Unpleasant sexuality and kinship in Bacillus subtilis


Bacillus subtilis A Gram-positive, non-pathogenic, mobile and rod-shaped soil bacterium. Based on comparative genomic analysis In the microwave Members of this species are characterized by a large Genomic diversity. In addition, he is an owner Great ability for gene adaptation and differentiation: B. subtilisIn fact, it may be isolated in different environments – terrestrial and / or aquatic – and may grow in different environments within the fauna. Bacillus subtilis Conducts a very diverse social life, often controlled by so-called events Quorum sensing (QS; Figure 1). Those who are related to “sex” are also observed in the interaction and Exchange of genetic material. Typically, DNA acquisition occurs between closely related strains, but a potential exchange between the two interacting strains has also been observed.

Figure 1 – Bacterial quorum sensing [Fonte: Darcy Cook]

Recent parenting studies have shown that there is a tendency for highly genetically related strains To cooperate, When taking a less related strain Hostile behavior Which takes the form of murder.

However, in the context of the exchange of genetic material a Extended reunion. In particular, bringing capacity into non-related strains is associated with a High absorption of DNA Which, through larger genetic mutations, can result in increased strain adaptation rates.

Therefore, we are talking about a new and special evolutionary process that can be defined. “Pornography but safe sex“It simply came to our notice then DNA exchange Which seems to be useful for a variety of specifications to exclude non-specific and potentially risky DNA from other species.

Overall, what could be the best strategy for creating a new generation?

The simplest solution is made Genetic copy (Clone). This technique allows fast, efficient, and accurate transmission of all genes to the next generation. Another possibility is to be engaged in “any kind of sex”. In this second way genetic material can be mixed / reconnected.

As a result, it’s a great way to have sex New combination of genes Even if it is not always evolutionarily convenient. So what could be the best strategy? The second, related to sexuality, is certainly good because it increases genetic diversity, thus accelerating the evolution and adaptation of the population to altered environmental conditions.

Sexuality in the bacterial world

Assuming that sex exists because it allows new genetic combinations, it creates variety that could be useful for adaptation, for specific reasons. “Bacterial sex“It is not yet clear whether it has evolved to maximize diversity and adaptation, to preserve / repair existing genes, or to obtain DNA as a source of energy (food).

Certainly, bacteria do not engage in sexual reproduction but practice so-called horizontal gene transfer (HGT), Which is generally considered to be a combination of three distinct processes: Transformation, addition and transduction. Law HGT Bacteria represent the dominant force in evolution and it is now generally believed that this is a genetic process closely linked to bacterial adaptation.

In particular, bacterial mutation involves the acquisition of extracellular DNA and integration into the genome. Furthermore, it represents the only process that is fully encoded on the chromosome and so it can evolve into a form.Bacterial sex“(Figure 2).

Figure 2 - Representation of DNA exchange / acquisition process [Credits: Vernikos et al., 2014]
Figure 2 – Representation of DNA exchange / acquisition process [Fonte: Vernikos et al., 2014]

Bacillus subtilis It represents one of those naturally capable species, capable of achieving DNA from the outside. Studies on this organism have shown that the frequency of conversion decreases dramatically with the difference in donor / recipient hierarchy. Therefore, the most frequently absorbed DNA was that of closely related genetically related microorganisms.

The relationship between sexuality and kinship

The phenomenon of DNA exclusion from different microorganisms, not from closely related strains, seems to be similar to what happens when the same or different strains come in contact with each other. In fact, there is a selection / discrimination. In particular, boundaries occur between Less closely related strain (Non-relatives; <99.4% nucleotide identification), when in contact Highly related strain (Relatives; > 99.9% nucleotide identification) shows a swarm pattern involving fusion rather than border band formation (Figure 3).

Figure 3 - Sliding representation of relative and non-relative strains [Credits: Stefanic P. et al., 2021]
Figure 3 – Swarm representation of relative and non-relative strains [Credits: Stefanic P. et al., 2021]

However, despite the similarities, it is still not well understood how kinship can affect horizontal gene transfer and why. Bacillus Practicing these natural inequalities brings variety to the variety.

Analysis and results – developmental improvements associated with promiscuous sex

First, six wild strains were selected B. subtilis And their degree of relativity was calculated using average nucleotide identification. This verification confirms, with the performance of investigations related to the mobility of the flock, that I Highly related strain (99.94-99.97%) Merged with each otherWhen they form stumps Separation band They were less related (98.63-98.74%). Subsequently, it was investigated whether gene transfer through mutation occurs more frequently in pairs that form a separation band than in pairs formed during swarming.

In detail, intact cells were present where the relative strains converged, while non-kin strains had deflated cells associated with cell lysis at the points of separation. A number of previous works have shown that the release of stress and antimicrobials can create capacity in many species of cells due to lysis and consequent DNA secretion.

Even during this analysis, The DNA exchange rate was significantly higherr Pairs of non-relative strains (less related, isolated from each other and containing lysed cells at the point of separation) than pairs of relative strains (interconnected and mixed). The results obtained prove that efficiency is induced at the meeting point of less related non-relative (non-relative) strains and this phenomenon is further strengthened by the stress response.

In addition, as mentioned earlier, mutations can cause the absorption of alleles or genes with beneficial effects on fitness (ecological benefits), resulting in Evolutionary improvement Of the strain involved in the condition Adaptation to new electoral pressures.


Skill development is related to specific pheromones and strains carrying different pheromones appear to be able to hinder each other’s ability to develop in liquid media. The first analysis on this topic, how clear it isSkill up-control In the case of interaction and consequently greater DNA exchange. Furthermore, it has been shown that if reunification between more isolated DNAs is less effective, it is compensated by more efficient absorption of DNA.

We notice a “Bacterial sex“Inter-species that It seems to be much more of a less closely related (non-relative) subject through an up-control process of efficiency. Relying on and mediating kinship inequality is related to the response to stress sigW. By associating capacity with the lysis of neighboring strains, the potential for efficient addition of new alleles and genes is maximized.

In addition, the observed facts support the assumption that DNA is exploited to achieve “genome diversity” instead of “genome repair” or “power acquisition”.. Finally, in some ways B. subtilis Puts a “Pornography but safe sex“Therefore, a kind of DNA exchange between non-closely related strains is useful Improving genetic diversity and environmental adaptability.


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