04 April 2019

Effect of CO(2) Concentration on Uptake and Assimilation of Inorganic Carbon in the Extreme Acidophile Acidithiobacillus ferrooxidans.

DOI : 10.3389/fmicb.2019.00603

David S. Holmes, PhD.

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 (CO2) or as bicarbonate

(HCO3 -), 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 CO2 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 CO2 fixation was constructed from combined bioinformatic

and experimental approaches that suggests strategies for providing ecological

flexibility under changing concentrations of CO2 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.

Participating Center Researchers

Extremophile Genomics and Astrobiology Laboratory

PhD in Biochemistry, California Institute of Technology, USA.



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