The selective expression of carbonic anhydrase genes of Aspergillus nidulans in response to changes in mineral nutrition and CO2 concentration

Abstract

Carbonic anhydrase (CA) plays an important role in the formation and evolution of life. However, to our knowledge, there has been no report on CA isoenzyme function differentiation in fungi. Two different CA gene sequences in Aspergillus nidulans with clear genetic background provide us a favorable basis for studying function differentiation of CA isoenzymes. Heterologously expressed CA1 was used to test its weathering ability on silicate minerals and real-time quantitative PCR was used to detect expression of the CA1 and CA2 genes at different CO2 concentrations and in the presence of different potassium sources. The northern blot method was applied to confirm the result of CA1 gene expression. Heterologously expressed CA1 significantly promoted dissolution of biotite and wollastonite, and CA1 gene expression increased significantly in response to soluble K-deficiency. The northern blot test further showed that CA1 participated in K-feldspar weathering. In addition, the results showed that CA2 was primary involved in adapting to CO2 concentration change. Taken together, A. nidulans can choose different CA to meet their survival needs, which imply that some environmental microbes have evolved different CAs to adapt to changes in CO2 concentration and acquire mineral nutrition so that they can better adapt to environmental changes. Inversely, their adaption may impact mineral weathering and/or CO2 concentration, and even global change.

Keywords: Aspergillus nidulans; CO2 adaption; carbonic anhydrase; isoenzyme; mineral weathering.

Figure 1

SDS‐PAGE analysis of recombination CA1.

Figure 2

Gene expression of A. nidulans CA1 at different temporal sampling points. (A) the expression of CA1 gene with KCl or K‐feldspar at ambient atmosphere (0.039%); (B) CA1 gene expression with KCl or K‐feldspar at high CO ₂ concentration (3.9%). (C) Northern blot analyses of CA1 gene transcription at the 24 h sampling point for A. nidulans cultured in K‐feldspar or KCl containing media. Two‐tailed t‐test was used. Data shown were the mean (along with the standard deviation) of three independent experiments. *The results from the two treatments are significantly different.

Figure 3

pH values and dissolved oxygen in the medium and appearance of mycelium pellets at three sampling time. (A) pH values of the medium, A. nidulans was cultured with KCl or K‐feldspar, named as C or E, at ambient CO ₂ concentration; (B) C and E represent the pH values of medium containing KCl or K‐feldspar, respectively, at 3.9% CO ₂ concentration; (C) size and color of mycelium pellets at three sampling time; (D) the dissolved oxygen of medium at three sampling time. *The results from the two treatments are significantly different.

Figure 4

CA2 gene expression at different sampling times. (A) The expression of CA2 gene with KCl as the potassium resource at 0.039% or 3.9% CO ₂ concentration; (B) the expression of CA2 gene with KCl or K‐feldspar as the potassium resource at ambient atmosphere (0.039%). Two‐tailed t‐test was used. The mean (along with the standard deviation) were calculated based on three independent experiments. *The results from the two treatments are significantly different.