Expanding evolutionary theories of ageing to better account for symbioses and interactions throughout the Web of Life

How, when, and why organisms age are fascinating issues that can only be fully addressed by adopting an evolutionary perspective. Consistently, the main evolutionary theories of ageing, namely the Mutation Accumulation theory, the Antagonistic Pleiotropy theory, and the Disposable Soma theory, have formulated stimulating hypotheses that structure current debates on both the proximal and ultimate causes of organismal ageing. However, all these theories leave a common area of biology relatively under-explored. The Mutation Accumulation theory and the Antagonistic Pleiotropy theory were developed under the traditional framework of population genetics, and therefore are logically centred on the ageing of individuals within a population. The Disposable Soma theory, based on principles of optimising physiology, mainly explains ageing within a species. Consequently, current leading evolutionary theories of ageing do not explicitly model the countless interspecific and ecological interactions, such as symbioses and host-microbiomes associations, increasingly recognized to shape organismal evolution across the Web of Life. Moreover, the development of network modelling supporting a deeper understanding on the molecular interactions associated with ageing within and between organisms is also bringing forward new questions regarding how and why molecular pathways associated with ageing evolved. Here, we take an evolutionary perspective to examine the effects of organismal interactions on ageing across different levels of biological organisation, and consider the impact of surrounding and nested systems on organismal ageing. We also apply this perspective to suggest open issues with potential to expand the standard evolutionary theories of ageing.

Draft genome sequencing data of a feather mite, Amerodectes protonotaria Hernandes 2018 (Acariformes: Proctophyllodidae)

Feather mites are ubiquitous, permanent, obligate ectosymbionts of avian hosts and are a valuable natural system for studying host-symbiont evolutionary and ecological dynamics at multiple levels of biological organization. However, a lack of a sequenced genome impedes molecular studies using this system. Therefore, we present the first draft genome of a symbiotic feather mite, Amerodectes protonotaria Hernandes 2018. The genome sequence data presented here were derived from an individual female mite that was collected in the field from Protonotaria citrea, its only known host species. Short read sequence data were obtained using an Illumina NovaSeq 6000 platform. From these data, we assembled a 59,665,063 bp draft genome consisting of 2,399 contigs. Raw short reads and the assembled genome sequence are available at the National Center for Biotechnology Information (NCBI)'s Sequence Read Archive (SRA) under BioProject PRJNA884722. The data presented here are beneficial for future research on the biology and evolution of closely related mites and the genomics of host-symbiont interactions.

Depression of the soil arbuscular mycorrhizal fungal community by the canopy gaps in a Japanese cedar (Cryptomeria japonica) plantation on Lushan Mountain, subtropical China

Both canopy gaps (CG) and arbuscular mycorrhizal fungi (AMF) play key roles in seedling establishment and increasing species diversity in forests. The response of AMF to canopy gaps is poorly understood. To assess the long-term effects of canopy gaps on soil AMF community, we sampled soil from plots in a 50-year Cryptomeria japonica (L.f.) D. Don. plantation, located in Lushan Mountain, subtropical China. We analyzed the AMF community, identified through 454 pyrosequencing, in soil and edaphic characteristics. Both richness and diversity of AMF in CG decreased significantly compared to the closed canopy (CC). The differences of the AMF community composition between CG and CC was also significant. The sharp response of the AMF community appears to be largely driven by vegetation transformation. Soil nutrient content also influenced some taxa, e.g., the low availability of phosphorus increased the abundance of Acaulospora. These results demonstrated that the formation of canopy gaps can depress AMF richness and alter the AMF community, which supported the plant investment hypothesis and accentuated the vital role of AMF-plant symbioses in forest management.

Synthesis and release of fatty acids under the interaction of Ulva pertusa and Heterosigma akashiwo by stable isotope analysis

Symbiosis of marine algae is inevitable in the marine environment, and species may occur interaction on the growth. In this study, the macroalgae Ulva pertusa and marine microalgae Heterosigma akashiwo were selected as target species to study the interaction mechanism between them. After the 8 days of co-cultivation, the inhibition on growth was observed for both of U. pertusa and H. akashiwo. Eight fatty acids in U. pertusa was detected, with the significant decrease in contents of polyunsaturated fatty acids (PUFAs) especially for C18:2, C18:3n-3 and C18:3n-6. Twelve fatty acids in H. akashiwo was detected, with the significant change for PUFAs. PUFA concentrations in the co-culture group were less than those in the mono-culture. Meanwhile the principal component analysis was conducted to insight into the interaction between U. pertusa and H. akashiwo by fatty acids content and carbon stable isotope ratio of fatty acids (δ¹³C_FAs). Fatty acid content could not distinguish mono and co-culture. However, δ¹³C_FAs could distinguish not only the culture time of algae, but also the living environment of algae. In addition, this study combined fatty acids content and δ¹³C_FAs to explore the release of fatty acids by algae into the seawater. The C18:3n-3 was identified as the allelochemical released by U. pertusa to inhibit the growth of H. akashiwo. The ratio of δ¹³C_FAs in seawater decreased. This study provides a theoretical basis for the symbiosis of marine algae, and a new method of compound-specific stable carbon isotopes was used to better explore the metabolism of fatty acids in algae.

