The research team, led by Sachin Naik and Michelle Jones, drew on a curated collection of 1,044 rhizobacterial isolates originally recovered from ornamental greenhouse crops grown in peat-based substrates. Rather than relying on the traditional tricalcium phosphate assays that dominate the phosphate-solubilizing bacteria literature, the team targeted iron phosphate directly, reasoning that the calcium-focused screens used in most prior studies may miss the strains most relevant to soilless production. Peat substrates contain significant intrinsic iron, much of it bound to organic matter, and under the mildly acidic to near-neutral conditions typical of greenhouse containers, phosphorus is progressively sequestered into stable iron phosphate precipitates that resist conventional fertilizer corrections.

To find bacteria that could liberate this trapped nutrient, the researchers deployed a high-throughput malachite green colorimetric assay. Each isolate was grown in triplicate in minimal medium containing iron phosphate dihydrate as the sole phosphorus source, and after four days of incubation the soluble phosphorus released into the culture supernatant was quantified spectrophotometrically. The results revealed a strikingly stratified microbial landscape: nearly 70 percent of the isolates showed minimal solubilization below 8 percent, about 28 percent displayed moderate activity, and only 24 isolates, a mere 2.3 percent of the collection, exceeded the 25 percent threshold set for high performers. Notably, Bacillus velezensis, the phosphate-solubilizing strain included as a commercial reference from the biostimulant Lalrise Vita, showed almost no activity against iron phosphate, solubilizing less than 3 percent.

Whole-genome sequencing of the top performers revealed a taxonomically diverse guild dominated by the genera Pantoea, Bacillus, Priestia, Paenibacillus, Pseudomonas, and Stenotrophomonas. Average nucleotide identity analysis confirmed species-level assignments for most strains, and the isolates proved remarkably cosmopolitan in origin, having been recovered from zinnia, vinca, petunia, geranium, and coleus. This broad host distribution suggests these bacteria are not tightly host-specific but instead occupy shared rhizosphere niches across taxonomically diverse plant families, a property that could make them useful in the mixed plantings and crop rotations common in commercial greenhouse operations.

The critical question, of course, was whether laboratory solubilization would translate into real plant benefit. Twenty-seven candidate strains were tested in a high-throughput greenhouse experiment using French marigold ‘Durango Yellow’ grown in peat-perlite substrate adjusted to pH 7.0, a deliberately severe phosphorus-limiting condition. After seedling establishment, insoluble iron phosphate served as the sole phosphorus source, and bacterial treatments were applied as weekly substrate drenches for four weeks. A laser-based digital phenotyping platform measured plant biomass, leaf area, and spectral reflectance indices that track chlorophyll content, canopy greenness, and senescence. Five strains emerged as clear winners: Pantoea communis C3A8, Pantoea formicae C8D10, Pseudomonas sp. C6E7, Pseudomonas sp. C9D1, and Priestia megaterium C3F10.

Intriguingly, two of those five, strains C3F10 and C9D1, had shown only about 3 percent solubilization in the in vitro assay, yet they ranked among the top performers in the greenhouse screen. This disconnect between biochemical activity in a flask and plant growth promotion in a pot carries an important lesson for biofertilizer development: in vitro solubilization percentage alone does not reliably predict in planta performance. The researchers deliberately included low and mid-range solubilizers in their greenhouse trials to test this very question, and the answer was unambiguous. Success in the rhizosphere depends on far more than raw solubilizing chemistry, encompassing colonization ability, stress tolerance, and the competitive exploitation of root-derived carbon.

A second, more rigorous validation experiment with 30 replicate blocks confirmed the greenhouse results at pH 6.5. Pantoea communis strain C3A8 delivered the strongest overall response, significantly increasing shoot digital biomass and 3D leaf area while boosting the green leaf index and shifting canopy color composition toward healthier green hues. Most tellingly, plants inoculated with C3A8 accumulated significantly more phosphorus in their shoot tissue than controls. Because iron phosphate was the only phosphorus supplied during the treatment period, this tissue analysis provides direct evidence that the bacterium released plant-available phosphorus from the insoluble iron phosphate pool. The authors believe this is the first report of phosphate solubilization ability in P. communis, expanding the known functional diversity of a genus previously represented mainly by P. agglomerans in this literature.

