Vertical transmission of cyanobacterial symbionts in the marine sponge Chondrilla australiensis (Demospongiae)

The cyanobacterial symbionts of the marine sponge Chondrilla australiensis (Demospongiae) were examined using fluorescent microscopy and Transmission Electron Microscopy. Unicellular cyanobacteria with ultrastructure resembling Aphanocapsa feldmannii occur in the cortex and bacterial symbionts are located throughout the mesohyl. In C. australiensis, the developing eggs are distributed throughout the mesohyl and are surrounded by nurse cells attached to them by thin filaments. The nurse cells form cytoplasmic bridges with the eggs, apparently releasing their contents into the egg cytoplasm. The presence of cyanobacterial and bacterial symbionts inside developing eggs and nurse cells in 25% of female Chondrilla australiensiswas established using Transmission Electron Microscopy, suggesting that these symbionts are sometimes passed on to the next generation of sponges via the eggs.     

Cryptic diversity of the symbiotic cyanobacterium Synechococcus spongiarum among sponge hosts

Cyanobacteria are common members of sponge-associated bacterial communities and are particularly abundant symbionts of coral reef sponges. The unicellular cyanobacterium Synechococcus spongiarum is the most prevalent photosynthetic symbiont in marine sponges and inhabits taxonomically diverse hosts from tropical and temperate reefs worldwide. Despite the global distribution of S. spongiarum , molecular analyses report low levels of genetic divergence among 16S ribosomal RNA (rRNA) gene sequences from diverse sponge hosts, resulting either from the widespread dispersal ability of these symbionts or the low phylogenetic resolution of a conserved molecular marker. Partial 16S rRNA and entire 16S–23S rRNA internal transcribed spacer (ITS) genes were sequenced from cyanobacteria inhabiting 32 sponges (representing 18 species, six families and four orders) from six geographical regions. ITS phylogenies revealed 12 distinct clades of S. spongiarum that displayed 9% mean sequence divergence among clades and less than 1% sequence divergence within clades. Symbiont clades ranged in specificity from generalists to specialists, with most (10 of 12) clades detected in one or several closely related hosts. Although multiple symbiont clades inhabited some host sponges, symbiont communities appear to be structured by both geography and host phylogeny. In contrast, 16S rRNA sequences were highly conserved, exhibiting less than 1% sequence divergence among symbiont clades. ITS gene sequences displayed much higher variability than 16S rRNA sequences, highlighting the utility of ITS sequences in determining the genetic diversity and host specificity of S. spongiarum populations among reef sponges. The genetic diversity of S. spongiarum revealed by ITS sequences may be correlated with different physiological capabilities and environmental preferences that may generate variable host–symbiont interactions.     

Differential Thermal Analysis of Milk Proteins

Differential thermal analysis (DTA) was used for study of milk protein denaturation. Protein solutions produced an endothermic peak of characteristic shape and temperature of peak minimum. The peak minimum is considered the coagulation temperature of the protein.

The influence of pH and additives such as sugars and NaCl was clearly observed on the thermograms of β-lactoglobulin solution. Addition of κ-casein to β-lactoglobulin solution showed an inhibitory effect on the heat coagulation.

Solid proteins produced two-stage exothermic peaks between 200°C and 400°C.

DTA was a useful method in the study of heat denaturation and degradation of protein.     

Diversities of coral-associated bacteria differ with location, but not species, for three acroporid corals on the Great Barrier Reef

Patterns in the diversity of bacterial communities associated with three species of Acropora ( Acropora millepora, Acropora tenuis and Acropora valida ) were compared at two locations (Magnetic Island and Orpheus Island) on the Great Barrier Reef to better understand the nature and specificity of coral–microbial symbioses. Three culture-independent techniques demonstrated consistent bacterial communities among replicate samples of each coral species, confirming that corals associate with specific microbiota. Profiles were also conserved among all three species of Acropora within each location, suggesting that closely related corals of the same genus harbor similar bacterial types. Bacterial community profiles of A. millepora at Orpheus Island were consistent in samples collected throughout the year, indicating a stable community despite temporal changes. However, DGGE and T-RFLP profiles differed on corals from different reefs. Nonmetric multidimensional scaling of T-RFLP profiles showed that samples grouped according to location rather than coral species. Although similar sequences were retrieved from clone libraries of corals at both Magnetic and Orpheus Island, differences in the relative dominant bacterial ribotypes within the libraries drive bacterial community structure at different geographical locations. These results indicate certain bacterial groups associated specifically with corals, but the dominant bacterial genera differ between geographically-spaced corals.     

Layers of symbiosis--visualizing the termite hindgut microbial community

Jared Leadbetter takes us for a nature walk through the diversity of life resident in the termite hindgut--a microenvironment containing 250 different species found nowhere else on Earth. Jared reveals that the symbiosis exhibited by this system is multi-layered and involves not only a relationship between the termite and its gut inhabitants, but also involves a complex web of symbiosis among the gut microbes themselves.     

Introductory comments

Abstract

Associated microorganisms have been described in numerous marine sponges. Their metabolic activity, however, has not yet been investigated in situ. We quantified for the first time microbial processes in a living sponge. Sulfate reduction rates of up to 1200 nmol cm^?3d^?1 were measured in the cold-water bacteriosponge Geodia barretti . Oxygen profiles and chemical analysis of sponge tissue and canal water revealed steep oxygen gradients and a rapid turnover of oxygen and sulfide, dependent on the pumping activity of the sponge. Identification of the microbial community with fluorescently labelled oligonucleotide probes (FISH) indicates the presence of sulfate-reducing bacteria belonging to the Desulfoarculus/Desulfomonile/Syntrophus -cluster in the choanosome of this sponge. Analysis of lipid biomarkers indicates biomass transfer from associated sulfate-reducing bacteria or other anaerobic microbes to sponge cells. These results show the presence of an anoxic micro-ecosystem in the sponge G. barretti, and imply mutualistic interactions between sponge cells and anaerobic microbes. Understanding the importance of anaerobic processes within the sponge/microbe system may help to answer unsolved questions in sponge ecology and biotechnology.     

