Establishment and Application of Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry for Detection of Shewanella Genus.

Shewanella species are widely distributed in the aquatic environment and aquatic organisms. They are opportunistic human pathogens with increasing clinical infections reported in recent years. However, there is a lack of a rapid and accurate method to identify Shewanella species. We evaluated here matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for rapid identification of Shewanella. A peptide mass reference spectra (PMRS) database was constructed for the type strains of 36 Shewanella species. The main spectrum projection (MSP) cluster dendrogram showed that the type strains of Shewanella species can be effectively distinguished according to the different MS fingerprinting. The PMRS database was validated using 125 Shewanella test strains isolated from various sources and periods; 92.8% (n = 116) of the strains were correctly identified at the species level, compared with the results of multilocus sequence analysis (MLSA), which was previously shown to be a method for identifying Shewanella at the species level. The misidentified strains (n = 9) by MALDI-TOF MS involved five species of two groups, i.e., Shewanella algae-Shewanella chilikensis-Shewanella indica and Shewanella seohaensis-Shewanella xiamenensis. We then identified and defined species-specific biomarker peaks of the 36 species using the type strains and validated these selected biomarkers using 125 test strains. Our study demonstrated that MALDI-TOF MS was a reliable and powerful tool for the rapid identification of Shewanella strains at the species level.

[Transfer calibration for alcohol determination using temperature-induced shortwave near infrared spectra].

The authors studied the temperature influence on short-wave near-infrared spectra of ethanol aquatic solution and utilized four methods to establish the transfer partial least squares (PLS) calibration model: direct transfer calibration, global calibration, orthogonal signal correction (OSC) and generalized least squares weighting (GLSW). The PLS models were built at four temperatures: 15, 25, 35 and 40 degrees C. The results showed that direct calibration provided high prediction bias: significantly high positive prediction bias for a temperature lower than calibration temperature and negative bias for higher temperatures. By using the global correction, OSC and GLSW, the systematic errors could be reduced. However, the global correction needed more calibration samples and built a more complex model. The OSC and GLSW methods provided better predictions using fewer latent variables. By using the GLSW method, prediction bias less than 0.1% and RMSEP less than 0.9% were obtained. The absolute prediction error of GLSW method was less than 1.5%. Additionally, the GLSW provided smaller prediction error at every researched temperature using fewer latent variables than OSC. Thus, GLSW was superior to OSC and could establish more robust transfer calibration model.

Short-wave near-infrared spectrometer for alcohol determination and temperature correction.

A multichannel short-wave near-infrared (SW-NIR) spectrometer module based on charge-coupled device (CCD) detection was designed. The design relied on a tungsten lamp enhanced by light emitting diodes, a fixed grating monochromator and a linear CCD array. The main advantages were high optical resolution and an optimized signal-to-noise ratio (0.24 nm and 500, resp.) in the whole wavelength range of 650 to 1100 nm. An application to alcohol determination using partial least squares calibration and the temperature correction was presented. It was found that the direct transfer method had significant systematic prediction errors due to temperature effect. Generalized least squares weighting (GLSW) method was utilized for temperature correction. After recalibration, the RMSEP found for the 25°C model was 0.53% v/v and errors of the same order of magnitude were obtained at other temperatures (15, 35 and 40°C). And an r(2) better than 0.99 was achieved for each validation set. The possibility and accuracy of using the miniature SW-NIR spectrometer and GLSW transfer calibration method for alcohol determination at different temperatures were proven. And the analysis procedure was simple and fast, allowing a strict control of alcohol content in the wine industry.