Volunteering Opportunity

Volunteering Opportunity

White Hands Environmental Society of Jordan is NGO , NPO located in Amman- Im Al Summaq , our mission is to facilitate the cooperation of scientists, economists, engineers, entrepreneurs, educators and decision makers from around the globe in pursuing sustainable development and environmental conservation in Jordan, while empowering youth and women to jointly work for a greener, more sustainable future. 

As part of youth empowerment in the field of environmental leadership, we have established "Environmental Leaders Club" to foster the environmental voluntary work among the youth. We would like to invite you to join our growing the community, by joining the club you will have the chance:

•       To help in solving the grim reality of environmental problems in Jordan

•       Have the priority to participate in any of the NGO activities

•       Shape your communication skills in working area

•       Meet people and social networking with people with the same interest

•       Volunteers involved in the NGO activities will get certificate of volunteering issued by the NGO : that could be used while applying for jobs in different organizations , community service requirements  for the university  or while applying for different educational exchange programs

Required qualifications

•       Active young citizens or want to become active citizens

•       No previous experiences is required

•       Applicants from all age , Jordanian cities , educational level or background are welcomed to apply

Interested applicants should send their resumes and cover letter to the following email addresses: Nura.whe@gmail.com  or eiman.whe@gmail.com

Halobacterium Salinarum

By Nura Abboud

 28/6/2008

    Archaea discovery by Woese et al in 1977 has opened a new age of research in the life sciences, as it produced for the first time the three armed tree of life [15, 21] Archaea are ubiquitous, gaining  the  nickname of extremophiles  [21, 22]  that can be classified  according  to  their  extreme  habitats:  Thermophiles,  Methanogens  and halophiles  [15].  An  example  of  a  well-adapted  and  widely  distributed  halophilic microorganism  is Halobacterium [5]. Formally,  the species Halobacterium salinarum (HS), Halobacterium halobium  (that was  discovered by D. Oesterhelt et  al  in 1971) [10], and Halobacterium cutirubrum were considered separate species, but recently it was decided that they are similar enough to be regarded as one species named (HS). A microorganism that has features similar to HS has been described more than 80 years ago [11].   

    Despite its name, this marine microorganism is not a bacterium, but a gramnegative,  rod-shaped  archaeon  that  reproduces  by  binary  fission  and  does  not  form spores.  It  is a single celled motile archaeon. [2, 4, 64]. HS  is a good archaeal model for  the  study  of  archaeal  genetics  [18],  as  it  has  interesting  properties  and  genetic variability [2]. HS is an obligatory halophile that can be found in bodies of salt water, such  as  salt  lakes,  the Dead Sea,  and  in  evaporation  ponds  [3,  5]. Moreover, it has been occasionally isolated from salt-heavy food such as salt pork and sausages. HS plays an important role in the spoilage of many products preserved by the addition of salt. Studies showed that it is possible to grow cultures of HS in a chemically defined media [4].  

HS exhibits a highly acidic cytoplasm saturated with KCl,  potassium acts as an antifreeze/coolant  to keep the cell metabolism functioning [4, 16]  the metabolism of this chemoorganotrophic archaeon is largely unknown [17] Further Studies shown that  the  most  important  factor  in  determining  halobacterial  growth  is  NaCl concentration.  Generally,  it  is  assumed  that  HS  requires  a  high  concentrations  of NaCl,  a  solute  that  cannot  be  replaced,  to  maintain  their  glycoprotein  cell  wall structure  that  is negatively charged  , as  it  is contains a high number of acidic amino and  is  stabilize  only  in  the  presence  of  a  high  sodium  cation  concentration.  The positive charge of sodium prevents the negative charges from repelling each other and lysing the cell [30]. HS requires more than three M mol of NaCl for growth and grows best  at  30°C.  NaCl  concentration  reduction  causes  structural  deformations  of halobacterial  cells.  A  recent  study  done  by  C.  Zenget  et  al  has  shown  that  the optimum NaCl concentrations is 3.9 M mol and not 5.5 M mol, as mentioned in most previous literature. Further investigation of the influence of NaCl concentration on HS growth in the same study found that increasing NaCl concentration above 3.9 M mol, the cell start to lyse  [17].  

