Earthworm Effects without Earthworms: Inoculation of Raw Organic Matter with Worm-Worked Substrates Alters Microbial Community Functioning

Earthworms are key organisms in organic matter decomposition because of the interactions they establish with soil microorganisms. They enhance decomposition rates through the joint action of direct effects (i.e. effects due to direct earthworm activity such as digestion, burrowing, etc) and indirect effects (i.e. effects derived from earthworm activities such as cast ageing). Here we test whether indirect earthworm effects affect microbial community functioning in the substrate, as when earthworms are present (i. e., direct effects).To address these questions we inoculated fresh organic matter (pig manure) with worm-worked substrates (vermicompost) produced by three different earthworm species. Two doses of each vermicompost were used (2.5 and 10%). We hypothesized that the presence of worm-worked material in the fresh organic matter will result in an inoculum of different microorganisms and nutrients. This inoculum should interact with microbial communities in fresh organic matter, thus promoting modifications similar to those found when earthworms are present. Inoculation of worm-worked substrates provoked significant increases in microbial biomass and enzyme activities (β-glucosidase, cellulase, phosphatase and protease). These indirect effects were similar to, although lower than, those obtained in pig manure with earthworms (direct and indirect earthworm effects). In general, the effects were not dose-dependent, suggesting the existence of a threshold at which they were triggered.Our data reveal that the relationships between earthworms and microorganisms are far from being understood, and suggest the existence of several positive feedbacks during earthworm activity as a result of the interactions between direct and indirect effects, since their combination produces stronger modifications to microbial biomass and enzyme activity

Las lombrices de tierra y los microorganismos: desentrañando la caja negra del vermicompostaje

Earthworms affect microorganisms both directly (enhancing or reducing their populations by digesting the substrate) and indirectly (derived effects, such as the production of castings in the fresh substrate). To separate these effects we performed three experiments. In the first, we studied the whole process of vermicomposting, using Eisenia fetida and pig manure in all stage, from fresh residue to vermicompost. In the second experiment, we inoculated pig manure with vermicompost to study the indirect effects of earthworms on decomposition. In the third, we analysed the fresh casts to study direct effects of earthworms on microorganisms. Earthworms promoted significant increases in both microbial biomass and activity when they were present in the layers, and in aged layers where earthworm were absent, microbial stabilization occurred, with reduced biomass and activity. Inoculation with vermicompost produced the same increases in microbial biomass and activity, and although these increments were not as high as in presence of earthworms, indirect effects were strong enough to alter the dynamics of organic matter decomposition. In castings, microbial biomass increased, while activity decreased, suggesting the presence of other factors involved in earthworm-microbial relationships, beyond simple digestion and inoculation effects.Los efectos de las lombrices sobre los microorganismos son directos (incremento o descenso de sus poblaciones al digerir el sustrato) e indirectos (efectos derivados de los directos, como la aparición de las deyecciones en el sustrato fresco). Para delimitar y poder estudiar estos efectos por separado realizamos tres experimentos. En el primero estudiamos el proceso de vermicompostaje con Eisenia fetida de purín de cerdo en todas sus etapas, desde el residuo fresco hasta obtener el vermicompost. En el segundo inoculamos vermicompost en purín de cerdo fresco para estudiar los efectos indirectos de las lombrices de tierra en la degradación del purín. En el tercero analizamos las deyecciones frescas para estudiar los efectos directos de las lombrices de tierra en los microorganismos. Las lombrices de tierra dividieron el proceso de vermicompostaje en dos etapas, una inicial, asociada a su presencia en el residuo, caracterizada por el aumento de la biomasa y actividad de los microorganismos; y la etapa final, asociada a la ausencia de las lombrices de tierra, caracterizada por la disminución de la biomasa y actividad microbiana. El inóculo de vermicompost en purín de cerdo produjo el mismo efecto (aumento inicial y posterior descenso) aunque de menor entidad, probando la existencia de efectos indirectos de las lombrices de tierra en el vermicompostaje. En las deyecciones de las lombrices aumentó la biomasa microbiana y la actividad disminuyó, lo que sugiere la existencia de factores implicados en las relaciones lombrices-microorganismos más allá de la simple digestión y los procesos asociados a la inoculación de las deyecciones en el sustrato

