Nutrient smuggling: Commensal gut bacteria‐derived extracellular vesicles scavenge vitamin B12 and related cobamides for microbe and host acquisition

Abstract

The processes by which bacteria proactively scavenge essential nutrients in crowded environments such as the gastrointestinal tract are not fully understood. In this context, we observed that bacterial extracellular vesicles (BEVs) produced by the human commensal gut microbe Bacteroides thetaiotaomicron contain multiple high-affinity vitamin B 12 binding proteins suggesting that the vesicles play a role in micronutrient scavenging. Vitamin B 12 belongs to the cobamide family of cofactors that regulate microbial communities through their limited bioavailability. We show that B. thetaiotaomicron derived BEVs bind a variety of cobamides and not only deliver them back to the parental bacterium but also sequester the micronutrient from competing bacteria. Additionally, Caco-2 cells, representing a model intestinal epithelial barrier, acquire cobamide-bound vesicles and traffic them to lysosomes, thereby mimicking the physiological cobalamin-specific intrinsic factor-mediated uptake process. Our findings identify a novel cobamide binding activity associated with BEVs with far-reaching implications for microbiota and host health.

Differential temporal release and lipoprotein loading in B. thetaiotaomicron bacterial extracellular vesicles

“…Consequently, to examine the dynamics of vesicle release, we formulated a chemically defined media for the growth of B. thetaiotaomicron free of animal‐derived products. This media was developed by building on our previously reported media and is referred to as BDMr6 (Juodeikis et al., 2022). In comparing the concentration of particles and lipid in this media with BHIH, yeast extract and tryptone, BDMr6 contained no detectable particles (Figure 1b).…”

“…Brain Heart Infusion (Oxoid) supplemented with 4‐μM hemin (BHIH) or Bacteroides Defined Media r6 (BDMr6) was used to culture cells. BDMr6 media is a further minimalised defined media for growing B. thetaiotaomicron based on our previously published media (Juodeikis et al., 2022) consisting of: 100 mM potassium phosphate pH 7.8 (KH 2 PO 4 9.2 mM; K 2 HPO 4 90.8 mM), 15 mM NaCl, 8.5 mM (NH 4 ) 2 SO 4 prepared in dH 2 O and sterilised; sterile glucose added to 30 mM and media moved to anaerobic cabinet to equilibrate for at least 24 h; after equilibration sterile components added to final concentrations: 100 μM MgCl 2 ; 50 μM CaCl 2 ; 2 mM L‐Cysteine hydrochloride; 10 μM FeSO 4 ; during inoculation sterile components added to concentrations: 200 μM L‐methionine; 50 nm Protoporphyrin IX (prepared in 50% ethanol; 50 mM NaOH). All components purchased from Sigma‐ Aldrich unless otherwise specified.…”

“…Nanoparticle quantification was carried out as previously described (Juodeikis et al., 2022). Briefly, particles were quantified using the ZetaView instrument (Particle Metrix) with ZetaView (version 8.05.12 SP1) software running a 2 cycle 11 position high frame rate analysis at 25°C.…”

“…Bacteroides thetaiotaomicron is a widely used model organism to study Bacteroides , particularly in understanding their extensive capacity to break down complex carbohydrates (Briliūtė et al., 2019; Lapébie et al., 2019). The bacterium releases a large number of bacterial extracellular vesicles (BEVs) which contain a specific proteome and interact with their environment (Durant et al., 2020; Jones et al., 2020; Juodeikis et al., 2022; Valguarnera et al., 2018).…”

Systemic Metabolic Depletion of Intestine Microbiome Undermines Melanoma Immunotherapy Effectiveness

“…Microbial-derived cobalamin and other corrinoids may serve an ecological role, be distributed by producers within the community, and be utilized by cobalamin-auxotrophic microbes [49]. On the other hand, corrinoids can be shared between microbes and Caco epithelial cells via vesicular transport [50]. Therefore, adding additional cobalamin from the gut microbes as a supplement to the diet-derived form may help the immune system’s ability to fight tumors.…”