"Candidatus Hydrogenisulfobacillus filiaventi" strain R50 gen. nov. sp. nov., a highly efficient producer of extracellular organic compounds from H2 and CO2

Production of organic molecules is largely depending on fossil fuels. A sustainable alternative would be the synthesis of these compounds from CO₂ and a cheap energy source, such as H₂, CH₄, NH₃, CO, sulfur compounds or iron(II). Volcanic and geothermal areas are rich in CO₂ and reduced inorganic gasses and therefore habitats where novel chemolithoautotrophic microorganisms for the synthesis of organic compounds could be discovered. Here we describe "Candidatus Hydrogenisulfobacillus filiaventi" R50 gen. nov., sp. nov., a thermoacidophilic, autotrophic H₂-oxidizing microorganism, that fixed CO₂ and excreted no less than 0.54 mol organic carbon per mole fixed CO₂. Extensive metabolomics and NMR analyses revealed that Val, Ala and Ile are the most dominant form of excreted organic carbon while the aromatic amino acids Tyr and Phe, and Glu and Lys were present at much lower concentrations. In addition to these proteinogenic amino acids, the excreted carbon consisted of homoserine lactone, homoserine and an unidentified amino acid. The biological role of the excretion remains uncertain. In the laboratory, we noticed the production under high growth rates (0.034 h^-1, doubling time of 20 h) in combination with O₂-limitation, which will most likely not occur in the natural habitat of this strain. Nevertheless, this large production of extracellular organic molecules from CO₂ may open possibilities to use chemolithoautotrophic microorganisms for the sustainable production of important biomolecules.

Isolation and identification of 4-α-rhamnosyloxy benzyl glucosinolate in Noccaea caerulescens showing intraspecific variation

Glucosinolates are secondary plant compounds typically found in members of the Brassicaceae and a few other plant families. Usually each plant species contains a specific subset of the ∼ 130 different glucosinolates identified to date. However, intraspecific variation in glucosinolate profiles is commonly found. Sinalbin (4-hydroxybenzyl glucosinolate) so far has been identified as the main glucosinolate of the heavy metal accumulating plant species Noccaea caerulescens (Brassicaceae). However, a screening of 13 N. caerulescens populations revealed that in 10 populations a structurally related glucosinolate was found as the major component. Based on nuclear magnetic resonance (NMR) and mass spectrometry analyses of the intact glucosinolate as well as of the products formed after enzymatic conversion by sulfatase or myrosinase, this compound was identified as 4-α-rhamnosyloxy benzyl glucosinolate (glucomoringin). So far, glucomoringin had only been reported as the main glucosinolate of Moringa spp. (Moringaceae) which are tropical tree species. There was no apparent relation between the level of soil pollution at the location of origin, and the presence of glucomoringin. The isothiocyanate that is formed after conversion of glucomoringin is a potent antimicrobial and antitumor agent. It has yet to be established whether glucomoringin or its breakdown product have an added benefit to the plant in its natural habitat.