Biology subjects

Weissberg, O.

Publications and source records attributed to Weissberg, O..

5 recordsLinked to original sources

bioRxiv2024

Diversity in the Utilization of Different Molecular Classes of Dissolved Organic Matter by Heterotrophic Marine Bacteria

Heterotrophic marine bacteria utilize and recycle dissolved organic matter (DOM), impacting biogeochemical cycles. It is currently unclear to what extent distinct DOM components can be utilized by different heterotrophic clades. Here, we ask how a natural microbial community from the Eastern Mediterranean Sea responds to different molecular classes of DOM. These molecular classes - peptides, amino acids, amino sugars, disaccharides, monosaccharides and organic acids - together comprise much of the biomass of living organisms, released upon their death as DOM. Bulk bacterial activity increased after 24-hours for all treatments relative to the control, while glucose and ATP uptake decreased or remained unchanged. The relative abundance of several bacterial families, assessed using 16S rRNA amplicon sequencing, increased in some treatments: peptides promoted an increase in Pseudoalteromonadaceae, disaccharides promoted both Pseudoalteromonadaceae and Alteromonadaceae, and most other treatments were dominated by Vibrionaceae. While some results were consistent with recent laboratory-based studies, for example Pseudoalteromonadaceae favoring peptides, other clades behaved differently. Alteromonadaceae, for example, grew well in the lab on many substrates but dominated in seawater samples when disaccharides were added. These results highlight the diversity in DOM utilization among heterotrophic bacteria and complexities in the response of natural communities. ImportanceThe marine DOM pool contains numerous molecular classes, which change depending on the phytoplankton species, environmental conditions and interactions with other microbes, viruses and predators. In turn, the availability of these macromolecular pools affects the composition and function of the whole microbial community. Tracing the path between different carbon sources to specific microbes is another step towards revealing the dynamic interaction between bacteria and the DOM pool. This is especially important in warm and oligotrophic marine systems (e.g., Eastern Mediterranean Sea) where nutrients are scarce and may therefore affect microbial activity and growth.

microbiology↗

bioRxiv2023

Collaborative metabolic curation of an emerging model marine bacterium, Alteromonas macleodii ATCC 27126

Inferring the metabolic capabilities of an organism from its genome is a challenging process, relying on computationally-derived or manually curated metabolic networks. Manual curation can correct mistakes in the draft network and add missing reactions based on the literature, but requires significant expertise and is often the bottleneck for high-quality metabolic reconstructions. Here, we present a synopsis of a community curation workshop for the emerging model marine bacterium Alteromonas macleodii ATCC 27126 and its genome database in BioCyc, focusing on pathways for utilizing organic carbon and nitrogen sources. Due to the scarcity of biochemical information or gene knock-outs, the curation process relied primarily on published growth phenotypes and bioinformatic analyses, including comparisons with related Alteromonas strains. We report full pathways for the utilization of the algal polysaccharides alginate and pectin in contrast to inconclusive evidence for one carbon metabolism and mixed acid fermentation, in accordance with the lack of growth on methanol and formate. Pathways for amino acid degradation are ubiquitous across Alteromonas macleodii strains, yet enzymes in the pathways for the degradation of threonine, tryptophan and tyrosine were not identified. Nucleotide degradation pathways are also partial in ATCC 27126. We postulate that demonstrated growth on nitrate as sole N source proceeds via a nitrate reductase pathway that is a hybrid of known pathways. Our evidence highlights the value of joint and interactive curation efforts, but also shows major knowledge gaps regarding Alteromonas metabolism. The manually-curated metabolic reconstruction is available as a "Tier-2" database on BioCyc. ImportanceMetabolic reconstructions are vital for the systemic understanding of an organisms ecology. Here, we report the outcome of a collaborative, interactive curation workshop to build a curated "metabolic encyclopedia" for Alteromonas macleodii ATCC 27126, a marine heterotrophic bacterium with widespread occurrence. Curating pathways for polysaccharide degradation, one-carbon metabolism, and others closed major knowledge gaps, and identified further avenues of research. Our study highlights how the combination of bioinformatic, genomic and physiological evidence can be harvested into a detailed metabolic model, but also identifies challenges if little experimental data is available for support. Overall, we show how an interactive get-together by a diverse group of scientists can advance the ecological understanding of emerging model bacteria, with relevance for the entire scientific community.

microbiology↗

bioRxiv2023

CTCF regulates anxiety and depression like behavior and maintenance of neuronal identity in the adult mouse brain

