EFFECT OF THE MICROBIAL COMMUNITY COMPOSITION ON PLANT-INSECT INTERACTIONS

EFFECT OF THE MICROBIAL COMMUNITY COMPOSITION ON PLANT-INSECT INTERACTIONS

Miquel Alsina, Berta Casal, Irene Costa i Aniol Ventolà

INTRODUCTION

It exists a big number of microorganism interactions in the ecosystems, which can be beneficial, antagonistic, with physic and biochemical competence or regulated by abiotic and biotic factors.  These interactions have a direct influence in the plant-insect dynamism and they can modify the composition of the microbial communities. That’s why in this article we want to demonstrate the importance between microbial communities and their coexistence with plants and insects, and what’s the effect in the equilibrium in a general ecosystem. Therefore, the bacterial communities can occupy different functional spaces, transforming the atmosphere with their activity and modifying the natural selection pressure, favouring the presence of different organisms. 

INTERACTION PLANT-INSECT AND MOCROBIAL COMMUNITY ECOLOGY

There are different interactions between plants, insects and microbial communities. That interactions can have a negative action to the plant (herbivore or parasite), even so they can be positive as in the mutualism organisms or neutral. When we study the plants, we can remark that most of them have symbiosis relationships with mycorrhiza fungi, so we can observe that the presence of microorganisms in a determinate ground can be inhibited or favoured and consequently they are going to interfere directly to the growth and general state of the plant. That is one of the important reasons why we must comment the importance of the presence or absence of microorganisms in the vegetal communities.

The type of relationship in the ecosystem plant, insect and microorganism is defined by two of them; positive, when we talk about symbiosis, and negative, when the parasitism is the cause. These relationships are very specific and concrete, therefore a species totally depend of the presence of the other one to perpetuate. This term is known as coevolution. For example, termites have a coevolution line joint with the microorganisms in charge of the lysis of lignin.

Generally, microbial communities are inserted in complex trophic networks where they could exert their influence and be influenced at different levels (Pieterse and Dicke, 2007).

Figure 1: Representative examples of how microbial can influence complex trophic network.

MECHANISMS BY WHICH THESE MICROBES INTERFERE WITH PLANT-INSECT INTERACTIONS

Interferences with the plant’s defence signs:

These interferences are born from the associations of the roots of the plant with the bacterial communities of the ground, which can be beneficial or pathogens.  It is known that the rhizobacteria cause the induced systematic resistance against pathogens and promotes the growth of the plant. Therefore, the bacterial communities influence the plant and insect interactions, altering the signalling pathways for the defence of the plant, so they can give protection versus chewing insects, or they can weaken the defence system against insects that feed on sap.

Figure 2: example of the ISR (induced systematic resistance) caused by soil bacteria associated to the roots of the plant. Font: https://link.springer.com/article/10.1007/s00425-016-2543-1

Production of toxins

Many of the microbes associated to plants can interfere directly to the insects that predate them, interfering in the physic conditions of these because they produce toxins. For example, the bacteria that use the pores of access to the hemocele, which cause septicaemia and the consequent death of arthropods, this effect is also accelerated because these defenders’ bacteria produce additional toxins which interfere in the immune system and they promote infections.

INSECTS

Regarding to insects, recent studies have shown the existence of many microorganisms which were unknown. Most of them are faculty symbionts, and some of them live in the insects’ intestinal tract as intestinal partners.  Even though these microorganisms aren’t essentials for the reproduction or the host survival, they can significantly affect in the ecological dynamic of these species because they can modify the physiology, the answers that they can give to de defensive systems of the plant and the protection mechanisms against natural enemies.

The proteobacteria, specifically enterobacteria are the most common associates in herbivores insects. This group includes many types if symbionts with different functions like for example the Bunchnera to the thugs, Acetobacter and Lactobacilius to the Drosophila, the Firmicutes and bacteriodetes to the insects which they feed on cellulose… These bacteria are lodged in different parts of the host, in the case of forced symbionts are placed in structures of insects destined for this purpose and called bacteriocist. The collaborators in the nutritional functions are accommodate in the intestine, but they can also be in the insects’ reproductive organs influencing the proportion of sexes in a population. But maybe, the more important fact to determine the place where the microorganisms are placed, it’s that it can influence in the spread of diseases by both insects and plants. This is the case of the communities that are in the salivary glands of herbivore insects, causing the rapid expansion of pathogens. A good example of this fact is the flavescence dorée, caused by Candidatus Phytoplasma vitis, propagated by a grasshopper.

 PLANTS

Unlike the insects, the plants have a bigger range of microbial pathogens, with commensalism, parasitism and mutualism relationships. In this way, the relation of plant’s specialization and it’s ubication allow to classify the big number of microorganisms which have an influence in vegetal process in two groups.

With exuberant wealth and a large role diversification, we found the bacteria which colonize the subterranean tissues or the part of the rhizosphere. A good example are the rizobis bacteria, a nitrogen fixers that allow the metabolic use of it by the host. On the other hand, we found the bacteria who develop in the phyllosphere, or in the postral part of the plant. Although having a great wealth of bacteria which influence the host, the most known are those that affect the stem and the leaves, like the proteobacteria. However, the great diversity of bacteria that act on the rest of the plant located in the phyllosphere are unknown.

ANTROPHOLOGYCAL UTILITIES 

The relationships mentioned previously have an important role in agriculture and pest control, that can favour the sector and improve the results. Currently, there are some actions in the control of the “Eruga del Boix” (Cydalima Perspectalis) with a bacillus named Bacillus thuringiensis kurstaki. 

There are microbial that they are associated to the molecular patrons of plants, and they can be used to control any pathogen, for instance Bascillus miycoide, a microorganism who modify the plant behaviour allowing it to generate antagonistic proteins, preventing the optimal conditions for the pathogen who infects the plant. Moreover, the Lysobacter Enzymogenes that induce foliar peroxidase.

CONCLUSIONS

In the last years, the technologies they have made us able to observe and study a big variety of bacteria communities which they couldn’t be cultivated. These data have allowed us the wide range of relationships between microbes, insects and plants. From momentary interactions to long term relationships. Currently it is clearly demonstrated that the acquisition of microbial communities has strong ecological and evolutionary impacts for the host. This fact is shown in a variety of relationships, from strict parasitism to forced mutualism.

It has been demonstrated, therefore, that microbial communities can act as determinants of a population since they are key factors in the regulation of the relationships between plants and insects. 

BIBLIOGRAPHY

• Becerra Z. Rasgos funcionales de comunidades bacterianas asociadas a ecosistemas naturales: Revisión sistemática. 2017.p. 12-214

• Cano, M.A. Interacción microorganismos benéficos. Rev. U.D.C.A Act. & Div. Cient. 2011;14(2): 15 – 31

• Felton GW, Tumlinson JH. Plant–insect dialogs: complex interactions at the plant–insect interface. Dins: Current Opinion in Plant Biology; 2008, Volume 11, Issue 4, p.457-463.

•  Martínez Medina A, Ramírez Romero R. Relaciones dañinas, neutras o positivas: el caso de los microorganismos, los insectos y las plantas. Rev. Elementos. 2011; 84 (18):53.
• Sugio,A. i Dubreuil,G. I Giron,D. i Simon,J. (2014). Plant–insect interactions under bacterial influence: ecological implications and underlying mechanisms. Journal of Experimental Botany, Volume 66,467–478. Recuperat de https://doi.org/10.1093/jxb/eru435