Diversity, structure and sources of bacterial communities in earthworm cocoons

Animals start interactions with the bacteria that will constitute their microbiomes at embryonic stage. After mating, earthworms produce cocoons externally which will be colonized with bacteria from their parents and the environment. Due to the key role bacterial symbionts play on earthworm fitness, it is important to study bacterial colonization during cocoon formation. Here we describe the cocoon microbiome of the earthworms Eisenia andrei and E. fetida, which included 275 and 176 bacterial species, respectively. They were dominated by three vertically-transmitted symbionts, Microbacteriaceae, Verminephrobacter and Ca. Nephrothrix, which accounted for 88% and 66% of the sequences respectively. Verminephrobacter and Ca. Nephrothrix showed a high rate of sequence variation, suggesting that they could be biparentally acquired during mating. The other bacterial species inhabiting the cocoons came from the bedding, where they accounted for a small fraction of the diversity (27% and 7% of bacterial species for E. andrei and E. fetida bedding). Hence, earthworm cocoon microbiome includes a large fraction of the vertically-transmitted symbionts and a minor fraction, but more diverse, horizontally and non-randomly acquired from the environment. These data suggest that horizontally-transmitted bacteria to cocoons may play an important role in the adaptation of earthworms to new environments or diets.Ministerio de Economía y Competitividad | Ref. CTM2013-42540-RMinisterio de Economía y Competitividad | Ref. AGL2017-86813-RXunta de Galicia | Ref. ED431B-2016/04

Analysis of the stress state of a halved and tabled traditional timber scarf joint with the Finite Element Method

The purpose of this study is to determine the stress distribution in the carpentry joint of halved and tabled scarf joint with the finite element method (FEM) and its comparison with the values obtained using the theory of Strength of Materials. The stress concentration areas where analyzed and the influence of mesh refinement was studied on the results in order to determine the mesh size that provides the stress values more consistent with the theory. In areas where stress concentration is lower, different mesh sizes show similar stress values. In areas where stress concentration occurs, the same values increase considerably with the refinement of the mesh. The results show a central symmetry of the isobar lines distribution where the centre of symmetry corresponds to the geometric centre of the joint. Comparison of normal stress levels obtained by the FEM and the classical theory shows small differences, except at points of stress concentration

Microbial biomass governs enzyme activity decay during aging of worm-worked substrates through vermicomposting,”

ABSTRACT Vermicomposting is the biooxidation and stabilization of organic matter involving the joint action of earthworms and microorganisms, thereby turning wastes into a valuable soil amendment called vermicompost. Studies have focused on the changes in the type of substrates available before and after vermicomposting, but little is known on how these changes take place, especially those changes related with maturation of vermicompost. This study investigated the effects of aging on the microbiological properties of fresh vermicompost produced from pig slurry by analyzing the substrate after the earthworms had left it. We incubated 16-wk-old vermicompost and sampled it after 15, 30, 45, and 60 d analyzing microbial biomass and activity (assessed as microbial biomass N and basal respiration respectively) and four enzymatic activities (b-glucosidase, cellulase, protease, and alkaline phosphatase). Aging of vermicompost resulted in decreases of microbial biomass and activity. Three of the four enzymes analyzed also showed decrease. An initial increase followed by a rapid decrease in alkaline phosphatase was also recorded. High and significant correlations between microbial biomass and b-glucosidase (r 5 0.62, P , 0.001), cellulase (r 5 0.56, P , 0.01), and protease (r 5 0.82, P , 0.001) were found. Results suggest that there may be two steps involved in the aging dynamics of vermicompost with regards to extracellular enzyme activity; the first step was characterized by a decrease in microbial populations, which resulted in a reduction in the synthesis of new enzymes. The second step was the degradation of the pool of remaining enzymes. This dynamic does not seem to be affected by earthworms because similar decaying patterns of microbial biomass and activity were found in substrate where earthworms were present

