Could Microbiota Manipulation Shift the Outcome of Infection in a Sex-dependent Way? An Insight into Recently Published Research Paper by Department of Biology at Ashoka University

Sexual differences in immune responses are common across animal species and have significant implications for disease dynamics and pathogen evolution. These sex-based differences can be influenced by various biological and environmental factors such as hormonal regulation, reproductive strategies, life history and immune system investment. Recently, the microbiota—the diverse community of microorganisms residing in animals—has emerged as a potential contributor to sex-specific immune outcomes. However, there remains a lack of direct experimental evidence linking microbiota composition to sex-specific differences in pathogen susceptibility.

This recently published study by Professor Imroze Khan and his team aims to address the gap by investigating whether sex-based variations in microbiota contribute to differing infection outcomes between males and females. The broader goal was to understand whether microbiota-driven differences in immunity are causative rather than merely correlative, and how such effects vary between sexes.

The Journey: Motivation Factor and How the Research Evolved

The motivation for the study came from unexpected observations during preliminary assays, where researchers noted differences in microbiota composition between male and female beetles. Additionally, females were consistently more vulnerable to infection by Bacillus thuringiensis, a common entomopathogenic bacterium. These patterns raised the possibility that the microbiota might underlie—or at least contribute to—the observed sexual dimorphism in immune outcomes. Unlike prior studies that focused on correlations between microbiota and immune function, this research was designed to directly test causation by experimentally altering the microbiota.

The researchers used Tenebrio molitor beetles (mealworm beetles) as their model system to explore how manipulating microbial communities impacts survival and immune responses after bacterial infection.

The central questions driving the research were: Do males and females harbour different microbial communities? If so, do these differences influence their ability to survive infection? And critically, if the microbiota is altered or removed, can these sex-specific differences in susceptibility be reversed?

To explore these questions, researchers used dietary treatments to manipulate microbiota composition in beetles. Three treatment groups were established: one group was maintained on a normal diet preserving natural microbial communities; another group received a broad-spectrum antibiotic-supplemented diet to deplete the microbiota; and in a third group, microbiota-depleted females were fed faecal matter from other beetles to reintroduce microbes. Following these treatments, beetles were infected with B. thuringiensis, and various metrics were measured: post-infection survival, pathogen load, microbiota profiles, and expression levels of immune-related genes—particularly two antimicrobial peptides (AMPs), tenecin 1 and tenecin 2.

Key Findings of the Research

The results revealed significant sex-specific effects. Under normal conditions, males were more successful at surviving infection, exhibiting lower bacterial loads and better infection clearance than females. When the microbiota was depleted, female survival significantly improved, effectively narrowing the gap between sexes.

In contrast, male survival remained unchanged after microbiota depletion. Notably, when microbiota-depleted females were recolonised by consuming faecal matter, their susceptibility to infection returned to baseline levels. These findings suggest that the microbiota plays a detrimental role in female infection outcomes, while having little to no effect on males.

Interestingly, microbiota composition after recolonisation was not identical to the original microbial profile in untreated females, yet the effect on susceptibility was restored. This indicates that the outcome may not depend on specific bacterial species, but rather on the overall composition or function of the microbiota. Further, while tenecin 1 expression was lower in females under normal conditions—a potential factor in their increased vulnerability—this gene-expression difference did not consistently align with survival outcomes across all treatments. This points to a complex relationship between immune gene regulation, microbial composition, and infection resistance.

Speaking about the contribution of this research in the broader context, Professor Imroze underlines, “Our research contributes to a broader understanding of host–microbe interactions and suggests that sex should be considered a key factor in studies of immunity, disease susceptibility, and even in the design of microbiota-targeted therapies.”

The Scope of the Study:

The wider impact of this research lies in its demonstration that microbiota can drive sex-specific differences in immune responses. These findings challenge the view that immunity is governed solely by intrinsic genetic or physiological traits, highlighting the influence of microbial communities.

The study opens new avenues for understanding the interplay between sex, microbiota, and immunity and emphasises the importance of considering sex as a biological variable in both experimental design and therapeutic development.

It also raises intriguing evolutionary questions. Why do females maintain a microbiota that appears to reduce their infection resistance? Could certain microbes provide other physiological advantages—such as aiding in reproduction or nutrient absorption—that outweigh the costs to immune defense? These possibilities warrant further investigation.

Conclusion:

On a broader scale, the study emphasises the importance of considering sex as a key biological variable in microbiota research, particularly when designing treatments like probiotics or immune-boosting therapies, which may have sex-specific effects.

In summary, the study illustrates that the microbiota plays a crucial and sex-specific role in shaping host immunity and pathogen susceptibility. It reinforces the importance of adopting a holistic approach to studying host-pathogen interactions—one that incorporates not just genetics and physiology, but also the microbial communities that the hosts harbour within themselves.