ميكروبيولوجى

اولا انا اسمى نيرين ثانيا دى معلومات للناس اللى بيهتموا بالميكرو بيولوجى وهافهم اللى ميعرفوش علم الميكرو هو علم دراسه الكاثنات الدقيقه زى البكتريا والفيروسات يارب المووضع يفيدكم


the definition of bacteria genetic



-The study of gene structure and function in bacteria. Genetics itself is concerned with determining the number, location, and character of the genes of an organism. The classical way to investigate genes is to mate two organisms with different genotypes and compare the observable properties (phenotypes) of the parents with those of the progeny. Bacteria do not mate (in the usual way), so there is no way of getting all the chromosomes of two different bacteria into the same cell. However, there are a number of ways in which a part of the chromosome or genome from one bacterium can be inserted into another bacterium so that the outcome can be studied.




-All organisms have diverged from a common ancestral prokaryote whose precise location in the evolutionary tree is unclear. This has resulted in three primary kingdoms, the Archaebacteria, the Eubacteria, and the Eukaryotae. All bacteria are prokaryotes, that is, the “nucleus” or nucleoid is a single circular chromosome, without a nuclear membrane. Bacteria also lack other membrane-bounded organelles such as mitochondria or chloroplasts, but they all possess a cytoplasmic membrane. Most bacteria have a cell wall that surrounds the cytoplasmic membrane, and some bacteria also contain an outer membrane which encompasses the cell wall. Duplication occurs by a process of binary fission, in which two identical daughter cells arise from a single parent cell. Every cell in a homogeneous population of bacterial cells retains the potential for duplication. Bacteria do not possess the potential for differentiation (other than spore formation) or for forming multicellular organisms.


bacterial cell structure:

- essential components: basic structures present in all bacteria ( cell wall , cytoplasmic membrane, cytoplasm and nuclear material)

- non essential components: present in some bacteria species (capsules ,fimbriae,flagella and spores)


Bacterial genetic information

-Bacterial genetic information is stored in the :

*chromosome
*plasmids
-some interesting genetic elements
*transposons: (jumping genes) are important in moving antibiotic resistance genes between the chromosome and plasmids

bacterial chromosomes


* usually circular

* condensed into the nucleoside

* there is nuclear membrane
acts as the template for the synthesis of the other)

* replication starts

* Replication semi-conservatively (one DNA stand from a specific site – the origin of replication



* the genome is HAPLOID( only one chromosome per cell)


* genes performing linked functions are grouped together in OPERONs

* chromosome size can very between species

-the smallest is MYCOPLASAMA genitalium

E.COLI is average size-


Plasmids

extra -chromosomal genetic elements that may be regarded as :

INTRA -CELLULAR PATHOGENS

- -non essential for survival of the bacterium

-generally a small percentage of the host cells contain a particular plasmid (this can change due to selective pressure)
- they ensure their spread by partition between cells or by CONJUGAYION between donor cells and recipient cells

- plasmids are circular DNA molecules-

-replication is similar to that of the chromosome and starts at the ORIV

characteristic COPY NUMBER -

-there may be INCOMPATIBILITY between groups of plasmids

phenotypic properties carried by plasmids-

ANTIBIOTOC RESUSTANCE
usually enzymatic inactivation of the antibiotic

VIRULENCE FACTOR
toxins:e.g.entropathic E.coli -

adherence factors: e.g. pili in E.coli -
phenotypic properties carried by plasmids:


-PRODUCTION OF ANTI-MICROBIAL AGENTS


antibiotics*

*bacteriocins


-METABOLIC PA THWAYS

*pseudomonas spp- catabolic activity for camphor, toluene, salicylic acid



plasmids are self-transmissible by CONJUGATION
plasmids encode the SEX-PILUS and other transfer genes
conjugation is the major mechanism of transfer of antibiotic resistance genes
some plasmids may be transferred (mobilised) even if they do not contain all the genes required for conjugation






Bacterial variations on the methionine salvage pathway.




BACKGROUND: The thiomethyl group of S-adenosylmethionine is often recycled as methionine from methylthioadenosine. The

corresponding pathway has been unravelled in Bacillus subtilis. However methylthioadenosine is subjected to alternative degradative pathways depending on the organism. RESULTS: This work uses genome in silico analysis to propose methionine salvage pathways for Klebsiella pneumoniae, Leptospira interrogans, Thermoanaerobacter tengcongensis and Xylella fastidiosa. Experiments performed with mutants of B. subtilis and Pseudomonas aeruginosa substantiate the hypotheses proposed. The enzymes that catalyze the reactions are recruited from a variety of origins. The first, ubiquitous, enzyme of the pathway, MtnA (methylthioribose-1-phosphate isomerase), belongs to a family of proteins related to eukaryotic intiation factor 2B alpha. mtnB codes for a methylthioribulose-1-phosphate dehydratase. Two reactions follow, that of an enolase and that of a phosphatase. While in B. subtilis this is performed by two distinct polypeptides, in the other organisms analyzed here an enolase-phosphatase yields 1,2-dihydroxy-3-keto-5-methylthiopentene. In the presence of dioxygen an aci-reductone dioxygenase yields the immediate precursor of methionine, ketomethylthiobutyrate. Under some conditions this enzyme produces carbon monoxide in B. subtilis, suggesting a route for a new gaseous mediator in bacteria. Ketomethylthiobutyrate is finally transaminated by an aminotransferase that exists usually as a broad specificity enzyme (often able to transaminate aromatic aminoacid keto-acid precursors or histidinol-phosphate). CONCLUSION: A functional methionine salvage pathway was experimentally demonstrated, for the first time, in P. aeruginosa. Apparently, methionine salvage pathways are frequent in Bacteria (and in Eukarya), with recruitment of different polypeptides to perform the needed reactions (an ancestor of a translation initiation factor and RuBisCO, as an enolase, in some Firmicutes). Many are highly dependent on the presence of oxygen, suggesting that the ecological niche may play an important role for the existence and/or metabolic steps of the pathway, even in phylogenetically related bacteria. Further work is needed to uncover the corresponding steps when dioxygen is scarce or absent (this is important to explore the presence of the pathway in Archae) The thermophile T. tengcongensis, that thrives in the absence of oxygen, appears to possess the pathway. It will be an interesting link to uncover the missing reactions in

anaerobic environment


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