Novel multicellular prokaryote discovered next to an underground stream

A qualitative assessment of limits of active flight in low density atmospheres

Exoplanet atmospheres are expected to vary significantly in thickness and chemical composition, leading to a continuum of differences in surface pressure and atmospheric density. This variability is exemplified within our Solar System, where the four rocky planets exhibit surface pressures ranging from 1 nPa on Mercury to 9.2 MPa on Venus. The direct effects and potential challenges of atmospheric pressure and density on life have rarely been discussed. For instance, atmospheric density directly affects the possibility of active flight in organisms, a critical factor since without it, dispersing across extensive and inhospitable terrains becomes a major limitation for the expansion of complex life. In this paper, we propose the existence of a critical atmospheric density threshold below which active flight is unfeasible, significantly impacting biosphere development. To qualitatively assess this threshold and differentiate it from energy availability constraints, we analyze the limits of active flight on Earth, using the common fruit fly, Drosophila melanogaster, as a model organism. We subjected Drosophila melanogaster to various atmospheric density scenarios and reviewed previous data on flight limitations. Our observations show that flies in an N2-enriched environment recover active flying abilities more efficiently than those in a helium-enriched environment, highlighting behavioral differences attributable to atmospheric density vs. oxygen deprivation.

Cellular arrangement impacts metabolic activity and antibiotic tolerance in Pseudomonas aeruginosa biofilms

Cells must access resources to survive, and the anatomy of multicellular structures influences this access. In diverse multicellular eukaryotes, resources are provided by internal conduits that allow substances to travel more readily through tissue than they would via diffusion. Microbes growing in multicellular structures, called biofilms, are also affected by differential access to resources and we hypothesized that this is influenced by the physical arrangement of the cells. In this study, we examined the microanatomy of biofilms formed by the pathogenic bacterium Pseudomonas aeruginosa and discovered that clonal cells form striations that are packed lengthwise across most of a mature biofilm's depth. We identified mutants, including those defective in pilus function and in O-antigen attachment, that show alterations to this lengthwise packing phenotype. Consistent with the notion that cellular arrangement affects access to resources within the biofilm, we found that while the wild type shows even distribution of tested substrates across depth, the mutants show accumulation of substrates at the biofilm boundaries. Furthermore, we found that altered cellular arrangement within biofilms affects the localization of metabolic activity, the survival of resident cells, and the susceptibility of subpopulations to antibiotic treatment. Our observations provide insight into cellular features that determine biofilm microanatomy, with consequences for physiological differentiation and drug sensitivity.

Halopseudomonas species: Cultivation and molecular genetic tools

The Halopseudomonas species, formerly classified as Pseudomonas pertucinogena lineage, form a unique phylogenetic branch within the Pseudomonads. Most strains have recently been isolated from challenging habitats including oil- or metal-polluted sites, deep sea, and intertidal zones, suggesting innate resilience to physical and chemical stresses. Despite their comparably small genomes, these bacteria synthesise several biomolecules with biotechnological potential and a role in the degradation of anthropogenic pollutants has been suggested for some Halopseudomonads. Until now, these bacteria are not readily amenable to existing cultivation and cloning methods. We addressed these limitations by selecting four Halopseudomonas strains of particular interest, namely H. aestusnigri, H. bauzanensis, H. litoralis, and H. oceani to establish microbiological and molecular genetic methods. We found that C4 -C10 dicarboxylic acids serve as viable carbon sources in both complex and mineral salt cultivation media. We also developed plasmid DNA transfer protocols and assessed vectors with different origins of replication and promoters inducible with isopropyl-β-d-thiogalactopyranoside, l-arabinose, and salicylate. Furthermore, we have demonstrated the simultaneous genomic integration of expression cassettes into one and two attTn7 integration sites. Our results provide a valuable toolbox for constructing robust chassis strains and highlight the biotechnological potential of Halopseudomonas strains.

Multicellular magnetotactic bacterial consortia are metabolically differentiated and not clonal

Consortia of multicellular magnetotactic bacteria (MMB) are currently the only known example of bacteria without a unicellular stage in their life cycle. Because of their recalcitrance to cultivation, most previous studies of MMB have been limited to microscopic observations. To study the biology of these unique organisms in more detail, we use multiple culture-independent approaches to analyze the genomics and physiology of MMB consortia at single cell resolution. We separately sequenced the metagenomes of 22 individual MMB consortia, representing eight new species, and quantified the genetic diversity within each MMB consortium. This revealed that, counter to conventional views, cells within MMB consortia are not clonal. Single consortia metagenomes were then used to reconstruct the species-specific metabolic potential and infer the physiological capabilities of MMB. To validate genomic predictions, we performed stable isotope probing (SIP) experiments and interrogated MMB consortia using fluorescence in situ hybridization (FISH) combined with nano-scale secondary ion mass spectrometry (NanoSIMS). By coupling FISH with bioorthogonal non-canonical amino acid tagging (BONCAT) we explored their in situ activity as well as variation of protein synthesis within cells. We demonstrate that MMB consortia are mixotrophic sulfate reducers and that they exhibit metabolic differentiation between individual cells, suggesting that MMB consortia are more complex than previously thought. These findings expand our understanding of MMB diversity, ecology, genomics, and physiology, as well as offer insights into the mechanisms underpinning the multicellular nature of their unique lifestyle.

Active Spaghetti: Collective Organization in Cyanobacteria

Filamentous cyanobacteria can show fascinating examples of nonequilibrium self-organization, which, however, are not well understood from a physical perspective. We investigate the motility and collective organization of colonies of these simple multicellular lifeforms. As their area density increases, linear chains of cells gliding on a substrate show a transition from an isotropic distribution to bundles of filaments arranged in a reticulate pattern. Based on our experimental observations of individual behavior and pairwise interactions, we introduce a nonreciprocal model accounting for the filaments' large aspect ratio, fluctuations in curvature, motility, and nematic interactions. This minimal model of active filaments recapitulates the observations, and rationalizes the appearance of a characteristic length scale in the system, based on the Péclet number of the cyanobacteria filaments.

Cell arrangement impacts metabolic activity and antibiotic tolerance in Pseudomonas aeruginosa biofilms

Cells must access resources to survive, and the anatomy of multicellular structures influences this access. In diverse multicellular eukaryotes, resources are provided by internal conduits that allow substances to travel more readily through tissue than they would via diffusion. Microbes growing in multicellular structures, called biofilms, are also affected by differential access to resources and we hypothesized that this is influenced by the physical arrangement of the cells. In this study, we examined the microanatomy of biofilms formed by the pathogenic bacterium Pseudomonas aeruginosa and discovered that clonal cells form striations that are packed lengthwise across most of a mature biofilm's depth. We identified mutants, including those defective in pilus function and in O-antigen attachment, that show alterations to this lengthwise packing phenotype. Consistent with the notion that cellular arrangement affects access to resources within the biofilm, we found that while the wild type shows even distribution of tested substrates across depth, the mutants show accumulation of substrates at the biofilm boundaries. Furthermore, we found that altered cellular arrangement within biofilms affects the localization of metabolic activity, the survival of resident cells, and the susceptibility of subpopulations to antibiotic treatment. Our observations provide insight into cellular features that determine biofilm microanatomy, with consequences for physiological differentiation and drug sensitivity.