    In terms of energy production, HS has diverse ways of generating energy. HS

has  the ability  to oxidize various metabolites under aerobic conditions. HS  is also a facultative  phototrophe  that  can  carry  out  photosynthesis.  When  respiration  and nutrients are plentiful, HS will seek darkness. It can also grow in the absence of both respiration and photorespiration through the fermentation of arginine that can be only substituted by serine [29 ]                                    

    HS is capable of both chemo- and phototaxis. It contains four different retinal photosynthetic  proteins  that  are  structurally  similar  involved  in  light  energy conversion and signal transduction. Bacteriorhodopsin (BR) and Halorhodopsin (HR) are the light-driven ion pumps. BR is a proton pump that converts light energy into a proton  gradient, while HR  is  a  chloride  pump  that  allows HS  to maintain  the  high internal salt concentration. Sensory rhodopsin I and II are photoreceptor pigments that act as light sensors that control the swimming behavior of the cell. SRI enables both a photophilic  response  to  orange  light and a photophobic  response  to UV  light, while SRII  enables  a  photophopic  response  to  blue  light. HtrII  and HtrI  are  the  accessory transducer proteins of SRII and SRI, respectively. The function of these proteins is to transmit photosignals  from  the  receptor  to proteins  in  the cytoplasm  that control  the action of  the flagellar motor. Moreover, HtrII  from HS acts as a chemotransducer  to sense serine [14, 22, 24, 26, 28, and 29]. According to Mironova, O et al, “HtrII is the only archaeal transducer that accepts signals from two different sources.” [24].

     Under  constant  environmental  conditions,  HS  swims  by  means  of  rotating flagella,  and  in  the  absence  of  a  stimulus  performs  a  random walk. HS  reverses  its swimming direction about every 09-29 seconds, based on the spontaneous switching of  the  flagella motor  from clockwise  (CW,  forward  swimming)  to counterclockwise (CCW,  reverse  swimming)  or  vice-versa.  This  switching  causes  a  reversal  of  the swimming  direction.  CW  movement  of  flagella  is  a  response  toward  photophilic signals from SRI that helps HS to move toward the orange light signals where HR and BR  are most  active. CCW movement  is  a  photophobic  response  from SRI  to  avoid harmful UV  light, and SRII  to avoid  blue  light. HS  seeks darkness, where  there are plenty of nutrients [28]   HS  is  responsible  for  the bright  pink or  red appearance of  the Dead Sea and other  bodies  of  salt water  due  to BR. BR was  discovered  by D. Oesterhelt  et  al  in 1973  [30],  and  is  apoprotein  encoded by bop  gene  and  linked  to  retinal  proteins.  It serves as the active photosynthetic pigment that allows the archaeon to live with light as the only energy source [6, 29].  BR is expressed under anaerobic growth conditions [13]. Although the detailed molecular mechanism of proton translocation of BR is not completely  understood  [22],  BR  itself  has  structural  similarities  with  the  seven proteins that are found in nerve cells of higher animals. 

    Recently,  a  new  homologue  of  ferritin,  DpsA,  has  been  found  in  HS  as  a

DNA-protecting protein under starvation conditions. DpsA is a true ferritin, but differs from  the  function  and  regulation  of  other  ferritins. These  findings  strongly  suggest that not all functions of ferritins are yet known. This is of special interest, because the Dps-ferritin of HS appears  to operate with typical modulating  regulators of bacteria, while the activity of the transcription apparatus is like that of eukarya [16, 19].  

    What can HS do? Scientists  are working  to  blend  the  genes  of Halophiles,  including HS, with crop genes to make plants more tolerant to soil with a higher than average salinity [5, 23]. Halophiles  are  studied  by  astrologists  at NASA, who  propose  that Halophiles may be representatives of life forms that may exist elsewhere in the universe, and HS may be a  representative of  life  in the deep ocean of Europa, one of Jupiter’s moons [9]. HS  is  also  one  of  the  few  reported  organisms which  can  use  large  potassium gradients in a battery-like manner to serve as long term energy storage. Moreover, HS contains enzymes such as amylase, lipase and protease that are both stable and active under high salt concentrations, but have not been studied for related applications [20].  

