Biofilms are structured communities of bacteria encased in a self-produced matrix of proteins, extracellular DNA, and polysaccharides. Within these fortresses, pathogens become dramatically more tolerant of antibiotics and immune attack, which is why biofilms complicate the treatment of cystic fibrosis lungs, chronic wounds, medical implants, and catheter-associated infections. Pseudomonas aeruginosa and Staphylococcus aureus are flagship biofilm builders, and both appear on global lists of antibiotic-resistant priority pathogens. An enzyme that can chew through the proteinaceous scaffolding of a biofilm, or disrupt the physiology of the cells inside it, therefore represents a genuinely different therapeutic strategy: rather than killing bacteria outright, it dismantles the architecture that makes them so hard to eradicate.

Serratiopeptidase, sometimes marketed as serrapeptase, is an extracellular protease naturally secreted by Serratia marcescens. It has been used for decades, particularly in Japan and India, as an anti-inflammatory and anti-edema agent, and earlier studies have hinted that it can affect Pseudomonas physiology and biofilm integrity. What has been missing is a rigorous, quantitative characterization of a purified preparation, since crude enzyme mixtures make it impossible to attribute activity to a single protein. The new study addressed this gap with a four-step purification pipeline: precipitation, dialysis, ion-exchange chromatography, and gel filtration chromatography, which together yielded a 15.91-fold increase in purity, sufficient for reliable biochemical and kinetic analysis.

With the purified enzyme in hand, the team determined its molecular weight to be approximately 47 kilodaltons, consistent with the serralysin-like metalloproteases produced by Serratia species. The enzyme displayed broad substrate specificity but showed its highest affinity toward casein, a milk protein commonly used as a benchmark substrate in protease assays. Activity peaked at pH 7 and 40 degrees Celsius, close to physiological conditions, and the enzyme proved remarkably durable under these optima, retaining 89.2 percent and 82.4 percent of its activity, respectively, after 60 minutes of incubation. That combination of neutral pH preference and moderate temperature optimum is exactly what one would want in a therapeutic protein intended to function inside the human body.

The kinetic analysis revealed an enzyme of impressive catalytic power. The Michaelis constant, Km, was 0.034 millimolar, equivalent to 842 micrograms per milliliter, indicating tight substrate binding, while the maximum velocity, Vmax, reached 738.2 units per milliliter. The turnover number, kcat, came in at 55.3 per second, meaning each enzyme molecule processes more than 55 substrate molecules every second. Dividing kcat by Km yields a catalytic efficiency of 1.64 × 10⁶ per molar per second, a figure that places this serratiopeptidase firmly in the category of highly efficient catalysts. For a protein being considered as a drug candidate, such numbers matter: an efficient enzyme can deliver biological effects at lower doses, reducing cost and potential side effects.

Equally informative was the enzyme’s response to chemical modulators. Metal ions including zinc, cobalt, barium, and manganese enhanced activity, as did the non-ionic detergent Tween-20 and the reducing agent beta-mercaptoethanol. Conversely, EDTA, a chelator that strips away metal cofactors, and PMSF, a classic serine protease inhibitor, both shut the enzyme down. This dual sensitivity is diagnostic: it confirms that the SP6 enzyme is a serine-metalloprotease, a hybrid classification consistent with the serralysin family, in which a catalytic serine operates within a metal-dependent active site. Knowing this helps predict how the enzyme will behave in complex biological environments and informs strategies for stabilizing it in formulation.

Perhaps the most clinically relevant findings concern stability and resistance to degradation. The enzyme retained 61.31 percent of its activity after 60 days of storage at 4 degrees Celsius, a refrigerated shelf life that simplifies handling and distribution. More strikingly, it resisted digestion by trypsin and by human serum, with in vitro half-lives of 4 and 5 hours, respectively. Therapeutic proteins typically face rapid destruction by circulating proteases and serum components, so a bacterial enzyme that survives hours in serum-like conditions is unusual and valuable. The authors note that extending the half-lives of therapeutic proteins is a major focus of drug development, and intrinsic resistance to proteolysis gives this enzyme a head start.

