Background
When we think of predators in nature, bacteria is not the first thing that comes to mind. Yet, Bdellovibrio bacteriovorus, the focus of a recent (2018) study by Im et al., is a predatory bacteria that preys on gram-negative bacteria, which have an outer membrane, by breaking down their biofilms and invading the bacteria to consume them. B. bacteriovorus does this by entering the bacteria though the periplasm. However, it does not solely prey upon these bacteria for food, it also grows and divides within its prey.
Hansol Im et al’s study, “Bdellovibrio bacteriovorus HD100, a predator of Gram-negative bacteria, benefits energetically from Staphylococcus aureus biofilms without predation” considers the interactions between this predatory, gram-negative bacteria and S. aureus, a gram-positive bacteria. The researchers paid particular attention to the benefits that B. bacteriovorus is able to obtain from the biofilm without killing this bacteria.
Biofilms, which are a primary focus of this research, are very important to bacteria. Biofilms are colonies of bacteria whose secretions allow them to bind to each other and the surface of their environment, liquid or solid. This provides several benefits to the bacteria including communication methods and antibiotic resistance.
Diagram from Laloux’s research on the life cycle of B. bacteriovorus, using E. coli as an example.
The diagram above shows the life cycle of B. bacteriovorus. The bacteria invade the prey, consume it, and then grow and divide. While this is not a specific example from the study central to this blog post, and it depicts E. coli rather than S. aureus, it is an excellent diagram of the overall lifecycle.
Artistic rendering of the B. bacteriovorus, created by Donald Bliss and Sriram Subramaniam, published by NIH.
Methods
As part of their research, these scientists considered a couple different aspects of the interactions between B. bacteriovorus and S. aureus and set up their experiments accordingly. One of the first things they considered was the ability of B. bacteriovorus to break down the biofilm of the gram-positive bacteria. In order to test this, the researchers set up their experiment using well plates and allowed S. aureus biofilms time to grow before introducing B. bacteriovorus to the plate.
Once B. bacteriovorus was added, the plates were left for 24 hours. In order to have a point of comparison, the researchers also set up an experiment in which S. enterica, a known prey of B. bacteriovorus, was used in place of S. aureus. This would provide the researchers with a point of comparison and the results were quite interesting. After allowing the plates to sit for 24 hours, the researchers discovered that B. bacteriovorus was able to break down the biofilms of S. aureus almost as effectively as it breaks down the biofilms of its prey. The researchers hypothesized that this was likely the result of the proteases, an enzyme that breaks down proteins into amino acids, which are released by B. bacteriovorus to help break down biofilms. The results of this experiment are shown in Figure 1C.
In order to be thorough, a follow up experiment was conducted with the purpose of determining if proteases were causing the breaking down of the biofilms. In this experiment, the cells of B. bacteriovorus were washed in order to remove any extracellular proteases and then introduced to the S. aureus biofilms. The results showed that while the biofilms were broken down, they did not break down to the same extent, which we can see in Figure 1F.
Figure Analysis
Figure 1C showing a control group and two experimental groups. The experimental group, 10% HBD culture, consisted of HEPES control buffer and B. bacteriovorus.
In Figure 1C, we can see that B. bacteriovorus was just as effective at breaking down the biofilms of its prey, S. enterica, as it was at breaking down the biofilms of a bacteria that it does not prey upon. This is extremely interesting and we can see that, compared to the control groups in which the biofilm level is at 100%, there is minimal difference in the remaining biofilm after 24 hours of exposure to B. bacteriovorus.
The remaining biofilm of S. enterica, which B. bacteriovorus preys on, was approximately 40% while the remaining biofilm of S. aureus, a gram-positive bacteria not preyed upon by B. bacteriovorus, had just under 40% of its biofilm remaining after 24 hours.
Figure 1F from the study showing biofilm levels from washed and unwashed B. bacteriovorus cells in the secondary experiment.
In Figure 1F, we can see the results of the secondary experiment. When the washed B. bacteriovorus cells were added to the plate with the S. aureus biofilm, the biofilm was broken down, however, there was more remaining biofilm after 24 hours. In this experiment, there was about 50% remaining biofilm, rather than the 40% depicted in Figure 1C. This indicates that the proteases are important in breaking down the biofilms of gram-positive bacteria such as S. aureus.
There is one more noteworthy and interesting result from these experiments. Not only does this predator cause the biofilms to break down, B. bacteriovorus also uses the amino acids from these broken down biofilms to its benefit. It uses them as a source of energy. The researchers measured ATP levels in B. bacteriovorus and found that they were significantly higher after the bacteria was exposed to the biofilms. Without killing these gram-positive bacteria, B. bacteriovorus is able to benefit from them.
Conclusions, Implications and Future Research
In conclusion, this research demonstrated that B. bacteriovorus is able to not only break down the biofilms of bacteria that it preys upon but other types of bacteria as well. There was almost no difference in the ability of B. bacteriovorus to break down the biofilms of bacteria that it preys upon and those of bacteria that it does not prey upon. This research also demonstrated that B. bacteriovorus is able to gain energy through these interactions which is beneficial.
Furthermore, since very little research has been done on the interactions between B. bacteriovorus and gram-positive bacteria, Im et al. point out that further studies are needed to more fully understand how this bacteria works and interacts with other types of bacteria.
Finally, since it is known that B. bacteriovorus preys upon many different human pathogens that are gram-negative, this research may even have implications for other aspects of human medicine and pathogens that are gram-positive. This would be an excellent focus of future research.
About the Author
Daniela Fraser '23 is a senior at Mount Holyoke College, majoring in Anthropology with a minor in Biology. She has been on the Varsity Equestrian Team since freshman year and will be attending nursing school after graduation.
No comments:
Post a Comment