Allies and Enemies: How the World Depends on Bacteria by Anne Maczulak Read Free Book Online Page A

on intestinal bacteria to participate in the enzymatic digestion of food. The numbers reach 1012 cells per gram of digested material. Monogastric animals such as humans and swine absorb nutrients made available by the body’s enzymes as well as nutrients produced by bacteria. When
    the bacteria die and disintegrate in the intestines, the body absorbs
    the bacterial sugars, amino acids, and vitamins (B-complex and vitamin K) the same as dietary nutrients are absorbed. Cattle, goats, rabbits, horses, cockroaches, and termites, by contrast, eat a fibrous diet high in cellulose and lignin that their bacteria must break down into compounds called volatile fatty acids. Glucose serves as the main energy compound for humans, but volatile fatty acids power ruminant animals (cattle, sheep and goats, elephants, and giraffes) and animals with an active cecum (horses and rabbits).
     
    chapter 1 · why the world needs bacteria
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    Rumen bacteria carry out anaerobic fermentations. Almost every
    organic compound in the rumen becomes saturated there by fermentative bacteria before moving on to the intestines. As a result, ruminants such as beef cattle deposit saturated fats in their body tissue.
    Nonruminant animals, such as pigs and chicken, carry out fermentations to a lesser extent and their meat contains less saturated fat.
    How important are all these bacteria in keeping animals alive?
    Germfree guinea pigs grow smaller than normal, develop poor hair
    coat, and show symptoms of vitamin deficiency compared with animals with a normal microbial population. Germfree animals also
    catch infections more than populated animals. On the upside,
    germfree animals never experience tooth decay!
    Bacteroides, Eubacterium, Peptostreptococcus, Bifidobacterium, Fusobacterium , Streptococcus , Lactobacillus , and E. coli of the human intestines also produce heat in the same way wine fermentations produce heat. This heat loss is inefficient for the bacteria—any energy that dissipates before it can be used is lost forever—but the
    body uses it to maintain body temperature. The large numbers of
    normal intestinal bacteria also outcompete small doses of food illness
    bacteria such as Salmonella , Clostridium , Bacillus , Campylobacter , Shigella, Listeria , and E. coli .
    E. coli is the most notorious of foodborne pathogens and also the most studied organism in biology. In fact, E. coli plays a minor role in the digestive tract; other bacteria outnumber it by almost 1,000 to one. E. coli has become the number one research tool in microbiology for two reasons. First, this microbe cooperates in the laboratory.
    E. coli is a facultative anaerobe, meaning it grows as well with oxygen as without it. It requires no exotic nutrients or incubation conditions, and it doubles in number so rapidly that a microbiologist can inoculate it into nutrient broth in the morning and have many millions of cells that afternoon. The second reason for using E. coli in biology relates to the ease of finding it in nature: The human bowel and that of most other mammals produce a constant supply.
    The origins of our bacteria
    Infants have no bacteria at birth but start establishing their skin flora within minutes and digestive tract populations soon after. E. coli , 30
    allies and enemies
    lactobacilli, and intestinal cocci latch on to a baby during birth and
    become the first colonizers of the infant’s digestive tract. Babies get additional bacteria for a reason that scares germophobes: fecal and nonfecal bacteria are everywhere, and people ingest large amounts each day. Fecal bacteria disseminate beyond the bathroom to coun—tertops, desks, refrigerator handles, keyboards, remote controls, and
    copy machine buttons. Any object repeatedly touched by different people contains fecal bacteria. Newborns get these bacteria every time they handle toys or crawl on the floor, and then put their hands or other objects in their mouth. Adults similarly receive fecal bacteria, called