CCCTC-binding factor (CTCF) is a chromatin binding factor that binds to DNA sequence specific sites and, together with cohesin complex, establishes chromatin loops and regulates gene expression. CTCF was previously implicated as a major contributor in neural development. Genetic aberrations in CTCF are associated with intellectual disability, aggression, attention deficit, and autistic behavior. Previous mice-model studies have identified a necessary role for CTCF during development of CaMKIIa expressing excitatory neurons in the ability of learning and memory. However, it is not clear if CTCF is only necessary for development in the brain, or also in maintenance of neuronal functions and behavior in the adulthood. In the current study, adulthood-specific knockout of CTCF in excitatory neurons induced an elevation in anxiety and depression related behavior and a decrease in seeking social novelty. Depression and apathy-like behavior was reversed by treatment with serotonin specific reuptake inhibitor sertraline. Golgi staining analysis reveals major regression of dendritic complexity in the hippocampus and prefrontal cortex. In parallel, there is increased DNA compaction and decreased global H3K9 acetylation. Single nuclei RNA sequencing confirms a retreat in neuronal subtype identity in excitatory neurons after knockout. Gene ontology analysis display upregulation of genes that related regulation of cell population, neuronal development and neuronal differentiation and migration. These findings determine that CTCF is required for a propriate function of the mature excitatory neurons, independent of roles during development. Significance StatementThe gene CTCF is an important regulator of gene expression. Mutations in CTCF have been identified in individuals with a range of neurodevelopmental disorders, including intellectual disability and autism. However, it is unknown if CTCF is important only for neuronal development, or plays functional roles in the brain during adulthood. The current study finds that CTCF deletion during adulthood in excitatory neurons induces a behavioral phenotype that that includes increase in anxiety and depression-like behavior and changes in social behavior. In addition, CTCF depletion in adulthood affects the morphology, identity and gene expression of these specific types of neurons. Therefore, CTCF is not only important in brain development, but also in maintenance of proper neuronal function and behavior during adulthood.

neuroscience↗

bioRxiv2022

Significant organic carbon acquisition by Prochlorococcus in the oceans

Marine phytoplankton are responsible for about half of the photosynthesis on Earth. Many are mixotrophs, combining photosynthesis with heterotrophic assimilation of organic carbon but the relative contribution of these two carbon sources is not well quantified. Here, single-cell measurements reveal that Prochlorococcus at the base of the photic zone in the Eastern Mediterranean Sea are obtaining only ~20% of carbon required for growth by photosynthesis. Consistently, laboratory-calibrated evaluations of Prochlorococcus photosynthesis indicate that carbon fixation is systematically too low to support published in situ growth rates in the deep photic layer of the Pacific Ocean. Furthermore, agent-based model simulations show that mixotrophic cells maintain realistic growth rates and populations 10s of meters deeper than obligate photo-autotrophs, deepening the nutricline and Deep Chlorophyll Maximum by ~20 m. Time-series of Prochlorococcus ecotype-abundance from the subtropical North Atlantic and North Pacific suggest that up to 30% of the Prochlorococcus cells live where light intensity is not enough to sustain obligate photo-autotrophic populations during warm, stratified periods. Together, these data and models suggest that mixotrophy underpins the ecological success of a large fraction of the global Prochlorococcus population and its collective genetic diversity.

microbiology↗

bioRxiv2021

Phototroph-heterotroph interactions during growth and long-term starvation across Prochlorococcus and Alteromonas diversity

Microbial interactions such as those between phytoplankton and bacteria been studied intensively using specific model organisms, due to their potential impact on ecosystems and biogeochemistry. Yet, to what extent interactions differ between closely related organisms, or how these interactions change over time or culture conditions, remains unclear. Here, we characterize the interactions between five strains each of two globally abundant marine microorganisms, Prochlorococcus (a phototroph) and Alteromonas (a heterotroph), from the first encounter between individual strains and over more than a year of repeated cycles of exponential growth and long-term nitrogen starvation. Prochlorococcus-Alteromonas interactions had little effect on traditional growth parameters such as Prochlorococcus growth rate, maximal fluorescence or lag phase, affecting primarily the dynamics of culture decline, which we interpret as representing cell mortality and lysis. The shape of the Prochlorococcus decline curve and the carrying capacity of the co-cultures were determined by the phototroph and not the heterotroph strains involved. Comparing various mathematical models of culture mortality suggests that Prochlorococcus death rate increases over time in mono-cultures but decreases in co-cultures, with cells potentially becoming more resistant to stress. Our results demonstrate intra-species differences in ecologically-relevant co-culture outcomes. These include the recycling efficiency of N and whether the interactions are mutually synergistic or competitive. They also highlight the information-rich growth and death curves as a useful readout of the interaction phenotype. Significance StatementInteractions between phytoplankton and marine bacteria impact global ecosystems and biogeochemistry. Here, we explore how intra-species variability affects the interactions between Prochlorococcus, a globally abundant photosynthetic cyanobacetrium and Alteromonas, a heterotrophic bacterium that lives off and recycles organic matter. Under nitrogen starvation, Prochlorococcus growing alone increasingly accumulate damage and die, whereas in co-culture with Alteromonas they become increasingly resilient. The specific Prochlorococcus strain had a much larger effect on co-culture behavior than the Alteromonas strain, determining whether the interactions are mutually synergistic or potentially competitive. These results show how ecologically relevant outcomes of interactions may vary between closely related microorganisms, and highlight growth and death curves from laboratory (co)-cultures as information-rich views of microbial growth and death.

microbiology↗