Abstract
Oxalate-degrading bacteria comprise a functional group of microorganisms, commonly found in the gastrointestinal tract of mammals. Oxalate is a plant secondary compound (PSC) widely produced by all major taxa of plants and as a terminal metabolite by the mammalian liver. As a toxin, oxalate can have a significant impact on the health of mammals, including humans. Mammals do not have the enzymes required to metabolize oxalate and rely on their gut microbiota for this function. Thus, significant metabolic interactions between the mammalian host and a complex gut microbiota maintain the balance of oxalate in the body. Over a dozen species of gut bacteria are now known to degrade oxalate. This review focuses on the host-microbe and microbe-microbe interactions that regulate the degradation of oxalate by the gut microbiota. We discuss the pathways of oxalate throughout the body and the mammalian gut as a series of differentiated ecosystems that facilitate oxalate degradation. We also explore the mechanisms and functions of microbial oxalate degradation along with the implications for the ecological and evolutionary interactions within the microbiota and for mammalian hosts. Throughout, we consider questions that remain, as well as recent technological advances that can be employed to answer them.
Highlights
Mammalian physiology is greatly influenced by complex, metabolic interactions between the mammalian host and the microbiota
Dozens of bacterial species have been isolated from the GI tract of mammals that are capable of biotransforming toxic plant secondary compound (PSC) into non-toxic by-products
In contrast to individuals inoculated with probiotics, natural populations of oxalate-degrading bacteria persist in the gut, even after several generations on a low oxalate diet [49,52,55,58,97]
Summary
Mammalian physiology is greatly influenced by complex, metabolic interactions between the mammalian host and the microbiota. The biotransformation of toxins is an important function provided by gut microbes that contributes to the normal physiology of the host. Many commonly consumed plants contain plant secondary compounds (PSCs) that can alter the physiological homeostasis of mammals [14,15,16,17,18] These PSCs can lead to mortality or disease when consumed in high doses [14,15,16,17,18]. Despite the toxicity and widespread occurrence of oxalate, mammals do not produce enzymes capable of biotransforming the compound and instead rely on limiting absorption, excretion, or microbial degradation [29,33,43,44]. We explore the effects of oxalate on whole microbial communities and the ecological interactions that facilitate the degradation of oxalate by the gut microbiota of mammals.
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