SUPERVISOR PLACEMENT 2013-2014 SESSION

PROF. I. M EZEONU 1. ADEOYE ENOCH ADEMOLA 2010/173424 MCB 2. ARUMA HENRY FIDELIS 2010/173401 MCB 3. EMEJULU KENECHUKWU N 201O/174589 MCB 4. IGATA EMEKA H 201O/173339 MCB 5. NKPOZI GOODLUCK OGOCHUKWU 201O/173334 MCB 6. OBODOECHI AMANDA O 201O/173934 MCB 7. OKOYE CHIDIMMA MIRABEL 201O/173418 MCB 8. OPUSUNJU TAMUNOKURO 2011/178506 MCB 9. URAMA KELVIN CHICHEBE 201O/173800 MCB 10. UCHEGBU CHIOMA ANN 201O/171074 MCB/CHEM 11. NGWOKE PERPETUA OBIAGELI 201O/171052 BCH/MCB PROF. J. I OKAFOR 1. AGASHI LEVI NNAEMEKA 2010/171096 MCB 2. ASOGWA ERNEST OSITA 201O/171055 MCB 3. ENEH ONYEDIKACHI MARTINS 201O/173585 MCB 4. IGBOANUSI KINGSLEY KELECHI 201O/171098 MCB 5. NNABUEZE CHIAMAKA SYLVIA 201O/171061 MCB 6. ODO HEZEKIAH C 201O/173345 MCB 7. OKOYE CHINWEKENE PERPETUA 201O/175254 MCB 8. TOR S. AUGUSTINE 201O/173329 MCB 9. URAMA KINGSLEY CHINEDU 201O/173797 MCB 10. UGWOKE BLESSING G.C 201O/174023 MCB/CHEM 11. NWACHUKWU EBERECHI STELLA 201O/173328 BCH/MCB PROF. J.C OGBONNA 1. 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EDOH CHIDERA VIVIAN 201O/173584 MCB 3. EZENYI CHIDOZIE JUDE 201O/173420 MCB 4. MANU THEODORA CHINENYE 201O/171111 MCB 5. NWEKE OGECHUKWU MICHAEL 201O/172841 MCB 6. OKEKE AMALA IRENE 201O/174595 MCB 7. ONWUMERE MICHAEL CHINONSO 201O/173406 MCB 8. UGWUANYI RITA NWAKAEGO 201O/171097 MCB 9. NWOSU CHINWE LAURA 201O/173533 MCB/BCH 10. ELEANYA CHUKWUEMEKA P 201O/173530 BCH/MCB 11. OKPALA IFENNA M 201O/173562 BCH/MCB DR. S.C ENEMUOR 1. AMAJE PAUL O 201O/173581 MCB 2. EDUOK IME ENEFIOK 201O/172932 MCB 3. EZEORA KASIEMOBI CHIAGOZIE 201O/171123 MCB 4. MBA CHIKEZIE EUNICE 201O/171119 MCB 5. NZEAKO ONYEBUCHI GODWIN 201O/174634 MCB 6. OKEKE HARRISON N 201O/173330 MCB 7. ONWURA NKEM SANDRA 201O/173409 MCB 8. UGWUASAYA OSITA EMMANUEL 2010/173337 MCB 9. NWOSU FRANKLIN CHIMA 201O/175303 MCB/CHEM 10. IBEKAM ONYINYE M 201O/171513 MCB/BCH 11. EWELUM CHISOM P 201O/171044 BCH/MCB 12. ONYENEKE MMASINACHI J 201O/174904 BCH/MCB A.C MGBEAHURUIKE 1. ANADI JACINTA CHIDINMA 201O/173421 MCB 2. EGBUCHULAM PASCHAL C 201O/173340 MCB 3. EZIAKOR CHINWE RACHAEL 201O/173405 MCB 4. MBANEFOH SIMON I 2006/141922 MCB 5. OBI CHIDINMA MAUREEN 201O/173940 MCB 6. OKEKE TOCHUKWU CHIDERA 201O/174707 MCB 7. ONWURAH OKWUDILI S.L 2010/173414 MCB 8. UGWUIJEM EJIKE E 201O/173923 MCB 9. OKAFOR CHINENYE CYNTHIA 201O/173560 MCB/CHEM 10. EZEMA BARTHOLOMEW 201O/174507 BCH/MCB 11. OZIOKO EMEKA EPHRAIM 201O/171066 