Symbiosis

Distribution and relative abundance of three protist genera within the Zootermopsis nevadensis nuttingi hindgut Abstract The termite Zootermopsis nevadensis nuttingi, which inhabits coastal forests of the western United States, plays an important ecological role in the breakdown and digestion of wood. Vital to this role are symbiotic protists residing in the termite’s hindgut. Five protist genera of varying size and morphology make up this gut community, but very little is known about their spatial organization within the hindgut or the number of protist cells per host. To resolve this issue, we used light microscopy and a hemocytometer to determine the distribution of the larger protist genera across hindgut segments. We found that Streblomastix were the most abundant cells in all three segments, but especially in the anterior hindgut. Trichomitopsis cells were significantly more abundant in the posterior hindgut. Trichonympha were the least abundant overall, often reaching their highest abundance in the middle segment but with a more variable distribution. Understanding the distribution of different protists within the hindgut may improve our understanding of the ecological relationships among protists, as well as their individual roles in lignocellulose digestion, contributing to a better understanding of the symbiotic system as a whole.

Gregarious true- colonies of ciliate Vorticella oceanica on a chain forming diatom Chaetoceros coarctatus : indicating change in the nature of association Abstract Eco-commensal association between the chain forming planktonic diatom Chaetoceros coarctatus and the peritrich aloricate ciliate Vorticella oceanica is well known in tropical waters. This epibiosis provides several advantages to the epibiont V. oceanica, and includes protection, buoyancy, drift, supply of resources and possible assistance in reproduction. While it is a well-established fact that the host usually remains neutrally affected, without any gain or loss due to the attached epibiont, in the present study, the host showed signs of negative impact due to overgrowth of the epibiont. The present study noted for the first time a gregarious stage of V. oceanica ‘true colony’ from the coastal waters off the central west coast of India. The true-colonies of V. oceanica impacted the C. coarctatus chains as V. oceanica swarmed with high density and disintegrated the host setae. This study discusses all the stages of attachment of this species- specific consortium, along an estuarine gradient, and its possible ecological implications.

Fungal diversity in rhizosphere of root-knot nematode infected tomatoes in Tunisia Abstract This research explores the occurrence and diversity of fungi associated with root-knot nematodes (Meloidogyne spp.) infestations on tomato crops in bioclimatic zones of Tunisia. One hundred and thirty five tomato samples (roots and soil) collected between 2011 to 2013 from tomato fields were screened for Oomycetes and other fungi. A high level of fungal diversity was found in the presence of Meloidogyne spp. A total of 31 fungal species belonging to 17 different genera were recovered from roots and soil samples collected in fields infested with root-knot nematode. The most frequent fungal species associated with the nematode was Fusarium oxysporum (11%) followed by Fusarium solani(6%). The species composition was dependent on environmental conditions. Temperature seems to be important as the rhizosphere microflora in the Kebili and Tozeur areas with ‘saharien’ bioclimatic stages was different from other localities. Our findings may be valuable for predicting this disease complex.

Interactive effects of Epichloë fungal and host origins on the seed germination of Achnatherum inebrians Abstract Cool-season grasses have developed a symbiotic relationship with Epichloë endophytes. In many environments, Epichloë endophytes have been shown to be mutualistic symbionts of plants by increasing the fitness of their host against abiotic or biotic stresses. The effects of Epichloë endophytes on other fitness-correlated plant characteristics are less intensively studied, and the results are usually variable and contradictory. In this study, we evaluated the effects of endophyte infection on seed germination in Achnatherum inebrians from four origins. Our results indicate that the germination rate of the seeds collected from alpine regions was higher at low temperatures than that of seeds with desert and arid grassland origins. By contrast, a higher germination percentage was detected in seeds with desert and arid grassland origins than in those with alpine origins in higher temperatures. Epichloë endophyte infection affects the cardinal temperatures of seeds from different origins. Endophyte-infected seeds have a lower base temperature and a higher ceiling temperature than their endophyte-free counterparts. The value of the base temperature was higher in seeds with alpine grassland origins than in those with desert and arid grassland origins. However, the ceiling temperature was higher in seeds with desert and arid grassland origins than in those with alpine grassland origins. Consequently, future experiments should consider the effects of endophytes on seed germination and seedling recruitment in suboptimal climatic conditions.

Functional roles of fungal endophytes in host fitness during stress conditions Abstract Fungal endophytes live symbiotically within healthy plant tissues and found to be associated with all host plants studied till date in all natural ecosystems with varied geographical areas. These microbes benefit the plants by conferring resistance to several biotic and abiotic stresses and also influence the soil rhizosphere environment. The endophytic fungi may affect plant phenotypic and functional traits by promoting nutrient/mineral uptake and alters defensive pathways. The importance of fungal endophytes to ecosystem functioning via soil processes is also aroused increasing interest during the past decade as host-fungal interaction affects ecology, distribution, and diversity of plants. The present review ascertains the role of fungal endophytes on host ecological fitness during different stress conditions.

New evidence about the interactions between liverworts in the genus Symphyogyna (Pallaviciniaceae) and Arbuscular Mycorrhizal Fungi Abstract Arbuscular Mycorrhizal Fungi (Glomeromycotina) have been recorded in several species of thalloid liverworts of the genus Symphyogyna (Pallaviciniaceae, Marchantiophyta). In this work we report a relationships established between Arbuscular Mycorrhizal Fungi and three further species of this genus. These associations display Paris-type morphology. Brief descriptions and illustrations of the characteristic structures are presented for the arbuscular associations in S. circinata Nees & Mont., S. hymenophyllum (Hook.) Mont. & Nees and S. rubritincta A. Evans.

