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Well can a bacterium be used as a vector?I have learnt that Agrobacterium tumifacian can be used to deliver a gene of interest in plant cells but on a book in a multiple choice question it says that only plasmid and bacteriophage can be used and not the bacteria to deliver a gene of interest to a host cell.enter image description here

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  • $\begingroup$ It's a matter of semantics. Some would want 'vector' to be used strictly for plasmids, viruses and the like (see, for instance, the Wikipedia page). Others, like @physics12 below, would include whole bacteria since they can act as carriers of foreign DNA. $\endgroup$ – Adhish May 4 '20 at 18:51
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Yes, Agrobacterium is indeed a very widely used vector in plants. So it wouldn't be wrong to consider bacteria as vectors. Just to add, it's worth noting that in recent times, bacterial vector options have been explored in the case of humans also, especially in the case of gene therapy for cancer treatment, though its success hasn't been demonstrated yet. Refer https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3056088/ for more information on this.

To conclude, bacteria can be considered as a vector undoubtedly.

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  • $\begingroup$ Welcome to Biology.SE! This is a good answer, and it would greatly benefit from inclusion of a few citations for the things you claim (i.e. bacteria as a vector in plants, bacteria as vectors for gene therapy in cancer treatment). If you haven't yet, please check out the tour. $\endgroup$ – acvill Apr 30 '20 at 11:15
  • $\begingroup$ Well 'Twinkle sheen' if the bacterium just tranfers its plasmid into the cell and the plasmid is responsible for introducing the gene of interest and not the bacterium itself then can't we apply the same logic to bacteriophages.Bacteriophages do not act as a vector but only their genetic material does. $\endgroup$ – Anket Aulakh May 1 '20 at 2:47
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    $\begingroup$ Thank you Dirigible. I've added a link for reference. $\endgroup$ – physics12 May 1 '20 at 12:13
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Agrobacterium tumefaciens and Agrobacterium rhizogenes are soil-based plant pathogenic bacterial strains containing plasmid. This plasmid is known as Ti plasmid and is responsible for inducing tumor. Part of this plasmid called T-DNA can be integrated into the host chromosomes. So, this bacterium plasmid act as vector, but not the whole bacterial cell.

(Via: https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/agrobacterium-tumefaciens)

This is true with all the pathogenic bacterial strains, as they can transfer their DNA material to cause pathogenicity. So, these pathogenic strains can be used in genetic engineering to transfer particular gene to host/mammalian cell. Using bacteria as a vector to treat cancer or various other pathological conditions is still at developmental stage.

(Via: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3056088/ https://www.ncbi.nlm.nih.gov/pubmed/16362987/)

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The conceptual mistake that you're making is that, Agrobacterium Tumifaciens, being a bacterium, contains additional genetic material within its cell, called the 'Ti plasmid'. Hence it is quite justified that the plasmid within the bacterium is acting as a vector, or a carrier of a foreign gene and not the whole bacterium itself.

Hence the answer provided in the book is correct.

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    $\begingroup$ Saying the Ti plasmid and not the Agrobacterium is the carier of DNA is like saying the passanger seat and not the airplane is the carier of humans across vast distances. Try spraying the plant with purified Ti plasmid - no transformation will happen. $\endgroup$ – BagiM Apr 29 '20 at 15:19
  • $\begingroup$ Wow. That's an analogy like, Take some pasta, take some hot water, keep them side by side and voila! By magic the pasta will cook itself. You're very wrong my friend. The bacteria by itself can't cause transformation until the plasmid is activated using Calcium ions by heat shock. This means, when seen at a deeper level, it's the plasmid that's actually causing the transformation and not the bacteria by itself. Thus your comment made no sense. There may be a plane to carry humans, but the pilot, who switches on the plane is not there, so will the plane be able to fly by itself? $\endgroup$ – Srutanik Bhaduri Apr 29 '20 at 17:38
  • $\begingroup$ I’ve edited your Answer for English because the argument in your first paragraph is reasonable as an explanation of the expected answer to that educational abomination known as an MCQ. I leave you to delete the second paragraph with the reference to reverse transcriptase and bacteriophage. Quickly, before anyone else reads it. $\endgroup$ – David Apr 29 '20 at 21:03
  • $\begingroup$ I deleted it, but may I know the reason why you told me to do so? $\endgroup$ – Srutanik Bhaduri Apr 30 '20 at 3:59
  • $\begingroup$ I suggested you deleted it because reverse transcriptase is not found in bacteria or bacteriophages, nor is it necessary for cloning into bacteriophage vectors. $\endgroup$ – David Apr 30 '20 at 18:22

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