Comparative analysis reveals distinctive genomic features of Taiwan hot-spring cyanobacterium Thermosynechococcus sp. TA-1

Comparative genomic analysis of a novel heat-tolerant and euryhaline strain of unicellular marine cyanobacterium Cyanobacterium sp. DS4 from a high-temperature lagoon

BACKGROUND

Cyanobacteria have diversified through their long evolutionary history and occupy a wide range of environments on Earth. To advance our understanding of their adaptation mechanisms in extreme environments, we performed stress tolerance characterizations, whole genome sequencing, and comparative genomic analyses of a novel heat-tolerant and euryhaline strain of the unicellular cyanobacterium Cyanobacterium sp. Dongsha4 (DS4). This strain was isolated from a lagoon on Dongsha Island in the South China Sea, a habitat with fluctuations in temperature, salinity, light intensity, and nutrient supply.

RESULTS

DS4 cells can tolerate long-term high-temperature up to 50 ℃ and salinity from 0 to 6.6%, which is similar to the results previously obtained for Cyanobacterium aponinum. In contrast, most mesophilic cyanobacteria cannot survive under these extreme conditions. Based on the 16S rRNA gene phylogeny, DS4 is most closely related to Cyanobacterium sp. NBRC102756 isolated from Iwojima Island, Japan, and Cyanobacterium sp. MCCB114 isolated from Vypeen Island, India. For comparison with strains that have genomic information available, DS4 is most similar to Cyanobacterium aponinum strain PCC10605 (PCC10605), sharing 81.7% of the genomic segments and 92.9% average nucleotide identity (ANI). Gene content comparisons identified multiple distinct features of DS4. Unlike related strains, DS4 possesses the genes necessary for nitrogen fixation. Other notable genes include those involved in photosynthesis, central metabolisms, cyanobacterial starch metabolisms, stress tolerances, and biosynthesis of novel secondary metabolites.

CONCLUSIONS

These findings promote our understanding of the physiology, ecology, evolution, and stress tolerance mechanisms of cyanobacteria. The information is valuable for future functional studies and biotechnology applications of heat-tolerant and euryhaline marine cyanobacteria.

Population genomics of a thermophilic cyanobacterium revealed divergence at subspecies level and possible adaptation genes

BACKGROUND

Cyanobacteria are diverse phototrophic microbes with ecological importance and potential for biotechnology applications. One species of thermophilic cyanobacteria, Thermosynechococcus taiwanensis, has been studied for biomass pyrolysis, estrogen degradation, and the production of bioethanol, monosaccharide, and phycocyanin. To better understand the diversity and evolution of this species, we sampled across different regions in Taiwan for strain isolation and genomic analysis.

RESULTS

A total of 27 novel strains were isolated from nine of the 12 hot springs sampled and subjected to whole genome sequencing. Including strains studied previously, our genomic analyses encompassed 32 strains from 11 hot springs. Genome sizes among these strains ranged from 2.64 to 2.70 Mb, with an average of 2.66 Mb. Annotation revealed between 2465 and 2576 protein-coding genes per genome, averaging 2537 genes. Core-genome phylogeny, gene flow estimates, and overall gene content divergence consistently supported the within-species divergence into two major populations. While isolation by distance partially explained the within-population divergence, the factors driving divergence between populations remain unclear. Nevertheless, this species likely has a closed pan-genome comprising approximately 3030 genes, with our sampling providing sufficient coverage of its genomic diversity. To investigate the divergence and potential adaptations, we identified genomic regions with significantly lower nucleotide diversity, indicating loci that may have undergone selective sweeps within each population. We identified 149 and 289 genes within these regions in populations A and B, respectively. Only 16 genes were common to both populations, suggesting that selective sweeps primarily targeted different genes in the two populations. Key genes related to functions such as photosynthesis, motility, and ion transport were highlighted.

CONCLUSIONS

This work provides a population genomics perspective on a hot spring cyanobacterial species in Taiwan. Beyond advancing our understanding of microbial genomics and evolution, the strains collected and genome sequences generated in this work provide valuable materials for future development and utilization of biological resources.

Genomic and phenotypic characterization of Thermosynechococcus-like strains reveals eight species within the genus Thermosynechococcus and a novel genus Parathermosynechococcus gen. nov

Thermophilic unicellular cyanobacteria of the family Thermosynechococcaceae are essential primary producers and integral components of many microbial mats found in hot springs of Asia and North America. Historically, based on their simple morphology, these organisms, along with members of taxonomically unrelated thermophilic Thermostichaceae have been described with a generic term, "Synechococcus", used for elongated unicellular cyanobacteria. This has created significant misperception in the scientific literature regarding the taxonomic status of these essential thermophilic primary producers and their relationship with Synechococcus sensu stricto. In this manuscript, we attempted a genome-driven taxonomic reevaluation of the family Thermosynechococcaceae. Application of genomic analyses such as GTDB classification, ANI/AAI and phylogenomics support the delineation of eight species within genus Thermosynechococcus. Two subspecies were further identified within T. taiwanensis by dDDH and phylogenomics. Moreover, the results also suggest the presence of two putative new genera phylogenetically alongside genus Thermosynechococcus, a thermophilic genus Parathermosynechococcus represented by PCC 6715 and a non-thermophilic genus represented by PCC 6312. The proposed genospecies and new genera were further integrated with morphological and/or ecological information. Interestingly, the phylogeny of 16S-23S ITS achieved a better taxonomic relationship than that of 16S rRNA and supported the genome-based classification of Thermosynechococcus spp. Finally, the pan-genome analysis indicated a conserved pattern of genomic core among known members of Thermosynechococcus.