Growth and physiological responses of perennial ryegrass to an AMF and an Epichloë endophyte under different soil water contents Abstract Arbuscular mycorrhizal fungi (AMF) and endophytic Epichloë are two important symbiotic microorganisms of perennial ryegrass (Lolium perenne). The present study evaluates the individual and combined effects of AMF and Epichloëon drought stress. Plant growth, phosphorus (P) uptake, chlorophyll content, net photosynthetic rate (Pn), soluble sugar concentration, malondialdehyde (MDA) concentration, and antioxidant enzyme activities were measured in a greenhouse experiment. Both AMF and Epichloë significantly increased Pn and total P content for each soil water content. In addition, the presence of AMF increased plant total dry weight, root activity, and soluble sugar concentration at each soil water content. Furthermore, catalase activity increased and MDA concentration decreased at 30% soil water content (SWC). Infection with Epichloë increased the polyphenol oxidase activity of plants for both non-AMF and AMF treatments at 30% SWC. AMF + Epichloë treatments increased plant P uptake, Pn, root activity, and soluble sugar concentration at each soil water content (SWC) (P < 0.001), and increased peroxidase (POD) activity at 30% SWC (P < 0.001). Plant-AMF-Epichloë symbiosis alleviated the damage caused by drought stress by promoting P uptake, photosynthesis, and the accumulation of osmoregulatory substances.

Wheat landraces with low mycorrhizing ability at field respond differently to inoculation with artificial or indigenous arbuscular mycorrhizal fungal communities Abstract Conventional farming is not sustainable in a context of climate change and of dramatic reductions in natural resource stocks worldwide. A change of paradigm towards more sustainable farming is necessary, based on the preservation and management of ecosystem services. The soil is a reservoir of organisms beneficial for plant production. Among these are arbuscular mycorrhizal fungi. Nevertheless, the response of plants – especially cereal landraces – to mycorrhization, and the effect of domestication on the response to mycorrhization are controversial. In the present paper we investigated the response of four wheat landraces with a low mycorrhizogenous ability to inoculation with the indigenous arbuscular mycorrhizal fungi community or an artificial community in greenhouse and field conditions. We showed that the community of arbuscular mycorrhizal fungi can have an effect on yield, even in wheat landraces with a low mycorrhizogenous ability. We also highlighted the importance to properly choose the criteria (phenotypic criteria as root and shoot biomasses versus quality criteria as grain quality) used to measure this possible gain.

Seasonality and latitudinal variability in the diatom-cyanobacteria symbiotic relationships in the coastal waters of the Red Sea, Saudi Arabia Abstract The seasonal and spatial dynamics of diatom-cyanobacteria associations were observed in the coastal waters of the Gulf of Aqaba as well as in the northern and central Red Sea, Saudi Arabia. However, there was an absence of such associated observations in the southern Red Sea. The heterocystous endosymbiotic cyanobacteria Richelia intracellularis J. Schmidt, 1901 was found living in association with five centric diatom species, including Rhizosolenia styliformis T. Brightwell, 1858, Rhizosolenia hebetata Bailey, 1856, Rhizosolenia imbricata Brightwell, 1858, Guinardia cylindrus (Cleve) Hasle, 1996 and Proboscia alata (Brightwell) Sundström, 1986. All five diatom species were observed with R. intracellularis in the central Red Sea region, while R. intracellularis was not found with R. imbricata and P. alata in the other Red Sea regions. The density of symbiotic diatom cells showed seasonal variations in the northern and central Red Sea, and the densities were the most conspicuous in these regions compared to the Gulf of Aqaba region. There was seasonal variation in the percent occurrence of the symbiotic diatoms compared to the nonsymbiotic diatoms. Symbiotic associations between the diatoms and R. intracellularis were only evident within the central Red Sea region from April to October. Multiple R. intracellularis trichomes inside the diatom host cells were common in the central Red Sea, while the other Red Sea regions showed only single trichomes. The size of the individual trichomes of R. intracellularis growing inside the host cells was entirely dependent on the size of the respective diatom species (r = 0.781, P < 0.01). The complete absence of such specific relations in the southern Red Sea reveals the possibility of different ecological conditions in the region.

Diversity of endosymbiotic Symbiodiniaceae in giant clams at Dongsha Atoll, northern South China Sea Abstract Despite the importance of endosymbiotic dinoflagellates in the ecology of giant clams, the diversity and distribution of Symbiodiniaceae in different tridacnine species remain relatively poorly studied. Using a DNA metabarcoding approach based on the nuclear ribosomal ITS2 marker, this study examined the patterns of Symbiodiniaceae diversity and composition in two giant clam species, Tridacna maxima (n = 32) and Tridacna noae (n = 41) found at Dongsha Atoll, the largest atoll in the northern South China Sea. Both species of giant clams hosted Symbiodiniaceae from genera Symbiodinium (formerly Clade A), Cladocopium (formerly Clade C) and Durusdinium (formerly Clade D). Tridacna maxima harboured Cladocopium preferentially, followed by Symbiodinium and Durusdinium, while T. noae hosted Durusdinium most abundantly, followed by Symbiodinium and Cladocopium. Endosymbiont diversity also varied between host species—T. maxima contained 11 species while T. noae had 13 species. Among the endosymbionts, Cladocopium goreaui (ITS2 type C1) was most common in both host species. Further analyses revealed that endosymbiont species richness was influenced primarily by depth, size, and, to some extent, geographic locality of giant clams. Endosymbiont community structure was significantly different between host species and this variation was primarily driven by depth. Even though both tridacnine species share similar habitats on coral reefs, the contrasting diversity and composition of Symbiodiniaceae present in each species may underlie the host’s adaptability to micro- and macro-environmental changes. These results not only provide a baseline of the various endosymbionts occurring in giant clams on an isolated reef ecosystem, they provide useful information for predicting impacts on these host species that could arise due to climate-related environmental stressors.