For the first time, a team of researchers, including Associate Professor Dr. Toshiki Furuya from the Department of Applied Biological Science, Tokyo University of Science, Japan, have isolated microorganisms from passion fruit Passiflora edulis seeds.
According to a report from Phys.org, similar to popular human gut-resident bacteria, the inside of a plant can also serve as home to microbes.
Residing inside stems, fruits, leaves, roots, and even seeds, as well as developing a synergistic relationship with their host, these so-called "endophytic" bacteria don't need to necessarily harm the plant. Rather, they are frequently useful in germination, growth, and defense.
Nevertheless, the plant interiors contain many secondary metabolites, which, this study indicated, are natural bioactive compounds with strong antimicrobial properties, making such an environment normally antagonistic for microbes.
Mechanisms of the Microbes Inside the Seeds Uncovered
The study, Diversity, and characteristics of culturable endophytic bacteria from Passiflora edulis seeds, published in the MicrobiologyOpen journal, unearths these microbes' surviving mechanisms inside the seeds.
The scientists, in their research, focused, specifically on the seeds of passion fruits. Such seeds are filled with secondary metabolites that have strong antimicrobial properties like piceatannol and resveratrol, the former present at high levels of up to 2.2 mg/g.
Additionally, Dr. Furuya revealed the reasoning behind choosing passion seeds for this particular research. The professor explained, the unusually high concentration of piceatannol, described in the National Library of Medicine, protects the said seeds from bacteria.
He also said they thought it would be interesting to find out if any endophytic microbe could endure such an extreme environment, and if so, how is it possible.
'Endophytes'
According to the Tokyo University of Science, previous reports have it that endophytes with the capability to survive in an environment rich in biologically active compounds had biocatalytic activities associated with these compounds' metabolism.
The fact that these compounds' biocatalytic potential could be oppressed for treatment reasons made researchers more eager to explore the existence of endophytic microbes.
The researchers collected the surface-sterilized seeds of naturally grown passion fruit before cutting or crushing them and putting them on solid agar-based growth media to observe bacterial growth.
While there was no appearance of the microbial colony from the homogenized or cut seeds, remarkably, the seedlings developing the cut seeds, when they got exposed to growth media, gave rise to bacterial colonies.
Then, the researcher carried out sequencing to determine the microbes that appeared on the agar plate where the seeds were placed.
Remarkable Results
The results of the study were remarkable. The researchers isolated 19 strains from the seedlings, which included three formerly unreported variants of microbes from various genera.
Essentially, the scientists hypothesized that inside the seeds, piceatannol exerted bacterial growth-stalling or bacteriostatic, instead of bacteria-killing or bactericidal effect on the residing microorganisms.
The study's co-author Aoi Ishida explained, because of the existence of a high piceatannol concentration, the growth of microbes was stagnated inside the passion fruit seed, although when transmitted to the next-generation seedlings during germination, the microbes were relieved from piceatannol's effect and able to regrow.
Lastly, the researchers found, too, that Brevibacterium sp. PE28-2, one of the microbes, has the capability of "converting resveratrol and piceatannol to their derivatives. This is the first-ever endophyte exposed to such an activity.
Related information about piceatannol is shown on Muscadinex's YouTube video below:
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