The origin of symbiogenesis: An annotated English translation of Mereschkowsky's 1910 paper on the theory of two plasma lineages

In 1910, the Russian biologist Konstantin Sergejewitch Mereschkowsky (Константин Сергеевич Мережковский, in standard transliterations also written as Konstantin Sergeevič Merežkovskij and Konstantin Sergeevich Merezhkovsky) published a notable synthesis of observations and inferences concerning the origin of life and the origin of nucleated cells. His theory was based on physiology and leaned heavily upon the premise that thermophilic autotrophs were ancient. The ancestors of plants and animals were inferred as ancestrally mesophilic anucleate heterotrophs (Monera) that became complex and diverse through endosymbiosis. He placed a phylogenetic root in the tree of life among anaerobic autotrophic bacteria that lack chlorophyll. His higher level classification of all microbes and macrobes in the living world was based upon the presence or absence of past endosymbiotic events. The paper's primary aim was to demonstrate that all life forms descend from two fundamentally distinct organismal lineages, called mykoplasma and amoeboplasma, whose very nature was so different that, in his view, they could only have arisen independently of one another and at different times during Earth history. The mykoplasma arose at a time when the young Earth was still hot, it later gave rise to cyanobacteria, which in turn gave rise to plastids. The product of the second origin of life, the amoeboplasma, arose after the Earth had cooled and autotrophs had generated substrates for heterotrophic growth. Lineage diversification of that second plasma brought forth, via serial endosymbioses, animals (one symbiosis) and then plants (two symbioses, the second being the plastid). The paper was published in German, rendering it inaccessible to many interested scholars. Here we translate the 1910 paper in full and briefly provide some context.

Trophic Ecology of the Tropical Pacific Sponge Mycale grandis Inferred from Amino Acid Compound-Specific Isotopic Analyses

Many sponges host abundant and active microbial communities that may play a role in the uptake of dissolved organic matter (DOM) by the sponge holobiont, although the mechanism of DOM uptake and metabolism is uncertain. Bulk and compound-specific isotopic analysis of whole sponge, isolated sponge cells, and isolated symbiotic microbial cells of the shallow water tropical Pacific sponge Mycale grandis were used to elucidate the trophic relationships between the host sponge and its associated microbial community. δ¹⁵N and δ¹³C values of amino acids in M. grandis isolated sponge cells are not different from those of its bacterial symbionts. Consequently, there is no difference in trophic position of the sponge and its symbiotic microbes indicating that M. grandis sponge cell isolates do not display amino acid isotopic characteristics typical of metazoan feeding. Furthermore, both the isolated microbial and sponge cell fractions were characterized by a similarly high ΣV value-a measure of bacterial-re-synthesis of organic matter calculated from the sum of variance among individual δ¹⁵N values of trophic amino acids. These high ΣV values observed in the sponge suggest that M. grandis is not reliant on translocated photosynthate from photosymbionts or feeding on water column picoplankton, but obtains nutrition through the uptake of amino acids of bacterial origin. Our results suggest that direct assimilation of bacterially synthesized amino acids from its symbionts, either in a manner similar to translocation observed in the coral holobiont or through phagotrophic feeding, is an important if not primary pathway of amino acid acquisition for M. grandis.

Quantitative 3D-imaging for cell biology and ecology of environmental microbial eukaryotes

We present a 3D-fluorescence imaging and classification tool for high throughput analysis of microbial eukaryotes in environmental samples. It entails high-content feature extraction that permits accurate automated taxonomic classification and quantitative data about organism ultrastructures and interactions. Using plankton samples from the Tara Oceans expeditions, we validate its applicability to taxonomic profiling and ecosystem analyses, and discuss its potential for future integration of eukaryotic cell biology into evolutionary and ecological studies.

Quantitative 3D-imaging for cell biology and ecology of environmental microbial eukaryotes

We present a 3D-fluorescence imaging and classification tool for high throughput analysis of microbial eukaryotes in environmental samples. It entails high-content feature extraction that permits accurate automated taxonomic classification and quantitative data about organism ultrastructures and interactions. Using plankton samples from the Tara Oceans expeditions, we validate its applicability to taxonomic profiling and ecosystem analyses, and discuss its potential for future integration of eukaryotic cell biology into evolutionary and ecological studies.

