The draft genome of Andean Rhodopseudomonas sp. strain AZUL predicts genome plasticity and adaptation to chemical homeostasis.

The genus Rhodopseudomonas comprises purple non-sulfur bacteria with extremely versatile metabolisms. Characterization of several strains revealed that each is a distinct ecotype highly adapted to its specific micro-habitat. Here we present the sequencing, genomic comparison and functional annotation of AZUL, a Rhodopseudomonas strain isolated from a high altitude Andean lagoon dominated by extreme conditions and fluctuating levels of chemicals. Average nucleotide identity (ANI) analysis of 39 strains of this genus showed that the genome of AZUL is 96.2% identical to that of strain AAP120, which suggests that they belong to the same species. ANI values also show clear separation at the species level with the rest of the strains, being more closely related to R. palustris. Pangenomic analyses revealed that the genus Rhodopseudomonas has an open pangenome and that its core genome represents roughly 5 to 12% of the total gene repertoire of the genus. Functional annotation showed that AZUL has genes that participate in conferring genome plasticity and that, in addition to sharing the basal metabolic complexity of the genus, it is also specialized in metal and multidrug resistance and in responding to nutrient limitation. Our results also indicate that AZUL might have evolved to use some of the mechanisms involved in resistance as redox reactions for bioenergetic purposes. Most of those features are shared with strain AAP120, and mainly involve the presence of additional orthologs responsible for the mentioned processes. Altogether, our results suggest that AZUL, one of the few bacteria from its habitat with a sequenced genome, is highly adapted to the extreme and changing conditions that constitute its niche.

Urine dilution with a synthetic wastewater (Syntho) boosts the electricity production in a bio-electrochemical system powered by un-pretreated human urine.

Human urine can be turned into electricity in bio-electrochemical systems. The acclimation of electro-active bacteria to culture media with increasing urine concentrations has led to raising the obtained current densities, which typically followed a Monod-like evolution profile as a function of urine concentration. However, the acclimation protocol has been so far evaluated using pretreated urine samples (fermented or precipitated), not raw (un-pretreated) urine. We demonstrate that, when un-pretreated urine is used, the microbial adaptation to increasingly concentrated urine leads to a current density profile that does not reach a saturation-like phase, but follows a Han/Levenspiel-type trend (bell-shaped). By diluting un-pretreated urine with a synthetic domestic wastewater (Syntho) up to concentrations matching those of the maximum in the Han/Levenspiel-like current profile (15-20% v/v) it is possible to avoid the drop in the electro-active response, generating anodic current densities as high as 3.6 ± 0.2 A.m-2 (per actual surface area), 35-fold higher than those reached in pure un-pretreated urine.

Biochemical capacitance of Geobacter sulfurreducens biofilms.

An electrical model able to decouple the electron pathway from microbial cell machinery impedance terms is introduced. In this context, capacitance characteristics of the biofilm are clearly resolved. In other words, the model allows separating, according to the advantage of frequency and spectroscopic response approach, the different terms controlling the performance of the microbial biofilm respiratory process and thus the directly related electricity production process. The model can be accurately fitted to voltammetry measurements obtained under steady-state conditions and also to biofilm discharge amperometric measurements. The implications of biological aspects of the electrochemical or redox capacitance are discussed theoretically in the context of current knowledge with regard to structure and physiological activity of microbial Geobacter biofilms.

Crystallographic orientation and electrode nature are key factors for electric current generation by Geobacter sulfurreducens.

We have investigated the influence of electrode material and crystallographic structure on electron transfer and biofilm formation of Geobacter sulfurreducens. Single-crystal gold-Au(110), Au(111), Au(210)-and platinum-Pt(100), Pt(110), Pt(111), Pt(210)-electrodes were tested and compared to graphite rods. G. sulfurreducens electrochemically interacts with all these materials with different attachment kinetics and final current production, although redox species involved in the electron transfer to the anode are virtually the same in all cases. Initial bacterial colonization was fastest on graphite up to the monolayer level, whereas gold electrodes led to higher final current densities. Crystal geometry was shown to have an important influence, with Au(210) sustaining a current density of up to 1442±101µAcm(-2) at the steady state, over Au(111) with 961±94µAcm(-2) and Au(110) with 944±89µAcm(-2). On the other hand, the platinum electrodes displayed the lowest performances, including Pt(210). Our results indicate that both crystal geometry and electrode material are key parameters for the efficient interaction of bacteria with the substrate and should be considered for the design of novel materials and microbial devices to optimize energy production.