Effect of CO2 Concentration on Uptake and Assimilation of Inorganic Carbon in the Extreme Acidophile Acidithiobacillus ferrooxidans

Abstract

This study was motivated by surprising gaps in the current knowledge of microbial inorganic carbon (Ci) uptake and assimilation at acidic pH values (pH < 3). Particularly striking is the limited understanding of the differences between Ci uptake mechanisms in acidic versus circumneutral environments where the Ci predominantly occurs either as a dissolved gas (CO 2 ) or as bicarbonate (HCO 3 - ), respectively. In order to gain initial traction on the problem, the relative abundance of transcripts encoding proteins involved in Ci uptake and assimilation was studied in the autotrophic, polyextreme acidophile Acidithiobacillus ferrooxidans whose optimum pH for growth is 2.5 using ferrous iron as an energy source, although they are able to grow at pH 5 when using sulfur as an energy source. The relative abundance of transcripts of five operons (cbb1-5) and one gene cluster ( can - sulP ) was monitored by RT-qPCR and, in selected cases, at the protein level by Western blotting, when cells were grown under different regimens of CO 2 concentration in elemental sulfur. Of particular note was the absence of a classical bicarbonate uptake system in A. ferrooxidans . However, bioinformatic approaches predict that sulP , previously annotated as a sulfate transporter, is a novel type of bicarbonate transporter. A conceptual model of CO 2 fixation was constructed from combined bioinformatic and experimental approaches that suggests strategies for providing ecological flexibility under changing concentrations of CO 2 and provides a portal to elucidating Ci uptake and regulation in acidic conditions. The results could advance the understanding of industrial bioleaching processes to recover metals such as copper at acidic pH. In addition, they may also shed light on how chemolithoautotrophic acidophiles influence the nutrient and energy balance in naturally occurring low pH environments.

A Model of Aerobic and Anaerobic Metabolism of Hydrogen in the Extremophile Acidithiobacillus ferrooxidans

“…Five operons (cbb1-5) in the At. ferrooxidans genome, encoding enzymes and structural proteins involved in Ci assimilation via the Calvin-Benson-Bassham (CBB) pathway, have been described (Esparza et al, 2010(Esparza et al, , 2019. In this work, we investigated changes in the expression of all five cbb operons during aerobic and anaerobic growth of At.…”

“…The form II seems to be synthesized constitutively, independent of O 2 concentration. Rubisco form II has a weak affinity for CO 2 (Esparza et al, 2019), which might explain its higher abundance compared to IAc and IAq. Nevertheless, a large subunit of the form IAc (CbbL1) and both subunits of the form IAq (CbbL2S2) were significantly more abundant during aerobic growth of At.…”

“…As carboxylation and oxidation of RuBP coincide, both reactions may compete in the same active place. Enzymes passing the carbon from 3-phosphoglycerate produced by Rubisco via the CBB and glycolysis pathways to pyruvate and glycogen metabolism pathways are encoded by the cbb3 operon (Esparza et al, 2019), the expression profile of which is shown in Figure 2. The initial Ci assimilation pathways during H 2 oxidation are proposed in Figure 4.…”

From Laboratory towards Industrial Operation: Biomarkers for Acidophilic Metabolic Activity in Bioleaching Systems

“…A similar strategy was used to opportunely predict oil contamination in the marine environment [ 20 ]. However, up to our knowledge, the analysis of functional genes as biomining community traits was only reported by using cultured microorganisms and in laboratory-controlled conditions [ 21 , 22 ]. Our research work focuses on applying molecular microbial markers for a better control and bioleaching efficiency enhancement.…”

Seleção e isolamento de bactérias fixadoras de CO2 para a purificação de gases de combustão e de gás natural.

“…Segundo estudos, embora altas pCO2 (% CO2) possam acarretar maior disponibilidade de DIC no meio de cultura, também tendem a promover alterações no pH dos cultivos e no metabolismo de bactérias, microalgas e cianobactérias (BAE et al, 2001;POURJAMSHIDIAN et al, 2019;JIN et al, 2020;ESPARZA et al, 2019). Por exemplo, quando cultivada sob atmosfera de 20 % v/v CO2 (1 atm), a bactéria Acidithiobacillus ferrooxidans sofre alterações metabólicas e cresce a uma taxa 2 vezes menor que a observada em cultivos sob 5% v/v CO2…”