Fig. 2

Identification levels for two MALDI systems (a) with a difference map showing the distribution of identification levels between fuel type (b). (a) The adopted identification levels are: high-confidence (score ≥ 2.000), low-confidence (1.700 ≤ score ≤ 1.999), no identification (score < 1.699), and no peaks found. Asterisks indicate levels of statistical significance: *≥0.05, **≥0.01. (b) The sizes of the nodes correspond to the number of microorganism identifications in different types of fuels (red nodes) and different identification levels (blue nodes). The thickness of the connections between nodes correlates with the number of identifications, which are noted along the connections.