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BALOs: voracious good bacteria

BALOs: voracious good bacteria

Bacteria in general have bad connotations: infection and illness to name a few.  But increasing awareness about the benefits of probiotics and natural gut bacteria have taught us that not all bacteria are bad: there are good bacteria too.  Bdellovibrio is in the good bacteria category and recent discoveries about it are spurring more possible uses.

Bdellovibrio bacteriovorus, which was first discovered in 1962, is a gram-negative, aerobic bacteria, which means it has a hard, outer shell that resists the purple stain used to differentiate strains of bacteria.  (For more information on gram negative and gram positive bacteria, check out our post here.)

Bdellovibrio is also a predator.  It is capable of killing and replicating inside over 100 different types of Gram-negative bacteria, including antibiotic-resistant pathogens, giving it a reputation of being a “living antibiotic”.  These prey bacteria include such well-known pathogens as Escherichia coli, Helicobacter pylori, Klebsiella pneumoniae, Pseudomonas, and Salmonella.  This predation behavior has even spawned a new acronym for this type of bacteria: Bdellovibrio and Like Organisms, or BALOs.

According to the following analysis, Bdellovibrio sounds like a voracious alien by attaching to, penetrating, and killing host bacteria, then using them to incubate its own progeny:  “In the wild, B. bacteriovorus uses chemotaxis and a single polar flagellum to hunt groups of prey bacteria. Once in close proximity, B. bacteriovorus collides with individual prey and attaches through an unknown mechanism. Next, B. bacteriovorus invades the prey periplasm (layers around the cell), likely through use of retractable pili, and secretes hydrolytic enzymes that kill the prey within 10 to 20 min of invasion. The predator subsequently remodels host peptidoglycan to form the spherical bdelloplast, where it degrades intracellular contents to fuel its own filamentous growth (liquidates the insides of the prey to fuel replication). Finally, 3 to 4 h following initial contact, the prey cell is lysed (ruptured), and four to six daughter cells emerge from their protected niche (the bdellovibrio babies emerge). Wow!   

Bdellovibrio is found naturally in soil and water, including rivers, lakes, the open ocean, and sewage and wastewater treatment plants (WWTPs).  They are also found in the gills of certain aquatic animals like crabs and oysters, and some mammal intestines.  

Here are some of the proposed uses of BALOs:

  • It could be used in a probiotic to foster healthy human gut microbiota (Higher Prevalence and Abundance of Bdellovibrio bacteriovorus in the Human Gut of Healthy Subjects)

  • It could be an effective treatment for pneumonia in lungs, as both B. bacteriovorus and M. aeruginosavorus could reduce the burden of K. pneumoniae in rat lungs, and B. bacteriovorus treatment is also effective in Yersinia pestis infection of mouse lungs. However, it was found that B. bacteriovorus and M. aeruginosavorus did not reduce pathogenic colonies in the blood, as it did in the lungs of these animals.  (Predatory Bacteria Attenuate Klebsiella pneumoniae Burden in Rat Lungs, Susceptibility of Virulent Yersinia pestis Bacteria to Predator Bacteria in the Lungs of Mice)

  • It could be an effective treatment for Cystic Fibrosis (CF), in which patients have a defective gene that hampers immune response and causes them to be prone to chronic lung infections with an exaggerated inflammatory response.  In CF patients, instead of a diversity of microbiota, only two pathogenic microbes prevail, namely usually the Gram-negative P. aeruginosa and the Gram-positive S. aureus.  Therefore Bdellovibrio was used in a 2014 study to “challenge” these 2 strains in a lab setting, and it was able to reduce the biofilm of both cultures dramatically, even in “flow” settings.  The scientists were even able to photograph (at 30-50 times magnification) Bdellovibrio preying on S. aureus bacteria (see photo below).

Source: Study: Bdellovibrio bacteriovorus directly attacks Pseudomonas aeruginosa and Staphylococcus aureus Cystic fibrosis isolates

  • Prolong food storage:  This study proposes that Bdellovibrio could be used to prolong the shelf life and reduce additives to packaged meat, because it was tested on chicken slices and canned beef and found to reduce colonies of E.Coli by 4.3 log and 2.1 log respectively.  The Bdellovibrio was able to lyse (rupture) all the strains of E. Coli that were tested.  In a separate investigation of Bdellovibrio and E. Coli, this video shows how an actual Bdellovibrio cell multiplies inside an E.Coli cell and destroys it from the inside out.

  • It’s already been recognized as a mode of controlling bacteria in water supply systems.  In 2020 in Varberg, Sweden, a municipal water supply company decided to replace its chlorination system with ultrafiltration, which is an ultrafine mesh filter that prevents microbes from passing through.  Scientists monitored the results closely following discontinuation of chlorine, and some bacteria grew, but then decreased drastically.  By the third month, Bdellovibrio had flourished and harmful bacteria had diminished.  This showed that chlorine had actually suppressed the natural predatory action of bdellovibrio in the biofilm on the inside of drinking water distribution pipes where the good and bad bacteria live. (Predatory bacteria could be used to purify water in the future, study suggests)

So, what’s keeping us from using BALOS as natural antibiotics?  Of course, scientists want to make sure that there will be no harm to humans.  A number of studies using the two BALOs B. bacteriovorus and M. aeruginosavorus “demonstrate their inability to invade mammalian cells, and no apparent pathological effects or signs of cytotoxicity or reduction in cell viability, supporting the proposition that these two BALOs are inherently non-pathogenic to mammals.” (Biotechnological Potential of Bdellovibrio and Like Organisms and Their Secreted Enzymes)  However, scientists are also concerned that prey bacteria could become resistant to it, if it incompletely eradicates the prey. 

In addition, varying amounts of oxygen are necessary for BALOs to work on their prey.  Finally, in complex microbial environments like in our bodies or even in a wastewater treatment plant, it’s not always easy to predict how introduced BALOs will change the biome or which microbes they will prey on, although some do have preferred prey.  Certain chemicals also reduce their effectiveness.

In conclusion, it’s amazing what goes on all around us in microscopic realms.  BALOs could be harnessed in many different ways to improve our health: just the Swedish experiment of removing chlorine showed that it’s not always necessary to use harmful chemicals to kill bad microbes.  Although a lot more research needs to be done, it’s good to know that there are bacteria out there that are on our side! 

Photo by CDC on Unsplash