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This was originally written for the Species page, but was only added in a very abreviated form. I would like to propose inserting it into this article, following the "Classification and identification" section.
Total number of bacterial species (estimated): 5–10, or even 1,000 million (identified and unidentified) bacteria worldwide.
Of the 6,000 to 170,000 identifiedprokaryotic species there are:
16,000 prokaryotic species "seen by science", based on the number of different 98% unique 16S_ribosomal_RNA sequences in databases as of 2004. This analysis was based on a total of 56,215 16S rRNA gene sequences, the total number of 16S rRNA gene sequences in 2010 was 1,483,016, almost 30 times as many.
This paper: The All-Species Living Tree project. Yarza et al. 20008 http://www.ncbi.nlm.nih.gov/pubmed/18692976 provides a lower-bound estimate of 6728, since the Type Species they are describing are a subset of named species, almost all of which have been grown in pure culture and are in collections (see article).
While the estimates of 5–10 million bacteria are still current, and probably better supported (as pointed out elsewhere, the species concept is even more difficult for these organisms) the paper listed below  cites a range from 10^7 to 10^9 (10 to 1,000 million) for the estimated number of species on the planet.
There is also published estimates of 35,498 total species richness, based on the 16,000 species that have been "seen by science". This latter value is based on the number of different 16S_ribosomal_RNA or RRNA genes (also see Molecular_phylogenetics) that are 98% or more divergent as described in this paper: Status of the Microbial Census. Schloss and Handelsman. 2004 http://www.ncbi.nlm.nih.gov/pubmed/15590780. However, the data they were basing their estimate on was much less than is in current databases, so I referenced release 10 to the RDP for a current number.
I've included values from the NCBI GenBank database's Taxonomy section since it is current, and the repository for all sequences. NCBI also has a taxonomic identifier for each sequence. 
^ abYarza, P.; Richter, M.; Peplies, J. R.; Euzeby, J.; Amann, R.; Schleifer, K. H.; Ludwig, W.; Glöckner, F. O.; Rosselló-Móra, R. (2008). "The All-Species Living Tree project: A 16S rRNA-based phylogenetic tree of all sequenced type strains". Systematic and Applied Microbiology31 (4): 241–250. doi:10.1016/j.syapm.2008.07.001. PMID18692976.edit
I fixed the first sentence and changed part of the first paragraph. The introductory portion of this article needs major revisions though. The information is helpful, but the first and second paragraphs duplicate their efforts. They could be consolidated. Secondly, I like including the history, and some of it may be useful to introduce the reader to the topic. I'll continue working on the introduction. If you see improvements make them; I've given my opinion on the topic. Theropod (talk) 23:53, 26 June 2013 (UTC)Theropod
Ah, taxonomy. As of right now, there is both a domain and kingdom named "Bacteria" and they're basically the same thing. Some of this problem is that splitting things into these sort of groups is going to always have some subjectivity. But because the terminology is still used as a kingdom, I'd argue to keep that term in. Scaldwell17 (talk) 17:33, 9 January 2014 (UTC)
1. The Wikipedia article on archaea says they are "prokaryotes, meaning that they have no cell nucleus or any other membrane-bound organelles within their cells." The present article on bacteria says that bacteria are prokaryotes that "rarely harbour membrane-bound organelles." This is confusing. Are there bacteria that harbour membrane-bound organelles? If yes, the archaea article is wrong, and the phrase quoted here should be corrected. If no, the text in this article containing "rarely harbour membrane-bound organelles" should be modified to be clearer. The Wikipedia article on prokaryote says that "prokaryotes are a group of organisms whose cells lack a membrane-bound nucleus". This sounds like the archaea text is misleading. I'm confused.
