Announcing the khmer-protocols project

(with Camille Scott, Michael Crusoe, and Leigh Sheneman; Josh Rosenthal contributed to eel-pond; and Adina Howe contributed to kalamazoo)

This summer, I spent a lot of time writing up computational protocols for both mRNAseq and metagenome assembly in the Amazon cloud.

I'm happy to announce that they are now available! Here's the link.

Both protocols rely heavily on khmer, and use both partitioning and digital normalization.

The Eel Pond mRNAseq Assembly Protocol

Link: https://khmer-protocols.readthedocs.org/en/v0.8.3/mrnaseq/

This protocol, named after the harbor in Woods Hole surrounded by the Marine Biological Lab, is a lightweight mRNAseq assembly protocol that, for 50-100m reads, should take 1-3 days on a single m1.xlarge AWS machine (see Leigh Shemenan's blog post for more information). It walks the user through:

  • adapter trimming with Trimmomatic
  • quality filtering with fastx
  • digital normalization with khmer
  • assembly with the Trinity pipeline
  • setting up a little personal BLAST server in the cloud
  • annotating the sequences against the mouse proteome
  • diferential expression analysis of multiple samples with RSEM

We would particularly like to thank Dr. Josh Rosenthal of the UPR, and Dr. Leslie Babonis of the Whitney Marine Lab, for helping with testing out this protocol.

The Kalamazoo Metagenome Assembly Protocol

Link: https://khmer-protocols.readthedocs.org/en/v0.8.3/metagenomics/

This protocol, named after the funniest-sounding city in Michigan, is a reasonably lightweight metagenome assembly protocol. For most metagenomes it should be executable on moderate to high-end cloud resources. It walks the user through:

  • adapter trimming with Trimmomatic
  • quality filtering with fastx
  • digital normalization with khmer
  • assembly with Velvet, IDBA, and SPADes;
  • annotating assemblies with Prokka;
  • setting up a little personal BLAST server in the cloud

The metagenome protocol is a bit less mature than the mRNAseq protocol, but should still be useful.

Basic Information

If you need help, or are interested in discussing, helping out, or otherwise kibbitzing, sign up for the "protocols" mailing list.

The khmer-protocols source is here on github. There is an issue tracker as well; dump unresolved questions there.

Pre-Answered Questions

Why aren't you just using the Trinity pipeline (for mRNAseq assembly)?

A few reasons. One is that the Trinity pipeline is heavier-weight than our protocol, and will require more computational resources; another part of it is that I don't want to have to coordinate with them as we evolve our protocol (and I would imagine the same is true in reverse); a third is that we are using some of our own special sauce, and want the leisure to explore and evolve our own techniques.

Someone else claims they have a better protocol than yours. Why should I use yours?

You shouldn't! But please use someone's rather than inventing your own, until you have a good reason otherwise. Thanks in advance.

So then why did you invent your own?

Umm... we don't know of any good lightweight protocols for the cloud, honestly. Plus we think very highly of our special sauce.

Why are you releasing these as protocols, rather than as pipelines? I'd rather not have to type out all that stuff!

There are lots of reasons, but the simplest is that it's actually quite hard to write a robust pipeline that anyone can run. Plus, the protocols are kind of easy to remix, because it's clear what data goes on to the next step at each point; this is not so true of pipelines, which are large, opaque bodies of code. So if you want to try out a different trimmer, or avoid digital normalization, it's easy to figure out how to modify our instructions!

More generally, I think the right philosophical approach to be taking is to teaching people how to do a certain amount of their own cooking, as opposed to providing completely prepackaged meals. Not only is it potentially healthier, you get some sense of what is actually in the prepackaged meals. (This is very much the Software Carpentry mentality.)

I used your protocol and got sucky results. Your protocol sucks and I hate you.

I'm sorry to hear that! ...could you share your sucky results so that we can improve our protocol? Thanks!

I ignored your advice and modified your protocol and got way better results. Your protocol sucks. Ha ha!

Great! ...could you share your improvements? Thanks! We'd be happy to give you credit in both the protocol and subsequent publications.

Your protocol isn't as good as it could be. I invented a nifty piece of software that solves a bunch of problems and is way cool.

Great! ...could you share? Thanks! We'd be happy to give you credit in both the protocol and subsequent publications.

I have 454, Ion Torrent, or PacBio data. Can we integrate this?

Not sure how to do that yet. Sorry!

I'd like to contribute; how can I?

Discuss on the mailing list, and/or submit pull requests (see github flow for more info on pull requests).

This is awesome! I have money to give you!

Great! We take donations in unmarked 20s and 50s.

Longer-term hopes

  1. I hope these protocols have a clarifying effect for people who want to gain a better understanding of the various steps involved in doing de novo mRNAseq assembly. In particular, it's remarkably difficult to find a detailed HOWTO on how to deal with raw reads all the way through annotation and differential expression analysis.
  2. Imagine a world where it's copy-and-paste, and $150 of compute resources, to assemble and annotate a transcriptome! Wouldn't that be neat?
  3. We are planning to instrument the protocols with all sorts of performance metrics and diagnostic outputs, so that we can understand where the bottlenecks are. (See Leigh's initial blog post on this.)
  4. Right now there's no good way to investigate the impact of different primer trimming and quality filtering programs, much less different assemblers, on the output. We will be building such tools around these protocols.
  5. We'd like to set up comparative metrics, both on the computational side and on the performance side (think Assemblathon 2, but for transcriptomes and metagenomes). This will help us evaluate our own future work, as well as serve as one possible platform for evaluating and reviewing new assemblers.
  6. Hopefully people will get angry with us for being so naive about transcriptome and metagenome assembly and demonstrate to us why we are wrong. Then we will fix our protocols accordingly.
  7. Some time soon we plan to start offering to run your animal mRNAseq assemblies for you, using these protocols. Read more here.
  8. These protocols can also serve as substrates for the development, testing, and integration of new technology, like error correction.

8. Did I mention everything's on github? It's also under CC0, like almost everything else we do. This means that

  • you can copy, adapt, modify, and remix the protocols;
  • you can contribute openly, with credit, to them, via a well-understood process (again, see github flow);
  • and, of course, you can do whatever else you want to do with them.
  1. Sequencing is now an undergraduate-level project, but I don't think de novo assembly is just yet. Hopefully we can help make it one!

I've already found these protocols really useful just for my own lab and my collaborators; I hope the larger world finds them just as useful.

--titus

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