Epigeic earthworms exert a bottleneck effect on microbial communities through gut associated processes

Background: Earthworms play a critical role in organic matter decomposition because of the interactions they establish with microorganisms. The ingestion, digestion, assimilation of organic material in the gut and then casting is the first step in earthworm-microorganism interactions. The current knowledge of these direct effects is still limited for epigeic earthworm species, mainly those living in man-made environments. Here we tested whether and to what extent the earthworm Eisenia andrei is capable of altering the microbiological properties of fresh organic matter through gut associated processes; and if these direct effects are related to the earthworm diet. Methodology: To address these questions we determined the microbial community structure (phospholipid fatty acid profiles) and microbial activity (fluorescein diacetate hydrolysis) in the earthworm casts derived from three types of animal manure (cow, horse and pig manure), which differed in microbial composition. Principal Findings: The passage of the organic material through the gut of E. andrei reduced the total microbial biomass irrespective of the type of manure, and resulted in a decrease in bacterial biomass in all the manures; whilst leaving the fungi unaffected in the egested materials. However, unlike the microbial biomass, no such reduction was detected in the total microbial activity of cast samples derived from the pig manure. Moreover, no differences were found between cast samples derived from the different types of manure with regards to microbial community structure, which provides strong evidence for a bottleneck effect of worm digestion on microbial populations of the original material consumed. Conclusions/Significance: Our data reveal that earthworm gut is a major shaper of microbial communities, thereby favouring the existence of a reduced but more active microbial population in the egested materials, which is of great importance to understand how biotic interactions within the decomposer food web influence on nutrient cycling.Ministerio de Ciencia e Innovación | Ref. CTM2009-0847

Glucocorticoids modulate gastrointestinal microbiome in a wild bird.

It has recently been hypothesized that stress exposure (e.g. via glucocorticoid secretion) may dysregulate the bacterial gut microbiome, a crucial \u27organ\u27 in animal health. However, whether stress exposure (e.g. via glucocorticoid secretion) affects the bacterial gut microbiome of natural populations is unknown. We have experimentally altered the basal glucocorticoid level (corticosterone implants) in a wild avian species, the yellow-legged gul

Changes in the composition and function of bacterial communities during vermicomposting may explain beneficial properties of vermicompost

Vermicomposting is the process by which organic waste is broken down through the synergistic actions of earthworms and microbial communities. Although vermicomposting has been shown to effectively reduce organic biomass and generate high-quality fertilizer for plants, little is known about the bacterial communities that are involved in this decomposition process. Since optimization of vermicomposting for commercial use necessitates additional knowledge of the underlying biological processes, this study sought to characterize the bacterial succession involved in the vermicomposting of Scotch broom (Cytisus scoparius), a leguminous shrub that has become invasive around the world with consequences for the dynamics and productivity of the ecosystems they occupy. Scotch broom was processed in a pilot-scale vermireactor for 91 days with the earthworm species Eisenia andrei. Samples were taken at the initiation of vermicomposting, and days 14, 42 and 91, representing both active and mature stages of vermicomposting. Significant changes (P < 0.0001) in the bacterial community composition (richness and evenness) were observed throughout the process. Increases in taxonomic diversity were accompanied by increases in functional diversity of the bacterial community, including metabolic capacity, streptomycin and salicylic acid synthesis, and nitrification. These results highlight the role of bacterial succession during the vermicomposting process and provide evidence of microbial functions that may explain the beneficial effects of vermicompost on soil and plants.Ministerio de Economía y Competitividad | Ref. CTM2013-42540-RMinisterio de Economía y Competitividad | Ref. AGL2017-86813-RXunta de Galicia | Ref. ED431B 2016/043Xunta de Galicia | Ref. ED431F 2018/05Ministério da Educação e Ciência | Ref. IF/00764/2013Ministerio de Economía y Competitividad | Ref. RYC-2016-2123