hostassociated

Host-associated refers to organisms, microbes, genes, or other biological material that live on or inside a host organism, or maintain a close ecological relationship with it. The term is used across biology to distinguish these entities from free-living environmental communities. Host-associated life can include endosymbionts within tissues, epibiotic microbes on surfaces, and microbial communities in or on tissues such as the gastrointestinal tract, skin, oral cavity, or plant roots and leaves.

Relationships between hosts and their associated entities are diverse and commonly categorized as mutualistic, commensal, or parasitic. Mutualists benefit both host and microbe; commensals benefit the microbe without harming or helping the host; parasites benefit the microbe at a cost to the host. Host-associated communities can be specific to a host species or more generalists, and they may be transmitted vertically (from parent to offspring) or horizontally (between individuals or through the environment). In plants, for example, root-associated microbiota (the rhizosphere and endosphere) influence nutrient uptake and health; in animals, the gut, skin, and mucosal surfaces host complex microbial ecosystems that can affect digestion, immunity, and disease risk.

Methods to study host-associated communities include sampling of tissues or surfaces, followed by sequencing-based approaches such as 16S rRNA gene profiling, metagenomics, or metatranscriptomics. Challenges include contaminating host DNA, variability due to diet or environment, and ethical considerations in human studies.

Understanding host-associated microbiomes informs health, agriculture, and ecology, highlighting how hosts and their associated communities influence each other’s biology and evolution.