Bdellovibrio

Transcription

Bdellovibrio

Bio 230 - Microbiology - Spring 2010
Study Guide 16
http://cvtree.cbi.pku.edu.cn/pics/gallery/72-k6.png
Alpha-Proteobacteria
http://www.life.umd.edu/classroom/bsci424/BSCI223WebSiteFiles/AlphaProteobacteria.gif
Beta-Proteobacteria
http://www.life.umd.edu/classroom/bsci424/BSCI223WebSiteFiles/BetaProteobacteria.htm
Gamma-Proteobacteria
Epsilon-Proteobacteria
MAT Database
MAT (methionine adenosyltransferase
E.C.2.5.1.6.) is a housekeeping metabolic
enzyme that catalyzes the synthesis of
SAM (S-adenosylmethionine) from ATP
and methionine.
http://www2.iib.uam.es/gfsanchez/MAT/Main.htm
Bdellovibrio species are found in river
water or soil and live an intraperiplasmic
existence. To enrich for Bdellovibrio use
NB/500 (nutrient broth at 1:500 dilution)
and mix with hot soft agar with E. coli at
30 °C for one week.
http://en.wikipedia.org/wiki/Bdellovibrio
http://commtechlab.msu.edu/sites/DLC-ME/curious/caOc96LC.gif
http://www.bbc.co.uk/radio4/science/media/bdellovibrio-bacteria.jpg
https://www.cals.ufl.edu/SOS/ppprez/Pathogens%20as%20Prey%20Presentation.ppt.
On the Hunt
• Attack state – highly
mobile and can not
reproduce
• Moves very fast 160
um/s (human moving 4
mph)
• Chemotaxis - chemical
sensing to find “target
rich” environments
Bdellovibrio attached to a cell of Pseudomonas
http://www.microgen.ouhsc.edu/b_bacter/b_bacter_home.htm
Chemotaxis
• Bdellovibrio genome contains 18 known
chemotaxis genes and 1 known aerotaxis genes
• At least one gene shown to directly contribute to
predation efficiency
• Actual chemical molecules and signals used are
unknown
• Chemotaxis likely used to find environments
favorable to prey species
• Quorum sensing signals are not utilized
Attacking Prey
• Target of attack on prey outer cell membrane
is unknown
• No known mechanisms of resistance in prey
• Likely target is either non-specific or highly
conserved receptor necessary for cell
viability
• Subject of intense research as exact target has
been naturally selected as a favorable
strategy and may lead to development of
novel antibiotics
Entry and Attachment
• Bdellovibrio uses flagella to make physical
contact, grabs on with pili
• Attachment is initially reversible, becomes
permanent after initial “recognition” step
• May have preferred prey – attachment rates
differ in mixed populations
• Enters through hole induced in outer
membrane by peptidoglycan hydrolysis
Formation of the Bdelloplast
• Bdellovibrio restabilizes prey outer
membrane to contain nutrients and protect
against dehydration
• Bdellovibrio attaches to the inner membrane
causing the cytoplasm to round up into the
osmotically stable Bdelloplast
• Exact mechanism of Bdelloplast formation
is unknown but prey membrane maintains
structural integrity
• Bdellovibrio begins to extract and digest
prey cellular components
Prey Utilization
• Nearly all of the prey bacteria is utilized
• Prey components are broken down via
hydrolysis and used to replicate additional
Bdellovibrio or metabolized for energy
• About 50% of prey nucleic acid utilized for
de novo synthesis
• Ribose from other 50% metabolized for
energy
• Final rupture of cell wall degrades
peptidoglycans, liberating sugars and amino
acids that can be used by Bdellovibrio
Hydrolysis
• Few prey molecules utilized intact, must break
down for own biosynthesis
• Large number of genes for hydrolytic enzymes
• Radiolabeling and electrophoresis confirm prey
molecules are degraded before synthesis
Synthesis
• Sophisticated coordination by predator
regulators ensures smooth pathway from
degradation to synthesis
• Hydrolytic degradation products
incorporated into ongoing synthesis
• Regulators are unknown
• Bdellovibrio genome contains many
synthesis genes, including 3 for ATP alone
Cell Membrane Construction