     HS  has  received much  interest  as  it  is  the  key  organism  for  producing BR, which  is  currently  the  only  known  structure  that  allows  non-chlorophyll  based photosynthesis. BR  is currently being developed  for applications  in  optical  security, [7] and optical data storage [8]. In a recent study by B. Zabut et al, HS has been used in hydrogen gas production as a key organism  that produces BR, but  lacks both  the system and the enzymes that can reduce protons into molecular hydrogen. To produce hydrogen  gas,  packed  cells  of  HS  or  its  plasma  membrane  combined  with Rhodobacter  sphaeroides  (RS)  are  used  in  a  photobioreactor.  RS  is  the  most promising photosynthetic bacteria of the several species of microorganisms that have been found to produce hydrogen, due to its high activity in hydrogen production under anaerobic  conditions.  Photobiological  hydrogen  could  be  an  environmentally acceptable energy production method due to the fact that hydrogen gas is a renewable energy  source.  However,  the  photobioreactor  process  still  needs  serious improvements to become feasible for energy production [7].

   

   Industrially-produced highly saline environments are frequently contaminated by  toxic  organic  compounds.  Microorganisms  that  are  able  to  degrade  organic compounds under high saline conditions would be valuable for their ability to “clean” out these environments. Based on the fact that Haloarchaea possesses some degree of organic degrading capacity, Dong-Jin Ha et al suggest the usage of HS as a biological treatment  tool  for  highly  saline  industrial  waste  effluents  that  contaminate  the environment.  Their  study  evaluated  the  usage  of  HS  in  order  to  degrade  the  IPA (isopropyl alcohol) that is used in a number of industries, including pharmaceuticals, textile  production,  and  cosmetics.  Their  results  indicate  that  the  GAPDH  isolated from HS may be valuable in industries involving IPA processing [20].

 

References:

1.  DeLong, E. "Oceans of Archaea." Features 69 (2003): 503-511. May 2008

<http://www.asm.org/ASM/files/CCLIBRARYFILES/FILENAME/00000006

33/nw10030124p.pdf>. 

2.  Falb, M. et al "Metabolism of Halophilic Archaea." Extremophiles (2008):

196-177. May 2008 

<http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=2262144&blobtype

=pdf>.

3.  "Halophiles." May 2008 <http://library.thinkquest.org/CR0212089/halo.htm>.

4.  DasSarma, S. "Extreme Halophiles are Models for Astrobiology." American

Scoiety for Micorbiology. May 2008

<http://www.asm.org/microbe/index.asp?bid=41227>.

5.  Váró, G. et al  "Photocycle of Halorhodopsin From Halobacterium

Salinarium." Biophysical Journal (1995): 2062-2072. 

6.  Cercignani, G. "Photoresponses of Halobacterium Salinarum to Repetitive

Pulse Stimuli." Biophysical Journal 75 (1998): 1466-1472.

7.  B. Zabut, U, et al. "Hydrogen Gas Production by Combined Systems of

Rhodobacter Sphaeroides O.U.001 and Halobacterium Salinarum in a

Photobioreactor." International Journal of Hydrogen Energy (2006): 1553-

1562.

8.  Beznosov, S. N. et al “On the Multicomponent Nature of Halobacterium

Salinarum Flagella." Published in Mikrobiologiya 76 (2007): 494-501. 

9.  http://www.chemistry.ohiostate.

edu/~coe/chem694_2005/694_newclass/w3_bio.ppt#307,18

10. http://www.chemistry.ohiostate.

edu/~coe/chem694_2005/694_newclass/w3_bio.ppt#307,5 

11.  Pfeiffer, F.et al "Evolution in the Laboratory: the Genome of Halobacterium

Salinarum Strain R1 Compared to That of Strain NRC-1." Elsevier 91 (2008):

335-346. 

12. M. Engel. et al "Microprobe Analysis of Inorganic Elements in Halobacterium

Salinarum." Cell Biology International 29 (2005): 616-622.

13. Varo, G. et al "Photo Cycle of Halorhodopsin From Halobacterium

Salinarium." Biophysical Journal 68 (1995): 2062-2072. 

