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  • Calculating phiX concentration...

    Hi all!
    I'm a new user of MiSeq and I'm confused about phiX concentrarion to spike in.
    In Nextera XT DNA protocol they show a list of dilutions to prepare a final solution of phiX 12,5 pM. Then you have to mix 30 uL of phiX 12,5 pM with 570 uL of pooled libraries, so you are diluting phiX 20 times: the new concentration will be less than 1 pM.

    Is that right??!!! Please anyone can explain to me?
    I'm not sure how much phiX I have to see in %aligned to know that my run was ok.

    Thank youuuuuuu
    Soledad

  • #2
    The phiX is just there as a control. You don't want it present at high concentrations.
    The MiSeq usually needs at least 1% phiX or it won't show error rate results. But if you have .125pM phiX in a 8pM pool, that will be plenty high enough.

    --
    Phillip

    Comment


    • #3
      Thanks Phillip!!!

      I need to understand how much phiX (in percentage) I have in my final pool (including phiX spike in). For example, in my first run I did exactly I described above for spike-in and I have 1,2% aligned of phiX. So, I want to know if using that dilutions I put really 1,2% of phiX in the 600 uL that I used to charge the cartridge.

      I hope you can help me!!
      Thanks

      Soledad

      Comment


      • #4
        Originally posted by soleulloa View Post
        Thanks Phillip!!!

        I need to understand how much phiX (in percentage) I have in my final pool (including phiX spike in). For example, in my first run I did exactly I described above for spike-in and I have 1,2% aligned of phiX. So, I want to know if using that dilutions I put really 1,2% of phiX in the 600 uL that I used to charge the cartridge.

        I hope you can help me!!
        Thanks

        Soledad
        I guess you did, or you would not have gotten 1.2% aligned. Or am I missing something?

        --
        Phillip

        Comment


        • #5
          It's not exactly on topic but close enough:

          I recently had some trouble getting my desired % of PhiX clusters. I'm doing amplicon sequencing (16 S, 2x300 v3 on MiSeq) needing higher PhiX concentrations. In one run, I spiked in 5 % but I had only around 1.5 % of PhiX clusters. Another run had 15 % spiked in, and resulted in a mere 4 % of PhiX clusters. This wasn't enough to get solid diversity, which is why the quality of the first few bases was pretty poor and the overall intensities weren't that high. The run was still fine overall but I can't say I'm too happy with it.
          The lot numbers of PhiX used were different for both runs and both weren't the lot numbers of faulty PhiX that circled around some time ago.
          What might be the cause for this? I'll perform some more amplicon sequencing shortly, and it would be great to know what I can do to improve this situation.

          Comment


          • #6
            @dfhdfh: I seem recall a recent email from Illumina about quality problems with some phiX lots (at least in the US). May want to check with your local FAS, if you did not email an email.

            Comment


            • #7
              Originally posted by GenoMax View Post
              @dfhdfh: I seem recall a recent email from Illumina about quality problems with some phiX lots (at least in the US). May want to check with your local FAS, if you did not email an email.
              Thanks for your reply. However, like I said, the used lot numbers were not listed by Illumina.

              Comment


              • #8
                The email I recall was from last couple of months (sorry I don't work in the lab). Is that the one you are thinking of?

                If you suspect more lots may be affected, it would not be bad to report this lot to illumina (probably that is how the other lots were identified as bad). You can at least get a free replacement.

                Comment


                • #9
                  Yes, this is the email I'm thinking of.

                  I called Illumina, they said they haven't received any notifications with issues concerning these lot numbers.

                  I bought another new PhiX and hope it'll work this time around.

