biopython format_alignment gives incorrect output when submit job to the cluster

Question

[wangyunfeng0317]

Dear all, I try to call mutations comparing one contig to the reference sequence using pairwise alignment. Biopython provides a perfect package which is called pairwise2 and format_alignment. When I run my script everything goes fine and it gives an output like this

ACCCCACGCCC
|||||.|||||  
ACCCCCCGCCC
Score=46

But when I submit my script to the cluster which uses the PBS system, the output seems kind of incorrect as follows.

ACCCCACGCCC
|||||||||||  
ACCCCCCGCCC
Score=46

There are no error messages at all. And I have no idea why the output changes when I submit it to the cluster. I guess this might be a bug of the function format_alignment. It's really hard for me to find the SNP with my own eyes using a result like this.

Can anyone help me to solve this problem? Many thanks!

[AK]

Hi wangyunfeng0317,

Try to explicitly use python 3 in the script which you submitted to the PBS system.

When using python 3, the following results:

A-CCCCACGCCC
| |||| |||||
ACCCCC-CGCCC
  Score=10

ACCCCACGCCC
|||||.|||||
ACCCCCCGCCC
  Score=10

Will become these using python 2:

A-CCCCACGCCC
||||||||||||
ACCCCC-CGCCC
  Score=10

ACCCCACGCCC
|||||||||||
ACCCCCCGCCC
  Score=10

[Joe]

I think it's more likely that the system python (which may happen to be Py2) is looking at an out of date BioPython library. pairwise2 was rewritten in 1.68 I believe.

Can you please let us know what versions you're using 'locally' and what versions the scheduler picks when it launches the script/program?

[AK]

👍 Indeed, from 3 April 2018: Biopython 1.71:

The output of function format_alignment in Bio.pairwise2 for displaying a pairwise sequence alignment as text now indicates gaps and mis-matches.

[wangyunfeng0317]

Dear jrj.healey, thanks for your quick answer. My local python version is 3.7.3. And this time I specify the absolute path of my python3 in the script to be submitted and everything goes fine!! So I guess you're right. The python will try to look at an out of date library if I do not specify the full path.