14. Mironova, O.S. et al  "Functional Characterization of Sensory Rhodopsin II

From Halobacterium Salinarum Expressed in Escherichia Coli." FEBS Letters

579 (2005): 3147-3151.

15. Choi, A .et al “Glu-56 in HtrI is Critical for Phototaxis Signaling in

Halobacterium Salinarum." Integrative Biosciences 9 (2005): 139-144.

16. Reindela,  S.,  et  al  “Fertin:  the  DpsA-Homologue  of  the  Archaeon

Halobacterium  Salinarum  is  a  Ferritin."  Biochimica  Et  Biophysica  Acta

(2002): 140-146.

17. Zeng, C. et al “Investigation of the Influence of NaCl Concentration on

Halobacterium Salinarum Growth." Journal of Thermal Analysis and

Calorimetry 84 (2006): 625-630.

18.  Gonzalez, O. et al "- Reconstruction, Modeling & Analysis of Halobacterium

Salinarum R-1 Metabolism." Molecular BioSystems (2007). 

19. Matzank, B et al . "Expression and Regulation Pattern of Ferritin-Like DpsA

in the Archaeon Halobacterium Salinarum." Biometals (2006): 19-29.

Nura Abboud

June 2008–06–28

  5

20. Jin Ha, D, et al "Proteome Analysis of Halobacterium Salinarum and

Characterization of Proteins Related to the Degradation of Isopropyl Alcohol."

Biochemica ET Biophysica Acto 1774 (2006): 44-50.

21. Rajagopal N. et al "Archaea and the New Age of Microorganisms" Tree 13

(1998),

22. ZaccaiU, G. "Moist and Soft, Dry and Stiff: a Review of Neutron Experiments

on Hydration- Dynamics Activity Relations in the Purple Membrane of

Halobacterium Salinarum." Biophysical Chemistry 86 (2000): 249-257.

23.  Zeng, C., et al. "Investigation of the Influence of NaCl Concentration on HS."

Journal of Thermal Analysis and Calorimetry, 84 (2006): 625-630.

24. Mironova, O et al . "Functional Characterization of Sensory Rhodopsin II

From Halobacterium Salinarum Expressed in Escherichia Coli." FEBS Letters

(2005): 3147-3151. 

25. Marhuenda-Egea, et al F. "Enzymatic Activity of an Extremely Halophilic

Phosphatase from the Archaea Halobacterium Salinarum in Reversed

Micelles." Journal of Molecular Catalysis (2000): 555-563

26. Cercignani, G. et al "Photoresponses of Halobacterium Salinarum to

Repetitive Pulse Stimuli." Biophysical Journal 75 (1998): 1466-1472.

27. Zeth, K. "Iron-Oxo Clusters Biomineralizing on Protein Surfaces: Structural

Analysis of Halobacterium Salinarum DpsA in Its Low- and High-Iron

States." PNAS (2004): 3147-3151.

28. Naber, H. "Two Alternative Models for Spontaneous Flagellar Motor

Switching in Halobacterium Salinarium." Academic Press Limited (1996).

29. "Halobacterium Salinarum - Overview." MPI of Biochemistry. May 2008

<http://www.biochem.mpg.de/en/rd/oesterhelt/web_page_list/Org_Hasal/inde

x.html>.

30. Oren, Aharon. Halophilic Microorganism and Their Environment. Kluwer.

<http://books.google.com/books?id=m2h9xtsLgQIC&pg=PA74&lpg=PA74&

dq=halobacterium+glycoprotein&source=web&ots=imk0gi5lzY&sig=jFaPOG

YopFKjBPMMr_-VKzjEkk&

hl=en&sa=X&oi=book_result&resnum=1&ct=result>.

Colicin by Nura A. Abboud

         Bacteriocins comprise a large and diverse family of antimicrobial toxins which has been identified in most microbial species of bacteria and Archaea. What unites them as a group is that they are all ribosomally synthesized bactericidal proteins. In addition, unlike most classical antibiotics, they are active against species that are closely related to the producing strains [1-5].

