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Virologists. You might know a couple of them, but unless you are a virologist yourself, the probability that you have collaborated with one in the past is low. The community is relatively small, but they pack a heavy punch and are expected to play a leading role in the research into pathogens that lies ahead. You may ask why we think virologists are our future. Suffice it to say that it is not just because they have invented technologies that belong to the space age, including use of viruses as vehicles to shuttle genes into cells[1], organic nanoparticles with specific tools attached to their surfaces to get inside target cells[2], and using genetically modified viruses as therapies to fight against cancer[3]. Did you know that virologists currently only know of about 3,200 viral species but that more than 320,000 mammal-associated viruses[4] are thought to await discovery? Just think about the viruses hidden in the Arctic ice[5] or in the insects and other animals from once cut-off regions in the world, which now face ever-increasing human exposure[6]. But a heroic (as well as an apocalyptic) role for virologists may also be on the horizon, as the adoption of phage therapy may, in the future, be used to control harmful bacteria when antibiotics fail
Dihydroxynaphthalene (DHN) melanin is produced by diverse Ascomycetes via slightly differing biosynthetic routes. The polyketide synthases (PKS) release the heptaketide YWA1, the hexaketide AT4HN or the pentaketide T4HN. The first two products are deacetylated by ‘yellowish-green’ hydrolases to T4HN, and T4HN is further converted by a core set of enzymes to DHN. Final polymerization steps are accomplished by multicopper oxidases. DHN melanogenesis is often regulated in a spatial and temporal fashion resulting e.g., in melanized reproduction and survival structures of the foliar plant pathogen Botrytis cinerea (Schumacher 2016, Mol Microbiol). In contrast, a polyphyletic group of Ascomycetes (microcolonial fungi/ black yeasts) dwelling in hostile habitats such as bare rock surfaces in hot and cold deserts, exhibits constitutive melanogenesis. Here, DHN melanin builds a protective layer around all vegetative cells thus contributing to the survival of diverse environmental stresses even without specialized reproduction structures. For studying the relevance of constitutive DHN melanogenesis for tolerance of abiotic and biotic stresses, adhesion to substrates and subsequent damage of colonized surfaces, the rock-inhabiting fungus Knufia petricola was chosen as gene functions in this fungus can be studied by CRISPR/Cas9-based genome editing. The putative melanogenic genes were identified in the genome of K. petricola, deleted to confirm their involvement in DHN melanogenesis and co-expressed in Saccharomyces cerevisiae for reconstruction of the synthesis pathway. Phenotypes of DHN-deficient mutants are studied. Here, we will discuss the role of the DHN melanin layer on the outer cell wall in tolerating UV irradiation.
Nutrient acquisition strategies of plants regulate water flow and mass transport within ecosystems, shaping earth surface processes. Understanding plant strategies under current conditions is important to assess and predict responses of natural ecosystems to future climate and environmental changes. Nitrogen (N) and potassium (K) (re-)utilization from topsoil and their acquisition from subsoil and saprolite were evaluated in a continental transect, encompassing three study sites – an arid shrubland, a mediterranean woodland, and a temperate rainforest – on similar granitoid parent material in the Chilean Coastal Cordillera. The short-term (<1 year) plant N and K acquisition was traced with 15N and the K analogs rubidium and cesium. To do so, the tracers were either injected into topsoil, subsoil, or saprolite, in the immediate vicinity of eight individual plants per study site and injection depth. The long-term (>decades) K uplift by plants was investigated by the vertical distribution of exchangeable K+ and Na+. Recoveries of 15N and K analogs by arid shrubland plants were similar from topsoil, subsoil, and saprolite. Mediterranean woodland shrubs recovered the tracers primarily from topsoil (i.e., 89 % of recovered 15N and 84 % of recovered K analogs). Forest plants recovered the tracers from topsoil (15N = 49 %, K analogs = 57 %) and partially from greater depth: 38 % of recovered 15N and 43 % of recovered K analogs were acquired from subsoil and saprolite, respectively. Low nutrient accessibility in the topsoil (e.g., because of frequent droughts) drives shrubland plants to expand their N and K uptake to deeper and moister soil and saprolite. Woodland and forest plants dominantly recycled nutrients from topsoil. In the forest, this strategy was complemented by short-term uplift of N and K from depth. The vertical distribution of exchangeable K indicated long-term uplift of K by roots in all three sites. This highlighted that long-term K uplift from depth complements the nutrient budget across the continental transect.
