the extreme natural conditions to whic microorganisms can physiologically adapt. It appears that the formation of biofilms is a crucial strategy that microbes use to withstand this harsh environment.

Hydrothermal vents occur globally at sea-floor spreading zones, where extremely hot and acidic lavas and anoxic hydrothermal fluids, enriched in dissolved heavy metals and reactive gases mix with cold, oxygenated seawater to precipitate metal sulfides and form spectacular features such as black smokers (i.e., vents). These vents host a wide array of microbial communities and unique animals. Microbial biomass abundantly associates with vent chimneys of either sulfide or carbonate, and varies with the degree of hydrothermal activity   

• Beneficial biofilms in water and wastewater treatment

Biofilms are widely used in environmental engineering systems as the powerhouse of treatment processes. For example, biofilms are used to remove organic matter in drinking water, a process called biologically active filtration (i.e., biofiltration). They are also used to remove biological nutrients in wastewater treatment. In both cases, bacteria are utilized for their ability to rapidly break down and transform complex organic compounds into simple forms that have fewer negative impacts on the receiving environment. Specifically, biofilm bacteria are much more efficient than planktonic cells in many treatment systems; the immobilized cells in biofilms will not be washed away, thus allowing for continuous treatment of large volumes of water. This engineering advantage also provides biofilm bacteria with a continuous source of food (i.e., carbon and other nutrients found in the untreated water), which allows the cells to thrive under an otherwise nutrient-poor condition.

Neutral fats or triglycerides, the major components of storage fats in plant and animal cells, consist of the alcohol glycerol linked to three molecules of fatty acids. Before a molecule of neutral fat can be metabolized, it must be hydrolyzed to its component parts.