The anti-biofilm experiments delivered the study’s headline result. Against Pseudomonas aeruginosa MTCC 2453, serratiopeptidase achieved a maximum biofilm inhibition of 41.65 percent at a concentration of 200 micrograms per milliliter, with an IC50 of 56.92 plus or minus 8 micrograms per milliliter. Against Staphylococcus aureus MTCC 1430, the maximum inhibition was 21.87 percent at the same dose, with an IC50 of 124.6 plus or minus 8 micrograms per milliliter. The authors are careful to define these IC50 values relative to the normalized response range, meaning they correspond to 50 percent of the observed inhibitory effect rather than absolute halving of biofilm mass, a methodological honesty that strengthens the credibility of the data. The stronger effect against Pseudomonas aligns with earlier reports that serratiopeptidase alters the physiology of Pseudomonas isolates from cystic fibrosis patients and disrupts Pseudomonas biofilms and functional amyloids.

What makes these numbers exciting is not that the enzyme obliterates biofilms on its own, but that partial disruption is often enough to restore the vulnerability of embedded bacteria. Anti-biofilm agents are increasingly viewed as adjuncts: by loosening or thinning the matrix, they allow antibiotics and immune cells to reach cells that would otherwise remain sheltered. A 41.65 percent reduction in Pseudomonas biofilm formation, achieved by a single enzyme at a modest concentration, could meaningfully amplify the efficacy of co-administered antimicrobials. The enzyme’s activity at neutral pH and 40 degrees Celsius, its serum stability, and its resistance to trypsin all support the plausibility of such combination approaches.

Significant hurdles remain before serratiopeptidase reaches the clinic as an anti-biofilm drug. The current work used a partially purified preparation, and further purification, scale-up of production, formulation studies, toxicity testing, and ultimately animal and clinical trials will be required. The enzyme’s origin from Serratia marcescens, an opportunistic pathogen itself, raises production and safety questions that recombinant expression systems, which have already been used to produce serratiopeptidase in cell-free platforms, could help resolve. Nevertheless, by systematically documenting the enzyme’s molecular weight, kinetics, inhibitor profile, storage stability, serum resistance, and anti-biofilm potency, Kumar and Bhattacharya have transformed a supplement-shelf enzyme into a well-characterized candidate for rational development. As antibiotic resistance continues to erode the effectiveness of conventional drugs, enzymes that dismantle bacterial fortresses rather than merely poisoning the bacteria inside them may prove to be one of the most important weapons in the next generation of anti-infective therapy.

Subject of Research: Biochemical characterization and anti-biofilm activity of serratiopeptidase from Serratia marcescens SP6

Article Title: Elucidation of the biochemical properties of a partially purified Serratia marcescens SP6 serratiopeptidase with anti-biofilm efficacy

Article References: Kumar, S., & Bhattacharya, S. (2026). Elucidation of the biochemical properties of a partially purified Serratia marcescens SP6 serratiopeptidase with anti-biofilm efficacy. 3 Biotech, 16(10), Article 433. https://doi.org/10.1007/s13205-026-05063-9

Image Credits: AI Generated

DOI: 10.1007/s13205-026-05063-9

Keywords: serratiopeptidase, Serratia marcescens, biofilm, Pseudomonas aeruginosa, Staphylococcus aureus, protease, enzyme kinetics, antibiotic resistance, metalloprotease, anti-biofilm therapy, protein purification, therapeutic enzymes

The significance of the findings begins with the crop itself. Mung bean, originally domesticated in India, is now cultivated on roughly 7.3 million hectares globally, producing an estimated 6 million tons annually, with India, Myanmar, China, and Indonesia dominating the market. As a legume, it fixes atmospheric nitrogen through symbiosis with rhizobia, improving soil fertility and providing nitrogen inputs for subsequent crops, which makes it especially valuable in resource-limited farming systems. In Ethiopia, mung bean is an emerging crop concentrated in the North Shewa and South Wollo zones of the Amhara region and parts of Benishangul-Gumuz. Yet productivity remains stubbornly low: traditional varieties average about 0.5 megagrams per hectare, improved varieties can exceed 1.5 megagrams under optimal conditions, and the national average of 0.9 megagrams per hectare sits roughly 20 percent below the world average. Unpredictable rainfall, fungal pathogens, pests, poor agronomic practices, and limited access to quality inputs all conspire to hold yields back.

