U.S., Czech researchers uncover good, bad properties in common gut microbes
Bifidobacterium are with us at birth and play an important role in human health, yet much is still unknown about how they work.
Bifidobacterium are with us at birth and play an important role in human health, yet much is still unknown about how they work.
A study of transport proteins of the bifidobacterium species and their beneficial and pathogenic effects appears in Microbial Physiology, Sept. 23. The authors, Hassan Zafar and Milton Saier Jr., note the present work continues their ongoing investigations into all the major gut microbes.
Zafar is with the Department of Molecular Biology at the University of California San Diego, and Saier is with the Central European Institute of Technology, Masaryk University, Czech Republic.
The researchers analyze the transport proteins (transportomes) of nine bifidobacterial species: B. adolescentis, B. animalis, B. bifidum, B. breve, B. catenulatum, B. dentium, B. longum subsp. infantis, B. longum subsp. longum, and B. pseudocatenulatum.
Transport proteins are responsible for moving materials within an organism. The types of molecules that bacteria can transport can play a role in making them either helpful or harmful (pathogenic). Surprisingly the researchers found that many of the bacteria have pore forming toxins and drug exporters (things which usually play a role in pathogenesis).
All these species are known to have beneficial effects on health as probiotics. Yet, the authors found, all the species also have pathogenic potential. They note that B. bifidum, which is a "strictly probiotic" species, "contains fewer such transporters, thus indicative of limited interactions with host cells and other gut microbial counterparts."
The study emphasizes how transport proteins "assist these bacterial species in their probiotic and/or pathogenic roles."
The good and the bad
Bifidobacterium is "well represented" in human gut microbiomes, the researchers write, "particularly those of breast-fed infants."
"The increase in bifidobacterial populations in infants correlates with the suppression of growth of pathogenic microbes in the gut," they say. "Thus, an increase in the population of the members of this genus is considered to provide health benefits during early development of the human gut, and possibly throughout life."
In addition to the gut, bifidobacterial species are also found in the mouth and the genitourinary tract.
The bifidobacterial species also release bacteriocins, which are microbial peptides that act as antibiotics with anti-cancer effects. There is also evidence of bifidobacterial antifungal effects.
As for the pathogenic side of bifidobacterial species, the researchers analyze in detail the transportome function as pore-forming toxins and drug exporters. Pore formation is a measure of pathogenic virulence in bacteria. Drug exporting refers to the mechanism by which the transport proteins promote resistance to therapeutic drugs.
Findings
The study looked at the genome size of each bifidobacterial species, the total number of proteins found in each, the percentage of proteins that were transportomes, and where the species were located.
The researchers identified subclasses of transport proteins and their occurrence in each of the nine species of bifidobacteria. These included subclasses of pore-forming toxins, holins ("small trans-membrane `hole-forming' proteins), and various specialized transporters such as ATP-hydrolysis-driven transporters.
Because of their previous studies of other gut bacteria, they could compare the bifidobacteria properties with those of E. coli strains and Salmonella. One interesting finding is that the bifidobacterial species have a much higher percentage range of primary pyrophosphate hydrolysis-driven transport proteins than those found in E. coli and Salmonella.
The researchers suggest that the higher numbers of this type of transport protein may give the organism a "metabolic edge over their microbial neighbors for nutrient acquisition (higher affinities and greater concentration gradient generation) and, consequently, exhibit advantages for colonization within the largely anaerobic shared ecological niches of the human gut."
Future research
The researchers suggest that further studies using genetic manipulation could shed light on the role of bifidobacterium toxins and, perhaps, lead to the development of bifidobacterium strains that don't have as many toxins. Further work on the drug exporting role of transportomes also may help understanding of antibacterial resistance.
Summing up their work, the authors note that the trillions of microbes in the gut are "in constant contact with their host tissues and microbial neighbors."
"In such competitive and cooperative environments, only those species will survive and flourish that have efficient transportomes appropriate for their specific niches," they write. "This study, in conjunction with our previous genome projects on gut bacteria, discloses valuable insight about the roles of the transportomes in the context of the gut microbiome. The findings of this study will help genetic engineers to generate altered species of Bifidobacterium with increased probiotic attributes and decreased pathogenic potential."
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Hassan Zafar and Milton Saier, Jr. Comparative analyses of the transport proteins encoded within the genomes of nine bifidobacterium species. Microbial Physiology, Sept. 23, 2021.
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