Cryomyces antarcticus – a cryptoendolithic black fungus endemic to Antarctica – is taxonomically classified in phylum Ascomycota, class Dothideomycetes incertae sedis. C. antarcticus has shown high capability to survive extreme environmental conditions like those found in space (ionizing radiation, vacuum, microgravity), thus fueling fundamental astrobiological questions like “searching for life beyond Earth” (Onofri et al. 2020, Extremophiles Astrobiol Model). Its extraordinary resilience has been attributed to the presence of thick, highly melanized cell walls, which may contain both DHN and DOPA melanins (Pacelli et al. 2020, Appl Microbiol Biotechnol). To better understand the contribution of DHN melanin to the overall resilience of C. antarcticus, we initially adopted chemicals e.g., tricyclazole to inhibit the DHN melanin synthetic pathway; however, these studies gave inconclusive results. Eventually, we decided to generate melanin-deficient mutants by genetic engineering. Using the genetic toolkit developed for the black fungus Knufia petricola (Voigt et al. 2020, Sci Rep; Erdmann et al. 2022, Front Fungal Biol), we designed a strategy for mutating the key enzyme (polyketide synthase)-encoding gene capks1 by transient delivery of Cas9 and capks1-specific sgRNA from AMA-containing plasmids and PCR-generated donor DNA i.e., resistance cassettes flanked by ~75-bp-long sequences homologous to capks1. For this, the melanin-PKS encoding ortholog was identified in the C. antarcticus CBS 116301 genome (mycocosm.jgi.doe.gov) and used to design primers for re-sequencing of the capks1 locus in the strain CCFEE 515. Transformation of C. antarcticus is challenging because of its very slow growth; we expect that 4-6 months are needed from obtaining enough biomass for cell wall lysis until transferring putatively resistant transformants for genotyping. Important parameters were evaluated: protoplasts can be generated, and they survive the transformation procedure, and suitable concentrations of selective agents have been identified. Nowadays, we are waiting for the first C. antarcticus mutants considered to be deficient in DHN melanogenesis.
Drei grundlegend verschiedene Ansätze für Umweltsimulation werden an Beispielen illustriert:
(i) Ganzheitlicher Ansatz - Nachstellen von Umweltmilieus im Labor
Ziel ist hier das Nachstellen von (kombinierten) Umweltbedingungen im Labor; die Umweltparameter werden mit all ihren Wechselwirkungen aufgebracht.
Hauptnutzen ist eine gegenüber der natürlichen Beanspruchung erhöhte Reproduzierbarkeit der Umweltbedingungen. Hat man sein Laborsetup entwickelt, ist es auf verschiedene Materialien anwendbar.
Unter solchen Laborbedingungen ermittelte Lebensdauern sind dabei nicht auf die typischerweise sehr variablen Real-Umweltbedingungen übertragbar.
(ii) Parametrisierter Ansatz - Ermittlung einzelner Materialempfindlichkeiten
Hierbei werden im Labor die Wirkungen separater Umweltparameter auf Materialien nachgestellt. Für eine solche Separation der Einflussfaktoren ist insbesondere die Aufschlüsselung möglicher Wechselwirkungen der Umwelt-parameter (z.B. Mikroklima an bestrahlten Oberflächen) erforderlich. Einzelne (meist Alterungs-) Empfindlichkeiten können qualitativ nachgewiesen werden oder sogar – als Beanspruchungs-Wirkungs-Funktionen – quantifiziert werden, was einen wesentlichen Schritt in Richtung der Digitalisierung der Material¬prüfung darstellt. Insbesondere ist dann auch eine Lebensdauer-vorhersage für vorgegebene Zeitreihen der Beanspruchungs¬parameter umsetzbar.