BCH/MCB DR. C ONWOSI 1. ANEKE BLESSING IJEOMA 2010/171113 MCB 2. EJIANYA OGECHUKWU EDITH 201O/173413 MCB 3. EZUGWORIE FLORA NNENNA 201O/175256 MCB 4. MEZIAM AFOMA GRACE 201O/171121 MCB 5. OBI CHINELO ESTHER 201O/173339 MCB 6. OKEREKE ADAUGO CHIOMA 201O/171090 MCB 7. ONYEANU AUGUSTINE IKENNA 201O/173925 MCB 8. UHEGBU CHIBUZOR AUGUSTA 2010/173922 MCB 9. OKAH CHISOM HELEN 201O/171085 MCB/CHEM 10. EZEMA ONYINYECHI 201O/170569 BCH/MCB 11. UDUMA AMARACHI K 201O/173571 BCH/MCB MRS T.N NWAGU 1. ANTHONY DANIEL BENSON 201O/173422 MCB 2. EJIOFOR MILDRED C 201O/175258 MCB 3. GODSON CHIJIOKE C 201O/171101 MCB 4. MOKWENYEI-FRANCISCA-NKEM 2011/178507 MCB 5. OBIDIEGWU NWAMAKA LIVINA 201O/171143 MCB 6. OKEREKE CHIJIOKE SOLOMON 201O/173403 MCB 7. ONYEKURU CHIDIEBERE CHIJIOKE 201O/171114 MCB 8. UHUO ISAAC 201O/174636 MCB 9. ONWUKA UCHECHUKWU C.C 201O/174569 MCB/BCH 10. EZEORBA TIMOTHY 201O/173534 BCH/MCB 11. UGWOKE LAWRENCE O 201O/174025 BCH/MCB G.N OKPALA 1. ANYAEGBUNAM ZIKORA K.G 2008/160988 MCB 2. EJIOFOR NGOZI CHINENYERE 201O/175266 MCB 3. IBEKWE IFEANYICHUKWU I 201O/174903 MCB 4. NDUKWE JOHNSON KALU 201O/172850 MCB 5. OBIKWELU KOSISOCHUKWU HARRIET 201O/173937 MCB 6. OKOH GIDEON CHISIMDI 201O/173930 MCB 7. ONYEMA SUNDAY 201O/173342 MCB 8. UKA IJEOMA PRECIOUS 201O/171135 MCB 9. ONWUMERE CHINEYE MERCY 201O/171060 MCB/CHEM 10. IGBOKWE OBINNA G 201O/172836 BCH/MCB 11. UGWU UCHENNA A 201O/173496 BCH/MCB O.O ONYIA 1. ANYAENEWUSIM STEPHANIE CHINELO 201O/171099 MCB 2. EKWUEME NNEKA UCHECHUKWU 201O/173338 MCB 3. IBENYE CHINWEOKWU AUGUSTINA 2010/171138 MCB 4. NGWAKA ADAEZE CHIAZO 201O/171100 MCB 5. OBILOR EMMANUELA CHIDERA 201O/173936 MCB 6. OKORO NKEMJIKA MARYEDITH 201O/174508 MCB 7. ONYIA IZUCHUKWU GABRIEL 201O/171115 MCB 8. UMEH AFOMA LYNDA 201O/173402 MCB 9. ORJI CHISOM EMMENUELLA 201O/175246 MCB/CHEM 10. IGBOSUAH JOHN I 201O/173539 BCH/MCB 11. UGWUOKE BEDE CHUKWUDI 201O/174580 BCH/MCB DR. I.E NWEZE 1. ANYAMENE UKAMAKA CYNTHIA 2010/173964 MCB 2. ELEANYA CHINYERE PEACE 2010/175298 MCB 3. IDAM OGBONNIA EGWU 201O/173591 MCB 4. NGWU CHISOM LINDA 201O/173599 MCB 5. OBIORA EKENE HILARY 201O/173935 MCB 6. OKORONTA IKECHUKWU F 201O/174596 MCB 7. ONYIA OGECHUKWU SHEILA 201O/173565 MCB 8. UMENYI KENECHUKWU LINDA 201O/173921 MCB 9. OSITADINMA KINGSLEY OKEKE 201O/174572 MCB/BCH 10. NDUKA OGONNA JUDITH 201O/173546 BCH/MCB 11. UZOR JANE CHINENYENWA 201O/173578 BCH/MCB

SOME MCB MATERIALS(Microbial Physiology)- check it out.