Integrating multi-platform assembly to recover MAGs from hot spring biofilms: insights into microbial diversity, biofilm formation, and carbohydrate degradation

BACKGROUND

Hot spring biofilms provide a window into the survival strategies of microbial communities in extreme environments and offer potential for biotechnological applications. This study focused on green and brown biofilms thriving on submerged plant litter within the Sungai Klah hot spring in Malaysia, characterised by temperatures of 58-74 °C. Using Illumina shotgun metagenomics and Nanopore ligation sequencing, we investigated the microbial diversity and functional potential of metagenome-assembled genomes (MAGs) with specific focus on biofilm formation, heat stress response, and carbohydrate catabolism.

RESULTS

Leveraging the power of both Illumina short-reads and Nanopore long-reads, we employed an Illumina-Nanopore hybrid assembly approach to construct MAGs with enhanced quality. The dereplication process, facilitated by the dRep tool, validated the efficiency of the hybrid assembly, yielding MAGs that reflected the intricate microbial diversity of these extreme ecosystems. The comprehensive analysis of these MAGs uncovered intriguing insights into the survival strategies of thermophilic taxa in the hot spring biofilms. Moreover, we examined the plant litter degradation potential within the biofilms, shedding light on the participation of diverse microbial taxa in the breakdown of starch, cellulose, and hemicellulose. We highlight that Chloroflexota and Armatimonadota MAGs exhibited a wide array of glycosyl hydrolases targeting various carbohydrate substrates, underscoring their metabolic versatility in utilisation of carbohydrates at elevated temperatures.

CONCLUSIONS

This study advances understanding of microbial ecology on plant litter under elevated temperature by revealing the functional adaptation of MAGs from hot spring biofilms. In addition, our findings highlight potential for biotechnology application through identification of thermophilic lignocellulose-degrading enzymes. By demonstrating the efficiency of hybrid assembly utilising Illumina-Nanopore reads, we highlight the value of combining multiple sequencing methods for a more thorough exploration of complex microbial communities.

Thermophilic cyanobacteria-exciting, yet challenging biotechnological chassis

Thermophilic cyanobacteria are prokaryotic photoautotrophic microorganisms capable of growth between 45 and 73 °C. They are typically found in hot springs where they serve as essential primary producers. Several key features make these robust photosynthetic microbes biotechnologically relevant. These are highly stable proteins and their complexes, the ability to actively transport and concentrate inorganic carbon and other nutrients, to serve as gene donors, microbial cell factories, and sources of bioactive metabolites. A thorough investigation of the recent progress in thermophilic cyanobacteria reveals a significant increase in the number of newly isolated and delineated organisms and wide application of thermophilic light-harvesting components in biohybrid devices. Yet despite these achievements, there are still deficiencies at the high-end of the biotechnological learning curve, notably in genetic engineering and gene editing. Thermostable proteins could be more widely employed, and an extensive pool of newly available genetic data could be better utilised. In this manuscript, we attempt to showcase the most important recent advances in thermophilic cyanobacterial biotechnology and provide an overview of the future direction of the field and challenges that need to be overcome before thermophilic cyanobacterial biotechnology can bridge the gap with highly advanced biotechnology of their mesophilic counterparts. KEY POINTS: • Increased interest in all aspects of thermophilic cyanobacteria in recent years • Light harvesting components remain the most biotechnologically relevant • Lack of reliable molecular biology tools hinders further development of the chassis.

Genome-scale identification and comparative analysis of transcription factors in thermophilic cyanobacteria

BACKGROUND

The transcription factors (TFs) in thermophilic cyanobacteria might represent a uniquely evolved gene repertoire in light of the strong selective pressure caused by hostile habitats. Understanding the molecular composition of the TF genes in thermophilic cyanobacteria will facilitate further studies regarding verifying their exact biochemical functions and genetic engineering. However, limited information is available on the TFs of thermophilic cyanobacteria. Herein, a thorough investigation and comparative analysis were performed to gain insights into the molecular composition of the TFs in 22 thermophilic cyanobacteria.

RESULTS

The results suggested a fascinating diversity of the TFs among these thermophiles. The abundance and type of TF genes were diversified in these genomes. The identified TFs are speculated to play various roles in biological regulations. Further comparative and evolutionary genomic analyses revealed that HGT may be associated with the genomic plasticity of TF genes in Thermostichus and Thermosynechococcus strains. Comparative analyses also indicated different pattern of TF composition between thermophiles and corresponding mesophilic reference cyanobacteria. Moreover, the identified unique TFs of thermophiles are putatively involved in various biological regulations, mainly as responses to ambient changes, may facilitating the thermophiles to survive in hot springs.

CONCLUSION

The findings herein shed light on the TFs of thermophilic cyanobacteria and fundamental knowledge for further research regarding thermophilic cyanobacteria with a broad potential for transcription regulations in responses to environmental fluctuations.