(iii) Rückwirkungen auf die Umwelt
Umweltbeanspruchungen können zur Freisetzung von Schadstoffen in die Umwelt führen. Durch die Nachstellung kritischer, aber realitätsnaher Einsatzszenarien kann die Menge an freigesetzten Substanzen abgeschätzt werden.
Egal, welcher Ansatz verfolgt wird – ein Vergleich mit der oder einer Real-beanspruchung ist unerlässlich, ebenso wie die Messdatenaufzeichnung (data logging) aller potenziell relevanten Beanspruchungsparameter während dieser Realbeanspruchung.
Obwohl die naturnahe Umwelt – sowohl in der BAM als auch bei der GUS – gegenüber der technischen Umwelt eher untergeordnet auftritt, werden zur Illustration Beispiele aus der naturnahen Umwelt verwendet.
The bipartite interactions between insect hosts and their bacterial gut microbiota, or their bacterial pathogens, are empirically and theoretically well-explored. However, direct, and indirect tripartite interactions will also likely occur inside a host. These interactions will almost certainly affect the trajectory of pathogen virulence evolution, an area that is currently under researched. The interactions within tripartite associations can be competitive, that is, exploitative-competition, interference-competition or apparent-competition. Competitive interactions will be significantly influenced by non-competitive effects, for example, immunopathology, immunosuppression, and microbiota-mediated tolerance. Considering a combination of these interactions and effects, will enable an increased understanding of the evolution of pathogen virulence. This new perspective allows us to identify several novel research questions, which we hope will be a useful framework for future research.
Microcolonial black fungi are inhabitants of exposed natural and man-made surfaces in all climate zones. Genetic studies are hampered by slow growth, lacking sexual cycles and difficulties to transform these fungi. Recently, we implemented CRISPR/Cas9-based genetic tools enabling efficient targeted mutations of the rock inhabitant Knufia petricola (Eurotiomycetes/Chaetothyriales) for studying stress responses, the unusual types of cell division, mineral weathering and symbiotic interactions with phototrophic microbes (Voigt, Knabe et al. 2020, Sci Rep; Erdmann et al. 2022, Front Fungal Biol). To further explore the genome of this fungus as representative of the polyphyletic group of black fungi and to assign functions to yet unknown genes, a forward genetics approach is aimed. We chose the two-component Activator/ Dissociation (Ac/Ds) transposon system from maize for generating a collection of insertional mutants by in-vivo mutagenesis. For the optimal use of this genetic tool, an inducible promoter for the expression of the Ac transposase and by this the regulatable transposition of the resistance cassette-containing Ds transposon is requested. However, endogenous promoters for nitrate assimilation and galactose catabolism that are often used in fungi for regulatable gene expression are not inducible by their substrates in K. petricola suggesting that the regulatory networks for nutrient acquisition differ significantly in the oligotrophic black fungi. Therefore, the metabolism-independent Tet-on system was adopted and validated using a Ptet::gfp construct. No GFP fluorescence was detected in absence of the inducer doxycycline (DOX) while fluorescence intensities increased with increasing inducer concentrations. Consequently, the Tet-on system is suitable for regulatable expression of endogenous and foreign genes in K. petricola.
Black microcolonial fungi represent a group of ascomycetes with similar adaptations for existing in natural and anthropogenically created extreme habitats. They exhibit slow yeast-like or meristematic growth, do not form specialized reproduction structures and accumulate the black pigment 1,8-dihydroxynaphthalene (DHN) in the multilayered cell walls. We chose the rock inhabitant Knufia petricola of the Chaetothyriales as a representative for developing methods for genetic manipulation, simulation of mineral weathering and study of symbiotic interactions. Here, we report on the expansion of the genetic toolkit by more efficient multiplex CRISPR/Cas9 using a plasmid-based system for expression of Cas9 and multiple sgRNAs and three additional resistance selection markers. The targeted integration of expression constructs by replacement of essential genes for pigment synthesis allows for an additional color screening of the transformants. The black-pink screening due to the elimination of pks1 (melanin) was applied for promoter studies using GFP fluorescence as reporter, while the black-white screening due to the concurrent elimination of pks1 (melanin) and phs1 (carotenoids) was used to identify transformants that contain the two expression constructs for co-localization or bimolecular fluorescence complementation (BiFC) studies. In addition, two intergenic regions (igr1, igr2) were identified in which expression constructs can be inserted without causing obvious phenotypes. Plasmids of the pNXR-XXX series (Schumacher, 2012) and new compatible entry plasmids were used for fast and easy generation of expression constructs and are suitable for use in other fungal systems as well.
