Quantifying the contribution of primary production by sulfur-oxidizing bacteria (SOB) to benthic food webs is important for understanding energy and material flows in aquatic ecosystems, including chemosynthesis-based ecosystems. Sulfur stable isotope ratios (δ³⁴S) are a powerful tool for assessing sulfide utilization by SOB in sediments. In this review, I introduce the methodological approaches (δ³⁴S-based mixing model) used for estimating the contribution of SOB-derived organic matter to the nutrient resources of benthic fauna, and highlight three case studies that used this method in a deep-sea chemosynthesis-based ecosystem, whale-fall ecosystems, and a freshwater lake ecosystem. Finally, I discuss the advantages and limitations of this method for improving evaluations.

The search for extraterrestrial life is a major objective of planetary exploration, and the establishment of in situ analytical methods is essential given the difficulty of sample return missions. Amino acid analysis is a promising approach for life detection and generally requires a hydrolysis step as a pretreatment. In this study, we investigated the applicability of a noncorrosive solid acid catalyst as an alternative to conventionally used liquid acids for protein hydrolysis. Terrestrial soil samples were thermally treated with a solid acid catalyst, and liquid chromatography–mass spectrometry (LC/MS) was used to analyze the resulting products. Compared with non-hydrolyzed samples, increased signal intensities attributable to amino acids were observed. These results demonstrate that hydrolysis using a solid acid catalyst is applicable to chemically complex soil samples and represents a promising step toward the development of in situ amino acid analysis methods compatible with spacecraft for planetary exploration.