Bio Systems Biology Model Curation

Goal: Evaluate the quality and standards compliance of a genome-scale metabolic model to identify areas needing curation.

Approach: Run memote snapshot to score the model against SBML community standards, then use the Python API to inspect individual test failures and guide manual fixes.

# Install memote
pip install memote

# Run full quality report
memote report snapshot model.xml --filename report.html

# Quick score
memote run model.xml

# Continuous integration testing
memote run --pytest-args "--tb=short" model.xml

Memote Python API

import memote
import cobra

model = cobra.io.read_sbml_model('model.xml')

# Run all tests
result = memote.suite.api.run(model)

# Get score breakdown
scores = memote.suite.api.snapshot(model)
print(f"Total score: {scores['score']['total_score']:.2%}")

# Detailed test results
for test_name, test_result in scores['tests'].items():
    if not test_result['passed']:
        print(f"Failed: {test_name}")

Gap-Filling

import cobra
from cobra.flux_analysis import gapfill

model = cobra.io.read_sbml_model('model.xml')

# Load universal reaction database
universal = cobra.io.read_sbml_model('universal_model.xml')

# Find reactions to add for growth
# demand: reaction to optimize (usually biomass exchange)
# iterations: number of alternative solutions
solution = gapfill(model, universal,
                   demand=model.reactions.BIOMASS,
                   iterations=5)

# solution contains list of reaction sets to add
for i, rxn_set in enumerate(solution):
    print(f'Solution {i+1}: {[r.id for r in rxn_set]}')

# Add first solution
for rxn in solution[0]:
    model.add_reactions([rxn])

Identify Dead-End Metabolites

def find_dead_end_metabolites(model):
    '''Find metabolites that cannot be produced or consumed

    Dead-end metabolites indicate:
    - Missing reactions in the network
    - Incorrect reaction stoichiometry
    - Incomplete pathways
    '''
    dead_ends = []

    for met in model.metabolites:
        producing = [r for r in met.reactions if r.get_coefficient(met) > 0]
        consuming = [r for r in met.reactions if r.get_coefficient(met) < 0]

        if not producing or not consuming:
            dead_ends.append({
                'metabolite': met.id,
                'name': met.name,
                'producers': len(producing),
                'consumers': len(consuming)
            })

    return dead_ends


dead_ends = find_dead_end_metabolites(model)
print(f'Found {len(dead_ends)} dead-end metabolites')

Check Mass and Charge Balance

def check_reaction_balance(reaction):
    '''Check if reaction is mass and charge balanced

    Unbalanced reactions indicate:
    - Missing metabolites
    - Wrong stoichiometry
    - Proton accounting issues
    '''
    mass_balance = {}
    charge_balance = 0

    for met, coef in reaction.metabolites.items():
        # Check mass
        if met.formula:
            for element, count in met.elements.items():
                mass_balance[element] = mass_balance.get(element, 0) + coef * count

        # Check charge
        if met.charge is not None:
            charge_balance += coef * met.charge

    is_balanced = all(abs(v) < 1e-6 for v in mass_balance.values())
    is_charge_balanced = abs(charge_balance) < 1e-6

    return {
        'mass_balanced': is_balanced,
        'charge_balanced': is_charge_balanced,
        'mass_imbalance': {k: v for k, v in mass_balance.items() if abs(v) > 1e-6}
    }


# Check all reactions
unbalanced = []
for rxn in model.reactions:
    result = check_reaction_balance(rxn)
    if not result['mass_balanced']:
        unbalanced.append((rxn.id, result['mass_imbalance']))

Fix Gene-Protein-Reaction Rules

def standardize_gpr(model):
    '''Standardize gene-protein-reaction rules

    GPR format: (gene1 and gene2) or gene3
    - 'and' = protein complex (all genes required)
    - 'or' = isozymes (any gene sufficient)
    '''
    for rxn in model.reactions:
        if rxn.gene_reaction_rule:
            # Standardize formatting
            rule = rxn.gene_reaction_rule
            rule = rule.replace(' AND ', ' and ')
            rule = rule.replace(' OR ', ' or ')
            rxn.gene_reaction_rule = rule


def identify_orphan_reactions(model):
    '''Find reactions without gene associations

    Orphan reactions may be:
    - Spontaneous reactions
    - Unannotated genes
    - Transport reactions (often orphan)
    '''
    orphans = [r for r in model.reactions if not r.genes]

    # Classify orphans
    exchange = [r for r in orphans if r in model.exchanges]
    transport = [r for r in orphans if 'transport' in r.name.lower() or 't_' in r.id.lower()]
    other = [r for r in orphans if r not in exchange and r not in transport]

    return {
        'exchange': len(exchange),
        'transport': len(transport),
        'other': len(other),
        'total': len(orphans)
    }

Annotation Standards

def add_standard_annotations(model):
    '''Add standard database annotations

    Required annotations for SBML compliance:
    - KEGG IDs for reactions and metabolites
    - ChEBI IDs for metabolites
    - BiGG IDs if applicable
    '''
    for met in model.metabolites:
        if not hasattr(met, 'annotation'):
            met.annotation = {}

        # Add SBO term for metabolite
        met.annotation['sbo'] = 'SBO:0000247'  # Simple chemical

    for rxn in model.reactions:
        if not hasattr(rxn, 'annotation'):
            rxn.annotation = {}

        # Add SBO term based on reaction type
        if rxn in model.exchanges:
            rxn.annotation['sbo'] = 'SBO:0000627'  # Exchange
        else:
            rxn.annotation['sbo'] = 'SBO:0000176'  # Biochemical reaction

Related Skills

• systems-biology/metabolic-reconstruction - Generate draft models
• systems-biology/flux-balance-analysis - Test curated models
• pathway-analysis/kegg-pathways - Add KEGG annotations