• It is unclear if Bdellovibrio scavenges large
membrane molecules
• Current evidence suggests Bdellovibrio
synthesizes its own membrane
macromolecules
• Bdellovibrio Lipid A has a unique structure
• Outer Membrane Protein (OMP)
scavenging confirmed by SDS-PAGE,
refuted by mass spectroscopy
Nucleic Acid Synthesis
• Prey nucleic acids initially cuts with endonucleases
• Molecules then taken apart one at a time with
exonucleases
• To replicate offspring, Bdellovibrio must
synthesize much more nucleic than contained
within prey
– E coli prey cell contains 4M bp
– Bdellovibrio produced 4 offspring synthesizes
approximately 15M bp
Protein Synthesis
• Bdelloplast can not replicate full set of
amino acids
• This suggests Bdellovibrio is only
capable of protein synthesis with
access to prey amino acids
Reproduction
• # of offspring limited by raw
material available from prey
• As Bdelloplast grows it
elongates into a filamentous
structure containing all
replicated chromosomes
• As Bdellovibrio senses the
prey has become exhausted
the Bdelloplast is organized
and septates into the
individual progeny
• The remaining prey
membrane is lysed and
progeny are set free
Starr and Baigent,, JOURNAL OF BACTERIOLOGY, May, 1966 Vol. 91,
No. 5
Rickettsia rickettsi
Rickettsia is a genus of motile,
Gram-negative, non-sporeforming,
highly pleomorphic bacteria that
can present as cocci (0.1 µm in
diameter), rods (1-4 µm long) or
thread-like (10 µm long). Obligate
intracellular parasites, the
Rickettsia depend on entry, growth,
and replication within the
cytoplasm of eukaryotic host cells
(typically endothelial cells).
http://upload.wikimedia.org/wikipedia/commons/8/86/Rickettsia_rickettsii.jpg
Certain segments of Rickettsial genomes resemble that of
mitochondria.The deciphered genome of R. prowazekii is
1,111,523 bp long and contains 834 protein-coding genes.
Unlike free-living bacteria, it contains no genes for
anaerobic glycolysis or genes involved in the biosynthesis
and regulation of amino acids and nucleosides. In this
regard it is similar to mitochondrial genomes; in both
cases, nuclear (host) resources are used. ATP production in
Rickettsia is the same as that in mitochondria. In fact, of
all the microbes known, the Rickettsia is probably the
closest "relative" (in phylogenetic sense) to the
mitochondria. Unlike the latter, the genome of R.
prowazekii, however, contains a complete set of genes
encoding for the tricarboxylic acid cycle and the
respiratory chain complex.
Cyanobacteria are Old
Ancient Fossil Bacteria : Pictured above are two kinds
cyanobacteria from the Bitter Springs chert of central Australia,
a site dating to the Late Proterozoic, about 850 million years
old. On the left is a colonial chroococcalean form, and on the
right is the filamentous Palaeolyngbya.
http://www.ucmp.berkeley.edu/bacteria/cyanofr.html
Archaean: 3.8 to 2.5 billion years ago
A layered stromatolite,
produced by the activity
of ancient
cyanobacteria.
The layers were produced as calcium carbonate precipitated over the
growing mat of bacterial filaments; photosynthesis in the bacteria depleted
carbon dioxide in the surrounding water, initiating the precipitation. The
minerals, along with grains of sediment precipitating from the water, were
then trapped within the sticky layer of mucilage that surrounds the bacterial
colonies, which then continued to grow upwards through the sediment to
form a new layer. As this process occured over and over again, the layers of
sediment were created. This process still occurs today; Shark Bay in
western Australia is well known for the stromatolite "turfs" rising along its
beaches.
The Cyanobacteria are morphologically an
extremely diverse group.
So much so that without an electron
microscope, the botanists thought it was their