            The abundance of bacteriocins has lead researchers to suggest that they play a critical role in mediating microbial interactions, community dynamics, and in maintaining microbial diversity. An additional role has recently been proposed for bacteriocins produced by Gram-positive bacteria, in which they mediate quorum sensing [1, 5, 6]. From an ecological point of view, bacteriocins are anticompetitor molecules that enable bacteria to respond to environmental challenges by reducing competition from sensitive bacterial strains that share the same ecological niche and have similar nutritional requirements [2, 6, 7].

As a family, bacteriocins are classified into two main groups: the toxins produced by Gram-positive and Gram-negative bacteria. Gram-positive bacteria produce bacteriocins which are selfregulated by specific transport mechanisms; a good example are the bacteriocins produced by lactic acid bacteria that are used in the preservation of meat and milk [5]. The toxins produced by Gram-negative bacteria are usually released through cell lysis and are dependent on the host regulatory pathways, like the SOS regulation; the most extensively studied example of this group are the colicins [1, 6, 8].

Colicins represent a heterogeneous group of antimicrobial, high molecular weight proteins [2, 6, 9, 10], which  have a limited killing spectrum: they are toxic only  to competing E. coli strains and Enterobacteriaceae, such as Salmonella and Citrobacter [5, 6, 11, 12]. The relative abundance of colicinogenic E. coli strains in natural and clinical isolates was shown to be about 15-50% [2, 13-15].  To date, 34 types of colicins have been identified [2, 10];  they were divided into two groups based on their encoding plasmid, their release system, and their mode of action: Group A is comprised of colicins that are encoded on small plasmids, are released into the medium through the lysis of the producing cell, and are translocated across the membrane through the Tol system. This group includes colicins A, E1 to E9, K, L, N, S4, U, and Y [6, 9, 16-18]. Group B includes colicins that are encoded on large plasmids, colicins whose secretion mechanism is not through lysis, and that require the TonB system for translocation. This group includes colicins B , D, Ia, Ib, M, 5, and 10 [6, 9, 10, 17]. However, some colicins might belong to one group and share homologies with colicins of the other group, which is the case of colicins D and 10 [1, 6]. 

Colicins are encoded on operons that carry at least two, usually three genes: the colicin structural gene that encodes the toxin (cxa), followed by the immunity gene (cxi), which encodes a protein that provides the producing cell with specific protection against its own toxin. The third gene is the lysis protein encoding gene (cxl), or the bacteriocin release protein that facilitates the release of colicin through lysis of the cytoplasmic membrane of the producing cell [1-3, 5, 9, 10] .

The colicin toxins have three linearly organized functional domains: the central part (R-domain) is the colicin receptor-binding domain that is involved in recognition of specific receptors on the target cell outer membrane, whereas the N-terminal portion (T-domain) is involved in translocation across the outer membrane; finally, the C-terminus (P-domain) contains both the specific toxic activity and a binding site to the immunity protein [2, 5, 6, 9, 10, 19, 20].

In general, colicin killing of sensitive bacteria follows three steps: (i) binding of a colicin molecule to a specific receptor, mostly to ones involved in nutrient uptake, located outside the target bacterial outer membrane; (ii) translocating through the cell envelope using either the Ton or Tol systems; and (iii) having gained access to the cell interior, the toxin kills the target cell by one of a variety of ways, including: pore formation in the cytoplasmic membrane,  nonspecific degradation of cellular DNA by nuclease, inhibition of protein biosynthesis by the cleaving of 16s ribosomal RNA, or degradation of the bacterial cell wall resulting from inhibition of peptidoglycan synthesis [1, 2, 5, 9, 10].

Unlike bacteriocins produced by Gram-positive bacteria, the induction of the colicin gene clusters is controlled and regulated by the host cell’s pathways, mainly by the SOS system [1, 2, 6, 9]. Production of the toxins is induced under conditions of stress such as DNA-damage, increasing population density or nutrient depletion. Once the colicin is produced, it is released to the extracellular environment by the lysis protein, causing the host cell’s death [5, 18, 22]. However, only a small fraction (less than  3%) of colicinogenic cells of the population "commits suicide” [6, 11, 13, 15, 21, 22].

