Human impact on symbioses between aquatic organisms and microbes

Abstract

Aquatic organisms rely on microbial symbionts for coping with various challenges they encounter during stress and for defending themselves against predators, pathogens and parasites. Microbial symbionts are also often indispensable for the host's development or life cycle completion. Many aquatic ecosystems are currently under pressure due to diverse human activities that have a profound impact on ecosystem functioning. These human activities are also ex pected to alter interactions between aquatic hosts and their associated microbes. This can directly impact the host's health and -given the importance and widespread occurrence of microbial symbiosis in aquatic systems -the ecosystem at large. In this review, we provide an overview of the importance of microbial symbionts for aquatic organisms, and we consider how the beneficial services provided by microbial symbionts can be affected by human activities. The scarcity of available studies that assess the functional consequences of human impacts on aquatic microbial symbioses shows that our knowledge on this topic is currently limited, making it difficult to draw general conclusions and predict future changes in microbial symbiont−host relationships in a changing world. To address this important knowledge gap, we provide an overview of ap proaches that can be used to assess the impact of human disturbances on the functioning of aquatic microbial symbioses.

Host-microbiome transplants of the schistosome snail hostBiomphalaria glabratareflect species-specific associations

“…There are precedents with mosquito-borne diseases, such as malaria, dengue and chikungunya, where the release of microbiome-altered vectors reduced disease prevalence, both at a local and at a regional scale [3,9,10]. It is hypothesized that microbiomes might affect the outcome of parasitic flatworm infections in snails by competing for resources, producing antimicrobials or stimulating the host's immune response [11][12][13][14].…”

“…Although such controlled laboratory experiments will undoubtedly provide vital insights into the tripartite interaction between snails, bacteria and parasitic flatworms, extrapolation of patterns and protocols to field settings might prove complicated [5]. However, correlative field-based studies could fill these caveats and, likewise, transplant experiments could help discern correlation from causation in a controlled setting [14]. Correlative studies could help in identifying bacterial strains involved in snail resistance.…”

A broad‐taxa approach as an important concept in ecotoxicological studies and pollution monitoring

“…In Hydra , an increased tolerance to copper has been associated with the presence of microalgal symbionts (Karntanut & Pascoe, 2005), while in metal‐rich hydrothermal vent environments, symbiotic bacteria on mussels ( Bathymodiolus ; Hardivillier et al ., 2004) protect their host by transforming absorbed metal ions into metal particles. Additionally, microbial symbionts of aquatic invertebrates frequently provide their hosts with crucial micronutrients (Stock et al ., 2021). As an example, the settling of poriferan, cnidarian and mollusc larvae requires bacteria.…”

Zooplankton act as cruise ships promoting the survival and pathogenicity of pathogenic bacteria

“…Eckert et al 183 reported that zooplankton living in the same environment share similar microbes and have a similar richness, thus suggesting the influence of the environment on the microbiome of the zooplankton. An increase in water temperature can affect the host microbial community, either directly or indirectly by influencing the host physiology 186–188 . At temperatures above 15°C, the ability of V. cholerae to attach to chitinous surfaces of zooplankton is altered by increasing water temperature as a result of increased expression of the MSHA pilus and colonization factor GbpA 95 .…”

“…An increase in water temperature can affect the host microbial community, either directly or indirectly by influencing the host physiology. 186 , 187 , 188 At temperatures above 15°C, the ability of V. cholerae to attach to chitinous surfaces of zooplankton is altered by increasing water temperature as a result of increased expression of the MSHA pilus and colonization factor GbpA. 95 Water temperature does not seem to be the sole factor controlling this association, however, as planktonic V. cholerae are more frequent than zooplankton‐associated forms at temperatures above 15°C in the Chesapeake Bay.…”