That combination of biotic and abiotic pressures is precisely where endophytic bacteria enter the picture. Endophytes are microorganisms that live within plant tissues without causing disease, and they can benefit their hosts in two broad ways. Direct growth promotion occurs through the production of phytohormones, improved nutrient mobilization, and the induction of systemic tolerance to environmental stress. Indirect protection comes through competitive exclusion of pathogens and the secretion of antimicrobial metabolites such as lipopeptides, polyketides, and volatile organic compounds. Fungal pathogens like Aspergillus flavus pose a particularly serious threat because they produce aflatoxins that contaminate seeds and endanger human and animal health, making biocontrol agents that can target this fungus a priority for both food security and food safety.

To find candidate microbes, the team grew fifty Shewa-type mung bean seeds in vertisol soil at Addis Ababa Science and Technology University without any chemical fertilizers, irrigating weekly over three months until the plants reached the fruiting stage. They then collected fifty healthy root systems and fifty seeds and subjected them to a rigorous surface sterilization protocol involving sequential ethanol and sodium hypochlorite treatments. Crucially, the researchers validated the sterilization using two complementary methods: imprinting sterilized tissues onto nutrient agar plates and spread-plating the final rinse water. Only samples showing zero visible microbial growth after overnight incubation were used, ensuring that the bacteria recovered genuinely lived inside the plant tissues rather than on their surfaces. Macerated tissues were serially diluted and spread across four different growth media to capture as broad a range of the culturable endophytic community as possible.

The isolation effort yielded twenty-eight distinct bacterial endophytes, with more recovered from seeds, sixteen, than from roots, twelve, a distribution suggesting that seed-associated microbiomes may facilitate vertical transmission of beneficial bacteria across generations. Eight representative isolates, selected for their morphological diversity and labeled GMB R1, R2, S1 through S6, were chosen for detailed characterization. Biochemical profiling revealed that three isolates were Gram-positive while five were Gram-negative, all produced catalase, and all fermented glucose. Stress tolerance screening then uncovered a striking spectrum of resilience. Four isolates, GMB R1, R2, S5, and S6, showed robust thermotolerance, maintaining optical densities above 0.58 at 45 degrees Celsius, while others were thermosensitive and grew poorly above 37 degrees. GMB R2 displayed exceptional pH flexibility, losing less than 15 percent growth across the full range from pH 4 to pH 10, and GMB S5 proved the strongest halotolerant strain, sustaining growth at sodium chloride concentrations as high as 12 percent.

Heavy metal tolerance added another dimension to the functional portrait. When grown in media amended with lead acetate at concentrations from 50 to 300 micrograms per milliliter, all isolates grew at the baseline level, but growth inhibition increased with concentration in a strain-dependent manner. GMB R1 stood out as the most lead-tolerant, maintaining strong optical density across the entire gradient, with GMB R2 and GMB S5 close behind. The authors suggest that mechanisms such as exopolysaccharide production, metal sequestration, and efflux systems likely underpin this tolerance, and they highlight the strains as candidates for colonizing plants in heavy metal-contaminated agricultural soils, a growing problem in many intensively farmed regions.

The biocontrol results may prove the most immediately compelling. In dual culture assays on malt extract agar, GMB R1 and GMB R2 significantly suppressed Aspergillus flavus, reducing fungal mycelial growth by 66.7 percent and 73.3 percent respectively, compared with control colony diameters of 4.5 millimeters after seven days. Enzymatic profiling revealed strain-specific specialization that could contribute to this antagonism: GMB R1 showed the highest cellulase activity with an enzymatic index of 2.5, GMB R2 the highest chitinase activity at 1.6, and GMB S5 the highest protease activity at 2.0. Chitinase is particularly relevant to antifungal action because chitin is a structural component of fungal cell walls. Siderophore production, which starves pathogens of iron, was detected in seven of the eight isolates, and six isolates produced ACC deaminase, an enzyme that lowers plant ethylene levels and helps seedlings withstand stress. Notably, the study found no trade-off between stress adaptation and biocontrol capacity, meaning the hardiest strains were also among the best fungal antagonists.