                  Comment


                  • #10
                    Originally posted by dfhdfh View Post
                    It's not exactly on topic but close enough:

                    I recently had some trouble getting my desired % of PhiX clusters. I'm doing amplicon sequencing (16 S, 2x300 v3 on MiSeq) needing higher PhiX concentrations. In one run, I spiked in 5 % but I had only around 1.5 % of PhiX clusters. Another run had 15 % spiked in, and resulted in a mere 4 % of PhiX clusters. This wasn't enough to get solid diversity, which is why the quality of the first few bases was pretty poor and the overall intensities weren't that high. The run was still fine overall but I can't say I'm too happy with it.
                    The lot numbers of PhiX used were different for both runs and both weren't the lot numbers of faulty PhiX that circled around some time ago.
                    What might be the cause for this? I'll perform some more amplicon sequencing shortly, and it would be great to know what I can do to improve this situation.
                    Yes, we've had this problem as well -- phiX percents way below what we expected.

                    We actually check every batch of phiX we get on the bioanalyzer and generally they are much lower than the expected concentration. But rarely are they less than 50% of their specified concentration of 10nM. Even taking this into account we were sometimes seeing much, much lower % than expected phiX in MiSeq runs. Several fold lower as dfhdfh mentions above.

                    Note that these same batches of phiX gave us no such issues on our HiSeq runs. What seemed to work, although I'm not sure why, was to add the phiX to the library to be run, in the correct proportion, prior to denaturation.

                    --
                    Phillip

                    Comment


                    • #11
                      Originally posted by pmiguel View Post
                      What seemed to work, although I'm not sure why, was to add the phiX to the library to be run, in the correct proportion, prior to denaturation.

                      --
                      Phillip
                      +1 Phillip.

                      Consider creating a new post with an appropriate title to make this information readily visible. Buried deep in this post it may not show up easily in a search.

                      Comment


                      • #12
                        I almost always see (within 1 or 2%) the "correct" proportion of phiX relative to my amplicon library. However, I am adding 10% of 12.5 pM phiX to a 9.5 pM library to get this. And relative to what pmiguel said - I add it after the NaOH denaturation and dilution down to 9.5 pM, but I heat denature the final diluted pool to be sure of complete denaturation.

                        Comment


                        • #13
                          Well, within 1 or 2 % is just not good enough. When I'm doing amplicon sequencing and want to cut down on "wasting" reads on PhiX, I don't want to get 3 % instead of the 5 % I'm putting in. You say you're adding 10 % of 12.5 pM PhiX to a 9.5 pM library. This means you're adding way more PhiX than specified for 10 % in order to get to the cluster numbers you want? What percentage of PhiX clusters do you observe?

                          @pmiguel: That sounds interesting. Unfortunately, we're a rather small lab and can't afford to just do things like this for testing. But it shouldn't really make a difference whether you denature PhiX and your library seperately and then put them together or whether you put them together and then denature, should it?

                          At least I don't just seem to be too dumb to pipet together the correct percentages of two solutions
                          Last edited by dfhdfh; 05-20-2015, 11:06 PM.

                          Comment


                          • #14
                            Originally posted by dfhdfh View Post
                            @pmiguel: That sounds interesting. Unfortunately, we're a rather small lab and can't afford to just do things like this for testing. But it shouldn't really make a difference whether you denature PhiX and your library seperately and then put them together or whether you put them together and then denature, should it?
                            "Should" it? No. But we are not in "should" territory here. Things aren't working which suggests that something we think is true, isn't.

                            Since we were getting the expected cluster density from the library in the main denaturation and not getting what we expected from the phiX dentaturation, I decided we should just add the phiX to the main denaturation. That seemed to work. But it may have been a way to avoid some sort of error that was being made with the phiX denaturation. Actually, that is what I thought the issue was.

                            But now that I hear of what sounds like the same issue in another lab, I am not so sure.
                            --
                            Phillip

                            Comment


                            • #15
                              Two weeks from now, I'll run some bacterial total RNA libraries which shouldn't have too much of an issue with diversity. Maybe I'll try one the "Illumina way" and one the "pmiguel way" and see what the results will bring. Have to think about this.

                              Comment

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