Allies and Enemies: How the World Depends on Bacteria Read Online Free Page B
Author: Anne Maczulak
Tags: science, Reference, Non-Fiction
numerous flagella. Ten to 12 flagellated cells team up and then squiggle away from the main
colony. By forming teams of cells lined up in parallel, 50 times more
flagella power the cells forward than if one Proteus headed out on its
own. Several millimeters from the main colony, the swarmers stop and again begin to reproduce normally. As generations of progeny grow, they build a ring of Proteus around the original colony, shown in Figure 1.2. At a certain cell density in the ring, Proteus repeats the swarming process until a super-colony of concentric rings covers the entire surface. When two swarming Proteus colonies meet, they do not overrun each other. The two advancing fronts stop within a few ì m of each other, repelled by their respective defenses. Proteus produces an antibacterial chemical called bacteriocin. The specific bacteriocin of each swarmer colony protects its turf against invasion.
Other swarmer bacteria use hairlike threads called pili rather
than flagella, and cast their pili ahead to act as tethers. By repeatedly contracting, the cells drag themselves forward to up to 1.5 inches per hour. Petri dishes measure only 4 inches across, but if dishes were the size of pizzas, swarm cells would cover the distance.
Communities such as biofilm grow on surfaces bathed in moisture. Biofilms cover drinking water pipes, rocks in flowing streams,
plant leaves, teeth, parts of the digestive tract, food manufacturing lines, medical devices, drain pipes, toilet bowls, and ships’ hulls.
Unlike swarming colonies, biofilm contains hundreds of different
14
allies and enemies
species, but they too interact via quorum sensing. (Bacteria that merely attach to surfaces such as skin are not true biofilms because
they do not coalesce into a community that functions as a single entity.) Biofilm begins with a few cells that stick to a surface by laying down a coat of a sticky polysaccharide. Other bacteria hop aboard and build the diverse biofilm colony.
Figure 1.2 The swarming bacterium Proteus mirabilis. Proteus swarms outward from a single ancestor cell and forms concentric growth rings with each generation. (Courtesy of John Farmer, CDC Public Health Image Library) Biofilms facilitate survival by capturing and storing nutrients and
excreting more polysaccharide, which protects all the members
against chemicals such as chlorine. Eventually fungi, protozoa, algae,
and inanimate specks lodge in the conglomeration of pinnacles and
channels. When the biofilm thickens, signals accumulate. But
because many different species live in the biofilm, the signals differ.
Some bacteria stop making polysaccharide so that no more cells can
join the community. The decrease in binding substance causes large
chunks to break from the biofilm, move downstream, and begin new
biofilm. (This constant biofilm buildup and breakdown causes great
fluctuations in the number of bacteria in tap water. Within a few hours tap water can go from a few dozen to a thousand bacteria per
milliliter.) Meanwhile, other bacteria ensure their own survival by
chapter 1 · why the world needs bacteria
15
increasing polysaccharide secretion, perhaps to suffocate nearby
microbes and reduce competition.
Pathogens likely use similar strategies in infection by turning off
polysaccharide secretion. With less polysaccharide surrounding the bacteria, the cells can reproduce rapidly. Then when pathogen numbers reach a critical level in the infected area, polysaccharide secretion returns to quash competitors.
A second type of multispecies community, the microbial mat, functions in complete harmony. Microbial mats lie on top of still waters and are evident by their mosaic of greens, reds, oranges, and purples from pigmented bacteria. Two types of photosynthetic bacteria dominate microbial mats: blue-greenish cyanobacteria and purple sulfur-using bacteria. During the day, cyanobacteria multiply and fill the mat’s upper regions with oxygen. As night
colony. By forming teams of cells lined up in parallel, 50 times more
flagella power the cells forward than if one Proteus headed out on its
own. Several millimeters from the main colony, the swarmers stop and again begin to reproduce normally. As generations of progeny grow, they build a ring of Proteus around the original colony, shown in Figure 1.2. At a certain cell density in the ring, Proteus repeats the swarming process until a super-colony of concentric rings covers the entire surface. When two swarming Proteus colonies meet, they do not overrun each other. The two advancing fronts stop within a few ì m of each other, repelled by their respective defenses. Proteus produces an antibacterial chemical called bacteriocin. The specific bacteriocin of each swarmer colony protects its turf against invasion.
Other swarmer bacteria use hairlike threads called pili rather
than flagella, and cast their pili ahead to act as tethers. By repeatedly contracting, the cells drag themselves forward to up to 1.5 inches per hour. Petri dishes measure only 4 inches across, but if dishes were the size of pizzas, swarm cells would cover the distance.
Communities such as biofilm grow on surfaces bathed in moisture. Biofilms cover drinking water pipes, rocks in flowing streams,
plant leaves, teeth, parts of the digestive tract, food manufacturing lines, medical devices, drain pipes, toilet bowls, and ships’ hulls.
Unlike swarming colonies, biofilm contains hundreds of different
14
allies and enemies
species, but they too interact via quorum sensing. (Bacteria that merely attach to surfaces such as skin are not true biofilms because
they do not coalesce into a community that functions as a single entity.) Biofilm begins with a few cells that stick to a surface by laying down a coat of a sticky polysaccharide. Other bacteria hop aboard and build the diverse biofilm colony.
Figure 1.2 The swarming bacterium Proteus mirabilis. Proteus swarms outward from a single ancestor cell and forms concentric growth rings with each generation. (Courtesy of John Farmer, CDC Public Health Image Library) Biofilms facilitate survival by capturing and storing nutrients and
excreting more polysaccharide, which protects all the members
against chemicals such as chlorine. Eventually fungi, protozoa, algae,
and inanimate specks lodge in the conglomeration of pinnacles and
channels. When the biofilm thickens, signals accumulate. But
because many different species live in the biofilm, the signals differ.
Some bacteria stop making polysaccharide so that no more cells can
join the community. The decrease in binding substance causes large
chunks to break from the biofilm, move downstream, and begin new
biofilm. (This constant biofilm buildup and breakdown causes great
fluctuations in the number of bacteria in tap water. Within a few hours tap water can go from a few dozen to a thousand bacteria per
milliliter.) Meanwhile, other bacteria ensure their own survival by
chapter 1 · why the world needs bacteria
15
increasing polysaccharide secretion, perhaps to suffocate nearby
microbes and reduce competition.
Pathogens likely use similar strategies in infection by turning off
polysaccharide secretion. With less polysaccharide surrounding the bacteria, the cells can reproduce rapidly. Then when pathogen numbers reach a critical level in the infected area, polysaccharide secretion returns to quash competitors.
A second type of multispecies community, the microbial mat, functions in complete harmony. Microbial mats lie on top of still waters and are evident by their mosaic of greens, reds, oranges, and purples from pigmented bacteria. Two types of photosynthetic bacteria dominate microbial mats: blue-greenish cyanobacteria and purple sulfur-using bacteria. During the day, cyanobacteria multiply and fill the mat’s upper regions with oxygen. As night
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