# A modified targeted culturing approach provided a snapshot into interdependencies and resistome among core anaerobic bacteria of the healthy human gut

## TL;DR

This study used a new culturing method to explore interactions and antibiotic resistance among key gut bacteria, revealing complex relationships and potential roles in gut health.

## Contribution

A modified culturomics approach enabled targeted isolation and characterization of core anaerobic gut bacteria, uncovering their interdependencies and resistome.

## Key findings

- Bacteroides thetaiotaomicron showed dual roles in inhibiting pathogens and promoting probiotic growth.
- Whole genome sequencing linked observed phenotypes to potential genetic mechanisms.
- The method successfully isolated 21 core genera, including some reported for the first time.

## Abstract

The core anaerobic component of the human microbiome plays a critical role in preserving the overall structure and function of the microbiome. However, how these core strains interact with each other and with other gut microbes is largely unknown. We employed a modified culturomics approach to selectively culture these core genera from the human gut and provided a snapshot into their ecological interactions, clinically relevant resistome, and whole genome sequence (WGS)-based insights into their observed phenotypes. This strategy successfully isolated representatives of the targeted 21 core genera, with some isolates reported for the first time. Cross-interactions and resistome-based profiling revealed important insights. Out of the 440 interaction assessments, a significant proportion exhibited either cooperative or competitive effects on other core genera. Interestingly, Bacteroides thetaiotaomicron displayed dual roles, inhibiting potential pathogens while enhancing the growth of beneficial probiotic strains. Moreover, resistome profiling revealed variable resistance and susceptibility toward various antibiotics. WGS analysis revealed the ability of the selected organism to produce metabolites consistent with the observed phenotype. Our unique culturomics approach successfully isolated key anaerobic genera and revealed their complex interdependencies and clinically relevant resistance. Furthermore, our approach lays the foundation for exploring larger-scale microbial community dynamics in terms of interdependencies and for assessing how clinically significant antibiotics impact the key microbiome, something that may be important when making therapy decisions. In summary, our research improves our knowledge of the interactions present among core gut microorganisms and hints at possible mechanisms responsible for sustaining gut microbial homeostasis and rehabilitation.

This study presents a unique strategy for the targeted isolation and characterization of key interaction dynamics as well as the resistome of core anaerobic bacteria in the healthy human gut. By utilizing this targeted single, optimized core anaerobe-specific growth medium approach, we were able to culture a major proportion of the core anaerobic gut species, where some of those were cultured for the first time. Through the combinatorial approach of cross-interaction, antimicrobial resistance profiling, and whole genome sequencing (WGS) resolved functional insights, we uncovered interesting insights into interdependencies and competition among these core strains as well as their ecological flexibilities. Moreover, we observed that some strains, such as Bacteroides thetaiotaomicron and Bifidobacterium angulatum, are capable of either inhibiting or promoting the growth of certain strains, depending on the pairing. Such findings go against the traditional binary view of microbes as being purely commensal or pathogenic and suggest that microbial behavior is highly context-dependent. Furthermore, WGS analysis provided useful insights into the potential genomic basis of the observed phenotype. Taken together, our findings provide valuable data and enhance our current understanding of how core anaerobes interact with each other, survive, and adapt within the gut environment. Moreover, our work also lays the critical basis for a more rational design of synthetic microbial communities as well as precision-based microbiome aimed at targeted gut health rehabilitation, both with accuracy and sensitivity.