Cloning and Stress-Induced Expression Analysis of Calmodulin in the Antarctic Alga Chlamydomonas sp. ICE-L

A diguanylate cyclase regulates biofilm formation in Rhodococcus sp. NJ-530 from Antarctica

Biofilms represent a protective survival mode in which bacteria adapt themselves to the natural environment for survival purposes. Biofilm formation is regulated by 3,5-cyclic diguanylic acid (c-di-GMP), which is a universal second messenger molecule in bacteria. Diguanylate cyclase (DGC) catalyses c-di-GMP intracellular synthesis, which plays important roles in bacterial adaptation to the natural environment. In this study, the DGC gene was first cloned from Antarctic Rhodococcus sp. NJ-530. DGC contained 948 nucleotides and encoded 315 amino acids with a molecular weight of 34.6 KDa and an isoelectric point of 5.58. qRT-PCR demonstrated that the DGC expression level was significantly affected by lower salinity and temperature. Consistently, more biofilm formation occurred under the same stress. It has been shown that Rhodococcus sp. NJ-530 can adapt to the extreme environment in Antarctica, which is closely related to biofilm formation. These results provide an important reference for studying the adaptive mechanism of Antarctic microorganisms to this extreme environment.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-03093-z.

Revealing the Characteristics of the Antarctic Snow Alga Chlorominima collina gen. et sp. nov. Through Taxonomy, Physiology, and Transcriptomics

Snow algae play crucial roles in cold ecosystems, however, many aspects related to their biology, adaptations and especially their diversity are not well known. To improve the identification of snow algae from colored snow, in the present study we used a polyphasic approach to describe a new Antarctic genus, Chlorominima with the species type Chlorominima collina. This new taxon was isolated of colored snow collected from the Collins Glacier (King George Island) in the Maritime Antarctic region. Microscopy revealed biflagellated ellipsoidal cells with a rounded posterior end, a C-shaped parietal chloroplast without a pyrenoid, eyespot, and discrete papillae. Several of these characteristics are typical of the genus Chloromonas, but the new isolate differs from the described species of this genus by the unusual small size of the cells, the presence of several vacuoles, the position of the nucleus and the shape of the chloroplast. Molecular analyzes confirm that the isolated alga does not belong to Chloromonas and therefore forms an independent lineage, which is closely related to other unidentified Antarctic and Arctic strains, forming a polar subclade in the Stephanosphaerinia phylogroup within the Chlamydomonadales. Secondary structure comparisons of the ITS2 rDNA marker support the idea that new strain is a distinct taxon within of Caudivolvoxa. Physiological experiments revealed psychrophilic characteristics, which are typical of true snow algae. This status was confirmed by the partial transcriptome obtained at 2°C, in which various cold-responsive and cryoprotective genes were identified. This study explores the systematics, cold acclimatization strategies and their implications for the Antarctic snow flora.

Molecular cloning and functional analysis of a Δ12-fatty acid desaturase from the Antarctic microalga Chlamydomonas sp. ICE-L

Chlamydomonas sp. ICE-L, which can thrive in extreme environments of the Antarctic, could represent a promising alternative for polyunsaturated fatty acid (PUFA) production. A new Δ¹²-fatty acid desaturase (FAD)-encoding gene (Δ ¹² CiFAD), 1269 bp in size, was cloned from Chlamydomonas sp. ICE-L. Bioinformatics analysis showed that Δ ¹² CiFAD-encoded protein was homologous to known FADs with conserved histidine motifs, and localized to the chloroplast. Functional analysis of Δ ¹² CiFAD indicated that recombinant Synechococcus 6803 expressing Δ¹²CiFAD could accumulate C18:2, whereas recombinant Saccharomyces cerevisiae expressing this enzyme could not accumulate C18:2 or any other new fatty acids. These results indicate that Δ¹²CiFAD is a functional enzyme in the chloroplast that can adjust Chlamydomonas sp. ICE-L cell membrane fluidity to adapt to Antarctic extreme low-temperature environments, which give us insights into the frigostable and cold-resistant mechanisms of hypothermic organisms.

Isolation and Expression Analysis of Three Types of α-Carbonic Anhydrases from the Antarctic Alga Chlamydomonas sp. ICE-L under Different Light Stress Treatments

Carbonic anhydrases (CAs) are a class of zinc-containing metalloenzymes that can reversibly catalyse the hydration reaction of carbon dioxide. Antarctic algae are the most critical component of the Antarctic ecosystem; algae can enter the carbon cycle food chain by fixing carbon dioxide from the air. In this study, the complete open reading frames (ORFs) of CA1 (GenBank ID KY826431), CA2 (GenBank ID KY826432), and CA3 (GenBank ID KY826433), encoding CAs in the Antarctic ice microalga Chlamydomonas. sp. ICE-L, were successfully cloned using reverse transcription-polymerase chain reaction (RT-PCR). In addition, the expression patterns of CAs under blue light, under UV light, and in the dark were determined by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). The CA1, CA2, and CA3 ORFs encode proteins of 376, 430, and 419 amino acids, respectively. Phylogenetic analysis revealed that all amino acid sequences showed high homology with those of C. sp. ICE-L. There are six types of algal CAs; we hypothesised that the CAs studied here are most likely α-CAs. Expression analysis showed that the transcription level of the CAs was influenced by both UV light and blue light. These findings provide additional insight into the molecular mechanisms of CAs and will accelerate the development of CAs for applications in agriculture and environmental governance.