An attempt to differentiate Pseudomonas spp. and other soil bacteria by FT-IR spectroscopy

Pseudomonads are ubiquitous bacterial inhabitants of soil and surface water with a variety of metabolic capacities. The isolation and identification of these bacteria is often required. A variety of methods have been employed to confirm the presence of Pseudomonads in different environments. In our experiments we tested the usefulness of infrared signals which deliver fingerprint like patterns that could be used for probing the presence and perhaps also the identity of these bacteria. If cultivated in a minimum nutrient broth, Pseudomonas aeruginosa, Pseudomonas fluorescens, Pseudomonas putida, and Pseudomonas stutzeri delivered well differentiated IR spectra in the following waverange: 3300 cm^–1 for nucleic acids structures, 3000–2800 cm^–1 for cell membrane fatty acids, 1800–1500 cm^–1 for cell proteins, 1500–1400 cm^–1 for fatty acids, 1500–1200 cm^–1 for proteins and phospholipids, 1200–900 cm^–1 for glycopeptides and phosphate groups of nucleic acids constituents, 900–550 cm^–1 for less defined cell constituents. However, the spectra of the individual species resembled each other. Some differences in the intensity of the individual bands were observed between IR spectra obtained by either the absorption/transmission (A/T) or the attenuated total reflectance (ATR) scanning techniques. Alterations in the composition of nutrient broth resulted in changes of the absorption ratios between the 2925 cm^–1 and 1658 cm^–1 bands (fatty acids:proteins), and between the 1656 cm^–1 and 1080 cm^–1 bands (proteins:peptidoglycans/polysaccharides). Some minor differences were observed between freshly harvested and starved cell biomass. Although less laborious and time consuming the FT–IR spectroscopy seems not sensitive enough to become a useful  tool in a differentiation of Pseudomonas spp.