Microbiome reduction and endosymbiont gain from a switch in sea urchin life history

Animal gastrointestinal tracts harbor a microbiome that is integral to host function, yet species from diverse phyla have evolved a reduced digestive system or lost it completely. Whether such changes are associated with alterations in the diversity and/or abundance of the microbiome remains an untested hypothesis in evolutionary symbiosis. Here, using the life history transition from planktotrophy (feeding) to lecithotrophy (nonfeeding) in the sea urchin Heliocidaris, we demonstrate that the lack of a functional gut corresponds with a reduction in microbial community diversity and abundance as well as the association with a diet-specific microbiome. We also determine that the lecithotroph vertically transmits a Rickettsiales that may complement host nutrition through amino acid biosynthesis and influence host reproduction. Our results indicate that the evolutionary loss of a functional gut correlates with a reduction in the microbiome and the association with an endosymbiont. Symbiotic transitions can therefore accompany life history transitions in the evolution of developmental strategies

Chapter 5 Priority Species to Support the Functional Integrity of Coral Reefs

Ecosystem-based management on coral reefs has historically focused on biodiversity conservation through the establishment of marine reserves, but it is increasingly recognised that a subset of species can be key to the maintenance of ecosystem processes and functioning. Specific provisions for these key taxa are essential to biodiversity conservation and resilience-based adaptive management. While a wealth of literature addresses ecosystem functioning on coral reefs, available information covers only a subset of specific taxa, ecological processes and environmental stressors. What is lacking is a comparative assessment across the diverse range of coral reef species to synthesise available knowledge to inform science and management. Here we employed expert elicitation coupled with a literature review to generate the first comprehensive assessment of 70 taxonomically diverse and functionally distinct coral reef species from microbes to top predators to summarise reef functioning. Although our synthesis is largely through the lens of the Great Barrier Reef, Australia, a particularly data-rich system, it is relevant to coral reefs in general. We use this assessment to evaluate which taxa drive processes that maintain a healthy reef, and whether or not management of these taxa is considered a priority (i.e. are they vulnerable?) or is feasible (i.e. can they be managed?). Scientific certainty was scored to weight our recommendations, particularly when certainty was low. We use five case studies to highlight critical gaps in knowledge that limit our understanding of ecosystem functioning. To inform the development of novel management strategies and research objectives, we identify taxa that support positive interactions and enhance ecosystem performance, including those where these roles are currently underappreciated. We conclude that current initiatives effectively capture many priority taxa, but that there is significant room to increase opportunities for underappreciated taxa in both science and management to maximally safeguard coral reef functioning

Inoculant production and quality control

The manufacture of high-quality inoculants increases the potential for maximum nitrogen fixation in inoculated legumes (see Chapters 1, 5, 8 and 10). If legume inoculation is successful, the inoculant strain will colonise the rhizosphere and compete with resident soil rhizobia for nodulation sites on the host legume root. Researchers too must prepare high quality inoculants for experimental field trials, similar to those described in Chapter 8. Large-scale production of high-quality legume inoculants is complex. It requires expert skills in aseptic handling of rhizobia, an understanding of the conditions in which rhizobia grow and survive, research and development to find suitable carrier materials for inoculant formulation, and a program of quality control and quality assurance to maintain the manufacturing process and product integrity. There are several other publications describing methods involved in legume inoculant quality control; comprehensive texts have been published by Vincent (1970) and Somasegaran and Hoben (1994)

Biological nitrogen fixation in non-leguminous field crops: Facilitating the evolution of an effective association between 'Azospirillum' and wheat

Recent advances towards achieving significant nitrogen fixation by diazotrophs in symbioses with cereals are reviewed, referring to the literature on the evolution of effective symbioses involving rhizobia and 'Frankia' as microsymbionts. Data indicating that strains of 'Acetobacter' and 'Herbaspirillum' colonizing specific cultivars of sugarcane as endophytes make a significant contribution to the nitrogen economy of this crop improves the prospects that similar associative systems may be developed for other gramineous species such as rice and wheat. By contrast, the transfer of nodulation genes similar to those in legumes or 'Parasponia' to achieve nodulation in crops like rice and wheat is considered to be a more ambitious and distant goal. Progress in developing an effective associative system for cereals has been materially assisted by the development of genetic tools based on the application of 'lacZ' and 'gusA' fusions with the promoters of genes associated with nitrogen fixation. These reporter genes have provided clear evidence that 'crack-entry' at the points of emergence of lateral roots or of 2,4-D induced 'para'-nodules is the most significant route of endophytic colonization. Furthermore, using the laboratory model of 'para'-nodulated wheat, there is now evidence that the ability of azospirilla and other nitrogen fixing bacteria to colonize extensively as endophytes can be genetically controlled. The most successful strain of 'Azospirillum brasilense' (Sp7-S) for endophytic colonization and nitrogen fixation in wheat seedlings is a mutant with reduced exopolysaccharide production. Most other strains of azospirilla do not colonize as endophytes and it is concluded that though these are poorly adapted to providing nitrogen for the host plant, they are well adapted for survival and persistence in soil. A research program combining the study of endophytic colonization by azospirilla with an examination of the factors controlling the effectiveness of association (oxygen tolerance and nitrogen transfer) is now being pursued. It is proposed that a process of facilitated evolution of 'para'-nodulated wheat involving the stepwise genetic improvement of both the prospective microsymbionts and the cereal host will eventually lead to effective nitrogen-fixing associations. In the attempt to achieve this goal, continued study of the endophytes occurring naturally in sugar cane and other grasses (e.g. 'Azoarcus' sp.) should be of assistance

