Chapter 22 Human Microbiome The Human Microbiome An

Chapter 22 Human Microbiome

The Human Microbiome �An organized system of microbes exists within every healthy adult. �The microbiome consists of over 100 trillion organisms. �Microbial communities vary across locations on the body. �Microbial communities also vary among individuals.

The Human Microbiome • The Human Microbiome Project was completed in 2012, after following 242 healthy adults for 5 years. • Researchers identified bacteria by using DNA sequencing technology. • They found that microbial cells outnumber human cells by 10 to 1. • It is becoming clear that these microorganisms play a crucial role in human health. • The components of the individual microbial communities vary widely across locations on the body and among individuals. The particular bacteria that perform certain tasks may also vary among individuals.

Microbial Genes vs. Human Genes

Microbial Genes vs. Human Genes • The effects of the microbiome on human health are far -reaching. • Microbial genes influence health just as human genes do. • Researchers think that some diseases that appear to be heritable, but for which no human gene can be identified, may result because of genes contained within the microbiome. Because much of the microbiome passes from mother to child, these disease -causing bacterial genes may be passed from one generation to another.

Building a Microbiome

Building a Microbiome • Infants leave the womb without a single microbe. The first step in building a microbiome comes when the newborn passes through the birth canal and is coated with bacteria. • During pregnancy, the bacterial community within the mother’s birth canal changes considerably in preparation for the child’s birth. • After birth, the child picks up bacteria from his or her immediate environment. • Breastfeeding contributes a number of bacteria to the child’s microbiome; breast milk also supplies a sugar that nourishes gut bacteria in the newborn. • Children born by Caesarean section, as well as those who take high levels of antibiotics, have a higher rate of allergies and asthma.

Question The first step in building a microbiome occurs: A. B. C. D. in the womb. during the birth process. when the child begins to breathe air. when the child first eats.

Diseases Linked to Microbiome Imbalance �Diabetes �Heart disease �Asthma �Multiple sclerosis �Obesity

Diseases Linked to Microbiome Imbalance • Many other diseases have also been linked to a disruption in the microbiome. • Broad-spectrum antibiotics are the major culprit in microbiome disruption. Because antibiotics kill good bacteria along with the bad, an imbalance in the microbial community occurs. This allows bad bacteria to invade and reproduce, unchecked by the good bacteria. • It is not yet clear how the body knows which bacteria to kill and which ones to nourish.

Bacteria Flagella DNA Ribosomes Capsule Plasmid Cell wall Cytoplasmic membrane Pili

Bacteria • Bacteria are the chief inhabitant of the microbiome. • DNA is grouped in the cell’s central region. Bacteria do not have a membrane-enclosed nucleus or organelles • Some have a capsule: a gelatinous coating that keeps bacteria from drying out. The capsule also wards off attack by larger microorganisms (and white blood cells). • The cell wall is composed of a polysaccharide molecule called peptidoglycan. • The cytoplasmic membrane regulates flow into and out of cell. • Ribosomes synthesize proteins. • Pili are hair-like projections that allow bacteria to attach to cells and surfaces. • Small loops of DNA called plasmids allow bacteria to transmit DNA from one bacterial cell to another. This allows bacteria to be very adaptable; for example, it allows genes that resist an antibiotic to spread rapidly through a bacterial population.

Bacterial Shapes Cocci Bacilli Bacteria exist in one of three shapes: • Cocci are round or spherical. • Bacilli are rod-shaped. • Spirilla are spiral-shaped. Spirilla

Bacterial Shapes Diplococci Streptococci Staphylococci Some bacteria exist singly; others exist in aggregates or clusters. • Diplococci are cocci that exist sets of two, whereas monococci live singly. • Streptococci are cocci that exist in chain form. • Staphylococci are cocci that occur in clusters.

Identifying Bacteria Gram-positive bacteria Gram-negative bacteria �Have a thick layer of peptidoglycan in their cell walls, which retains the dye �Stain purple �Have a cell wall consisting of a thin layer of peptidoglycan and an outer membrane �Lose the dye when rinsed �Appear red or pink after a counterstain is applied

Identifying Bacteria • Gram staining—which involves applying dye to a bacterial sample—is almost always the first step in identifying the bacterial cause of an illness. • Whether or not the bacteria retain the dye determines whether the bacteria will be classified as Gram negative or Gram positive. • Although the technique can’t identify the species of bacteria causing an illness, the fact that it provides immediate results can be useful when making treatment decisions. • Because antibiotics such as penicillin work by attacking the peptidoglycan in the bacterial cell wall, they are more effective against Gram-positive bacteria.

Question Which bacterial structure allows bacteria to develop drug resistance? A. B. C. D. Capsule Pili Cytoplasmic membrane Plasmids

Viruses Capsid Capsomeres Envelope

Viruses • Viruses are extremely small infectious agents; most cannot even be seen under a light microscope. • Unlike bacteria, viruses are NOT cells. They cannot metabolize nutrients, produce or excrete wastes, move around on their own, or even reproduce on their own. • To reproduce, they must be inside of a host cell. • Viruses spark many diseases, including smallpox, AIDS, influenza, some cancers, and the common cold. • Viruses are simply a bundle of genetic material (either DNA or RNA) surrounded by a protein shell called a capsid. • Individual structural units called capsomeres join together to form the capsid. • Some viruses have an additional layer surrounding the capsid: a spikey lipid membrane called an envelope. The spikes help the viruses grip their target cell.

Viral Shapes Helical capsid Polyhedral capsid Complex capsid

Viral Shapes • The capsid may assume one of three basic shapes: • Helical viruses • Polyhedral viruses • Complex viruses • A capsule may or may not surround the capsid. • Bacteriophages (which infect bacterial cells) are complex viruses, consisting of a helical sheath and a complex head containing DNA or RNA. They use the tail fibers to attach to the surface of its host. They then uses the sheath like a syringe to inject its nucleic acid into the target cell.

Viral Replication

Viral Replication Viruses by themselves are inert. To replicate, they must invade a host cell and hijack that cell’s metabolic chemicals and ribosomes. 1. When a virus encounters a host cell, it binds to the cell’s surface. 2. The virus then penetrates the cell, either by fusing with the cell’s membrane or by causing the cell to engulf it. Once inside, the virus releases its DNA into the cell. 3. The virus then commandeers the host cell’s machinery, and the host begins producing viral nucleic acids instead of its own. Each nucleic acid is then encased in a capsid manufactured from the host’s amino acids. 4. The completed viruses are released from the cell, often destroying the host in the process. A single cell may produce from 10, 000 to 50, 000 new viruses in as little as 48 hours.

Fungi �Include molds and yeasts �Live in the soil, on plants, and in the air �Many fungal infections begin on the skin or in the lungs. �Persons most likely to develop fungal infections include those with weakened immune systems and those taking antibiotics.

Fungi • Some fungi reproduce through tiny spores in the air, making it possible to inhale the spores or for them to land on the skin. • When antibiotics disrupt the microbiome, a yeast-like fungus called Candida albicans—which normally resides on the skin as well as in the mouth, intestines, and vagina—often overgrows, resulting in vaginitis or oral thrush. • Athlete’s foot and ringworm are also fungal infections.

Question To reproduce, viruses: A. insert their DNA inside of a host cell. B. assume a host’s DNA. C. need only warmth and air; they can reproduce on any surface. D. first build a new capsid.