Digital Twins
For Microbial
Systems

1. DNA · Taxonomic identity & genetic potential

   Genome-based taxonomy establishes evolutionary identity; genome annotation describes encoded capabilities such as substrate utilization, complex-polysaccharide degradation and energy metabolism.

   Taxonomic foundation: Zheng et al. (2020), with Gänzle & Walter — reclassification of Lactobacillus. Supports genome-based classification of lactobacilli; organism-specific functional potential requires separate genome annotation and evidence.

2. RNA · Condition-responsive functions

   Transcriptomic evidence of expressed functions and responses under specified conditions. Induction requires a comparison between conditions; expression alone does not establish metabolic flux.

3. Metabolism · Functional activity

   Pathway evidence, substrate consumption and metabolite production constrain realized functions. Metabolite presence alone does not identify the producing organism or establish pathway flux.

4. Virulence · Context-dependent pathogenic potential

   Virulence-associated genes, their expression and relevant phenotypes inform potential for harm alongside host susceptibility and exposure. Gene detection alone does not establish pathogenicity.

5. Ecology · Lifestyle & functional guilds

   Keep ecological lifestyle distinct from functional guild membership. Host-adapted, nomadic and free-living lifestyles describe niche dependence; guilds group organisms by resource use or ecological function.

   Lifestyle framework: Duar et al. (2017), with Gänzle & Walter. Developed for lactobacilli; application to other organisms needs evidence.

6. Integrated agent identity

   Combine taxonomy, genetic potential, condition-specific activity, functional guilds and ecological lifestyle into a traceable agent profile. Record the evidence, uncertainty and missing layers; this identity does not replace taxonomic classification.

1. Substrate delivery & accessibility

   For the gut: dietary intake → host digestion and small-intestinal absorption → residual substrates delivered to the hindgut. Add host-derived inputs from secretion and tissue turnover: mucin glycans and protein, bile acids, digestive secretions and shed epithelial cells. Distinguish nutrient resources from compounds that microbes transform or that alter their environment: bile acids can act as metabolic substrates and selective pressures, while antimicrobial peptides can inhibit susceptible organisms. Delivery, reabsorption, local concentration and microbial transformation determine exposure; host secretion does not imply that the entire amount reaches the hindgut. Local accessibility also depends on substrate structure, transit and microbial processing.

2. Agent-specific resource use

   Determine whether each agent can degrade the substrate, transport the released products and metabolize them. A primary degrader may release products for other organisms, or retain them; shared access is not assumed.

3. Cross-feeding & mutual benefit

   One organism’s degradation products or metabolites can support another. Cross-feeding may be one-way; call it mutualism only when benefits to both partners are supported.

   Rakoff-Nahoum et al. (2016): cooperation within the gut microbiota.

4. Resource competition & interference competition

   Organisms may compete by consuming shared limiting resources, or by producing antimicrobial compounds, including bacteriocins and other antibiotics, that inhibit or kill susceptible competitors. Effects depend on production conditions, exposure, target susceptibility and resistance.

   Example: E. coli Nissle 1917 microcins limited competing Enterobacteriaceae in the inflamed mouse gut. Sassone-Corsi et al. (2016). This is a specific mechanism and context, not a universal interaction rule.

5. No detectable interaction

   Allow negligible effects under the tested conditions when organisms use distinct resources or have limited exposure to one another. Absence of a detected effect does not establish universal neutrality.

Proposed interaction framework. Assign mechanisms from strain- and condition-specific evidence; these interactions are not all implemented in the current demonstration models.

1. Diet & substrate supply

   Change dietary composition, fermentable substrates or feeding patterns to alter resource availability and microbial selection.

2. Drugs & antibiotics

   Represent compound-specific exposure, microbial susceptibility and resistance, including direct inhibition and indirect effects on the host or niche.

3. Live microbial preparations

   Introduce defined strains or consortia; evaluate survival, establishment, resource use and interactions with the resident community.

4. Bacteriophages

   Evaluate host-range-specific targeting, infection dynamics and bacterial resistance within the community context.

5. Niche conditions & combined strategies

   Test changes in physical conditions or delivery schedules, alone or in combination with other approaches, against the specified outcome.

Candidate simulation strategies, not treatment recommendations. Each requires mechanism-specific data and validation; support depends on the application model.