2. Is there a succinct summary of the difference between bacteria and archaea? I don't see one either here or in the article on archaea. I'd like something that is easy for a lay person to remember. The Wikipedia article on eukaryote says they all have a membrane-bound nucleus. That's easy for me to remember. It would also help to know what is positive or "pro" about prokaryotes. That, too, would make it easier for people to learn. I remember hearing that prokaryotes were originally distinguished from eukaryotes on the basis of a certain test in which prokaryotes accepted a stain and eukaryotes did not, although that may no longer be consistent with current usage. I don't find the word "stain" in either the eukaryote or the prokaryote article, so I don't know. However, I think it would help people remember some explanation is provided of what's "pro" about "prokaryotes". Perhaps a section on "History" could be added to the eukaryote and prokaryote articles explaining this.
3. Is there some reason bacteria, archaea, and eukaryota are spelled in some places with an initial capital, like Bacteria? If yes, is this explained in the current article and I missed it? If no, could this please be changed to conform with Wikipedia:Manual of Style/Capital letters?
Fungi is smelly stuff that grew on your Nan. — Preceding unsigned comment added by 220.127.116.11 (talk) 19:55, 13 May 2014 (UTC)
Bacteria also live in symbiotic and parasitic relationships with plants and animals.
This sentence from the first paragraph maybe should be re-written. Parasitism is a type of symbiosis. I would suggest "Bacteria also live in mutualistic, commensualistic, and parasitic relationships with plants, animals, and other organisms." — Preceding unsigned comment added by 18.104.22.168 (talk) 14:53, 17 May 2014 (UTC)
Bacteria also live in symbiotic and parasitic relationships with plants and animals.
This sentence from the first paragraph maybe should be re-written. Parasitism is a type of symbiosis. I would suggest "Bacteria also live in mutualistic, commensualistic, and parasitic relationships with plants, animals, and other organisms." — Preceding unsigned comment added by 22.214.171.124 (talk) 14:58, 17 May 2014 (UTC)
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I suggest a small grammar change in the section Classification and Identification. In the sentence "Once a pathogenic organism has been isolated, it can be further characterised by its morphology, growth patterns such as (aerobic or anaerobic growth, patterns of hemolysis) and staining." the open parentheses needs to be moved to replace the comma currently inside it, and another comma added after the end of the parentheses. This is the last sentence in the second to last paragraph in the section. 126.96.36.199 (talk) 17:45, 25 July 2014 (UTC)
Copyright violation and incorrect information about Gram stain type
Braineeee (talk) 20:32, 11 October 2014 (UTC)I'm in a Biology course in post secondary school (ie. College) and I needed to find some information about Gram staining. I found a page with the exact same image (from a published book) only a different color. Its the image claimed to have been made by LadyOfHats and uploaded by NI74 in 2006 on this page. Changing 10% of an image (ie. its color) or other copyrighted work does not make it yours to release for free on the internet or in the public domain. That is a violation of copyright law as well. The correct Gram stain for this type of bacteria is Gram negative (using a red/pink Safranin or Fuchsine) dye. The image on this page is blue, and that is completely incorrect, it should be pink. I'm just a tad bit upset that I had to add this comment, and I had to waste my time double checking this for a homework assignment. Other Wikipedia pages about bacteria have conflicting information with this one. My sources are: http://amrita.vlab.co.in/?sub=3&brch=73&sim=208&cnt=1 and http://en.wikipedia.org/wiki/Gram_staining.
Hi @Braineeee: Thanks for your post. Is Number 1 the image you refer to first? If it is then it's almost certain that the book you read copied the image from Wikipedia rather than the other way around. User:LadyofHats makes amazing illustrations and releases them into the public domain so that anyone can republish them wherever they like.
I think you also refer to number 2 which was taken from p4. of this paper and I agree that it is a little different to the original. The image is in the public domain however as it was created by employees of the Centre for Disease Control. Unfortunately it is difficult to find good images for us to use and in this case this might be the best that we can find and we need someone with a good microscope to donate a better one. SmartSE (talk) 21:37, 11 October 2014 (UTC)