Biology subjects

Santiago-Martinez, M. G.

Publications and source records attributed to Santiago-Martinez, M. G..

4 recordsLinked to original sources

bioRxiv2026

Maintenance cost of photosynthesis sets key ecological constraints on zooxanthellate corals

Ecological models using light limitation to explain coral depth distribution have largely disregarded the energetic cost of sustaining photosynthetic activity. Here, we quantified photosystem II (PSII) turnover across a depth-simulated light gradient in a zooxanthellate coral, measuring PSII half-life, D1 protein abundance, and PSII-complex gene expression. Maximum photosynthetic capacity remained stable across irradiance levels while respiration rose and PSII turnover accelerated as a power law, imposing increasing ATP demand at the shallowest depths. Declining D1 protein abundance alongside stable transcript levels demonstrated that this escalating maintenance cost operates through post-transcriptional regulation. Consequently, a decreasing fraction of photosynthetic usable energy is available for translocation to the coral host at high irradiance, as the energy required for PSII repair increases. Integrating these physiological constraints into a bio-optical model revealed that the balance between photosynthetic capacity and its maintenance cost defines an optimal depth, the Photosynthetic Usable Energy Supply (PUES) maximum, where host energetic returns are maximized. This framework provides a mechanistic basis for understanding depth distributions in symbiotic corals and extends as a predictive tool for any photosynthetic organism operating under variable irradiance, including forecasting how environmental degradation contracts viable depth ranges.

ecology↗

bioRxiv2026

Ecotourism activities alter diversity of bacteria, archaea, and fungi in the freshwater stream of the Agua Azul Waterfalls in southeastern Mexico

Natural freshwater streams harbor diverse microbial communities that support ecosystem functioning. Due to their great biodiversity and geomorphological characteristics, these ecosystems are often very attractive ecotourism destinations, which makes them highly vulnerable to anthropogenic disturbances. The Agua Azul Waterfalls (Cascadas de Agua Azul, in Spanish), a major tourist destination located in indigenous territories of southeastern Mexico (Chiapas, Mexico), offer a unique setting to investigate how sustained human activity influences microbial diversity and quality of water and sediments. To determine the ecological sensitivity of this freshwater stream to tourism pressure, we sampled sites spanning gradients of tourist activity and conducted an integrated analysis of water and sediment physicochemistry, elemental composition, and the composition of microbial communities (bacteria, archaea, and fungi). Areas associated with ecotourism activities showed notable changes in physicochemical parameters and microbial community composition, indicating localized impacts on this ecosystem. Furthermore, evidence of effective management by local Indigenous communities suggests a partial mitigation of anthropogenic disturbances through ecotourism activities. Our findings highlight the potential of microbial diversity in combination with physicochemical parameters as a tool to detect early stages of human impacts on freshwater ecosystems and establish a basis for future monitoring and conservation efforts. The distinctive characteristics of this site position it as a promising model for advancing our understanding of microbial diversity and the dynamics of freshwater stream ecosystems. ImportanceThis study shows evidence that ecotourism is already impacting the biodiversity and water quality of Agua Azul Waterfalls, a freshwater stream located within a protected natural area in southeastern Mexico. While the water still meets basic quality standards, areas with higher tourist activity show early signs of nutrient enrichment and measurable changes in the types of microbes present and the roles they play in this ecosystem. As the first analysis of microbial diversity in this ecosystem, our work highlights the value of microbes as early and sensitive indicators of human impact. By directly comparing tourist and non-tourist areas, we provide evidence of how recreational pressure is transforming this freshwater environment. We expect that our findings will help guide local communities and policymakers in creating more sustainable tourism practices to preserve the cultural and economic value of this ecosystem before irreversible damage occurs.

microbiology↗

bioRxiv2024

Carbonic anhydrase plays multiple roles in acetotrophic growth of a model marine methanogen from the domain Archaea

Carbonic anhydrase (CA) catalyzes the reversible hydration of CO2 to bicarbonate and a proton. The enzyme is universally distributed in all three domains of life and plays diverse physiological roles in the domains Eukarya and Bacteria. Remarkably, a physiological role has not been identified for any CA from the domain Archaea. Herein are described roles for a gamma class CA (Cam) from the methane-producing marine archaeon Methanosarcina acetivorans. Acetate-dependent growth of a {Delta}cam mutant showed an extended lag phase, lower final cell density, and metabolized acetate to a threshold of 20.0 mM compared to 1.0 mM for wild-type. Molar growth yields (Ymethane) were substantially greater for wild-type compared to the mutant. In contrast, growth parameters were identical for the methanol-grown wild-type and mutant. Rates of methane formation in resting cell suspensions containing 20.0 mM acetate were significantly less in the mutant versus wild-type and dependent on the presence of CO2. Rates for the wild-type decreased with increasing pH that was more pronounced for the mutant. CA activity was 100-fold greater in the membrane versus soluble fraction of acetate-grown cells. Addition of a surrogate CA stimulated acetate-dependent methanogenesis in resting cell suspensions of the mutant. The results support a role for Cam to supply protons for symport of acetate by the AceP symporter that also optimizes and facilitates growth at low acetate concentrations and high pH values encountered in the marine environment where M. acetivorans was isolated. Significance StatementAlthough CA plays major physiological roles in the domains Eukarya and Bacteria, a role has not been reported for the domain Archaea in which methanogens comprise the major group with abundant genomic annotations for CAs. Acetotrophic methanogens account for most of the methane produced in Earths biosphere where it is a major greenhouse gas. Although the biochemistry of the conversion of acetate to methane and carbon dioxide is well known, little is understood of acetate transport. The finding that CA has multiple roles facilitating thermodynamically constrained growth of a model marine acetotrophic methanogen has implications for advancing ecological understanding of the methane cycle that impacts global warming and climate change. Finally, the work is an introduction to anticipated physiological roles of CAs in the domain Archaea for which genomic annotations are abundant.

microbiology↗

bioRxiv2023

In vivo structure probing of RNA in Archaea: Novel insights into the ribosome structure of Methanosarcina acetivorans

Structure probing combined with next-generation sequencing (NGS) has provided novel insights into RNA structure-function relationships. To date such studies have focused largely on bacteria and eukaryotes, with little attention given to the third domain of life, archaea. Furthermore, functional RNAs have not been extensively studied in archaea, leaving open questions about RNA structure and function within this domain of life. With archaeal species being diverse and having many similarities to both bacteria and eukaryotes, the archaea domain has the potential to be an evolutionary bridge. In this study, we introduce a method for probing RNA structure in vivo in the archaea domain of life. We investigated the structure of ribosomal RNA (rRNA) from Methanosarcina acetivorans, a well-studied anaerobic archaeal species, grown with either methanol or acetate. After probing the RNA in vivo with dimethyl sulfate (DMS), Structure-seq2 libraries were generated, sequenced, and analyzed. We mapped the reactivity of DMS onto the secondary structure of the ribosome, which we determined independently with comparative analysis, and confirmed the accuracy of DMS probing in M. acetivorans. Accessibility of the rRNA to DMS in the two carbon sources was found to be quite similar, although some differences were found. Overall, this study establishes the Structure-seq2 pipeline in the archaea domain of life and informs about ribosomal structure within M. acetivorans.

biochemistry↗