Isolation and growth of rhizobia

This chapter describes basic techniques for the isolation and growth of rhizobia, some of which have been used for more than a century. While these techniques re¬tain their importance, the success of current and future rhizobiology studies and enterprises will depend on the training, skills and techniques described in this chapter. A note of caution: nodules (particularly those collected from the field) are not always occupied by a single rhizobial isolate nor even by a single micro-or¬ganism. Nodules of pea and lupin, for example, have been described as containing both the nitrogen-fixing symbiont and associative organisms such as Micromono¬spora (Trujillo et al. 2010). Hence, we must be prepared for a range of organisms to appear on growth plates during isolation procedures. Recognition of rhizobia when growing on a solid medium is an essential skill in rhizobiology

Root inoculation of green bell pepper ( Capsicum annum

Background: Consumption of bell peppers is recommended because of their bioactive compound content and their positive effects on health. Growth-promoting rhizobacteria are popular because of their ability to promote plant growth by improving the fixation of nutrients or by inducing a systemic response. Green bell pepper (Capsicum annum) roots were inoculated with an autochthonous strain of Bacillus amyloliquefaciens, at different stages of development: T1, inoculation in the seedbed before transplant; T2, inoculation at and after transplant; T3, inoculation in the seedbed, at and after transplant. Bell pepper plants without inoculation were considered as control. Physicochemical composition and antioxidant activity of the fruits were measured to select the best treatment. Results: T1 increased crude proteins, fat, Ca, Fe, vitamin C, total phenolic content, antioxidant capacity by DPPH and by ORAC. On the other hand, T1 decreased reducing sugars, K and Cu content. No significant differences for total carbohydrates, ash and photosynthetic pigments were found. Conclusion: Inoculated green bell peppers have enhanced its functional value and could be considered as an important source of bioactive compounds with elevated antioxidant activity. © 2019 Society of Chemical Industry.Fil: Cisternas Jamet, Jonathan. Universidad de La Serena; ChileFil: Salvatierra Martínez, Ricardo. Comisión Nacional de Investigación Científica y Tecnológica. Centro de Investigación Regional. Centro de Estudios en Zonas Áridas; ChileFil: Vega Gálvez, Antonio. Universidad de La Serena; ChileFil: Uribe, Elsa. Universidad de La Serena; ChileFil: Goñi, María Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Departamento de Ingeniería Química. Grupo de Investigación en Ingeniería en Alimentos; ArgentinaFil: Stoll, Alexandra. Comisión Nacional de Investigación Científica y Tecnológica. Centro de Investigación Regional. Centro de Estudios en Zonas Áridas; Chil

Critical parameters in facilitating the evolution of N₂-fixing symbiosis between diazotrophs and cereals

The key features of an experimental model for achieving significant biological N₂ fixation by associations between 'Azospirillum' and cereals are suggested to include adequate colonization, endophytic in nature to ensure both access to carbon substrates and suitable microaerobic oxygen conditions, and a means of ensuring adequate transfer of newly fixed nitrogen to the host plant. In our research program, we have exploited the property of synthetic plant hormones such as 2,4-dichlorophenoxyacetic acid to enhance access of azospirilla to protected niches such as the base of modified lateral roots ('para'-nodules) and channels between cortical cells. This approach has demonstrated the possibility of achieving such colonization. By using 'nifH-lacZ' fusions of 'A. brasilense' strains, we have been able to show a relationship between 'nifH' expression, oxygen pressure, and the magnitude of acetylene reduction rates in such associations. In addition, the significance of the 'flcA' (controlling flocculation) gene in effective colonization by regulating the expression of exopolysaccharides and the conversion of vegetative cells of azospirilla to cysts has been shown by the use of 'flcA'-mutants

Prospects for facilitated evolution of effective N₂-fixing associations with cereals: comparative performance of 'Azospirillum brasilense' Sp7-S with various free-living diazotrophs in para-nodulated wheat

By analogy with N₂-fixing sugar cane, achieving an effective N₂-fixing association between cereals and diazotrophs may require an endophytic mode of colonization, allowing better protection from oxygen and improved access to carbon substrates. Using nifA-lacZ as a genetic marker on a broad host-range plasmid pVK100, inserted into a range of free-living and associative N₂-fixing organisms, it has been possible to define their mode of colonization of the roots of wheat seedlings in addition to measuring the associated rates of nitrogen fixation. Of these bacterial strains, only 'Herbaspirillum seropedicae', 'Azorhizobium caulinodans' and a mutant strain of 'Azospirillum brasilense' (Sp7-S) displayed significant endophytic colonization of 2,4-D-treated wheat seedlings. By contrast, 'Acetobacter diazotrophicus', 'Azotobacter vinelandii', 'Derxia gummosa' and other 'Azospirillum' strains colonized at the rhizoplane. This chapter discusses these modes of colonization and the probable need for a stepwise process of facilitated evolution of selected diazatrophs and plants before an effective association can be achieved