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Chapter 21

Bacteria: The Deinococci and Nonproteobacteria

Gram Negatives

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Life on Earth evolved along three major lines, called domains, all derived from a common ancestor. Each domain contains several phyla. The domains,

Bacteria and Archaea, remained prokaryotic, whereas the third, Eukarya, evolved into the modern eukaryotic cell.

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Aquificae and Thermotogae

• Thermophiles that grow at temperatures above 85° C -Aquificae and Thermotogae

Figure 21.1

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Phylum Aquificae

• Thought to be deepest (oldest) branch of Bacteria

• Contains one class, one order, and five genera– two best studied genera are Aquifex

and Hydrogenobacter

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Genus Aquifex

• Thermophile with a growth optimum of 85°C and a maximum of 95°C

• Microaerophilic• Chemolithoautotroph

-uses hydrogen, thiosulfite, and sulfur as electron donor

-uses oxygen as electron acceptor

-genome ~1/3 size of E. coli

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Phylum Thermotogae

• Second deepest branch of Bacteria

• Contains one class, one order, and six genera– best studied genus is Thermotoga

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Genus Thermotoga

• Gram-negative rods– have outer sheathlike envelope that can

balloon out from ends of cell

• Thermophiles– optimum 80°C; maximum 90°C

– grow in active geothermal areas

– terrestrial solfataric springs

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Thermotoga…

• Chemoheterotrophs– have functional glycolytic pathway

– can grow anaerobically on carbohydrates and proteins digests

• e.g., Thermatoga maritima– ~24% of coding sequences are similar

to archaeal genes

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Figure 21.2

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Deinococcus-Thermus

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Genus Deinococcus

• Deinococcus is best studied

• Spherical or rod-shaped– associated in pairs or tetrads– stain gram-positive but do not have typical

gram-positive cell wall• layered outer membrane similar to gram-negatives

• L-ornithine in peptidoglycan

• lacks teichoic acid

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Figure 21.3

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Deinococcus…

• Mesophilic• Mesophilc, aerobic, produce acid• Extraordinarily resistant to desiccation

and radiation– can survive 3-5 million rad (100 rad lethal to

humans)

• Isolated from ground meat, feces, air, fresh water, and other sources, but natural habitat unknown

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Deinococcus……

• Genome consists of two circular chromosomes, a megaplasmid, and a small plasmid– radiation resistance due to ability to repair

genome when it is severely damaged

• Rapidly repairs fragmented DNA within 12-24 hours when exposed to radiation

• D. radiodurans shown to have an efficient DNA repair system

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Photosynthetic Bacteria

• Three groups of photosynthetic bacteria– the purple bacteria– the green bacteria– the cyanobacteria

• differ from the purple and green bacteria by carrying out oxygenic photosynthesis

– have two photosystems– use water as an electron donor and generate oxygen

during photosynthesis

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Bloom of Purple Sulfur Bacteria, Sulfide Spring, Madison, WI

Purple sulfur bacteria

Alga

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differences in absorptionspectra correlateswith ecologicaldistribution

Figure 21.4

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Taxonomy of Photosynthetic Bacteria

• Phylum Chloroflexi – green nonsulfur bacteria• Phylum Chlorobi – green sulfur bacteria• Phylum Cyanobacteria• Phylum proteobacteria purple bacteria

– purple sulfur bacteria– purple non-sufur bacteria

• phylum Firmicutes – heliobacteria

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Purple sulfur bacteria: Note the sulfur granules deposited

inside the cells

Green sulfur bacteria: Note the sulfur granules deposited

outside the cells

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Purple bacteria Halophilic Purple bacteria

Chlorosomes from green bacteria

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Phylum Chlorobi

• Green sulfur bacteria• Morphologically diverse

– rods, cocci, or vibrios; single cells, chains, or clusters

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Chlorobi…

• Have chlorosomes– ellipsoidal vesicles attached to plasma membrane– contain accessory photosynthetic pigments– most efficient light harvesting complexes found in

nature

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Chlorosomes –Green Sulfur & Green Non-sulfur

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Chlorobi…

• Lack flagella; nonmotile• Some have gas vesicles

– used to adjust depth of cell for adequate light and H2S

• Obligately anaerobic photolithoautotrophs– use H2S, elemental sulfur and H2 as electron

sources– elemental sulfur deposited outside cell

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Figure 21.5

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Phylum Chloroflexi

• Green nonsulfur bacteria

• Contains photosynthetic and nonphotosynthetic members– e.g., genus Chloroflexus –

photosynthetic

– e.g., genus Herpetosiphon - nonphotosynthetic

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Genus Chloroflexus• Thermophilic