The soil-feeding habit is an evolutionary novelty found in some advanced groups of termites. The study of such groups is important to revealing interesting adaptations to this way-of-life. The genus Verrucositermes is one such example, characterized by peculiar outgrowths on the head capsule, antennae and maxillary palps, which are not found in any other termite. These structures have been hypothesized to be linked to the presence of a new exocrine organ, the rostral gland, whose structure has remained unexplored.
We have thus studied the ultrastructure of the epidermal layer of the head capsule of Verrucositermes tuberosus soldiers.We describe the ultrastructure of the rostral gland, which consists of class 3 secretory cells only. The dominant secretory organelles comprise rough endoplasmic reticulum and Golgi apparatus, which provide secretions delivered to the surface of the head, likely made of peptide-derived components of unclear function. We discuss a possible role of the rostral gland of soldiers as an adaptation to the frequent encounter with soil pathogens during search for new food resources.
Stress is a normal part of life for fungi, which can survive in environments considered inhospitable or hostile for other organisms. Due to the ability of fungi to respond to, survive in, and transform the environment, even under severe stresses, many researchers are exploring the mechanisms that enable fungi to adapt to stress. The International Symposium on Fungal Stress (ISFUS) brings together leading scientists from around the world who research fungal stress. This article discusses presentations given at the third ISFUS, held in Sao Jose dos Campos, Sao Paulo, Brazil in 2019, thereby summarizing the state-of-the-art knowledge on fungal stress, a field that includes microbiology, agriculture, ecology, biotechnology, medicine, and astrobiology.
Knufia petricola is a black fungus that colonizes sun-exposed surfaces as extreme and oligotrophic environments. As ecologically important heterotrophs and biofilm-formers on human-made surfaces, black fungi form one of the most resistant groups of biodeteriorating organisms. Due to its moderate growth rate in axenic culture and available protocols for its transformation and CRISPR/Cas9-mediated genome editing, K. petricola is used for studying the morpho-physiological adaptations shared by extremophilic and extremotolerant black fungi. In this study, the bacteria-derived tetracycline (TET)-dependent promoter (Tet-on) system was implemented to enable controllable gene expression in K. petricola. The functionality i.e., the dose-dependent inducibility of TET-regulated constructs was investigated by using GFP fluorescence, pigment synthesis(melanin and carotenoids) and restored uracil prototrophy as reporters. The newly generated cloning vectors containing the Tet-on construct, and the validated sites in the K. petricola genome for color-selectable or neutral insertion of expression constructs complete the reverse genetics toolbox. One or multiple genes can be expressed on demand from different genomic loci or from a single construct by using 2A self-cleaving peptides, e.g., for localizing proteins and protein complexes in the K. petricola cell or for using K. petricola as host for the expression of heterologous genes.