Lecture note prepared by Dr Chukwudi Onwosi as part of MCB 301 (Microbial
Physiology)

A. MECHANOSENSITIVE ION CHANNELS
Mechanosensitive ion channels are integral membrane proteins that open and close in
response to mechanical stress applied either directly to the cell membrane (in the case of
intrinsically mechanosensitive channels) or indirectly, through forces applied to
cytoskeletal components. Mechanosensitive channels are quite diverse both physiologically
and structurally and have been discovered in all fundamental branches of the phylogenetic
tree, eukarya, eubacteria and archea. Prokaryotic mechanosensitive channels can be both
relatively simple and intrinsically mechanosensitive unlike the eukaryotes. Consequently,
bacterial chemical have been much more amenable to biochemical, biophysical and genetic
characterization, and hence can serve as models for establishing basic features of
mechanosensation that may also be relevant to the more complex eukaryotic
mechanosensitive channels.
Prokaryotic mechanosensitive channels have been proposed to function in the
response of a microorganism to an abrupt transition from a high to low osmotic strength
environment. The response mechanisms of bacteria to osmotic stress have been best
characterized in E. coli. During downshock conditions, when bacteria are shifted from a high
to a low osmolarity solution, water enters the cell and generates a large increase in turgor
pressure. Mechanosensitive channels embedded in the plasma membranes of bacteria can
respond to sudden increases in turgor pressure by opening under the most stressful
conditions, thereby releasing water and solutes from the cytoplasm to prevent cell lysis
during hyperosmotic shock. These channels are often nonselective and allow the passage of
an astonishing variety of solutes across the membrane, ranging from monovalent ions and
water to proteins such as thioredoxin. Based on their distinct conductances and activation
properties, three mechanosensitive channels have been identified in E. coli: the
mechnosensitive channels of large conductance (mscL), small conductance (MscS), and mini
conductance (MscM). These channels are located in the inner membrane of the bacteria.
MS channels in Archaea were only recently documented in patch clamp recordings
from three archaeal species occupying three different environmental niches: Haloferax
volcanii, Thermoplasma acidophilum and Methanococcus jannaschii. Whereas only one type
of MS channel has been characterized in cell membrane of Thermoplasma sp., two different
types of MS channels have been found in membranes of H. volcanii and M. jannashi. When
compared with their bacterial counterparts, the MS channels of Archaea share several
features with MscL and MscS:(i) activation by the bilayer mechanism, (ii) pressure and
voltage dependence, (iii) blockage by gadolinium, and (iv) activation by amphipaths. Three
types of MS channels were identified in E. coli, which based on their conductance were
named as MscM (M for mini), MscS (S for small) and MscL (L for large). The channel
conductance is paralleled by the amount of negative pressure required for the channel
activation. In contrast to MscL which is non-selective, MscS was found to be more selective
for anions over cations while MscM was reported to exhibit a slight preference for cations
over anions.
B. MEMBRANE TRANSPORT
Simple Diffusion
Passive diffusion is the translocation of a solute across a membrane down its electrochemical
gradient without the participation of a transport protein. Diffusion has a low temperature
coefficient and is non-specific. Typical biologically important compounds that follow this
mechanism are O2, CO2, NH3, and CH3COOH, –small, neutral molecules that are soluble in
lipid membranes
Facilitated Diffusion
Importantly, in free-living single-cell organisms such as bacteria, yeasts and algae, and in
certain plant and animal tissues, the rate of capture of nutrient from the environment by this
mechanism is too slow at the dilute concentrations that prevail in their normal environments
to support competitive growth. Thus, shortly after facilitated diffusion was proposed, it was
discovered that coupling of transport of an organic solute to trans-membrane gradients of
protons or sodium ions occurred.
Active Transport
Active transport is the movement of a molecule from a region of lesser concentration to an
area of greater concentration (against its electrochemical concentration gradient), requiring
the presence of specific integral membrane transport proteins and the input of metabolic
energy. This type of transport can be divided into distinct groups based upon the energy
used to drive transport.