domain, rather than that of the microbiologists
http://www.keweenawalgae.mtu.edu/ALGAL_PAGES/cyanobacteria.htm
http://www.bact.wisc.edu/Microtextbook/images/book_4/chapter_2/2-53.jpg
http://www.keweenawalgae.mtu.edu/ALGAL_IMAGES/cyanobacteria/Anabaena_jason_dbtow17_2016.jpg
http://biotech.szbk.u-szeged.hu/KK_Jegyzet/pic/heterocyst.gif
Anabaena filaments which have been genetically engineered so
that the heterocysts are expressing a fluorescent protein:
http://www.mun.ca/biochem/courses/3107/Topics/Site_specific_Recomb.html
The nif genes of K. pneumoniae are all clustered together in a 20
kb segment of the chromosome and they are all expressed as 7 or 8
operons:
* Dintrogenase reductase is a dimer of two identical sububits.
nifH codes for this subunit.
* Nitrogenase is a tetramer with two alpha and two beta
subunits.
o nifD codes for the alpha subunit of dinitrogenase.
o nifK codes for the beta subunit of dinitrogenase.
In Anabaena sp. PCC 7120, the nif genes were originally mapped
using vegetative cell DNA. A surprise finding was the fact that the
genes were not tightly clustered and, worse, the nifK gene was
located 11 kb away from nifD as shown in the following map:
This was troubling because NifK and NifD are required in
equimolar amounts in the cell and there was no obvious way to
regulate how this would be so.
The heterocyst map showed no intervening DNA between
nifK and nifD!
Further research proved what was going on. Heterocyst differentiation actually required
a site-specific recombination event to excise this intervening element. The
recombination is catalyzed by XisA which acts at two directly repeating 11 bp
sequences within the nifD gene (shown as large red triangles). Since the initial
discovery of this DNA rearrangement, two further DNA rearrangements have been
characterized:
* a 55 kb element that interrupts the fdxN gene is removed during heterocyst
differentiation. This recombination is catalyzed by the xisF gene which acts at two
directly repeating 5 bp sequences within the fdxN gene (shown as green triangles
above). As a result, the nifB-fdxN-nifS-nifU operon can then be expressed properly.
* a 10.6 kb element is excised from the hupL gene, which codes for the large subunit
of the enzyme hydrogenase, by site-specific recombination between 16 bp direct repeats
that flank the element late during heterocyst differentiation. This recombination is
catalyzed by the xisC gene which is also located at one end of the element. This
rearrangement permits a proper HupL protein to be synthesized.
In all three rearrangements, the enzyme that catalyzes the removal of the element is
encoded adjacent to one of the junctions within the element that is removed. XisA and
XisC are site-specific tyrosine recombinases - they are related to each other but distantly
related to other integrases.
http://edoc.hu-berlin.de/dissertationen/berg- holger-2003-07-11/HTML/chapter1.html
Cyanobacteria can play a in important
role in defining water quality
Geosmin
Toxins
http://ks.water.usgs.gov/Kansas/pubs/reports/ofr.02-337.tab01.gif
http://www.owwrc.com/publications/pub,%20Sue%20Watson%20Geosmin%20in%20W%20Lake%20ON.pdf
Microcystis aeruginosa
http://www.cyanobacteria-platform.com/main.html
The microcystins are a group of cyclic heptapeptide hepatotoxins
Microcystin LR, M2912
Potent inhibitor of protein
phosphatase types 1 and 2A;
has no effect on protein kinase
Cylindrospermopsin, C9866
Inhibition of protein synthesis.
Target organ = liver
http://www.sigmaaldrich.com/Area_of_Interest/Biochemicals/Enzyme_Explorer/Cell_Signaling_Enzymes/Cyanobacterial_Toxins.html#microcystinslr
http://ejournal.sinica.edu.tw/bbas/content/2000/3/130401.JPG
The End

Bdellovibrio

Transcription

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