Bioinformatics for Genome Bioinformatics for Genome data analysisdata analysis

Bioinformatics for Genome Bioinformatics for Genome data analysisdata analysis

Sachin PundhirSachin PundhirInformation OfficerInformation Officer

Bioinformatics sub-centreBioinformatics sub-centreSchool of Biotechnology, DAVV, IndoreSchool of Biotechnology, DAVV, Indore

Antibiotic resistance• Antibiotic resistance is the ability of a micro-organism to

withstand the effects of an antibiotic.

• Penicillin, discovered by Alexander Fleming in 1928 crippled many types of disease-causing bacteria.

• In 1980s, the perception was that we had overcome the bacterial infection problem. Drug companies weren't working on new agents. They were concentrating on other areas, such as viral infections.

• As compared to 0.02% of S. pneumoniae resistant to antibiotics, today 6.6% of them are resistant.

Why is it happening?

• Consequence of evolution via natural selection.

• The antibiotic action acts as an environmental pressure

• those bacteria which have a mutation allowing them to survive will live on to reproduce.

Measures to combat• Antibiotic resistance is inevitable, but there are measures

to make it slow.

• Repeated and improper uses of antibiotics are primary causes of the increase in drug-resistant bacteria.

• Do not take an antibiotic for a viral infection like a cold or the flu.

• Do not take expired medicines & do not skip doses

• Identify novel drug targets.

Novel drug targets• Daunting task considering the huge amount of microbial

genomic and proteomic data available in various public repositories like NCBI, TrEMBL and others.

• Whole genome sequence of more than 500 microbial genomes is available at NCBI’s genome database and sequencing of more than 1000 microbes is in progress.

• Escherichia coli CFT073 alone encodes for 5379 proteins.

• Challenge lies in finding subset of proteins encoded in a microbial genome that are vital for the pathogenicity of a pathogenic bacteria.

Horizontal gene transfer (HGT)

• process in which an organism transfers genetic material to another cell that is not its offspring.

• may account for 10 to 50% of all the genes in a bacterial or archaeal genome.

If involved in…………Fitness – Fitness islands

Resistance – resistance islands

Pathogenicity – Pathogenicity islands

What are PAIs?• Pathogenicity islands are distinct chromosomal regions of

pathogenic bacteria that contain genes encoding virulence factors viz. adhesins, toxins and invasions and contribute to the virulence of the respective pathogen.

PAI properties

1. Significant composition bias (%GC, dinucleotide & codon).

2. Presence of insertion elements.

3. Presence of one or more virulence factors.

4. Relative absence in related non-pathogenic species like E. coli 536 and E. coli K12.

Can we identify PAIs computationally?

• Yes, many prediction servers like ISLANDPATH, PAIDB are available online for the prediction of PAIs.

• But how we relate biological features of PAIs to computational algorithm scheme for PAI identification?

BIOINFORMATICS!!!

1. Composition bias analyses

• %GC bias%GC Bias (Cluster) = %GC (Cluster) - %GC

(Genome)

• Dinucleotide bias

• Codon bias

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Reference: Karlin, S. (2001) Detecting anomalous gene clusters and pathogenicity islands in diverse bacterial genomes. Trends Microbiol. 9, 335-343.

2. Insertion elements• Can be identified by keyword search of genome file

(Genbank or EMBL format) for the presence of tRNA, transposase and integrase

Available applications……

1. ISLANDPATH (Composition based):

• Based on composition bias, & • presence of insertion elements.

Limitation:Give much false positive results for PAIs as a region showing distinct nucleotide content may be alien to the host genome (HGT/ GIs) but may not necessarily be involved in pathogenicity

2. PAIDB (Composition and similarity based):

• Based on composition bias • presence of insertion elements, & • similarity search against known PAIs.

Limitation:The detected PAIs are limited by the query dataset of known PAIs.

What can be done?

• Some of the important features that can aid in further validating the role of a region in pathogenicity are:

– its relative absence in related non-pathogenic species

– presence of virulence factors in the potential PAI region

Our approach!!!

• Composition bias measurement (%GC, dinucleotide & codon bias)

• Reverse PSI-BLAST search against a profile database of virulence factors.

• Compare genome analysis for the analyzing the relative arrangement of a potential PAI in non-pathogenic species.

RPS-BLAST search• A profile database of virulence factors (VFPD) has been

developed using 213 protein families associated to virulence.

• Each region with significant composition bias is searched against VFPD and marked as potential PAI, if shows significant similarity in VFPD.

Compare genome analysis

• Potential PAI regions having significant composition bias and virulence factors are compared in non-pathogenic species using BLAST family of programs (BLASTp).

• Regions having no corresponding proteins in non-pathogenic species are marked as PAIs else marked a false positives and thus eliminated from the final results.

• Implemented as a prediction server available at www.davvbiotech.res.in/PredictBias

Advantages and findings!!!

• Performance measure analysis showed that afore mentioned approach significantly aids in reducing false positive results.

• potential PAI (ECP_1342 – ECP_1347) was identified.

• It encodes for probable multi-drug efflux proteins of which, ECP_1345 has significant similarity with ‘Acriflavin resistance protein family signature’ at an E-value of 0.0.

• Acriflavin resistance proteins are believed to protect the bacterium from hydrophobic inhibitors and mutations in these genes increases the susceptibility of E. coli to small inhibitor molecules like cephalothin and cephaloridine

Auto analysis

Bias results for P4 prophage in Bacillus subtilis

Manual analysis

Queries!!!!!!