Sound generation mechanism of compressible vortex reconnection

We study the sound generation mechanism of initially subsonic viscous vortex reconnection at vortex Reynolds number $Re~(\equiv \text {circulation}/\text {kinematic viscosity})=1500$ through decomposition of Lighthill's acoustic source term. The Laplacian of the kinetic energy, flexion product, enstrophy and deviation from the isentropic condition provide the dominant contributions to the acoustic source term. The overall (all time) extrema of the total source term and its dominant hydrodynamic components scale linearly with the reference Mach number $M_o$ ; the deviation from the isentropic condition shows a quadratic scaling. The significant sound arising from the flexion product occurs due to the coiling and uncoiling of the twisted vortex filaments wrapping around the bridges, when a rapid strain is induced on the filaments by the repulsion of the bridges. The spatial distributions of the various acoustic source terms reveal the importance of mutual cancellations among most of the terms; this also highlights the importance of symmetry breaking in the sound generation during reconnection. Compressibility acts to delay the start of the sequence of reconnection events, as long as shocklets, if formed, are sufficiently weak to not affect the reconnection. The delayed onset has direct ramifications for the sound generation by enhancing the velocity of the entrained jet between the vortices and increasing the spatial gradients of the acoustic source terms. Consistent with the near-field pressure, the overall maximum instantaneous sound pressure level in the far field has a quadratic dependence on $M_o$ . Thus, reconnection becomes an even more dominant sound-generating event at higher $M_o$ .

Suicidal chemotaxis in bacteria

Bacteria commonly live in communities on surfaces where steep gradients of antibiotics and other chemical compounds routinely occur. While many species of bacteria can move on surfaces, we know surprisingly little about how such antibiotic gradients affect cell motility. Here we study the behaviour of the opportunistic pathogen Pseudomonas aeruginosa in stable spatial gradients of a range of antibiotics by tracking thousands of cells in microfluidic devices as they form biofilms. Unexpectedly, these experiments reveal that individual bacteria use pili-based ('twitching') motility to actively navigate towards regions with higher antibiotic concentrations. Our analyses suggest that this biased migration is driven, at least in part, by a direct response to the antibiotics. Migrating cells can reach antibiotic concentrations hundreds of times higher than their minimum inhibitory concentration in a few hours and remain highly motile. However, isolating these cells - using fluid-walled microfluidic devices that can be reconfigured in situ - suggests that these bacteria are terminal and not able to reproduce. In spite of moving towards their death, we show that migrating cells are capable of entering a suicidal program to release bacteriocins that are used to kill other bacteria. Our work suggests that bacteria respond to antibiotics as if they come from a competing colony growing in the neighbourhood, inducing them to invade and attack. As a result, clinical antibiotics have the potential to serve as a bait that lures bacteria to their death.

Microenvironmental factors in cell segregation and heterogeneity in breast cancer development

ABSTRACTWe analyzed a quantitative model that describes the epigenetic dynamics during the growth and evolution of an avascular tumor. A gene regulatory network (GRN) formed by a set of ten genes that are believed to play an important role in breast cancer development was kinetically coupled to the microenvironmental agents: glucose, estrogens and oxygen. The dynamics of spontaneous mutations was described by a Yule-Furry master equation whose solution represents the probability that a given cell in the tissue undergoes a certain number of mutations at a given time. We assumed that mutations rate is modified by nutrients spatial gradients. The tumor mass was grown by means of a cellular automata supplemented with a set of reaction diffusion equations that described the transport of the microenvironmental agents. By analyzing the epigenetic states space described by the GRN dynamics, we found three attractors that were identified with the cellular epigenetic states: normal, precancer and cancer. For two-dimensional (2D) and three-dimensional (3D) tumors we calculated the spatial distributions of the following quantities: (i) number of mutations, (ii) mutations of each gene and, (iii) phenotypes. Using estrogens as the principal microenvironmental agent that regulates cells proliferation process, we obtained the tumor shapes for different values of the estrogen consumption and supply rates. It was found that he majority of mutations occurred in cells that were located close to the 2D tumor perimeter or close to the 3D tumor surface. Also It was found that the occurrence of different phenotypes in the tumor are controlled by the levels of estrogen concentration since they can change the individual cell threshold and gene expression levels. All the results were consistently observed for 2D and 3D tumors.

Disturbance and distribution gradients influence resource availability and feeding behaviours in corallivore fishes following a warm-water anomaly

Understanding interactions between spatial gradients in disturbances, species distributions and species’ resilience mechanisms is critical to identifying processes that mediate environmental change. On coral reefs, a global expansion of coral bleaching is likely to drive spatiotemporal pulses in resource quality for obligate coral associates. Using technical diving and statistical modelling we evaluated how depth gradients in coral distribution, coral bleaching, and competitor density interact with the quality, preference and use of coral resources by corallivore fishes immediately following a warm-water anomaly. Bleaching responses varied among coral genera and depths but attenuated substantially between 3 and 47 m for key prey genera (Acropora and Pocillopora). While total coral cover declined with depth, the cover of pigmented corals increased slightly. The abundances of three focal obligate-corallivore butterflyfish species also decreased with depth and were not related to spatial patterns in coral bleaching. Overall, all species selectively foraged on pigmented corals. However, the most abundant species avoided feeding on bleached corals more successfully in deeper waters, where bleaching prevalence and conspecific densities were lower. These results suggest that, as coral bleaching increases, energy trade-offs related to distributions and resource acquisition will vary with depth for some coral-associated species.