– often isolated form neutral to alkaline hot springs

– grow in form of orange-reddish mats

• Metabolism– anoxygenic photosynthesis

• does not use water as electron donor• photoheterotroph

– can grow aerobically as a chemoheterotroph

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Chloroflexus sp. Chloronema sp. on stratified Michigan Lake

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Phylum Cyanobacteria

• Largest, most diverse group of photosynthetic bacteria

• Most obligate photolithoautotrophs; some can grow slowly in dark as chemoheterotrophs

• One current classification system divides group into 62 species and 24 genera

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Photosynthesis in cyanobacteria

• Resembles that of eucaryotes– have chlorophyll a

• prochlorophytes have chlorophyll a and b

– have photosystem I and II– oxygenic photosynthesis

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Photosynthesis in cyanobacteria…

• Use phycobiliproteins as accessory pigments

• phycobilisomes, which line thylakoid membranes, contain phycocyanin and phycoerythrin

• prochlorophytes lack phycobilins

• use Calvin cycle to fix CO2

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Cyanobacterial Thylakoids and Phycobilisomes

Figure 21.6

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Figure21.7 (a)

containsphyco-bilinpigments

typicalgram-negativecellwall

siteofphoto-synthesis

nitrogenstoragepolymer

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Figure 21.7b

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Oxygenic Photosynthetic Bacteria

Figure 21.8

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Heterocysts

• Specialized cells used for nitrogen fixation– produced when organism is nitrogen deprived– differentiate from individual cells in filament

• involves reorganization of photosynthetic membranes

– thick heterocyst wall prevents O2 diffusion into heterocyst which would inactivate nitrogenase, enzyme responsible for nitrogen fixation

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Heterocysts and Akinetes

Figure 21.9

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Prochlorophytes

• Cyanobacteria in genera Prochloron, Prochlorococcus, and Prochlorothrix– distinguished by presence of chlorophyll a

and b and lack of phycobilins • are the only procaryotes to possess

chlorophyll b–makes them candidates as ancestors of endosymbionts that give rise to chloroplasts

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Prochloron

Figure 21.10

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Ecology of cyanobacteria

• Tolerant of environmental extremes– thermophilic species can grow at

temperatures up to 75°C– often are primary colonizers

• Can cause blooms in nutrient-rich ponds and lakes– some produce toxins

• Often form symbiotic relationships– e.g., are phototrophic partner in most lichens– e.g., symbionts with protozoa and fungi– e.g., nitrogen-fixing species form associations

with plants

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Figure 21.11

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Phylum Chlamydiae

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Genus Chlamydia

• Gram-negative bacteria– cell walls lack muramic acid and

peptidoglycan– have very small genomes

• Obligate intracellular parasites with unique developmental cycle– involving formation of elementary body (EB)

and reticulate body (RB) or initial body– found mostly in mammals and birds– some recently isolated from spiders, clams,

and freshwater invertebrates

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Figure 21.13b

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Chlamydial metabolism

• Appear to be energy parasites, obtaining ATP from host– do have genes for substrate-level

phosphorylation, electron transport, and oxidative phosphorylation

• Reticulate bodies have biosynthetic capabilities when supplied precursors from host; can synthesize some amino acids

• Elementary bodies seem to be dormant forms

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Important pathogens

• C. trachomatis– infects humans and mice– causes trachoma, nongonococcal urethritis,

and other diseases in humans

• C. psittaci– infects humans and many other animals– causes psittacosis in humans

• C. pneumoniae– common cause of human pneumonia

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Phylum Spirochaetes

• Gram-negative bacteria with distinctive structure and motility– slender, long with flexible helical shape– creeping (crawling) motility due to a

structure called an axial filament

• Chemoheterotrophs• Ecologically diverse

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Figure 21.14

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axial filament = complex of axial fibrils (periplasmic flagella)

Figure 21.15 (a1) and (a2)

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Figure 21.15 (b)

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Figure 21.15 (c) and (d)

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current thought:axial fibrils rotate, causingcorkscrew-shaped outer sheathto rotate and move cell throughsurrounding liquid

Spirochete Motility

Figure 21.16

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Symbiotic Associations

• Broad range of organisms

• Found in a variety of locations, for example– hindguts of termites

– digestive tracts of mollusks and mammals

– oral cavities of animals

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Spirochete-Protozoan Associations

Figure 21.17

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