Effect of Space Flight Factor on Dormant Stages in Aquatic Organisms: A Review of International Space Station and Terrestrial Experiments

This work is a review of the experiments carried out in the Russian segment of the ISS (inside and outside) from 2005 to 2016 on the effect of the space flight factor on the resting stages of organisms. In outer space, ultraviolet, a wide range of high and low temperatures, cosmic radiation, altered gravity, modified electromagnetic field, vacuum, factors of technical origin, ultrasound, microwave radiation, etc. and their combination determine the damaging effect on living organisms. At the same time, biological dormancy, known in a wide range of bacteria, fungi, animals and plants, allows them to maintain the viability of their dormant stages in extreme conditions for a long time, which possibly allows them to survive during space flight. From 2005 to 2016, the resting stages (propagules) of micro- and multicellular organisms were tested on the ISS to assess their ability to survive after prolonged exposure to the conditions of open space and space flight. Among the more than 40 species studied, about a third were dormant stages of aquatic organisms (eggs of cyprinodont fish, daphnia embryos, resting eggs of fairy shrimps, tadpole shrimps, copepods and ostracods, diapausing larvae of dipterans, as well as resting cysts of algae). The experiments were carried out within the framework of four research programs: (1) inside the ISS with a limited set of investigated species (Akvarium program); (2) outside the station in outer space without exposure to ultraviolet radiation (Biorisk program); (3) under modified space conditions simulating the surface of Mars (Expose program); and (4) in an Earth-based laboratory where single-factor experiments were carried out with neutron radiation, modified magnetic field, microwave radiation and ultrasound. Fundamentally new data were obtained on the stability of the resting stages of aquatic organisms exposed to the factors of the space environment, which modified the idea of the possibility of bringing Earth life forms to other planets with spacecraft and astronauts. It also can be used for creating an extraterrestrial artificial ecosystem and searching for extraterrestrial life.

Habitat Shift for Plankton: The Living Side of Benthic-Pelagic Coupling in the Mar Piccolo of Taranto (Southern Italy, Ionian Sea)

Resting stages represent the answer for species to the variability of environmental conditions. In confined marine habitats, variability of conditions is high, and bottoms host plankton resting stages in the so-called “marine cyst banks”. The Mar Piccolo of Taranto was chosen as a pilot site in which to investigate how marine cyst banks and plankton affect each other in the living part of the benthic–pelagic coupling. The attempt was based on the use of multiple devices for integrated sampling of benthic and pelagic stages and allowed us to identify 207 taxa/categories in the whole system (127 as active forms, 91 as resting stages). The sediments added 80 taxa to the plankton list obtained only from the water column, thus confirming the importance of this kind of approach in perceiving the actual diversity of the studied site. The sediment cyst bank involved 0.15–1.00% of its content in daily benthic-pelagic exchanges, in terms of cyst germination and import, respectively. In addition, the cyst production, which was higher than the cyst germination, is responsible for the existence of a permanent biological reservoir in the sediments. The benthic-pelagic coupling, however, was completely depicted in the present investigation only for seven taxa. This result is due to the still scant knowledge of the life cycles and life histories of single species. Apart from the identification difficulties that still have to be clarified (which cysts belong to which species), the cycle presence/absence is also characterized by the diversification of strategies adopted by each species. The observation of plankton dynamics from the benthos point of view was useful and informative, unveiling a huge assemblage of resting forms in the sediments only minimally affected by cyst import/export, because it is more devoted to a storing role over long periods. Consequently, the continuation of life cycle studies appears necessary to understand the diversity of strategies adopted by the majority of plankton species.

NPP-ID: Non-Pollen Palynomorph Image Database as a research and educational platform

Non-pollen palynomorphs (NPPs) form a large group of biological objects found in palynological slides besides pollen grains. This includes various remains of algae and fungi, shells, resting stages and eggs of invertebrates, among others. Publications of NPP-types started in the 1970s with studies of BvG and colleagues, and large numbers of new types continue to be published every year. For an overview of this diverse world of “extra fossils”, we created the Non-Pollen Palynomorph Image Database (NPP-ID) to gather NPP knowledge, structured by acronyms and known taxonomy to assist identification and palaeoecological interpretation (https://nonpollenpalynomorphs.tsu.ru/). An integral part is a database of illustrations, descriptions and ecological background of NPPs. While numerical data are routinely stored in open access repositories, the NPP-ID enables the definitions, identification and interpretation of the NPP taxa to be shared. The NPP-ID operates as an open research project aiming to provide open access to descriptions and illustrations of NPPs. However, due to publication rights, access to some original images is restricted and registration by users is required. We encourage palynologists to contribute to the further growth of the database by uploading their own microphotographs or drawings under an open access license. Contributors will be acknowledged by co-authorship in publications on updates of the NPP-ID.

