MiSeq v3 2x300 run, Low Q30

[ReGenMC]

I recently ran a ~400bp library prepped with NexteraXT on the MiSeq using reagents kit v3 for a 2x300 run. The project was DeNovo Assembly, paired end single index. I got high but in range cluster densities of 1383k/mm2 with 88.2% passing filter.

My issue is that the run only had 43% >Q30 bases. Does anyone have any ideas for troubleshooting?

[GW_OK]

Perhaps it's because you ran into the adapter and then the nothingness beyond while doing a 400bp insert on a 2x300 run?

[Wallysb01]

Yeah, GW is probably right. In a ~400bp library, a lot of your fragments will be <300bp. If you trim adapters, what happens? Also, you can run something like Flash to overlap your reads, and it may give you a better sense of the size distribution of your library as it was sequenced.

Remember even if a bioanalyzer says your library is one size, clustering on the flowcell is not necissarily going to occure with the same efficiency across the various sizes in your library. And in general, smaller fragments cluster better. So if you see 400bp on the bioanalyzer, don't be at all surprised if after sequencing the mean size is closer to 300bp.

[tbanks]

I just did two runs with the 600 cycle kit (2 x 300). One was 82%>Q30 and the other 81%. Average insert size of that library is 275 bp. 29 million reads passing filter for each run. I don't think it is your insert size.

Travis

[GenoMax]

At almost 1400 clusters/mm^2 you are at the outer bounds of recommended cluster density for v.3 chemistry. It is not surprising that your Q30 values have suffered as a result. Short of loading less and re-running there is nothing you can do about the existing Q-scores.

[nickloman]

We've run much higher cluster densities and still stayed within the performance spec for V3 kits which is >70% Q30. First off, report this run to Illumina and get the kit replaced. If this problems recurs with other runs then you will need to debug further, but it could just be a faulty reagent batch.

[heidurlo]

@nickloman
-How much higher cluster densities are we talking about?

I just ran a v3 600 cycle, cluster density around 1800k/mm2, and Q30 only 24%. The tech support told me that I had overclustering, which I believe, but I am just curious to know about your experience.

[GenoMax]

There is an implied aspect to @nickloman's comment. The value of cluster density is going to be somewhat dependent on the type and quality of the library e.g. if you are doing plain resequencing then you may be able to get away with higher densities as opposed to amplicon sequencing.

It is quite surprising how far one can push MiSeq limits and still keep getting good data. The cliff is precipitous and when you go over a limit the fall in quality may be similar to what you saw.

[Riddhi]

Hi i ran the Miseq V3 150 PE cycles with 12pM dilution and i got 1981K cluster with Q30 77.3%

can any body guide me to reduce cluster and increase the Q30?
Should i lower my library dilution?

[DJ Flowcell]

Hi Riddhi,

Yes, definitely lower your cluster counts through a library dilution. 1900K/mm2 is very high. The V3 kits function optimally between 1000 - 1300. You could literally split your final library dilution in HT1 in half and have good cluster counts with good quality too.

[justinjun]

Hi Riddhi,
I am surprised by the fact that 12pM can give you 1981K/mm2 cluster density.
I am a little bit doubting your DNA measurement. Do you use Qubit to do the measurement or what? I usually dilute my library to 14pM which, in turn, give me 1300~1400K density (I did run 3 times 2x300 run with different library with average DNA length of 600bp).
But, even with ~1400k density, Q30 is still pretty low (around 75%, though higher than kit performance spec.)
I am wondering how to increase the overall Q30? Any thought? Thanks.

[NextGenSeq]

What type of library? We see lower quality scores with amplicon libraries.

[justinjun]

What type of library? We see lower quality scores with amplicon libraries.

genomic DNA prepared using NEBNext Ultra DNA Library Prep Kit for Illumina, which has 10 cycle PCR amplification step.

[unladenedswallow]

Our collaborators mentioned they had encountered a similar situation where their fragment sizes were too small and it had 'read into the nothing beyond'. However, it seems like other people on this forum were getting decent results.

I recently did a 2 x 300 run with 1220K/mm2 cluster density and our Q30% started dropping rapidly at cycle 250. We loaded several libraries of different average fragment sizes (~380 bp to ~900 bp) at equal volumes.

Do you guys find that 2x300 V3 runs give less consistent results? We just started running 600 cycle runs.

I recently ran a ~400bp library prepped with NexteraXT on the MiSeq using reagents kit v3 for a 2x300 run.

Perhaps it's because you ran into the adapter and then the nothingness beyond while doing a 400bp insert on a 2x300 run?

[Brian Bushnell]

How are you calculating the fragment sizes? The sizes observed by some tools prior to sequencing do not always correlate well with the the sizes calculated bioinformatically after sequencing.