Mapping trait versus species turnover reveals spatiotemporal variation in functional redundancy in a plant-pollinator network

Functional overlap between species (redundancy) shapes competitive and mutualistic interactions, determining community responses to perturbations. Most studies view functional redundancy as static, even though individuals within species vary in traits over seasonal or spatial gradients. Consequently, we lack knowledge on trait turnover within species, how functional redundancy spatiotemporally varies, and when and where interaction networks are vulnerable to functional loss. Studying an Arctic bumblebee community, we investigated how body-size turnover with elevation and over a season shapes their host-plant interactions, and test how sensitive networks are to sequentially losing body-size groups. With trait turnover being larger than species, we found: i) late-season networks were less specialised when nodes comprised functionally similar bumblebees; ii) removal of bumblebee-body-size groups over species accelerated coextinction of host plants, with the magnitude varying in space and time. We demonstrate functional redundancy can vary spatiotemporally, and functional loss impacts interaction partners more than expected from species loss alone.

DISTRIBUTION OF ALIEN ZOOBENTHIC SPECIES ON THE SHELF OF THE BLACK SEA

The number of alien species in the zoobenthos of the Black Sea increased up to 65 species. Depending on the scale of their distribution in the Black Sea, non-native zoobenthos species are combined into three groups: 1) 5 species have spread in the entire sea, 2) 35 species were found in several areas, and 3) 25 species were found only in one of the areas of the sea. Six areas of the Black Sea shelf have been identified (Varna - Burgas, Danube, Northwestern, Crimean, Caucasian and Anatolian) in accordance with the seasonal and annual values of the thermohaline characteristics. The zoobenthos differed not only in quantity, but also in the composition of non-native species between the six areas of the shelf. The results of multivariate statistical analysis revealed a low level of similarity between these areas of the Black Sea shelf. The greatest similarity in the composition of alien species of zoobenthos was observed for the Danube region with the Varna and Burgas bays, which border each other. The species composition of the alien species of the Caucasian shelf was more similar to the Varna - Burgas and Danube areas than to the neighboring Crimean and Anatolian areas. Spatial gradients of temperature and salinity form hydrological fronts of water masses, which are a kind of ecological barriers and can limit the natural exchange of alien species between shelf areas.

Bacterial response to spatial gradients of algal-derived nutrients in a porous microplate

Photosynthetic microalgae are responsible for 50% of the global atmospheric CO2 fixation into organic matter and hold potential as a renewable bioenergy source. Their metabolic interactions with the surrounding microbial community (the algal microbiome) play critical roles in carbon cycling, but due to methodological limitations, it has been challenging to examine how community development is influenced by spatial proximity to their algal host. Here we introduce a copolymer-based porous microplate to co-culture algae and bacteria, where metabolites are constantly exchanged between the microorganisms while maintaining physical separation. In the microplate, we found that the diatom Phaeodactylum tricornutum accumulated to cell abundances ~20 fold higher than under normal batch conditions due to constant replenishment of nutrients through the porous structure. We also demonstrate that algal-associated bacteria, both single isolates and complex communities, responded to inorganic nutrients away from their host as well as organic nutrients originating from the algae in a spatially predictable manner. These experimental findings coupled with a mathematical model suggest that host proximity and algal culture growth phase impact bacterial community development in a taxon-specific manner through organic and inorganic nutrient availability. Our novel system presents a useful tool to investigate universal metabolic interactions between microbes in aquatic ecosystems.

TAMI-39. INTEGRATION OF SPATIALLY RESOLVED TRANSCRIPTOMICS AND METABOLOMICS UNCOVERS HYPOXIA-DRIVEN ACCUMULATION OF GENOMIC INSTABILITIES IN HUMAN GLIOMA

High-dimensional technologies have provided insights into transcriptional heterogeneity and dynamic plasticity which are hallmarks of brain tumors. Although scRNA-seq recovers the diversity of transcriptional states, their spatial context within the neuronal environment has remained unexplored. Here, we integrated spatially resolved transcriptomics and metabolomics to characterize the glioma landscape at multiple molecular levels. We integrated spatial transcriptomics (10X Visium, n= 28) and metabolomics (MALDI, n= 6) from primary and recurrent glioblastoma patients. Unsupervised cluster analysis and pattern recognition uncovered 5 spatially distinct transcriptional programs, shared across patients. These included three cell-specific developmental stages largely reflecting those that are part of recently suggested models. By integrating metabolome data, we identified an additional program encompassing reactive responses to hypoxia. Areas of hypoxic response were negatively correlated with proliferation (R2= -0.34, p< 0.001) and significantly enriched for gene expression signatures from the S-phase (p< 0.001). Modeling of transient spatial gradients using vector field predictions showed opposing vector directions of hypoxia response and migratory capacity, underpinning the “go-or-growth” theory, where cells either proliferate or migrate. Inferred copy-number alterations (CNA) revealed a significant increase in genomic instability, highly correlated to hypoxia response (R2= 0.78, p< 0.001). Near necrotic areas, we observed a significant accumulation of CNAs while proliferation was inhibited, and cells remained in the S-phase. We validated this hypothesis of hypoxia-driven accumulation of CNAs by chronic hypoxia cultures of primary patient-derived cell lines. A gain of chromosomal instability after long-term hypoxia was observed, suggesting that hypoxic areas in glioblastoma function as bioreactors for genomic instability. Our findings elucidate the evolution of resistant subclones in glioblastoma. They provide novel insights into the dynamic regulation and interaction between host and tumor and cast a new light on hypoxic and necrotic areas, which may represent the source of the heterogeneous and resistant nature of glioblastomas.