Chapter 22b Flashcards
Only microbes have genes for glycoside hydrolases and polysaccharide lyases that can
degrade cellulose, hemicellulose, and other insoluble polysaccharides
Cellulose is the mos
abundant component of plant fibers
Two digestive plans
Foregut fermentation –Hindgut fermentation–
Rumen
pecial digestive organ in some herbivorous mammals (cows, sheep, elk)
Site of cellulose digestion
anaerobic microbes-rumen
Biochemical reactions in the rumen
1010–1011 microbes/g of rumen
•Cellulolytic microbes that hydrolyze cellulose to free glucose that is then fermented, producing volatile fatty acids (VFAs) and CH4 and CO2
Rumen microbes
Synthesize VFAs • Directly digested and serve as protein
Anaerobic microbes
–Bacteria –Protists –Fungi –Archaea
Rumen microbes continued
• Cellulose decomposers • Starch decomposers • Lactate decomposers • Succinate decomposer • Pectin decomposer • Methanogens
All sites on a human that contains microorganisms are part of the
microbiome
Human Microbiome Project
Humans are monogastric and omnivorous
•1014 cells present in microbiome (= 10× more
bacterial cells than human cells)
The Human Gut Microbial Community
Microbes in gut affect early development, health, and predisposition to disease
•High variability in gut communities between
different individuals
Colonization of gut begins at birth-responsible for “maturing” of gastrointestinal tract
Triggering expression of human genes responsible
for nutrient uptake and metabolism –Recognition of gut microflora as nonforeign –Development of mucosal barrier
Human gut microorganisms produce
Enzymes –Amino acids –Vitamins
•Firmicutes (64%) •Bacteroides (23%) •Proteobacteria (8%) •Actinobacteria (3%)
Human gut microorganisms may play a role in
obesity
Mouth and skin are also heavily colonized by microorganisms
•Mouth:
At least 750 species of aerobic and anaerobic
bacteria –Methanogenic Archaea and yeast
Mouth and skin are also heavily colonized by microorganisms: skin:
19 bacterial phyla (over 200 genera)
•Corynebacterium (moist sites) •Propionibacterium (oily sites) •Staphylococcus (oily sites)
–Fungi (mainly yeast)
Heritable Symbionts of Insects
•Microbial symbionts can be acquired from :
–Environmental reservoir (horizontal transmission) –Parent (vertical or heritable transmission) –Heritable symbionts of insects are obligate (lack a
free-living replicative stage)
Primary
Primary symbionts—required for host reproduction
–Restricted to bacteriome, bacterial cells found in bacteriocytes
•Ex: Buchnera supplies amino acids to aphids
Secondary
Not required for reproduction –Not always present in every individual –Can invade different cells and live extracellularly –Must provide a benefit
•Nutritional •Protection from environment •Protection from pathogens
Some insects exploit the metabolic potential of the symbiont
•Primary symbionts exhibit extreme gene reduction
Genome of insect symbiont ~160 to 800 kbp –Genome of related free-living bacteria ~2 to 8 Mbp –Retain only genes needed for host fitness
•Lose catabolic genes •Pathogens normally lose anabolic genes
Termites
Decompose cellulose and hemicellulose
Termite gut consists of foregut, midgut, and hindgut
Posterior alimentary tract of higher termites
•Diverse community of anaerobes including cellulolytic
anaerobes
–Lower termites
•Anaerobic bacteria and cellulolytic protists
Aquatic Invertebrates as Microbial Habitats: Hawaiian Bobtail Squid
Aliivibrio fischeri and the Hawaiian bobtail squid
•A. fischeri bioluminesce in light organ
•camouflages the squid from predators
Aquatic Invertebrates as Microbial Habitats: Hawaiian Bobtail Squid continued
Highly specific •Benefits both partners •Horizontal transmission of
bacterial cells—colonization shortly after juvenile squid hatch
•Bioluminescence is controlled by quorum sensing
•A. fischeri is supplied with nutrients by the squid
Marine Invertebrates at Hydrothermal Vents and Gas Seeps
Primary producers in hydrothermal vents are chemolithotrophic microbes
•Diverse invertebrate communities develop near hydrothermal vents, including large tube worms, clams, mussels
Chemolithotrophic prokaryotes that utilize reduced
inorganic materials emitting from the vents form endosymbiotic relationships with vent invertebrates
Vent tube worms
Trophosome contains symbionts –Hemoglobin binds H2S and O2 –CO2 in blood
Leeches
Leeches are parasitic annelids (segmented worms)
•Feed on vertebrate blood and secrete anticoagulants and vasodilators
•Crop has Aeromonas and a Rikenella-like bacterium •Intestinum has complex community
•Bladder—Ochrobactrum
Reef-building corals
Coral skeleton very efficient light-gathering structure
•Phototrophic symbionts include cyanobacterium, rhodophytes, chlorophytes, dinoflagellates, and diatoms
Reef-Building Corals
Most ecologically significant between stony coral and the dinoflagellate Symbiodinium
•Reef-building corals reproduce sexually by releasing gametes into the seawater
•Algal symbionts are typically found in the egg
•Developing coral can also ingest dinoflagellates
•Cnidarians receive fixed carbon
•Dinoflagellate receives inorganic nutrients
Reef-Building Corals: Coral bleaching
- Loss of color caused by lysis of symbiont
* High temperature and high light impair the photosynthetic apparatus of dinoflagellate
