Identifying a key spot for electron mediator-interaction to tailor CO dehydrogenase's affinity.

Fe‒S cluster-harboring enzymes, such as carbon monoxide dehydrogenases (CODH), employ sophisticated artificial electron mediators like viologens to serve as potent biocatalysts capable of cleaning-up industrial off-gases at stunning reaction rates. Unraveling the interplay between these enzymes and their associated mediators is essential for improving the efficiency of CODHs. Here we show the electron mediator-interaction site on ChCODHs (Ch, Carboxydothermus hydrogenoformans) using a systematic approach that leverages the viologen-reactive characteristics of superficial aromatic residues. By enhancing mediator-interaction (R57G/N59L) near the D-cluster, the strategically tailored variants exhibit a ten-fold increase in ethyl viologen affinity relative to the wild-type without sacrificing the turn-over rate (kcat). Viologen-complexed structures reveal the pivotal positions of surface phenylalanine residues, serving as external conduits for the D-cluster to/from viologen. One variant (R57G/N59L/A559W) can treat a broad spectrum of waste gases (from steel-process and plastic-gasification) containing O2. Decoding mediator interactions will facilitate the development of industrially high-efficient biocatalysts encompassing gas-utilizing enzymes.

Production of Biohydrogen and/or Poly-ß-hydroxybutyrate by Rhodopseudomonas sp. Using Various Carbon Sources as Substrate.

The polyhydroxyalkanoates (PHA) are family of biopolyesters synthesized by numerous bacteria which are attracting a great attention due to their thermoplastic properties. Polyhydroxybutyrate (PHB) is the most common type of PHA which presents thermoplastic and biodegradable properties. It is synthesized under stressful conditions by heterotrophic bacteria and many photosynthetic microorganisms such as purple non-sulfur bacteria and cyanobacteria. Biological hydrogen (H2) production is being evaluated for use as a fuel since it is a promising substitute for carbonaceous fuels owing to its high conversion efficiency and high specific content. In the present work, the purple non-sulfur photosynthetic bacterium Rhodopseudomonas sp. for the simultaneous H2 photo-evolution and poly-ß-hydroxybutyrate (PHB) production has been investigated. Three different types of carbon sources were tested in the presence of glutamate as a nitrogen source in a batch cultivation system, under continuous irradiance. The results indicated the fact that the type of carbon source in the culture broth affects in various ways the metabolic activity of the bacterial biomass, as evidenced by the production of PHB and/or H2 and biomass. The best carbon source for PHB accumulation and H2 production by Rhodopseudomonas sp. turned out to be the acetate, having the highest H2 production (2286 mL/L) and PHB accumulation (68.99 mg/L, 18.28% of cell dry weight).

Characterization of a novel herbicide and antibiotic-resistant Chlorella sp. with an extensive extracellular matrix.

A herbicide and antibiotic-resistant microalgal strain, isolated from a eutrophic site at Giofyros river (Heraklion, Crete, Greece) was extensively characterized. In the presence of relatively high concentrations of common photosynthesis inhibitors (DCMU and atrazine), as well as various antibiotics (spectinomycin, kanamycin, and chloramphenicol), the green microalga was able to increase its biomass in approximately equal levels compared to the control. Despite the high concentrations of the inhibitors, photosynthetic efficiency and chlorophyll a amount per dry cell biomass were comparable to those of control cultures in almost all cases. 18S rDNA analysis showed that this microalga belongs to the Chlorella genus. Optical and electron microscopy studies revealed the presence of an extensive extracellular matrix (EM) that surrounds the cells and plays an important role in colony formation and cell-cell interactions. Fourier transform infrared spectroscopy provided evidence that the EM consists of a polysaccharide. This matrix could be separated from the cells with a simple centrifugation. Depending on growth conditions, the dry cell biomass of this Chlorella strain was found to contain 35-39% proteins and 27-42% carbohydrates. The results of this study have demonstrated that the EM plays a protective role for cell homeostasis maintenance against the various chemical agents. This green microalga is a suitable candidate for further studies regarding sustainable biomass production in waste waters for a series of applications.