The roles of DHN melanin and the stress-activated MAP kinase in the rock inhabitant Knufia petricola
(2023)
Black fungi/yeasts exhibit high stress tolerance, yeast‑like or meristematic growth, and constitutive 1,8-dihydroxynaphthalene (DHN) melanin formation. Due to their slow growth, robust cell walls and the lack of sexual cycles and genetic tools, the underlying mechanisms of their phenotypic traits have remained largely unexplored. Using recently developed genetic tools, it is now possible to manipulate the genome of the rock-inhabiting model fungus Knufia petricola. Thus, gene functions and the cell biology of black fungi can be studied using CRISPR/Cas9-based genome editing and live-cell imaging with genetically encoded fluorescent proteins. Here, we are addressing the question to which extent constitutive pigment formation (melanin and carotenoids) and responses mediated by the stress-activated mitogen-activated protein (MAP) kinase contribute to the observed extremotolerance of K. petricola. The mutations of pks1, phs1 and both genes result in melanin-free (pink), carotenoid-free (black) and pigment-free (white) strains, respectively. The other putative melanogenic genes were identified in the genome, deleted to confirm their involvement in DHN melanogenesis and co-expressed in Saccharomyces cerevisiae for reconstruction of the synthesis pathway. Sak1 encoding the stress-activated MAP kinase was deleted in the wild-type and different pigment-deficient backgrounds. Growth of the obtained single, double and triple deletion mutants was tested by droplet tests on media supplemented with different stress-inducing agents. The Δsak1 mutants show slightly reduced growth rates even without environmental pressure and are hypersensitive to different stresses: e.g. osmotic, oxidative, membrane, pH and heat stress. Melanin-free Δsak1 mutants are more sensitive than black Δsak1 mutants to some but not all stress conditions, suggesting that melanin and the SAK1 pathway have complementary roles in protecting K. petricola from stress.
Mitogen-activated protein (MAP) kinases are highly conserved in animals, plants, and fungi and represent fundamental parts of signaling networks in eukaryotic cells. Black DHN (1,8-dihydroxynaphthalene) melanin and orange carotenoids are produced by many fungi in specific cell types/under certain conditions for protecting cells from abiotic and/or biotic stresses. Microcolonial black fungi constitutively produce DHN melanin, contain the conserved carotenogenic gene cluster, exhibit slow yeast-like growth and survive in extreme environments. Thus, the question arises to which extent pigment formation and responses mediated by the stress-activated MAP kinase module contribute to the observed extremotolerance. We address this question in the rock inhabitant Knufia petricola, the only representative of the extremotolerant black fungi that is genetically amendable. Here, the mutations of pks1, phs1 and both genes result in melanin-free (pink), carotenoid-free (black) and pigment-free (white) strains, respectively (Voigt Knabe et al. 2020, Sci Rep). The gene encoding the stress-activated MAP kinase was deleted in the wild-type and different pigment-deficient backgrounds. In addition, strains were generated that express a GFP-SAK1 fusion protein from the sak1 locus to follow the cytosolic/nuclear shuttling of SAK1 upon stress. Growth of the obtained single, double and triple deletion mutants was tested by dropping cell suspensions on solid media supplemented with different stress-inducing agents. The Δsak1 mutants show slightly reduced growth rates even under non-stress conditions and are hypersensitive to different stress conditions: reduced growth is observed on media inducing, for instance, osmotic, oxidative, membrane, and pH stress, and upon incubation at 30 °C (heat stress). Melanin-free Δsak1 mutants are more sensitive than black Δsak1 mutants to some but not all stress conditions, suggesting that melanin and the SAK1 pathway have complementary roles in protecting K. petricola from stress.
Melanins are organic pigments produced by most fungi. These organisms either fix these pigments in their cell wall or secrete them into their extracellular environment to protect themselves against an array of physicochemical stresses (e.g., UV irradiation, desiccation, ...). Melanin can adsorb metals like Fe. How this affects fungal uptake of Fe and deterioration of Fe-containing minerals and metals is however less known. To study this, we use the model fungi Knufia petricola A95, a rock-inhabiting fungus known to deteriorate minerals and have melanised cell walls, and Amorphotheca resinae, able to contaminate fuel tanks, secrete melanin and corrode metals. In K. petricola, we have deleted genes involved in melanin production and Fe uptake using CRISPR/Cas. Through comparison of the geochemical signatures of these gene deletion mutants with those of the wild type (WT), we explore the specific mineral/metal deterioration mechanisms of melanised fungi.
