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

Effects of CO2 in fungi

Carbon dioxide supplies carbon for photosynthetic species and is a major product of respiration for all life forms. Inside the human body where CO2 is a by-product of the tricarboxylic acid cycle, its level reaches 5% or higher. In the ambient atmosphere, ∼.04% of the air is CO2. Different organisms can tolerate different CO2 levels to various degrees, and experiencing higher CO2 is toxic and can lead to death. The fungal kingdom shows great variations in response to CO2 that has been documented by different researchers at different time periods. This literature review aims to connect these studies, highlight mechanisms underlying tolerance to high levels of CO2, and emphasize the effects of CO2 on fungal metabolism and morphogenesis.

The multifunctional face of plant carbonic anhydrase

Although most studies on the ubiquitous enzyme carbonic anhydrase (CA) have indicated its significant role in plants to facilitate the diffusion of CO₂ to the site of inorganic carbon fixation, it is becoming increasingly likely that carbonic anhydrase isoforms also have diverse unexplored functions in plant cells. This review lays emphasis on additional roles of CA associated with many physiological, biochemical and structural changes in plant metabolism. The presented findings have revealed essential functions of CA isoforms in plant adjustment to both abiotic and biotic agents and developmental stimuli. However, sometimes it is difficult to separate the non-photosynthetic from the photosynthetic-related role of CAs during post-stress impaired metabolism, and the preventive CA outcome might be due to the effect of these enzymes on improvement of photosynthetic capacity. Finally, taking into account the experimental evidence, the direct and indirect functional roles of CAs in mitigating negative effects of environmental conditions are presented.

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

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.

A Global View of Gene Expression of Aspergillus nidulans on Responding to the Deficiency in Soluble Potassium

Many researchers have suggested that microbes can accelerate the weathering of silicate minerals. However, many genes and metabolic pathways related to microorganisms obtaining potassium (K) from silicate remain undiscovered. It is feasible to detect the gene expression within the scope of the whole genome through high-throughput sequencing. Surprisingly, only a few reports have shown fungal weathering of silicate using this technology. This study explored differences in gene expression of Aspergillus nidulans, which was cultured with different K sources, KCl, and K-feldspar. A. nidulans RNA was extracted by the construction of a cDNA library. Identification of K-acquisition-related genes with GO and KEGG pathway analysis revealed that primarily differentially expressed genes were related to the biosynthesis of amino acids. When these genes were grouped in accordance with the physiological functions, the genes involved in the synthesis of protease, ribosome, and mitochondria, trans-membrane transport, and oxidative phosphorylation were significantly different. Moreover, 20 genes selected were further tested using RT-qPCR. One half (10 genes) exhibited differential expression, which was consistent with the results of RNA-seq. Combining the results of RNA-seq and RT-qPCR, we summarised a possible way to obtain mineral K in A. nidulans as well. The differentially expressed genes and their associated metabolic pathways revealed will improve the understanding of the molecular mechanisms of microbial weathering of silicate minerals.