Strain specific: microbial strains involved in gut-brain signaling

Abstract

ability in the U.S (USBDC, 2013), the importance of this research cannot be overstated. Although the blueprint outlining the microbial role within gut-brain axis regulation is far from maturation, the current understanding is that certain microbial strains are able to induce measurable neurologic and behavioral effect through the modulation of inflammatory response, neurochemical concentration, barrier-integrity, and interaction with the vagus nerve. In order to understand, and potentially utilize these microbial capabilities, it is essential to distinguish between which microbes are inducing behavioral and or neurologic effect, and which pathway each microbe is using to do so. The complexity of this task resides in the significant microbial distinction expressed not only on a species level, but amongst microbial strains (Greenblum, Rogan, & Borenstein, 2015). Among the more than 7,000 microbial strains (Ley, Peterson, & Gordon, 2006), majority have not demonstrated direct behavioral or neurologic effect. The collection of strains that have been shown to induce measurable neurologic and behavioral manipulation belong to one of the three genus types Lactobacillus, Bifidobacterium, and Bacteroides (Mayer, Knight, Mazmanian, Cryan, & Tillisch, 2014). Amongst these genus types, a plethora of biologic and behavioral variances have been expressed on both a species and strain level. While variation across differing genus and species type is expected, differences expressed between microbial strains belonging to the same genus and species type is a surprising find in light of the genomic similarity expressed between them. Further investigation into these microbial variances can explain questions such as why, despite genomic similarities, only certain microbial strains are able to induce behavioral and neurologic effect. Why INTRODUCTION Despite the myriad of pills and procedures aiming to treat psychiatric abnormalities and conditions, there is still much to be discovered about the brain. Fortunately, exploration into the effect upon commensal microbiota within behavioral and neurologic regulation has created a path in which to further decode and explore this enigmatic terrain. Recent in vitro and in vivo experimentation has demonstrated microbial influence within complex emotive states such as depression, chronic stress, anxiety, and psychiatric disorder (Bailey et al., 2011; Bercik et al., 2010; Maes, Kubera, Leunis, & Berk, 2012; Rook & Lowry, 2008). While this field is emerging and many mechanistic factors facilitating the microbial influence within gut-brain axis regulation have yet to be identified, the work done thus far suggest a future in which the brain can be indirectly targeted for therapeutic benefit through manipulation of commensal microbiota (Clarke et al., 2014; Cryan & Dinan, 2012). At a time when neuropsychiatric disorders are the leading cause of disStrain Specific: Microbial Strains Involved in Gut-Brain Signaling