Fe isotope signatures of the biomass of melanin- and Fe uptake-deficient mutants of K. petricola revealed that Fe adsorbed either directly onto melanin or after being reduced by Fe reductases. Importantly, once adsorbed to melanin, Fe could not be mobilised and taken up into the cell: both the WT and its melanin-deficient mutant, previously grown at Fe replete conditions, showed similar growth at Fe deficient conditions.
Olivine dissolution experiments revealed that Fe oxidation inhibits dissolution. K. petricola was able to enhance dissolution when this inhibition is strongest (at pH 6) and prevented dissolution when this inhibition is weakest (at pH 4). The fungus therefore dissolves olivine by interacting with the oxidised Fe at the olivine surface. However, Fe uptake did not seem to be involved: mutants deficient in various Fe uptake mechanism dissolved olivine at the same rate as the WT. This indicates that Fe adsorption onto melanin might play a key role. This is also shown by K. petricola’s ability to enhance olivine dissolution even further if secreting a melanin precursor and A. resinae’s corrosion of carbon steel whilst secreting melanin. Combined, our results imply that the Fe adsorbed to melanin cannot be taken up but enables fungi to deteriorate Fe-containing substrates at a higher rate.
The roles extracellular polymeric substances (EPS) play in mineral attachment and weathering were studied using genetically modified biofilms of the rock-inhabiting fungus Knufia petricola strain A95. Mutants deficient in melanin and/or carotenoid synthesis were grown as air-exposed biofilms. Extracted EPS were quantified and characterised using a combination of analytical techniques. The absence of melanin affected the quantity and composition of the produced EPS: mutants no longer able to form melanin synthesised more EPS containing fewer pullulan-related glycosidic linkages. Moreover, the melanin-producing strains attached more strongly to the mineral olivine and dissolved it at a higher rate. We hypothesise that the pullulan-related linkages, with their known adhesion functionality, enable fungal attachment and weathering. The released phenolic intermediates of melanin synthesis in the Δsdh1 mutant might play a role similar to Fe-chelating siderophores, driving olivine dissolution even further. These data demonstrate the need for careful compositional and quantitative analyses of biofilm-created microenvironments.
Over the last few years, the Federal Institute for material research (BAM, Berlin) together with the Centre for the Study of Manuscript Cultures (CSMC, University of Hamburg) have initiated a systematic material investigation of black inks produced from Late Antiquity to the Middle Ages (ca. fourth century CE–fourteenth/fifteenth centuries CE), aimed primarily at extending and complementing findings from previous sporadic studies. Part of this systematic investigation has focused on Egyptian Coptic manuscripts, and the present preliminary study is one of its outputs. It centres on a corpus of 45 Coptic manuscripts—43 papyri and 2 ostraca—preserved at the Palau-Ribes and Roca-Puig collections in Barcelona. The manuscripts come from the Monastery of Apa Apollo at Bawit, one of the largest monastic settlements in Egypt between the Late Antiquity and the Early Islamic Period (sixth–eighth centuries CE). The composition of their black inks was investigated in situ using near-infrared reflectography (NIRR) and X-ray fluorescence (XRF). The analyses determined that the manuscripts were written using different types of ink: pure carbon ink; carbon ink containing iron; mixed inks containing carbon, polyphenols and metallic elements; and iron-gall ink. The variety of inks used for the documentary texts seems to reflect the articulate administrative system of the monastery of Bawit. This study reveals that, in contrast to the documents, written mostly with carbon-based inks, literary biblical texts were written with iron-gall ink. The frequent reuse of papyrus paper for certain categories of documents may suggest that carbon-based inks were used for ephemeral manuscripts, since they were easy to erase by abrasion.
