In situ liquid time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a powerful technique to study surface characterization of living biofilms in hydrated conditions. However, ToF-SIMS data analysis is still a great challenge in complicated bacterial biofilms, because many interference peaks from the medium may result in inaccurate interpretation. In this study, two syntrophic Geobacter populations are investigated using in situ liquid ToF-SIMS to reveal the biofilm surface changes between them due to direct interspecies electron transfer. By comparing spectral principal component analysis (PCA) results of all peaks and selected peaks, the authors find that spectral peak overlay is an effective strategy to reduce the matrix effect in handling complex ToF-SIMS data. Additionally, the spectral PCA results of high intensity and high resolution data obtained from liquid ToF-SIMS are compared. Selected peaks, amino acid peaks, and water cluster peaks spectral PCA produce nice separation among samples in both high intensity and high resolution data sets. However, the high resolution data show better separation between coculture planktonic and coculture aggregates, confirming that the higher mass accuracy is useful in the analysis of microbial samples. In conclusion, the results show that peak selection is critical for acquiring effective microbial information and interpretation of syntrophic Geobacter using spectral data from in situ liquid ToF-SIMS.

中文翻译：

---

主成分分析中的峰选择很重要：同养微生物的案例研究。

原位液体飞行时间二次离子质谱（ToF-SIMS）是研究在水合条件下活生物膜的表面表征的强大技术。但是，ToF-SIMS数据分析在复杂的细菌生物膜中仍然是一个巨大的挑战，因为来自培养基的许多干扰峰可能会导致解释不准确。在这项研究中，使用原位液体ToF-SIMS研究了两个同养的Geobacter种群，以揭示由于直接种间电子转移而造成的生物膜表面变化。通过比较所有峰和选定峰的光谱主成分分析（PCA）结果，作者发现，光谱峰覆盖是减少处理复杂ToF-SIMS数据时矩阵效应的有效策略。另外，比较了从液体ToF-SIMS获得的高强度和高分辨率数据的光谱PCA结果。选定的峰，氨基酸峰和水簇峰光谱PCA可在高强度和高分辨率数据集中的样品之间实现很好的分离。但是，高分辨率数据显示共培养的浮游生物和共培养的聚集体之间有更好的分离，这证实了更高的质量准确度可用于微生物样品的分析。总之，结果表明，峰选择对于获取有效的微生物信息和使用原位液体ToF-SIMS的光谱数据解释同养的地球细菌至关重要。在高强度和高分辨率数据集中，水簇峰光谱PCA可以很好地分离样品。但是，高分辨率数据显示共培养的浮游生物和共培养的聚集体之间有更好的分离，这证实了更高的质量准确度可用于微生物样品的分析。总之，结果表明，峰选择对于获取有效的微生物信息和使用原位液体ToF-SIMS的光谱数据解释同养的地球细菌至关重要。在高强度和高分辨率数据集中，水簇峰光谱PCA可以很好地分离样品。但是，高分辨率数据显示共培养的浮游生物和共培养的聚集体之间有更好的分离，这证实了更高的质量准确度可用于微生物样品的分析。总之，结果表明，峰选择对于获取有效的微生物信息和使用原位液体ToF-SIMS的光谱数据解释同养的地球细菌至关重要。