Bacteria normalize olfactory receptors

Bacteria normalize olfactory receptors Joshua Elkington Introduction

Recent discoveries of bacterial influences on host behavior and health hint that bacteria

could have a wide range of effects on host biology that defy current understanding. In this paper I will propose that bacterial signals normalize olfactory receptors within a host to mediate the smell recognition of self versus non-self. Using current knowledge of the effects of bacteria on smell in various organisms, I create a model where a bacterial signal trains an olfactory receptor to recognize certain bacteria as self. This model has a wide range of implications for maintenance of biological equilibrium and evolution of social preferences. Recognition of self versus non-self

Bacteria co-exist with a wide range of hosts from humans to flies, and their presence is

being revealed to have an important influence on many physiological phenomena. The model of bacterial normalization of smell within an organism assumes that there exists signal from bacteria that can interact with olfactory receptors. Therefore, a signal or many signals could interact with one or many olfactory receptors to induce a normalization response within a cell (Figure 1). This normalization could be cell intrinsic or extrinsic depending on the downstream

molecular events within a cell. A major implication of this model is that bacteria can train a host to tolerate their olfactory signals which could help with the discrimination of self versus nonself. Moreover, this mechanism could help recognition of kin if similar bacterial communities are shared within a population.



Figure 1 Model of bacterial normalization of olfactory receptors



Effects of microbiome coevolution on social preferences

This model is based on current data that shows bacterial influences on behavior

mediated by smell. Previous work has shown that in Drosophila melanogaster, larvae and adults were attracted to food that had been previously occupied by other larvae (1). This would indicate that an environmental factor influences this behavior. The authors went on to show that the larvae and adults were attracted to volatiles from the food (Figure 2). These results show that bacteria can have a profound influence on organismal choice.



Figure 2 Attraction to bacterial volatile molecules A-B Bar graphs showing larvae (A, C, D) or adult female flies (B) to axenic (bacteria-free) food with and without larvae with certain bacteria and standard food (1).

Similar worked done in Caenorhabditis elegans provides strong evidence that bacteria

can have an influence on olfactory functions. Prior work has shown that C. elegans will modify their preferences after exposure to certain bacteria (2). After exposure to pathogenic bacteria, worms will avoid odors from pathogenic bacteria and be attracted to odors of non-pathogenic

bacteria (Figure 3). These results suggest that bacterial can induce associative learning within an entire organism. This could be mediated by a signal specific to an olfactory receptor.

Figure 3 Food choice assay with Caenorhabditis elegans and certain classes of bacteria (2). Conclusions

In this paper, I create a model whereby bacteria can produce a signal to train a olfactory

receptor to induce host defense anergy against particular bacteria. I propose that this model implies that bacteria modulate smell to maintain a homeostatic relationship with their host.

He's starin' at me in disbelief My temper is buildin', he's starin' at me, I grab my key He's starin' at me, I started the car, then I tried to leave And somethin' told me to keep it in park until I could see The reason why he was mad at a stranger Like I was supposed to save him Like I'm the reason he's homeless and askin' me for a favor He's starin' at me, his eyes followed me with no laser He's starin' at me, I notice that his stare is contagious Cause now I'm starin' back at him, feelin' some type of disrespect If I could throw a bat at him, it'd be aimin' at his neck I never understood someone beggin' for goods Askin' for handouts, takin' it if they could And this particular person just had it down pat Starin' at me for the longest until he finally asked Have you ever opened up Exodus 14? A humble man is all that we ever need Tell me how much a dollar cost Kendrick Lamar – How Much A Dollar Cost

References 1. Venu, I. et al. "Social Attraction Mediated By Fruit Flies' Microbiome". Journal of Experimental Biology 217.8 (2014): 1346-1352. 2. Zhang, Yun, Hang Lu, and Cornelia I. Bargmann. "Pathogenic Bacteria Induce Aversive Olfactory Learning In Caenorhabditis Elegans". Nature 438.7065 (2005): 179-184.