Direct large-volume injection with liquid chromatography/high-resolution mass spectrometry for screening of bacterial growth substrates in tap water

Solid-phase extraction (SPE) is widely used for sample pretreatment before liquid chromatographymass spectrometry (LC/MS). However, it may constrain the comprehensiveness of non-targeted LC/MS analysis, as a fraction of dissolved organic matter (DOM) cannot be recovered by SPE. In this study, direct large-volume injection (dLVI) without SPE was applied to explore potential growth substrates that support the proliferation of Pseudomonas aeruginosa, an opportunistic pathogen found in tap water. Non-targeted analysis (NTA) detected 2,497 DOM components, of which 65 were screened as putative substrates for P. aeruginosa. Notably, none of the substrate candidates detected by dLVI were screened in the SPE analysis. Furthermore, the distributions of molecular descriptors, including unsaturation and oxidation states, differed significantly between these methods. These results highlight their methodological complementarity. LC/MS/MS analysis and co-chromatography identified one compound, C9H17NO3, as 7-keto-8-aminopelargonic acid (KAPA), an intermediate in biotin synthesis. Although KAPA did not support P. aeruginosa proliferation, the results indicated that it may contribute to microbial proliferation. This study underscores the potential of dLVI to reveal previously inaccessible DOM fractions.