Biology subjects

Mooshammer, M.

Publications and source records attributed to Mooshammer, M..

4 recordsLinked to original sources

bioRxiv2022

Taurine as a key intermediate for host-symbiont interaction in the tropical sponge Ianthella basta

Marine sponges are critical components of marine benthic fauna assemblages where their filter-feeding and reef-building capabilities provide bentho-pelagic coupling and crucial habitat. As potentially the oldest representation of a metazoan-microbe symbiosis, they also harbor dense, diverse, and species-specific communities of microbes, which are increasingly recognized for their contributions to dissolved organic matter (DOM) processing. Recent omics-based studies of marine sponge microbiomes have proposed numerous pathways of dissolved metabolite exchange between the host and symbionts within the context of the surrounding environment, but few studies have sought to experimentally interrogate these pathways. By using a combination of metaproteogenomics and laboratory incubations coupled with isotope-based functional assays, we showed that the dominant gammaproteobacterial symbiont Candidatus Taurinisymbion ianthellae residing in the marine sponge, Ianthella basta, expresses a pathway for the import and dissimilation of taurine, a ubiquitously occurring sulfonate metabolite in marine sponges. Candidatus Taurinisymbion ianthellae incorporates taurine-derived carbon and nitrogen while, at the same time, oxidizing the dissimilated sulfite into sulfate for export. Furthermore, we found that taurine-derived ammonia is exported by the symbiont for immediate oxidation by the dominant ammonia-oxidizing thaumarchaeal symbiont Candidatus Nitrosospongia ianthellae. Metaproteogenomic analyses also indicate that Candidatus Taurinisymbion ianthellae likely imports DMSP and possesses both pathways for DMSP demethylation and cleavage, enabling it to use this compound as a carbon and sulfur source for biomass, as well as for energy conservation. These results highlight the important role of biogenic sulfur compounds in the interplay between Ianthella basta and its microbial symbionts.

microbiology↗

bioRxiv2021

Kinetic Properties of Microbial Exoenzymes Vary with Soil Depth but Have Similar Temperature Sensitivities Through the Soil Profile

Current knowledge of the mechanisms and responses of soil organic matter (SOM) turnover to warming is mainly limited to surface soils, although over 50% of global soil carbon is contained in subsoils. Deep soils have different physicochemical properties, nutrient inputs and microbiomes, which may harbor distinct functional traits and lead to different SOM dynamics and temperature responses. We hypothesized that kinetic and thermal properties of microbial exoenzymes, which mediate SOM depolymerization, vary with soil depth, reflecting microbial adaptation to distinct substrate and temperature regimes. We determined the Michaelis-Menten (MM) kinetics of three ubiquitous enzymes involved in carbon (C), nitrogen (N) and phosphorus (P) acquisition at six soil depths down to 90 cm at a temperate coniferous forest, and their temperature sensitivity based on Arrhenius and Macromolecular Rate Theory (MMRT) models over six temperatures between 4-50{degrees}C. Maximal enzyme velocity (Vmax) decreased strongly with depth for all enzymes, both on a dry soil mass and a microbial biomass C basis, whereas their affinities increased, indicating adaptation to lower substrate availability. Surprisingly, microbial biomass-specific catalytic efficiencies also decreased with depth, except for the P-acquiring enzyme, indicating distinct nutrient demands at depth relative to microbial abundance. These results indicated that deep soil microbiomes encode enzymes with intrinsically lower turnover and/or produce less enzymes per cell, likely reflecting distinct life strategies. The relative kinetics between different enzymes also varied with depth, suggesting an increase in relative P demand with depth, or that phosphatases may be involved in C acquisition. Warming consistently led to increased Vmax and catalytic efficiency of all enzymes, and thus to overall higher SOM-decomposition potential, but enzyme temperature sensitivity was similar through the soil profile based on both Arrhenius/Q10 and MMRT models. Nevertheless, temperature directly affected the kinetic properties of different enzyme types in a depth-dependent manner, and thus the relative depolymerization potential of different compounds. Our results indicate that kinetic and thermal properties of exoenzymes are intrinsic traits of soil microbiomes adapted to distinct physicochemical conditions associated with different soil depths, and improve our conceptual understanding of critical mechanisms underlying SOM dynamics and responses to warming through the soil profile.

microbiology↗

bioRxiv2019

Chemosymbiotic bivalves contribute to the nitrogen budget of seagrass ecosystems

In many seagrass sediments, lucinid bivalves and their sulfur-oxidizing symbionts are thought to underpin key ecosystem functions, but little is known about their role in nutrient cycles, particularly nitrogen. We used natural stable isotopes, elemental analyses, and stable isotope probing to study the ecological stoichiometry of a lucinid symbiosis in spring and fall. Chemoautotrophy appeared to dominate in fall, when chemoautotrophic carbon fixation rates were up to one order of magnitude higher as compared to the spring, suggesting a flexible nutritional mutualism. In fall, an isotope pool dilution experiment revealed carbon limitation of the symbiosis and ammonium excretion rates up to 10-fold higher compared to fluxes reported for non-symbiotic marine bivalves. These results provide evidence that lucinid bivalves can contribute substantial amounts of ammonium to the ecosystem. Given the preference of seagrasses for this nitrogen source, lucinid bivalves contribution may boost productivity of these important blue carbon ecosystems.

ecology↗

bioRxiv2019

Characterization of a thaumarchaeal symbiont that drives incomplete nitrification in the tropical sponge Ianthella basta

Marine sponges represent one of the few eukaryotic groups that frequently harbor symbiotic members of the Thaumarchaeota, which are important chemoautotrophic ammonia-oxidizers in many environments. However, in most studies, direct demonstration of ammonia-oxidation by these archaea within sponges is lacking, and little is known about sponge-specific adaptations of ammonia-oxidizing archaea (AOA). Here, we characterized the thaumarchaeal symbiont of the marine sponge Ianthella basta using metaproteogenomics, fluorescence in situ hybridization, qPCR and isotope-based functional assays. "Candidatus Nitrosospongia bastadiensis" is only distantly related to cultured AOA. It is an abundant symbiont that is solely responsible for nitrite formation from ammonia in I. basta that surprisingly does not harbor nitrite-oxidizing microbes. Furthermore, this AOA is equipped with an expanded set of extracellular subtilisin-like proteases, a metalloprotease unique among archaea, as well as a putative branched-chain amino acid ABC transporter. This repertoire is strongly indicative of a mixotrophic lifestyle and is (with slight variations) also found in other sponge-associated, but not in free-living AOA. We predict that this feature as well as an expanded and unique set of secreted serpins (protease inhibitors), a unique array of eukaryotic-like proteins, and a DNA-phosporothioation system, represent important adaptations of AOA to life within these ancient filter-feeding animals. Originality-Significance StatementMany marine sponges harbor symbiotic members of the Thaumarchaeota, but there is generally only indirect evidence available about their functional role within these filter-feeding animals. Furthermore, the specific adaptations of thaumarchaeal symbionts to their sponge hosts are incompletely understood. In this study, we thoroughly characterized a thaumarchaeal symbiont residing in the reef sponge Ianthella basta and demonstrate by using a combination of molecular tools and isotope techniques, that it is the only ammonia-oxidizer in its host. In contrast to other sponges, I. basta does not contain nitrite-oxidizing microbes and thus excretes considerable amounts of nitrite. Furthermore, using metagenomics and metaproteomics we reveal important adaptations of this symbiont, that represents a new genus within the Thaumarchaeota, and conclude that it most likely lives as a mixotroph in its sponge host.

microbiology↗