Gut microbiome dysbiosis and honeybee health

Since a few decades, apiculture is facing important economic losses worldwide with general major consequences in many areas of agriculture. A strong attention has been paid towards the phenomenon named Colony Collapse Disorder in which colonies suddenly disappear with no clear explanations. Honeybee colonies can be affected by abiotic factors, such as environmental pollution or insecticide applications for agricultural purposes. Also biotic stresses cause colony losses, including bacterial (e.g. Paenibacillus larvae) and fungal (e.g. Ascosphaera apis) pathogens, microsporidia (e.g. Nosema apis), parasites (i.e. Varroa destructor) and several viruses. In the light of recent research, intestinal dysbiosis, considered as the relative disproportion of the species within the native microbiota, has shown to affect human and animal health. In arthropods, alteration of the gut microbial climax community has been shown to be linked to health and fitness disequilibrium, like in the medfly Ceratitis capitata for which low mate competitiveness is determined by a gut microbial community imbalance. According to these observations, it is possible to hypothesize that dysbiosis may have a role in disease occurrence also in honeybees. Here we aim to discuss the current knowledge on dysbiosis in the honeybee and its relation with honeybee health by reviewing the investigations of the microbial diversity associated to honeybees and the recent experiments performed to control bee diseases by microbial symbionts. We conclude that, despite the importance of a good functionality of the associated microbiota in preserving insect health has been proved, the mechanisms involved in honeybee gut dysbiosis are still unknown. Accurate in vitro, in vivo and in field investigations are required under healthy, diseased and stressed conditions for the host.     

Physiological variation among Tricholoma matsutake isolates generated from basidiospores obtained from one basidioma

Matsutake (Tricholoma matsutake) is a commercially valuable edible ectomycorrhizal mushroom. The physiological traits of T. matsutake have been previously assessed using mycelial isolates isolated from basidiomata; however, few studies have focused on basidiospores. Here, we report that sibling T. matsutake isolates generated from basidiospores on a single basidioma show distinct physiological variation. We first established 145 isolates of T. matsutake on modified Norkrans' C (MNC) agar medium and found that their radial growth varied significantly. The mycelial biomasses of nine isolates with different growth rates were reduced on low-carbon and low-nitrogen MNC media. However, the colony diam of one isolate was significantly elevated on low-carbon medium, and the colony diam of two isolates were significantly elevated on low-nitrogen medium. In co-cultures of two or three isolates, commensal and amensal interactions were observed. The physiological variation induced by low carbon and nitrogen levels and the mycelial interactions between sibling isolates imply mechanisms for the genetic and functional characteristics of mycelia of T. matsutake.     

An underground tale: contribution of microbial activity to plant iron acquisition via ecological processes

Background

Iron (Fe) deficiency in crops is a worldwide agricultural problem. Plants have evolved several strategies to enhance Fe acquisition, but increasing evidence has shown that the intrinsic plant-based strategies alone are insufficient to avoid Fe deficiency in Fe-limited soils. Soil micro-organisms also play a critical role in plant Fe acquisition; however, the mechanisms behind their promotion of Fe acquisition remain largely unknown.

Scope

This review focuses on the possible mechanisms underlying the promotion of plant Fe acquisition by soil micro-organisms.

Conclusions

Fe-deficiency-induced root exudates alter the microbial community in the rhizosphere by modifying the physicochemical properties of soil, and/or by their antimicrobial and/or growth-promoting effects. The altered microbial community may in turn benefit plant Fe acquisition via production of siderophores and protons, both of which improve Fe bioavailability in soil, and via hormone generation that triggers the enhancement of Fe uptake capacity in plants. In addition, symbiotic interactions between micro-organisms and host plants could also enhance plant Fe acquisition, possibly including: rhizobium nodulation enhancing plant Fe uptake capacity and mycorrhizal fungal infection enhancing root length and the nutrient acquisition area of the root system, as well as increasing the production of Fe³⁺ chelators and protons.     

Role of microorganisms in the evolution of animals and plants: the hologenome theory of evolution

We present here the hologenome theory of evolution, which considers the holobiont (the animal or plant with all of its associated microorganisms) as a unit of selection in evolution. The hologenome is defined as the sum of the genetic information of the host and its microbiota. The theory is based on four generalizations: (1) All animals and plants establish symbiotic relationships with microorganisms. (2) Symbiotic microorganisms are transmitted between generations. (3) The association between host and symbionts affects the fitness of the holobiont within its environment. (4) Variation in the hologenome can be brought about by changes in either the host or the microbiota genomes; under environmental stress, the symbiotic microbial community can change rapidly. These points taken together suggest that the genetic wealth of diverse microbial symbionts can play an important role both in adaptation and in evolution of higher organisms. During periods of rapid changes in the environment, the diverse microbial symbiont community can aid the holobiont in surviving, multiplying and buying the time necessary for the host genome to evolve. The distinguishing feature of the hologenome theory is that it considers all of the diverse microbiota associated with the animal or the plant as part of the evolving holobiont. Thus, the hologenome theory fits within the framework of the 'superorganism' proposed by Wilson and Sober.