As complex multipartite interactions among the coral host and coral-associated microbial entities including the dinoflagellate symbionts, bacteria, archaea and viruses, have been appreciated, a manipulatable, less-complex study system is desired to deepen our functional understanding of this fascinating symbiotic system. Among experimental manipulation approaches, removal of the algal symbionts using menthol is widely implemented; however, its effect on the rest of the coral-associated symbiotic members has not been explored, which is critical knowledge to assess experimental works using this popular method. This preprint by Puntin et al. (https://doi.org/10.1101/2023.08.23.554380) presents an important observation in this aspect. Their initial observations suggest that menthol-induced coral bleaching introduces stochastic changes in associated bacterial communities, which resemble dysbiosis, making bacterial communities more dissimilar from each other. They also observed low taxonomic diversity in bacterial communities on the corals maintained in aquaria over several months, worth noting as a positive value as an experimental system. Their data are preliminary by nature, while they present intriguing ideas that warrant further studies.

Reference

Puntin G, Wong JCY, Röthig T, Baker DM, Sweet M, Ziegler M (2024). The bacterial microbiome of symbiotic and menthol-bleached polyps of long-term aquarium-reared Galaxea fascicularis (2024). bioRxiv, ver.4., peer-reviewed and recommended by Peer Community In Microbiology. https://doi.org/10.1101/2023.08.23.554380 

Few studies deal with the understanding of disease ecology, especially in the agricultural domain. Soft rot Pectobacteriaceae are major plant pathogens that frequently co-infect potato tubers. Exploring their ecological relationships can provide valuable insights for effective monitoring and preventing disease. The study of Barny et al (2024) explores the dynamics of synthetic communities of soft rot Pectobacterium species (SRP) following in vitro and in vivo inoculations, focusing on the implications for disease development. To delve into co-infection dynamics, the authors constructed mixed populations comprising six strains, with three strains from each of two species. Through inoculations of both liquid cultures and potatoes, they observed outcomes using amplicon sequencing targeting the gapA gene, along with monitoring bacterial population sizes and symptoms on potato tubers. Results reveal intriguing patterns: competition among strains of the same species, cooperation through trophic interactions, and interference due to toxicity. Thanks to a modelling approach, they suggest that the presence of a cheater strain may be favoured when it is associated with an aggressive strain. This finding is crucial for field sampling strategies, as there is a risk that during an outbreak, only the cheater strain may be detected, potentially overlooking the problematic aggressive strain. 

While the study conducted by Barny et al. (2024) provides valuable insights into strain interactions, it also highlights areas for further exploration to enhance understanding. First, the extent to which different species occupy similar niches in real agricultural scenarios remains unclear. Additionally, comparative genomics analysis on strains and investigating specific gene candidates could offer valuable mechanistic insights into strain dynamics. These areas for future research offer chances to build up our knowledge base in this field and improve how we understand the interactions between bacteria in nature. The implications of the study extend beyond plant pathogens like SRP. Similar scenarios of complex diseases involving closely related species or strains competing within the same niche are observed in human pathogens as well.

Reference

Barny, M.-A., Thieffry, S., Gomes de Faria, C., Thebault, E., Pedron, J. (2024). Bacterial pathogens dynamic during multi-species infections. https://doi.org/10.1101/2023.12.06.570389