Molecular identification using 16S rRNA gene sequencing confirmed the taxonomy of three key isolates: GMB R1 matched Pseudomonas fluorescens with 99.87 percent similarity, GMB R2 showed 100 percent identity with Pantoea agglomerans, and GMB S5 aligned fully with Serratia marcescens. Sequencing failed for the remaining five isolates, likely due to suboptimal DNA template quality, so those strains are currently identified only by morphological and biochemical profiles, a limitation the authors candidly acknowledge. Partial 16S rRNA sequences for the three characterized strains have been deposited in NCBI GenBank under accession numbers OR974898.1, OR974899.1, and OR974900.1, and phylogenetic analysis using the maximum-likelihood method with 1,000 bootstrap replicates supported their taxonomic placements.

Perhaps the most eye-catching numbers come from the plant growth assays, conducted not on mung bean itself but on wheat (Triticum aestivum) and rapeseed (Brassica napus), demonstrating cross-host efficacy. In germination tests, GMB S6 increased wheat seedling radicle length to 12.4 centimeters and plumule extension to 18.9 centimeters, producing a vigor index of 3,067.4, roughly 140 percent above the uninoculated control. In pot trials over 90 days, GMB S5 produced wheat roots 77 percent longer than controls with an 85 percent increase in root dry weight. On rapeseed, GMB R1 extended radicle length by 149 percent and achieved a vigor index of 2,114.6, an 82 percent improvement, while GMB R2 generated the longest plumules at 9.1 centimeters and boosted rapeseed plumule length by 127 percent. Germination rates stayed high across all treatments, between 94 and 97 percent, indicating that the bacteria enhanced post-germinative development rather than germination itself. One isolate, GMB S2, actually inhibited plumule growth, a reminder that endophyte effects are strain- and context-dependent and that not every endophyte is benign or beneficial.

The authors are careful to frame the work as an exploratory baseline rather than a field-ready prescription. The sampling came from a single site and a single cultivar, physiological assays relied on optical density rather than viable cell counts, heavy metal testing used only lead as a model contaminant, and the inoculated bacteria were not re-isolated from wheat and rapeseed tissues to confirm true endophytic establishment. Field conditions, with competition from indigenous microbiota and environmental variability, will likely produce more modest gains than the laboratory and greenhouse results suggest. Still, the combination of thermotolerance, halotolerance, heavy metal resistance, siderophore production, lytic enzymes, ACC deaminase activity, antifungal activity against aflatoxigenic fungi, and cross-host growth promotion makes GMB R1, GMB R2, and GMB S5 stand out as promising multifunctional bioinoculants. Future work, including whole-genome sequencing, testing on the native mung bean host, consortium design, and multi-location randomized field trials, will determine whether these Ethiopian endophytes can translate their laboratory performance into real yields for marginal agroecosystems, where the need for sustainable alternatives to chemical inputs has never been greater.

Subject of Research: Stress-tolerant endophytic bacteria isolated from Ethiopian mung bean with biocontrol and plant growth-promoting traits

Article Title: Stress-resilient endophytic bacteria from mung bean (Vigna radiata L.) with biocontrol and plant growth-promoting potential

Article References: Abatenh, E., Kebede, M., & Abda, E. M. (2026). Stress-resilient endophytic bacteria from mung bean (Vigna radiata L.) with biocontrol and plant growth-promoting potential. International Microbiology. https://doi.org/10.1007/s10123-026-00897-y

Image Credits: AI Generated

DOI: 10.1007/s10123-026-00897-y

Keywords: endophytic bacteria, mung bean, Vigna radiata, biocontrol, Aspergillus flavus, plant growth promotion, Pseudomonas fluorescens, Pantoea agglomerans, Serratia marcescens, abiotic stress tolerance, aflatoxin, sustainable agriculture