The SOS response has been studied extensively in E. coli; the SOS genes are normally repressed and the SOS genes’ expression is the interplay of the LexA and RecA proteins that function as repressor and activator, respectively. Under standard conditions, colicin synthesis is switched off in most cells of a bacterial population as the SOS system is repressed by the LexA protein by binding to a conserved sequence upstream the operon. Under DNA damage, the LexA is derepressed by the activation of the RecA protein, which induces the cleavage of the LexA repressor, consequently provoking the induction of an ensemble of DNA repair proteins as well as the colicin encoding genes [2, 6, 10, 11, 13, 23-26].

So far, the regulation of only two colicins have been the subject of  extensive study: Colicin E1 was found to be produced in response to a variety of assaults, including mutagenic agents, anaerobiosis, nutrient depletion and catabolite repression, suggesting that regulators other than SOS agents interfere with this colicin transcription [27, 28]. Colicin K [29], on the other hand, was found to be mainly induced by guanosine tetraphosphate (ppGpp), while the SOS response was found to be a mild signal for its expression. Amino acid starvation  induced colicin K production [30, 31] while the expression invoked by DNA damage was not prominent.  Interestingly, both colicin E1 and K belong to group A colicins; therefore, what is known so far about colicins has been obtained from seemingly similar proteins [30].

Previous studies have explored the role that SOS triggers play in colicin production, investigating the regulatory elements involved in their expression; the results showed that certain triggers such as, bile salts and β-lactams antibiotics induce the production of colicins though not through the promoter region located upstream to the initiation codon [32], suggesting that different mechanisms are involved in regulating colicin expression [33].

References

1.         Riley, M.A. and J.E. Wertz, Bacteriocins: Evolution, ecology, and application. Annual Review of Microbiology, 2002. 56: p. 117-137.

2.         Cursino, L., et al., Recent updated aspects of colicins of Enterobacteriaceae. Brazilian Journal of Microbiology, 2002. 33(3): p. 185-195.

3.         Riley, M.A., Positive Selection for Colicin Diversity in Bacteria. Molecular Biology and Evolution, 1993. 10(5): p. 1048-1059.

4.         de Souza, E.L., C.A. da Silva, and C.P. de Sousa, Bacteriocins: Molecules of fundamental impact on the microbial ecology and potential food biopreservatives. Brazilian Archives of Biology and Technology, 2005. 48(4): p. 559-566.

5.         Njuguna, P., Studies on the Manipulation of Gastrointestinal Tract Bacteria, in Biological Sciences. 2005, University of Wollongong. p. 165.

6.         Cascales, E., et al., Colicin biology. Microbiology and Molecular Biology Reviews, 2007. 71(1): p. 158-229.

7.         Pagie, L. and P. Hogeweg, Colicin diversity: a result of eco-evolutionary dynamics. Journal of Theoretical Biology, 1999. 196(2): p. 251-+.

8.         Riley, M.A. and J.E. Wertz, Bacteriocin diversity: ecological and evolutionary perspectives. Biochimie, 2002. 84(5-6): p. 357-364.

9.         Hands, S.L., Biophysical investigations of the mechanism of colicin transloctaion in School of Pharmacy. 2004, University of Nottingham.

10.       Smarda, J. and D. Smajs, Colicins - Exocellular lethal proteins of Escherichia coli. Folia Microbiologica, 1998. 43(6): p. 563-582.

11.       Spangler, R., et al., Colicin Synthesis and Cell-Death. Journal of Bacteriology, 1985. 163(1): p. 167-173.

12.       Dale, J.W., Molecular genetics of bacteria. 3rd ed. 1998, West Sussex: John Wileyy & Sons Ltd. 310.

13.       Alonso, G., G. Vílchez, and V.R. Lemoine, How bacteria protect themselves against channel-forming colicins. INTERNATL MICROBIOL, 2000. 3: p. 81–88.

14.       Smarda, J., D. Smajs, and S. Horynova, Incidence of lysogenic, colicinogenic and siderophore-producing strains among human non-pathogenic Escherichia coli. Folia Microbiologica, 2006. 51(5): p. 387-391.

15.       Lancaster, L.E., W. Wintermeyer, and M.V. Rodnina, Colicins and their potential in cancer treatment. Blood Cells Molecules and Diseases, 2007. 38(1): p. 15-18.

16.       Lazdunski, C.J., et al., Colicin import into Escherichia coli cells. Journal of Bacteriology, 1998. 180(19): p. 4993-5002.

