First, we have generated new genomic information on a new UCYN-A sublineage via single-cell sorting and genomics, which allowed us to designed DNA probes targeting the ribosomal genes. These probes allowed to detect and distinguish new sublineages of the UCYN-A symbiosis in open ocean samples from the North Pacific Ocean and in coastal seawater samples collected nearby the Scripps Oceanographic Institution in San Diego (California, USA). In addition, through the analysis of metagenomic samples, we were able of reconstructing the partial genome of a third species of the UCYN-A group, and we used this information to explore the evolutionary relationship between this third species, called UCYN-A3, and the two previously identified species, i.e. UCYN-A1 and UCYN-A2. These findings were published in the format of a scientific article in the peer-review journal Environmental Microbiology (Cornejo-Castillo et al. 2019, Environmental Microbiology).
Second, we have discovered novel cellular mechanisms that directly affect the metabolic coupling between symbiotic partners and revealed the effect of environmental factors in the communication between symbiotic partners in the UCYN-A symbiosis. The analysis of all the publicly available cyanobacterial genomes led to uncover the distribution pattern of a genetic pathway involved in the protection from oxygen of the key enzyme for nitrogen fixation, which is an extremely oxygen-sensitive enzyme. Also, we designed an experimental setup to ascertain the role of light in the exchange of nutrients between symbiotic partners in the UCYN-A symbiosis. Our results demonstrated that the light period is critical for maintenance of regular patterns of gene expression, N2 fixation and symbiont replication and cell division. Our findings suggest a crucial role for the algal host of UCYN-A as a producer of fixed carbon, rather than light itself, in the regulation and implementation of the aforementioned cellular processes in UCYN-A. These findings were published in the prestigious peer-reviewed journal PNAS (Cornejo-Castillo & Zehr 2019. PNAS) and in Frontiers in Microbiology (Landa, Turk-Kubo, Cornejo-Castillo et al. 2021. Frontiers in Microbiology). Moreover, these results have also been presented in international scientific meetings and in social media.
Finally, we have described the distribution of symbiotic nitrogen-fixing microorganisms at the global ocean scale using high-throughput DNA and RNA sequencing data collected during the TARA Oceans expedition (
https://fondationtaraocean.org/en/expedition/tara-oceans/(se abrirá en una nueva ventana)). Besides, we explored two important aspects of nitrogen-fixing microorganisms, which are their nitrogen-fixation activity and their contribution to the sequestration of CO2 into the deep ocean. This part of the project concerning objective #3 has originated three scientific articles, one published in The ISME Journal (Cornejo-Castillo & Zehr 2021. The ISME Journal), one in Nature Communications (Pierella Karlusich et al. 2021. Nature Communications) and the third one has been posted in an open access repository BioRxiv (
https://tinyurl.com/37mewjxf(se abrirá en una nueva ventana)).