Primary active transport
Direct coupling of substrate transport to energy-producing processes such as respiration or
photosynthesis or ATP hydrolysis enables transport of a substrate against the concentration/
electrochemical gradient. The central examples in biology arise from the chemiosmotic
hypothesis of oxidative and photosynthetic phosphorylation, proposed in 1961,
suggesting that energy from light or released by oxidation of NADH and FADH2 is used to
transport protons across the membranes of thylakoids in plants and mitochondria in both
plants and animals. Energy release occurs in the form of electrons produced from the
breakdown of hydrogen originating from energy-rich molecules such as glucose. Energy
flow down the electron transport chain to an electron acceptor enables the transport of
protons across a closed membrane, thus generating potential energy in the form of a pH
gradient and an electrical potential across the membrane. This gradient is known as the
proton motive force (PMF), and is a store of energy that is used for the flow of protons back
across the membrane, down their electrochemical gradient, via a complex enzyme called
ATP synthase. This enzyme uses energy stored in the electrochemical gradient to generate
ATP from adenosine diphosphate (ADP) and organic phosphate (Pi). The overall process is
made possible by the impermeability of the membranes to H+ and OH– ions.
Secondary active transport
Secondary active transport proteins also take advantage of the PMF formed by the chemiosmotic
process by using the energy stored in the H+ electrochemical gradient to drive the
transport of a substrate against its concentration gradient. In addition to the PMF, other ion
electrochemical gradients that are formed in cells can be used to drive secondary active
transport systems, such as the Na+ electrochemical gradient.
Symport, antiport and uniport
Secondary active transport proteins can be divided into two types, symporters, in which the
substrate and the ion are moved in the same direction, and antiporters, where the substrate
is transported in the opposite direction to that of the ion. Some of these have evidently lost
the coupling to movement of a cation or another molecule and effect movement of one solute
only; they are known as uniporters (Figure X) (e.g., the GLUT family of transporters for
sugars, particularly glucose).
Figure 1. Secondary active transport systems in bacteria. An electrochemical gradient of
protons across the bacterial inner membrane is generated by respiration.
Uptake of Carbon Sources from the Medium (Phosphotransferase System)
The basic PTS consists of two cytoplasmic proteins called Enzyme I (EI, gene ptsI) and HPr
(ptsH) common to all sugars, which pass a phosphate derived from PEP to the sugar-specific
transporters, called Enzymes II (EII) (Figure 2). The EIIs are multidomain proteins where the
three domains, EIIA, EIIB, and EIIC can be found on one, two, three, or, occasionally, four
polypeptide chains. EIIA and EIIB are soluble cytoplasmic proteins whereas EIIC is an
integral membrane protein, which serves as the passage for the sugar through the
membrane.
EI autophosphorylates on a histidine residue and then passes the phosphate to the small
protein HPr. HPr distributes phosphates to the EIIA domain of any of the sugar-specific EII
transporters within the cell. From EIIA the phosphate is transferred to EIIB, another soluble
domain but which is associated with the cytoplasmic side of the inner membrane. From EIIB
the phosphate is transferred to the incoming sugar, as it is transported by the EIIC domain
across the cytoplasmic membrane. The phosphate is carried by a histidine residue in EI and
HPr but usually by a cysteine, in most EIIB domains. In the resting state, that is, in the
absence of a PTS sugar, the PTS proteins are predominately phosphorylated. It should be
noted that these phosphates are relatively labile and can be easily passed between different
EIIs via the HPr protein.
Figure 2 The glucose PTS in Escherichia coli. The phosphate from PEP is passed via a series
of cytoplasmic proteins EI (ptsI), HPr(ptsH), and EIIAGlc (crr) to the glucose-specific
transporter EIICBGlc (ptsG). Passage of glucose across the membrane via the EIICGlc
domain results in its simultaneous phosphorylation by EIIBGlc to give cytoplasmic Glc6P.
