Transcriptional evidence for metabolic differences between sessile (biofilm) and swimming (planktonic) modes of life. Genes encoding mixed acid fermentation enzymes are up-regulated in the biofilm (bottom part). As a result, two metabolites can be produced: acetyl-phosphate (acP) and acetate. The former can be used as a phospho-donor intermediate, while the later can be transformed to acetyl-CoA or released to the medium. They could be produced by fermentation of sugars via the Embden-Meyerhof-Parnas pathway to pyruvate, then to acetyl phosphate (acP) by pyruvate oxidase (PoxB), and finally to acetate by AckA. In contrast, genes encoding key TCA cycle enzymes are up-regulated in the swimming (planktonic) cells (top part; see also text for explanations). Circles indicate the name of the enzymes whose genes are being expressed in the Río Tinto samples (red, preferentially induced in biofilm; green, in planktonic cells; and yellow transcribed in both places). All of them have been identified in the L. ferrooxidans genome sequence draft (to be published elsewhere; see Additional file 1 Table S2, and Additional file 2). POR, pyruvate oxidoreductase system; Pta, phosphotransacetylase; Idh, NAD+ dependent isocitrate dehydrogenase; Acn, Aconitase; Mdh, Malate dehydrogenase; FumC, fumarate hydratase component C; SdhA, succinate dehydrogenase component A; SucCD, Succinate dehydrogenase; PpsA, phosphoenolpyruvate synthase; AccACD, acetyl-CoA carboxylase.