The genomic analysis explains why these strains differ so markedly in performance. Pantoea communis C3A8 and Pantoea formicae C8D10 each carry three copies of the gcd gene, which encodes glucose dehydrogenase, the central enzyme in gluconic acid-mediated inorganic phosphate solubilization, along with the pqqF and pqqL genes needed to synthesize its pyrroloquinoline quinone cofactor. Both also harbor extensive arsenals of phosphatase genes for mineralizing organic phosphorus, complete phosphate transport systems, and hundreds of genes for iron acquisition and root colonization. The Pseudomonas strains took a different genomic route, pairing single gcd copies with multiple pqqL copies, three copies of phoD and ppx in C6E7, and elevated counts of nitrogen acquisition and volatile synthesis genes. Priestia megaterium C3F10, remarkably, lacks gcd entirely and may instead rely on intracellular polyphosphate accumulation and controlled release, driven by five copies of the phosphoenolpyruvate synthase gene and multiple phoR regulatory copies.

Rhizosphere competence genes added another layer of ecological insight. The Pantoea strains carry multiple gene clusters for trehalose and mannitol catabolism, pathways linked to osmoprotection and persistence under the fluctuating moisture conditions of container substrates, while C3A8 uniquely encodes an inositol catabolic cluster, a trait shown in other bacteria to be essential for rhizosphere colonization. Priestia megaterium C3F10 carries gene clusters for sucrose and levan metabolism, which in other systems support biofilm formation and root surface attachment, along with the 3-oxoadipate pathway for degrading aromatic compounds derived from lignin and phenolic root exudates. The authors are careful to note that these genomic signatures generate hypotheses about mechanism rather than demonstrated links, and that direct substrate-level measurements of water-extractable phosphorus and rhizosphere enzyme activity will be needed to confirm which solubilization pathways operate in situ.

The practical implications extend well beyond ornamental horticulture. Greenhouse production depends almost entirely on fertigation, and the limited substrate volume and low cation exchange capacity of soilless containers routinely drive fertilizer runoff, phosphorus leaching, and environmental contamination. Growers frequently over-apply phosphorus to compensate for its rapid immobilization, a practice that wastes resources, disrupts micronutrient balance, and can even induce iron deficiency in crops. The five validated strains, with their complementary mechanisms spanning gluconic acid-mediated dissolution, organic phosphorus mineralization, nitrogen acquisition, and polyphosphate dynamics, suggest that microbial consortia could deliver synergistic benefits exceeding those of any single inoculant. If follow-up work confirms performance across diverse ornamental species and substrate types, these iron phosphate solubilizers could form the basis of biofertilizer formulations that let growers cut synthetic phosphorus inputs while maintaining crop quality, turning a stubborn chemistry problem into a biological opportunity.

Subject of Research: Iron phosphate solubilizing bacteria for sustainable phosphorus management in soilless greenhouse crop production

Article Title: High-throughput screening and genomic characterization of iron phosphate solubilizing bacteria for sustainable greenhouse production

Article References: Naik, S., Quijia-Pillajo, J., Chapin, L. J., & Jones, M. L. (2026). High-throughput screening and genomic characterization of iron phosphate solubilizing bacteria for sustainable greenhouse production. Plant and Soil. https://doi.org/10.1007/s11104-026-09134-x

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09134-x

Keywords: phosphate solubilizing bacteria, iron phosphate, greenhouse production, soilless substrate, plant growth promoting rhizobacteria, Pantoea communis, Pseudomonas, Priestia megaterium, whole genome sequencing, phosphorus availability, biofertilizer, controlled environment agriculture

Chitin is the star of this story. It is the second most abundant natural polymer on Earth after cellulose, forming the tough exoskeletons of crustaceans and insects as well as the cell walls of fungi. Chitinase enzymes break chitin down into smaller, soluble fragments that have uses ranging from agricultural biocontrol agents and fertiliser components to cosmetic ingredients and pharmaceutical precursors. The bottleneck has always been production: chitinase made by fermenting microbes is expensive, and purifying chitin from shrimp shells traditionally requires harsh chemical treatments that generate their own pollution. The Egyptian team set out to solve both problems at once by letting bacteria ferment raw shrimp shell waste directly, using the waste as the sole source of both carbon and nitrogen.