Our planet’s ecosystems – from its oceans to its forests – are teeming with microbes. DNA analysis of environmental samples shows that many of these microbes belong to a group known as protists. This group consists of single-celled organisms that are close relatives of fungi, plants and animals. Though protists are a widespread and diverse group, scientists know little about them. One reason for this is the lack of high-throughput ways to recognize and count protists in environmental samples.

Colin, Coelho et al. set out to tackle this blind spot in ecology and cell biology by developing an automated imaging system. The system needed to image many kinds of protist cells in enough detail to see the features inside. The end-result was a 3D-imaging technique called e-HCFM – which is short for “environmental high content fluorescence microscopy”. Colin, Coelho et al. went on to use the technique on 72 samples collected on an expedition across the world’s oceans. This allowed them to automatically image, recognize and classify over 330,000 organisms.

This approach and new dataset will benefit researchers working in many fields, from cell biology to ecology, computational biology and beyond. In the future, this imaging method might integrate with techniques that can analyze the DNA in individual cells. This would allow scientists to link protists’ visible features to their genetic information, in a way that will scale from single cells up to entire ecosystems.

Genome of Rhizobium leucaenae strains CFN 299(T) and CPAO 29.8: searching for genes related to a successful symbiotic performance under stressful conditions

Background

Common bean (Phaseolus vulgaris L.) is the most important legume cropped worldwide for food production and its agronomic performance can be greatly improved if the benefits from symbiotic nitrogen fixation are maximized. The legume is known for its high promiscuity in nodulating with several Rhizobium species, but those belonging to the Rhizobium tropici “group” are the most successful and efficient in fixing nitrogen in tropical acid soils. Rhizobium leucaenae belongs to this group, which is abundant in the Brazilian “Cerrados” soils and frequently submitted to several environmental stresses. Here we present the first high-quality genome drafts of R. leucaenae, including the type strain CFN 299^T and the very efficient strain CPAO 29.8. Our main objective was to identify features that explain the successful capacity of R. leucaenae in nodulating common bean under stressful environmental conditions.

Results

The genomes of R. leucaenae strains CFN 299^T and CPAO 29.8 were estimated at 6.7–6.8 Mbp; 7015 and 6899 coding sequences (CDS) were predicted, respectively, 6264 of which are common to both strains. The genomes of both strains present a large number of CDS that may confer tolerance of high temperatures, acid soils, salinity and water deficiency. Types I, II, IV-pili, IV and V secretion systems were present in both strains and might help soil and host colonization as well as the symbiotic performance under stressful conditions. The symbiotic plasmid of CPAO 29.8 is highly similar to already described tropici pSyms, including five copies of nodD and three of nodA genes. R. leucaenae CFN 299^T is capable of synthesizing Nod factors in the absence of flavonoids when submitted to osmotic stress, indicating that under abiotic stress the regulation of nod genes might be different.

Conclusion

A detailed study of the genes putatively related to stress tolerance in R. leucaenae highlighted an intricate pattern comprising a variety of mechanisms that are probably orchestrated to tolerate the stressful conditions to which the strains are submitted on a daily basis. The capacity to synthesize Nod factors under abiotic stress might follow the same regulatory pathways as in CIAT 899^T and may help both to improve bacterial survival and to expand host range to guarantee the perpetuation of the symbiosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2859-z) contains supplementary material, which is available to authorized users.

Extremotolerant fungi from alpine rock lichens and their phylogenetic relationships

Fungi other than the lichen mycobiont frequently co-occur within lichen thalli and on the same rock in harsh environments. In these situations dark-pigmented mycelial structures are commonly observed on lichen thalli, where they persist under the same stressful conditions as their hosts. Here we used a comprehensive sampling of lichen-associated fungi from an alpine habitat to assess their phylogenetic relationships with fungi previously known from other niches. The multilocus phylogenetic analyses suggest that most of the 248 isolates belong to the Chaetothyriomycetes and Dothideomycetes, while a minor fraction represents Sordariomycetes and Leotiomycetes. As many lichens also were infected by phenotypically distinct lichenicolous fungi of diverse lineages, it remains difficult to assess whether the culture isolates represent these fungi or are from additional cryptic, extremotolerant fungi within the thalli. Some of these strains represent yet undescribed lineages within Chaethothyriomycetes and Dothideomycetes, whereas other strains belong to genera of fungi, that are known as lichen colonizers, plant and human pathogens, rock-inhabiting fungi, parasites and saprotrophs. The symbiotic structures of the lichen thalli appear to be a shared habitat of phylogenetically diverse stress-tolerant fungi, which potentially benefit from the lichen niche in otherwise hostile habitats.