Allies and Enemies: How the World Depends on Bacteria Read Online Free PDF Page B

caused disease B, and so forth. Koch used potato slices for growing bacterial colonies and for his studies used only colonies that were isolated from all other colonies. This concept
    seems elementary today, but it helped microbiologists of Koch’s time
    rid their experiments of contaminants. To this day, prominent
    researchers have reported results only to make an embarrassing
     
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    retraction months later because all of the data were collected on a contaminant.
    When Hesse joined Koch’s laboratory, Koch had stopped using
    potato slices and substituted gelatin as a handier surface for growing
    pure colonies. Soon both men were grousing about gelatin’s flaws. In
    hot summers, the gelatin turned to liquid. Most other times, protein-degrading bacteria turned it into a useless blob. Hesse’s wife, Angelina, often came to the lab to help—this was a period in Germany when women were taking their first steps into professions.
    Lina, as Hesse called her, was an amateur artist and helped Koch and
    Hesse by drawing the bacterial colonies they had grown in the laboratory. She soon understood why the two microbiologists needed something better than gelatin. Lina suggested that they try agar-agar, a common ingredient at the time for solidifying puddings and jellies.
    Wolfgang, the Hesses’ grandson recalled in 1992, “Lina had learned
    about this material as a youngster in New York from a Dutch neighbor who had immigrated from Java.” People living in the warm East
    Indian climate noticed that birds gathered a substance from seaweed
     
    and used it as a binding material in nests. The material did not melt
    and did not appear to spoil—bacteria cannot degrade it.
    Hesse passed on to Koch the idea of replacing gelatin with agar-agar. Koch immediately formulated the agar with nutrients into a medium that melted when heat-sterilized and solidified when cooled (see Figure 1.3). Koch published a short technical note on the invention but mentioned neither of the Hesses. Lina lived for 23 years after her husband’s death in 1911 and saved as many of his lab notes as she could find. A few of those notes showed that Hesse and Lina had originated the idea of agar in microbial growth media, and they have since been recognized for their part in microbiology.
    Three years after Koch and Hesse switched to agar-based media,
    another assistant in the laboratory, Richard J. Petri, designed a shallow glass dish to ease the dispensing of the sterilized molten media.
    The dishes measured a little less than a half-inch deep and 4 inches in diameter. This Petri dish design has never been improved upon and is a staple of every microbiology lab today.
     

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    allies and enemies
    Figure 1.3 Pouring molten agar. Agar melts when sterilized, and then solidifies when it cools to below 110°F. The microbiologist here pours the agar asep-tically from a sterile bottle to a sterile Petri dish. (Courtesy of BioVir Laboratories, Inc.) The size of life
    Bacteria need only be big enough to hold their vital enzymes, proteins, and genetic machinery. Evolution has eliminated all extraneous structures. Also, a small, simple architecture allows for rapid reproduction, which aids adaptation. Bacterial metabolism is a model of efficiency because of a large surface-to-volume ratio that smallness creates. No
    part of a bacterial cell is very far from the surface where nutrients enter and toxic wastes exit. Eukaryotic cells that make up humans, algae, redwoods, and protozoa contain varied organelles each surrounded by a membrane. The surface-to-volume ratio in these cells is one-tenth that of bacteria, so shuttling substances across all those organelle membranes, the cytoplasm, and the outer membrane burns energy. Bacterial structure is less demanding and more efficient.
    Finally, small size contributes to massive bacterial populations that dwarf the populations of any other biota.
     
    chapter 1 · why the world needs