17.       Braun, V., S.I. Patzer, and K. Hantke, Ton-dependent colicins and microcins: modular design and evolution. Biochimie, 2002. 84(5-6): p. 365-80.

18.       Hands, S.L., et al., Interactions of TolB with the translocation domain of colicin E9 require an extended TolB box. Journal of Bacteriology, 2005. 187(19): p. 6733-6741.

19.       Buchanan, S.K., et al., Structure of colicin I receptor bound to the R-domain of colicin Ia: implications for protein import. Embo Journal, 2007. 26(10): p. 2594-2604.

20.       Fridd, S.L., I. Gokce, and J.H. Lakey, High level expression of His-tagged colicin pore-forming domains and reflections on the sites for pore formation in the inner membrane. Biochimie, 2002. 84(5-6): p. 477-483.

21.       Sze, C.C., L.M.D. Bernardo, and V. Shingler, Integration of global regulation of two aromatic-responsive sigma(54)-dependent systems: a common phenotype by different mechanisms. Journal of Bacteriology, 2002. 184(3): p. 760-770.

22.       Mulec, J., et al., A cka-gfp transcriptional fusion reveals that the colicin K activity gene is induced in only 3 percent of the population. Journal of Bacteriology, 2003. 185(2): p. 654-659.

23.       Janion, C., Some aspects of the SOS response system - A critical survey. Acta Biochimica Polonica, 2001. 48(3): p. 599-610.

24.       Shcaechter, M., in The Desk Encyclopedia of Microbiology 2003: Granger. p. 927-930.

25.       Perez-Capilla, T., et al., SOS-independent induction of dinB transcription by beta-lactam-mediated inhibition of cell wall synthesis in Escherichia coli. Journal of Bacteriology, 2005. 187(4): p. 1515-1518.

26.       Schuldiner, S., et al., Induction of SoS Functions by Alkaline Intracellular Ph in Escherichia-Coli. Journal of Bacteriology, 1986. 168(2): p. 936-939.

27.       Dongling Zheng, C.C., Jon L. Hobman and Stephen D. Minchin, Identification of the CRP regulon using in vitro and in vivo transcriptional profiling. Nucleic Acids Research, 2004. 32(19): p. 5874–5893.

28.       Salles, B., J.M. Weisemann, and G.M. Weinstock, Temporal control of colicin E1 induction. J Bacteriol, 1987. 169(11): p. 5028-34.

29.       Tsao, S.S. and W.F. Goebell, Colicin K .8. Immunological Properties of Mitomycin-Induced Colicin K. Journal of Experimental Medicine, 1969. 130(6): p. 1313-&.

30.       Kuhar, I. and D. Zgur-Bertok, Transcription regulation of the colicin K cka gene reveals induction of colicin synthesis by differential responses to environmental signals. Journal of Bacteriology, 1999. 181(23): p. 7373-7380.

31.       Jishage, M., et al., Regulation of or factor competition by the alarmone ppGpp. Genes & Development, 2002. 16(10): p. 1260-1270.

32.       Sharon-Gojman Revital, O.G., Regulation of Colicin Production by SOS Inducers. 2008, Ben Gurion University -Albert Katz International School for Desert Studies: Sde Boqer.

33.       Gillor, O., J.A.C. Vriezen, and M.A. Riley, The role of SOS boxes in enteric bacteriocin regulation. Microbiology-Sgm, 2008. 154: p. 1783-1792.

34.       Sharon-Gojman, R., Regulation of Colicin Production by SOS Inducers, in Department of Environmental Hydrology & Microbiology. 2008, Ben Gurion University of Negev: Sde Boqer.

35.       Deegan, L.H., et al., Bacterlocins: Biological tools for bio-preservation and shelf-life extension. International Dairy Journal, 2006. 16(9): p. 1058-1071.

36.       Diez-Gonzalez, F., Applications of bacteriocins in livestock. Curr Issues Intest Microbiol, 2007. 8(1): p. 15-23.

37.       Trautner, B.W., R.A. Hull, and R.O. Darouiche, Colicins prevent colonization of urinary catheters. Journal of Antimicrobial Chemotherapy, 2005. 56(2): p. 413-415.

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