The motivation behind the work is stark. Decades of intensive fertilizer and pesticide use have degraded soil structure, depleted organic matter, and undermined the biological activity that underpins long-term productivity. Microbial exopolysaccharides have attracted attention as a gentler alternative because of the multiple roles they can play in the soil environment. These long-chain carbohydrates help bacteria adhere to surfaces and form biofilms, but in the wider soil system they can improve water retention, stabilize soil aggregates, and modulate plant physiological responses to stress. Earlier studies have shown that EPS-producing bacteria can restrict sodium uptake in salt-stressed wheat seedlings, alleviate drought effects in sunflower and maize, and improve soil aggregation in degraded land. What has been less explored is the potential of bacteria that live as endophytes inside seeds themselves, a niche that offers a particularly intimate and protected association with the host plant.

The researchers began with a collection of 86 pearl millet seed endophytic bacteria, abbreviated PMSEB, previously isolated from surface-sterilized seeds. Screening for EPS production was carried out on two different growth media, Nutrient Agar and ATCC No. 14 medium, allowing the team to identify which strains were prolific polymer producers under laboratory conditions. Selected high-producing strains were then subjected to extraction, partial purification, and quantification of their exopolysaccharides, with carbohydrate content measured using the classical anthrone-sulfuric acid colorimetric method originally described by Dreywood in 1948. This pipeline, from raw culture to partially purified polymer, mirrors the practical steps any industrial production process would need to follow, making the study as much about process development as about discovery.

The first biological test was a seed germination bioassay using partially purified EPS applied at a concentration of 0.2 percent. The results showed a clear biostimulatory effect on early-stage wheat growth, with treated seeds germinating better and producing more vigorous seedlings than untreated controls. The team then explored dose dependence, testing EPS solutions at 0.25, 0.5, and 1 percent. The response varied with concentration, an important observation for anyone hoping to translate laboratory results into field-ready formulations, since overdosing a biostimulant can be as counterproductive as underdosing it. Three strains stood out from the pack: MPT27, PC7N47, and PC7T5, whose EPS produced significant improvements in seed germination, seedling dry weight, and vigor indices, the standard metrics used to quantify seedling quality in agricultural science.

Molecular identification revealed a taxonomically diverse trio. Strain MPT27 was identified as Atlantibacter hermannii, a member of the Enterobacteriaceae, while PC7N47 and PC7T5 were both classified as Bacillus subtilis subsp. subtilis, a species with a long and celebrated history in agricultural biotechnology. Partial 16S ribosomal RNA sequences for all three strains have been deposited in the NCBI GenBank database under accession numbers PQ182223, PQ182224, and PQ182225, providing a permanent record that other laboratories can use to obtain and verify the same organisms. The fact that two independent Bacillus isolates from the same seed source proved to be strong EPS producers underscores how common this trait may be among seed-associated beneficial bacteria.

Because yield matters as much as efficacy in any commercial context, the researchers systematically optimized EPS production for each strain. Culture conditions were tuned strain by strain, and the carbon source in the growth medium emerged as a decisive variable, with sucrose proving the most effective substrate for polymer synthesis. This kind of strain-specific optimization is a recurring theme in EPS bioprocess literature; studies on lactic acid bacteria, alkaliphilic Bacillus species, and marine isolates have all shown that medium composition, pH, and incubation parameters can swing production yields dramatically. The New Delhi team’s results confirm that there is no universal recipe, and that each promising organism requires its own tailored fermentation strategy before it can be considered a viable production platform.

Characterization of the extracted polymers revealed meaningful differences between strains, differences that could matter functionally in the field. Water absorption capacity, a key property for a compound intended to help soil retain moisture, varied among the EPS samples, as did antioxidant activity measured by the DPPH radical scavenging assay. Fourier-transform infrared spectroscopy, or FTIR, confirmed the presence of the characteristic functional groups of polysaccharides, including the broad hydroxyl stretching bands and carbon-oxygen signatures expected of carbohydrate polymers. Monosaccharide composition analysis added a structural dimension: the EPS from MPT27 and PC7N47 were heteropolysaccharides, built from more than one kind of sugar unit, whereas the polymer from PC7T5 was a homopolysaccharide composed of a single repeating sugar. Such structural distinctions often correlate with differences in rheology, solubility, and biological activity, and they give formulators a molecular handle for selecting the right polymer for a given application.

The broader significance of the study lies in its framing of EPS as a phytostimulant in their own right, decoupled from the living bacteria that make them. Applying purified or partially purified polymers avoids some of the regulatory and logistical complications of live microbial inoculants, which can be sensitive to storage conditions, compete poorly with native soil flora, or face import restrictions across borders. A stable carbohydrate formulation, by contrast, could be blended with seeds, delivered through irrigation, or combined with conventional inputs. Previous work by other groups has moved in this direction, including talc-based EPS formulations that enhanced sunflower growth under saline conditions and bioformulations combining bacterial cultures with their exopolysaccharides to improve pigeon pea productivity. The wheat results reported here extend that logic to a staple crop of global importance and to a novel source of polymers, the internal microbiome of seeds.

There are, of course, substantial steps between a germination paper assay and a farmer’s field. The experiments reported involve early-stage seedlings under controlled conditions, and the partially purified EPS preparations still contain undefined components that would need to be standardized for commercial use. Field-scale trials would need to test whether the germination and vigor benefits persist in real soils, whether the polymers interact constructively with fertilizers and pesticides already in use, and whether production costs can be brought down to levels that make economic sense for wheat growers operating on thin margins. The dose-dependent responses observed also suggest that application protocols will need careful calibration, possibly varying by soil type, climate, and crop variety.

Even so, the study offers a compelling glimpse of where agricultural biotechnology is heading. As the environmental costs of chemical-intensive farming become harder to ignore, researchers are increasingly mining the plant microbiome not just for organisms but for the molecules those organisms produce. Seed endophytes are a particularly attractive starting point because they are vertically transmitted, evolutionarily curated by the host plant, and already adapted to the crop environment. By screening 86 isolates, optimizing fermentation, and characterizing the resulting polymers down to their monosaccharide building blocks, Kamali and colleagues have demonstrated a complete discovery-to-characterization workflow for seed-derived EPS. Their three standout strains, including two Bacillus subtilis subspecies and an Atlantibacter hermannii, now join a short but growing list of microbes whose sugary secretions may help crops establish faster, cope with stress, and yield more, all while easing the chemical burden on the world’s farmland.

Subject of Research: Exopolysaccharides from pearl millet seed endophytic bacteria as phytostimulants for wheat growth

Article Title: Harnessing endophytic bacteria for enhanced wheat growth: extraction, optimization, and characterization of exopolysaccharides

Article References: Kamali, R., Grover, M., Singh, G., Kaushik, R., & Jaiswal, P. (2026). Harnessing endophytic bacteria for enhanced wheat growth: extraction, optimization, and characterization of exopolysaccharides. 3 Biotech, 16(11), Article 455. https://doi.org/10.1007/s13205-026-05074-6

Image Credits: AI Generated

DOI: 10.1007/s13205-026-05074-6

Keywords: exopolysaccharides, endophytic bacteria, wheat, pearl millet, biostimulants, Bacillus subtilis, seed germination, sustainable agriculture, FTIR, heteropolysaccharides, soil health, plant growth promotion