**Physiological states**. (a) principal component analysis.

vegetative,

sporulated,

*amyloliquefaciens*,

*cereus*,

*licheniformis*,

*megaterium*,

*sphaericus*,

*subtilis*,

*laterosporus*. Discriminating between vegetative and sporulated classes. Physiological states are labelled as

for vegetative and

for sporulated. Even though the species are not yet considered on this analysis, numbers (from 1 to 7) are shown beside the physiological state to indicate species type (see labels on the graph). The bar over the labels indicates that each point represents an average over all similar cases on the data set.

and

represent group centers for PC scores and the numbers (which represent

*m/z *intensities) are PC loadings. (b) Bayesian network model. Solid lines indicate a positive correlation between nodes, dashed lines indicate negative correlation and the thickness of the line indicates the strength of the correlation; therefore the thicker the line is the stronger the correlation. The number beside the line shows the partial correlation coefficient for that correlation.

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