Skin Microbiome, Metabolome and Skin Phenome, from the Perspectives of Skin as an Ecosystem

Abstract

Skin is a complex ecosystem colonized by millions of microorganisms, including bacteria, fungi, and viruses. Skin microbiota is believed to exert critical functions in maintaining host skin health. Profiling the structure of skin microbial community is the first step to overview the ecosystem. However, the community composition is highly individualized and extremely complex. To explore the fundamental factors driving the complexity of the ecosystem, namely the selection pressures, we review the present studies on skin microbiome from the perspectives of ecology. This review summarizes the following: (1) the composition of substances/nutrients in the cutaneous ecological environment that are derived from the host and the environment, highlighting their proposed function on skin microbiota; (2) the features of dominant skin commensals to occupy ecological niches, through self-adaptation and microbe–microbe interactions; (3) how skin microbes, by their structures or bioactive molecules, reshape host skin phenotypes, including skin immunity, maintenance of skin physiology such as pH and hydration, ultraviolet (UV) protection, odor production, and wound healing. This review aims to re-examine the host–microbe interactions from the ecological perspectives and hopefully to give new inspiration to this field.

Integration of skin phenome and microbiome reveals the ­key role of bacteria in human skin aging

“…It was proposed that distinct skin niches drive the local microbial composition [3,8,9]. In turn, skin commensals are able to modify local physiology, such as pH or hydration, by converting host-derived nutrients into acidic metabolites [7,[34][35][36][37][38].…”

“…The skin microbiome is highly correlated with skin aging features Skin aging is a dynamic process with a series of phenotypical changes in appearance and physiological parameters. These phenotypes can re ect the niche conditions, such as pH and hydration, or be ultimate manifestations of microbial metabolic activities [7].…”

“…Numerous variables were characterized to in uence skin bacterial communities, including host factors (such as race, gender, and age) and environmental factors due to occupation or lifestyle (e.g., diet, hygiene, skin product and medication) or other exposure (e.g., climate, geographical location, pollution, ultraviolet and other radiation) [4,5]. Nevertheless, from the perspective of classic ecology, given that skin is perceived as an ecosystem [3], the selection pressures shaping the ecosystem should be able to be simpli ed into three main elements: 1) resource availability (presence of nutrients); 2) environmental conditions (temperature, geographical access) and 3) biological factors (the occupation of the ecological niches through self-adaptation or microbe-microbe interactions predators and pathogens) [6,7]. Previous evidence also strongly suggested that distinct niches' physical and chemical landscape primarily drives the local microbial composition (niche selection) [3,[8][9][10].…”

“…Previous evidence also strongly suggested that distinct niches' physical and chemical landscape primarily drives the local microbial composition (niche selection) [3,[8][9][10]. In turn, the growth and metabolism of these micro-inhabitants modify the local niches, such as pH or moisture state, and reshape host skin phenotypes [3,7,11]. However, understanding skin microbiome-phenotype interaction is still ambiguous and needs systemic characterization.…”

Ultraviolet exposure regulates skin metabolome based on the microbiome

“…Skin metabolites originate from sweat, sebum (composed of lipids), interstitial fluid, protein degradation that occurs at the stratum corneum, and intracellular metabolites that play a role in immune responses 4 . Microbes that colonize the skin have a large reservoir of active enzymes that metabolize molecules and further influence the immune response 5 . In our previous work, we showed that the presence or absence of a microbiome determines the effect of UV radiation on cutaneous immune response 6 .…”