Genetic slippage after sex maintains diversity for parasite resistance in a natural host population

Although parasite-mediated selection is thought to be a major driver of host evolution, its influence on genetic variation for parasite resistance is not yet well understood. We monitored a large population of the planktonic crustacean Daphnia magna over eight years, as it underwent yearly epidemics of the bacterial pathogen Pasteuria ramosa. We observed a cyclical pattern of resistance evolution: resistant phenotypes increased in frequency throughout the epidemics, but susceptibility was restored each spring when hosts hatched from sexual resting stages, a phenomenon described as genetic slippage in response to sex. Collecting and hatching D. magna resting stages across multiple seasons showed that largely resistant host populations can produce susceptible offspring through recombination. Resting stages produced throughout the planktonic season accurately represent the hatching population cohort of the following spring. A genetic model of resistance developed for this host-parasite system, based on multiple loci and strong epistasis, is in partial agreement with these findings. Our results reveal that, despite strong selection for resistance in a natural host population, genetic slippage after sexual reproduction has the potential to maintain genetic diversity of host resistance.

Prochlorococcus Cells Rely on Microbial Interactions Rather than on Chlorotic Resting Stages To Survive Long-Term Nutrient Starvation

ABSTRACT Many microorganisms produce resting cells with very low metabolic activity that allow them to survive phases of prolonged nutrient or energy stress. In cyanobacteria and some eukaryotic phytoplankton, the production of resting stages is accompanied by a loss of photosynthetic pigments, a process termed chlorosis. Here, we show that a chlorosis-like process occurs under multiple stress conditions in axenic laboratory cultures of Prochlorococcus, the dominant phytoplankton linage in large regions of the oligotrophic ocean and a global key player in ocean biogeochemical cycles. In Prochlorococcus strain MIT9313, chlorotic cells show reduced metabolic activity, measured as C and N uptake by Nanoscale secondary ion mass spectrometry (NanoSIMS). However, unlike many other cyanobacteria, chlorotic Prochlorococcus cells are not viable and do not regrow under axenic conditions when transferred to new media. Nevertheless, cocultures with a heterotrophic bacterium, Alteromonas macleodii HOT1A3, allowed Prochlorococcus to survive nutrient starvation for months. We propose that reliance on co-occurring heterotrophic bacteria, rather than the ability to survive extended starvation as resting cells, underlies the ecological success of Prochlorococcus. IMPORTANCE The ability of microorganisms to withstand long periods of nutrient starvation is key to their survival and success under highly fluctuating conditions that are common in nature. Therefore, one would expect this trait to be prevalent among organisms in the nutrient-poor open ocean. Here, we show that this is not the case for Prochlorococcus, a globally abundant and ecologically important marine cyanobacterium. Instead, Prochlorococcus relies on co-occurring heterotrophic bacteria to survive extended phases of nutrient and light starvation. Our results highlight the power of microbial interactions to drive major biogeochemical cycles in the ocean and elsewhere with consequences at the global scale.

Algal communities of the waterbodies of Schirmacher Oasis, East Antarctica

In continental waterbodies of Antarctic oases specific algal communities are forming. The structure and dominating complex of species of this communities due to different distance from the seashore and latitude, the composition of the constituent rocks, altitude and the presence in the past of periods of contact with sea water is unique for different oases. It may vary in different waterbodies within one oasis besides.Aim of the research is to describe different types of algal communities from the continental waterbodies of Schirmacher Oasis and it’s confinement to the different types of waterbodies.Samples were collected from 173 waterbodies: 151 with stagnant water and 22 streams.During the study 64 species of Cyanoprokaryotes were found, and this group usually dominated in communities. Also 14 most frequent species of Chlorophyta, 12 most frequent species of Bacillariophyta, 6 species of desmid algae, 2 species of Xanthophyceae, 1 species of Eustigmatophyceae were noted in benthos. Usually resting stages and in one case — life cells of Golden algae (Chrysophyceae, Synurophyceae) were found in mats on the bottom of big lakes. Plankton algae in most of the waterbodies had very low abundance and diversity and were strongly influensed by trophic level. Benthic algal communities were much more diverse and abundant. Eight sustainable types of benthic algal communities were revealed in continental waterbodyes of Schirmacher Oasis. Form, colour, and species composition of bentic films and mats strongly depended on temperature, conductivity and pH of the waterbody and its depth.

Assessing morphological congruence in Dinobryon species and their stomatocysts, including a newly established Dinobryon pediforme–stomatocyst connection

The chrysophyte genus Dinobryon Ehrenberg consists of 44 taxa, which occur in freshwaters, rarely marine waters, mostly in temperate regions of the world. The taxa of Dinobryon produce characteristic solitary or dendroid colonies and resting stages called stomatocysts. Only 20 Dinobryon taxa have information on produced stomatocysts and only four stomatocysts are reliably linked with vegetative stages using modern identification standards employing scanning electron microscopy (SEM) analyses. In this study, an encysted material of Dinobryon pediforme (Lemmermann) Steinecke was collected in two lakes in contrasting regions of Poland. Light microscopy (LM) and scanning electron microscopy (SEM) analyses revealed that Dinobryon pediforme produces stomatocyst #61, Piątek J. that is described here as new morphotype following the International Statospore Working Group (ISWG) guidelines. This raises to five the number of reliable links between vegetative stages of Dinobryon species and corresponding stomatocysts. Phenotypic similarities between Dinobryon species and their stomatocysts, analysed for five reliably established links, showed no relationships in size and shape between loricas and stomatocysts belonging to the same species. The morphological characters of loricas and stomatocysts mapped onto the phylogenetic tree of the five Dinobryon species revealed only little congruence between their morphology and phylogenetic relationships.