In this study, we investigated an SBP (DctP ) of a tripartite ATP-independent periplasmic transport system (TRAP) in Advenella mimigardefordensis strain DPN7 . Deletion of dctP as well as of the two transmembrane compounds of the tripartite transporter, dctQ and dctM, impaired growth of A. mimigardefordensis strain DPN7 , if cultivated on mineral salt medium supplemented with d-glucose, d-galactose, l-arabinose, d-fucose, d-xylose or d-gluconic acid, respectively. The wild type phenotype was restored during complementation studies of A. mimigardefordensis ΔdctP using the broad host vector pBBR1MCS-5::dctP . Furthermore, an uptake assay with radiolabeled [ C(U)]-d-glucose clearly showed that the deletion of dctP , dctQ and dctM, respectively, disabled the uptake of this aldoses in cells of either mutant strain. Determination of K performing thermal shift assays showed a shift in the melting temperature of DctP in the presence of d-gluconic acid (K 11.76 ± 1.3 µM) and the corresponding aldonic acids to the above-mentioned carbohydrates d-galactonate (K 10.72 ± 1.4 µM), d-fuconic acid (K 13.50 ± 1.6 µM) and d-xylonic acid (K 8.44 ± 1.0 µM). The sugar (glucose) dehydrogenase activity (E.C.1.1.5.2) in the membrane fraction was shown for all relevant sugars, proving oxidation of the molecules in the periplasm, prior to transport.

The cultivation of cyanobacteria with the addition of an organic carbon source (meaning as heterotrophic or mixotrophic cultivation) is a promising technique to increase their slow growth rate. However, most cyanobacteria cultures are infected by non-separable heterotrophic bacteria. While their contribution to the biomass is rather insignificant in a phototrophic cultivation, problems may arise in heterotrophic and mixotrophic mode. Heterotrophic bacteria can potentially utilize carbohydrates quickly, thus preventing any benefit for the cyanobacteria. In order to estimate the advantage of the supplementation of a carbon source, it is essential to quantify the proportion of cyanobacteria and heterotrophic bacteria in the resulting biomass. In this work, the use of quantitative polymerase chain reaction (qPCR) is proposed. To prepare the samples, a DNA extraction method for cyanobacteria was improved to provide reproducible and robust results for the group of terrestrial cyanobacteria. Two pairs of primers were used, which bind either to the 16S rRNA gene of all cyanobacteria or all bacteria including cyanobacteria. This allows a determination of the proportion of cyanobacteria in the biomass. The method was established with the two terrestrial cyanobacteria Trichocoleus sociatus SAG 26.92 and Nostoc muscorum SAG B-1453-12a. As proof of concept, a heterotrophic cultivation with T. sociatus with glucose was performed. After 2 days of cultivation, a reduction of the biomass partition of the cyanobacterium to 90% was detected. Afterwards, the proportion increased again.

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Cyanobacteria developed an enormous reservoir of bioactive secondary metabolites in order to prevail against competitive microorganisms and harsh environmental impacts. Many cyanobacterial substances with vast economical, medical and biotechnological potential have been described in the past. However, most of the examined bacteria are aquatic strains. We want to take a closer look on their terrestrial relatives which also possess a rich secondary metabolome that is still to explore.

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