Optimizing Secondary Electrospray Ionization High-Resolution Mass Spectrometry (SESI-HRMS) for the Analysis of Volatile Fatty Acids from Gut Microbiome

Abstract

Gut microbiota plays essential roles in maintaining gut homeostasis. The composition of gut microbes and their metabolites are altered in response to diet and remedial agents such as antibiotics. However, little is known about the effect of antibiotics on the gut microbiota and their volatile metabolites. In this study, we evaluated the impact of a moderate level of ampicillin treatment on volatile fatty acids (VFAs) of gut microbial cultures using an optimized real-time secondary electrospray ionization coupled with high-resolution mass spectrometry (SESI-HRMS). To evaluate the ionization efficiency, different types of electrospray solvents and concentrations of formic acid as an additive (0.01, 0.05, and 0.1%, v/v) were tested using VFAs standard mixture (C2–C7). As a result, the maximum SESI-HRMS signals of all studied m/z values were observed from water with 0.01% formic acid than those from the aqueous methanolic solutions. Optimal temperatures of sample inlet and ion chamber were set at 130 °C and 85 °C, respectively. SESI spray pressure at 0.5 bar generated the maximum intensity than other tested values. The optimized SESI-HRMS was then used for the analysis of VFAs in gut microbial cultures. We detected that the significantly elevated C4 and C7 VFAs in the headspace of gut microbial cultures six hours after ampicillin treatment (1 mg/L). In conclusion, our results suggested that the optimized SESI-HRMS method can be suitable for the analysis of VFAs from gut microbes in a rapid, sensitive, and non-invasive manner.

Sensitivity of secondary electrospray ionization mass spectrometry to a range of volatile organic compounds: Ligand switching ion chemistry and the influence of Zspray™ guiding electric fields

“…The sensitivities for these acids are low, being comparable to those for the primary alcohols and the saturated aldehydes, as can be seen by the S values in Table 1. Note that in previous work 11 using calibration by standard mixtures of C2 to C7 carboxylic acids, a significant increase of the slope of calibration curve with the number of C atoms was observed.…”

Effects of Different Concentrations of Ganpu Tea on Fecal Microbiota and Short Chain Fatty Acids in Mice

“…Unabsorbed/digested food components in the small intestine is fermented by gut microbiota to engender SCFAs [47,48]. The formation of SCFAs is influenced by a variety of factors, including food intake, antibiotic treatment, and microbial population size [49,50]. At present, a large number of studies have proved that SCFAs play a key role in the interaction between intestinal microbial activity and host metabolism [51].…”

Analyses of short-chain fatty acids and exhaled breath volatiles in dietary intervention trials for metabolic diseases

“…Moreover, the use of many emerging MS-based analytical platforms, such as secondary electrospray ionization (SESI), 26,89,90 proton transfer reaction (PTR), 91 or selected ion flow tube mass spectrometry. 92 have become popular recently.…”

“…20,24 Previous studies have identified that the formation of SCFAs is influenced by various factors, including the pattern of food intake, antibiotics treatment, and microbial populations. 20,[25][26][27] In particular, carbohydrates are the main source of SCFAs production; meanwhile, amino acids, such as valine, leucine, and isoleucine from the protein breakdown are also involved in the production of branched SCFAs such as isobutyrate, isovalerate, and 2-methyl butyrate. 20 Earlier studies have described the metabolic routes of several SCFAs.…”