The termites are a derived eusocial lineage of otherwise non-social cockroaches. Understanding the proximal and ultimate drivers of this major evolutionary transition represents an important goal in biology. One outstanding question concerns the evolution of termite immunity, which is thought to have undergone broad-sweeping adaptations in order to enhance group-level immune protection. To understand the evolutionary origins of termite immunity, we conducted qualitative and quantitative transcriptome analyses along a gradient of sociality. Firstly, we aimed to identify large-scale genetic shifts in immune traits linked to eusociality by comparing immune gene repertoires in solitary and subsocial cockroaches and across a range of eusocial termite lineages. Secondly, we compared the responses of a solitary cockroach, a subsocial wood-roach and different castes of a lower termite species to a non-specific immune challenge, in order to understand how sociality may have influenced the evolution of immune gene regulation. Firstly, we found that termites have a broadly representative repertoire of canonical immune genes as compared to gregarious cockroaches and subsocial wood-roaches. Secondly, with respect to immune challenge, the solitary cockroach and the subsocial wood-roach displayed a similarly comprehensive induced response, while the termite response was considerably dampened by comparison and strongly influenced by caste; with reproductives displaying a generally higher constitutive level of immune-gene expression compared to sterile castes. In summary we did not find termite eusociality to be associated with significant changes in immune gene diversity, but rather to be linked with significant modifications to the regulation of immunity following the origin of division of labour.
The termites are a derived eusocial lineage of otherwise non-social cockroaches. Understanding the proximal and ultimate drivers of this major evolutionary transition represents an important goal in biology. One outstanding question concerns the evolution of termite immunity, which is thought to have undergone broad-sweeping adaptations in order to enhance group-level immune protection. To understand the evolutionary origins of termite immunity, we conducted qualitative and quantitative transcriptome analyses along a gradient of sociality. Firstly, we aimed to identify large-scale genetic shifts in immune traits linked to eusociality by comparing immune gene repertoires in solitary and subsocial cockroaches and across a range of eusocial termite lineages. Secondly, we compared the responses of a solitary cockroach, a subsocial wood-roach and different castes of a lower termite species to a non-specific immune challenge, in order to understand how sociality may have influenced the evolution of immune gene regulation. Firstly, we found that termites have a broadly representative repertoire of canonical immune genes as compared to gregarious cockroaches and subsocial wood-roaches. Secondly, with respect to immune challenge, the solitary cockroach and the subsocial wood-roach displayed a similarly comprehensive induced response, while the termite response was considerably dampened by comparison and strongly influenced by caste; with reproductives displaying a generally higher constitutive level of immune-gene expression compared to sterile castes. In summary we did not find termite eusociality to be associated with significant changes in immune gene diversity, but rather to be linked with significant modifications to the regulation of immunity following the origin of division of labour.
A broad suite of immune adaptations have evolved in social insects which hold close parallels with the immune systems of multicellular individuals. However, comparatively little is known about the evolutionary origins of immunity in social insects. We tackle this by identifying immune genes from 18 cockroach and termite species, spanning a gradient of social lifestyles. Termites have undergone contractions of major immune gene families during the early origin of the group, particularly in antimicrobial effector and receptor proteins, followed by later re-expansions in some lineages. In a comparative gene expression analysis, we find that reproductive individuals of a termite invest more in innate immune regulation than other castes. When colonies encounter immune-challenged nestmates, gene expression responses are weak in reproductives but this pattern is reversed when colony members are immune-challenged individually, with reproductives eliciting a greater response to treatment than other castes. Finally, responses to immune challenge were more comprehensive in both subsocial and solitary cockroaches compared to termites, indicating a reduced overall ability to respond to infection in termites. Our study indicates that the emergence of termite sociality was associated with the evolution of a tapered yet caste-adapted immune system.
Rock weathering is a key process in global elemental cycling. Life participates in this process with tangible consequences observed from the mineral interface to the planetary scale. Multiple lines of evidence show that microorganisms may play a pivotal—yet overlooked—role in weathering. This topic is reviewed here with an emphasis on the following questions that remain unanswered: What is the quantitative contribution of bacteria and fungi to weathering? What are the associated mechanisms and do they leave characteristic imprints on mineral surfaces or in the geological record? Does biogenic weathering fulfill an ecological function, or does it occur as a side effect of unrelated metabolic functions and biological processes? An overview of efforts to integrate the contribution of living organisms into reactive transport models is provided. We also highlight prospective opportunities to harness microbial weathering in order to support sustainable agroforestry practices and mining activities, soil remediation, and carbon sequestration.