Engineering the gut microbiome with metal-resistant bacteria could protect Artemia nauplii from cadmium toxicity.

Metal pollution and emerging contaminants, such as metal nanoparticles, are increasingly found in estuarine and coastal environments. These pollutants pose significant risks to aquatic life and human health and may affect food security. This study evaluates host-associated microbiome engineering as a biological method to reduce cadmium toxicity in an aquatic invertebrate model. We designed a consortium of metal-resistant bacteria through systematic screening and exclusion of isolates from various marine ecosystems. This process resulted in a functionally compatible consortium comprising Bacillus altitudinis, Lacticaseibacillus rhamnosus, Bacillus cereus and Weissella cibaria. The consortium members tolerated up to 1 mM CdCl2 independent of active efflux mechanisms, bile salts, and gastric juices, and formed stable biofilms. The strains did not display antagonistic behaviour towards each other and effectively inhibited pathogenic Vibrio spp. from both environmental and clinical sources. Scanning electron microscopy (SEM) and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) analyses confirmed the maintenance of cell wall integrity under cadmium stress and the presence of bioaccumulation factors greater than one. Artemia nauplii pre-colonized with the bacterial consortium demonstrated a 33.6% increase in survival during acute (1.5 mM) cadmium exposure compared to untreated controls. These findings suggest that microbiome-based interventions can enhance host tolerance to metal pollution and represent a promising biological approach to mitigating the ecological impacts of metal contamination in aquatic environments.