C. MICROBIAL PHOTOSYNTHESIS
Photosynthetic bacteria play many important roles in the environment. As much as a third of
the earth’s photosynthesis is performed by microorganisms in the oceans. Six bacterial
phyla include photosynthetic members. Five of them are termed anoxygenic because they
are unable to oxidize water and evolve oxygen. Two of these possess type II reaction
centers, which are basically similar to the Blc. viridis reaction center. Their terminal electron
acceptors are quinones. Members of two phyla possess type I reaction centers. These have
quinone acceptors, but rather than becoming doubly reduced and dissociating, the final
quinone acceptor donates an electron to a bound iron-sulfur center. Their core proteins are
homodimers (identical monomers), rather than heterodimers like the L and M proteins of
purple bacteria; they are flanked by two symmetrical light-harvesting domains. Members of
the sixth phylum, the cyanobacteria, have both type I and type II reaction centers,
connected in series. They are able to oxidize water and evolve oxygen and are termed
oxygenic. The Cyanobacteria are oxygenic, i.e., they can oxidize water and evolve oxygen
and possess both type I and type II reaction centers. They have light-harvesting systems
known as phycobilisomes whose chromophores (light-absorbing entities) are linear
tetrapyrroles known as phycobilins. They are found in many environments, are active
nitrogen fixers and are responsible for the toxic blooms that appear in eutrophic waters. The
bacterium Halobacterium halobium performs photosynthesis in a quite different way. Rather
than chlorophyll, it uses bacteriorhodopsin, a carotenoid-containing protein resembling the
visual pigment rhodopsin, to capture the energy of light in a process that does not involve
electron transfer.
Cyclic and non-cyclic photophosphorylation
Fig. 3. Model of possible interactions between linear and cyclic electron transport
pathways. Electrons flowing into a plastoquinone pool from Photosystem II reduce
cytochrome b6 f complexes in the appressed regions of the thylakoid membrane. These
flow via plastocyanin to PSI and from there to ferredoxin. Reduced ferredoxin can reduce
NADP, via FNR or can feed electrons to a plastoquinone pool in the stromal lamellae via
either a PGR5 dependent pathway or an NDH dependent pathway. Reduced PQ then
reduces cytochrome b6 f complexes in non-appressed membrane regions. This in turn
reduces plastocyanin and PSI. Plastoquinone in the stacked and unstacked regions
represent isolated pools due to restricted diffusion in the membrane. Plastocyanin is able to
move more or less freely in the thylakoid lumen and exists in equilibrium with P700 and
cytochrome f. Partitioning of electrons between linear and cyclic pathways occurs at the
step of ferredoxin oxidation only.
D. CARBON DIOXIDE FIXING PATHWAYS
i. Calvin cycle or Calvin-Benson-Bassham (CBB) pathway
Calvin cycle (Fig. 4) is the first cycle known to be present for carbon dioxide fixation.
Occurrence of calvin cycle is diversified among many organisms i.e. eukaryotes and
prokaryotes. Within eukaryotes it is found in plants and algae while in prokaryotes it is
found to be operating in eubacteria. Within bacterial domain calvin cycle has been reported
in green-sulfur bacteria- Oscillochloris trichoides, α proteobacteria- Xanthobacter flavus,
Rhodobacter capsulatus, Rhodobacter sphaeroides, Oligotropha carboxidovorans; β
proteobacteria- Aquaspirillum autotrophicum (now known as Herbaspirillum autotrophicum)
and Ralstonia eutropha; γ proteobacteria- Hydrogenovibriomarinus, Acidithiobacillus
thiooxidans (Thiobacillus thiooxidans II) and Acidithiobacillus ferrooxidans; cyanobacteria-
Synechocystis sp. and Anabaena variabilis. The pathway starts with the carboxylation of
Ribulose-1,5-biphosphate (RuBP) to 3- phosphoglycerate (PGA) by RuBisCO (Ribulose-1,5-
bisphosphate carboxylase oxygenase). Then, 3-phosphoglycerate is reduced to
glyceraldehyde-3-phosphate via. 1,3-diphosphoglycerate as an intermediate.And after the
series of reactions, RuBP is regenerated from glyceraldehyde-3-phosphate. There are 13
enzymes involved in calvin cycle and out of these, RuBisCO has been deeply studied.
RuBisCO and phosphoribulokinase (PRK) are the key enzymes of this pathway.
Figure 4: The calvin cycle
Other major pathways for carbon assimilation include the following:
ii. Reductive TCA cycle or reverse citric acid cycle
iii. Reductive acetyl Co-A pathway or Wood-Ljungdahl pathway
iv. 3-Hydroxypropionate pathway/malyl-CoA pathway (3-HP)