Phototrophic epilithic biofilms harbour a distinct assemblage of heterotrophic bacteria, cyanobacteria and photoautotrophic algae. Secretion of extracellular polymeric substances (EPS) by these organisms and the physicochemical properties of the EPS are important factors for the development of the biofilms. We have isolated representative diatom and bacteria strains from epilithic biofilms of Lake Constance. By pairwise co-cultivating these strains we found that diatom growth and EPS secretion by diatoms may depend on the presence of individual bacteria. Similar results were obtained after addition of spent bacterial medium to diatom cultures, suggesting that soluble substances from bacteria have an impact on diatom physiology. While searching for putative bacterial signal substances, we found that concentrations of various dissolved free amino acids (DFAA) within the diatom cultures changed drastically during co-cultivation with bacteria. Further, the secretion of extracellular carbohydrates and proteins can be influenced by bacteria or their extracellular substances. We have performed mass spectrometric peptide mapping to identify proteins which are secreted when co-cultivating the diatom Phaeodactylum tricornutum Bohlin and Escherichia coli. The identified proteins are possibly involved in signalling, extracellular carbohydrate modification and uptake, protein and amino acid modification, and cell/cell aggregation of diatom and bacteria strains. Our data indicate that diatom-bacteria biofilms might be regulated by a complex network of chemical factors involving EPS, amino acid monomers and other substances. Thus interactions with bacteria can be considered as one of the main factors driving biofilm formation by benthic diatoms.

RNAs are ideal for the design of gene switches that can monitor and program cellular behavior because of their high modularity and predictable structure-function relationship. We have assembled an expression platform with an embedded modular ribozyme scaffold that correlates self-cleavage activity of designer ribozymes with transgene translation in bacteria and mammalian cells. A design approach devised to screen ribozyme libraries in bacteria and validate variants with functional tertiary stem-loop structures in mammalian cells resulted in a designer ribozyme with a protein-binding nutR-boxB stem II and a selected matching stem I. In a mammalian expression context, this designer ribozyme exhibited dose-dependent translation control by the N-peptide, had rapid induction kinetics and could be combined with classic small molecule-responsive transcription control modalities to construct complex, programmable genetic circuits.

The G-quadruplex forming sequence d[(G4CT)3G4] shows complete and continuous quadruplex interconversion upon increasing K+-concentrations and pronounced K+ selectivity.

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