The researchers began by screening four thermophilic bacterial strains from their culture collection: Bacillus amyloliquefaciens BT 2022, Bacillus licheniformis Basma87, Priestia megaterium AMD 2024, and the actinobacterium Streptomyces maritimus MSQ-2021. Thermophiles were a deliberate choice. Growing at elevated temperatures reduces the risk of contamination by ordinary mesophilic microbes, lowers cooling costs in an industrial fermenter, and often coincides with faster enzyme kinetics. When the four strains were grown on media containing nothing but shrimp shell waste, Priestia megaterium AMD 2024 emerged as the clear winner, degrading the chitin matrix most vigorously and releasing the highest chitinolytic activity into the culture broth.

With the champion strain identified, the team turned to optimisation, first using the familiar one-variable-at-a-time approach, in which a single fermentation parameter is adjusted while everything else is held constant. This systematic sweep identified a sweet spot: shrimp shell waste at a concentration of 5 percent, incubation at 60 degrees Celsius for 72 hours, a neutral pH of 7.0, shaking at 200 revolutions per minute, and an inoculum size of 2 percent. Under these conditions the culture produced 93.24 units per millilitre of chitinase activity, a respectable figure that confirmed the concept. But OVAT has a well-known weakness. It cannot detect interactions between variables, and in fermentation biology those interactions are often where the real gains hide. A temperature that works at one pH may fail at another, and substrate concentration can shift the entire response surface.

To capture those hidden interactions, the researchers moved to response surface methodology, a statistical framework that models the output of a process as a mathematical surface over multiple input dimensions. The first stage used a Plackett–Burman design, an efficient screening tool that evaluates many factors simultaneously with a minimal number of runs, allowing the team to identify which variables exerted the strongest influence on enzyme yield. The significant factors then fed into a central composite design, which samples the response surface around an optimal region and fits a quadratic model to locate the true maximum. The outcome was dramatic: chitinase activity climbed to 273.3 units per millilitre, a 2.93-fold increase over the OVAT baseline. For bioprocess engineers, the result is a textbook demonstration of why statistical design has largely replaced trial-and-error optimisation in modern industrial biotechnology.

The enzyme then had to be recovered from the broth. The team used ammonium sulphate precipitation, a classic low-cost purification step in which increasing salt concentrations progressively crash proteins out of solution. The 60 to 80 percent saturation fraction proved the richest, delivering 260.0 units per millilitre of activity while retaining 95.13 percent of the original enzymatic function. This partial purification strikes a pragmatic balance for industrial applications: the enzyme is concentrated and freed from the bulk of unwanted proteins without the expense of chromatographic polishing that would be unnecessary for many agricultural and cosmetic uses.

Perhaps the most consequential finding for commercial prospects came from the safety testing. The purified enzyme was applied to HFB4, a normal human skin cell line, in cytotoxicity assays. Even at the maximum concentration tested, equivalent to 260.0 units per millilitre of activity, the enzyme showed no toxic effects on the skin cells, confirming its biocompatibility. That single result opens doors well beyond waste management. Chitinases with demonstrated skin safety can be considered for cosmetic formulations, where chitin-derived oligosaccharides are prized as moisturising and film-forming agents, and for biomedical applications where contact with living tissue is unavoidable.

The broader significance of the study lies in its circular economy logic. Shrimp processing generates enormous quantities of shell waste that is rich in chitin, protein, and minerals, and disposal of that waste is a genuine environmental burden for coastal nations, including Egypt’s rapidly growing aquaculture and seafood sectors. By feeding the waste directly to a thermophilic bacterium, the process simultaneously treats a pollutant and manufactures a product, converting a disposal cost into a revenue stream. Because the bacteria use the shells as their only feedstock, the process avoids the chemical demineralisation and deproteinisation steps of conventional chitin processing, cutting reagent consumption and effluent load. The authors frame the work explicitly as an eco-friendly solution, and the numbers support that framing: a waste-derived substrate, a low-energy thermophilic fermentation, and a benign purification route.

There are, of course, steps between a well-optimised laboratory fermentation and an industrial process. Scale-up will require confirming that the statistical optimum holds in larger vessels, where mixing, oxygen transfer, and heat removal behave differently from shake flasks. Downstream processing will need to be tailored to each target market, since an enzyme destined for a cosmetic cream faces stricter purity requirements than one sprayed on a field to suppress fungal pathogens. Nonetheless, the study provides a complete proof of concept, from strain selection through statistical optimisation to purification and safety assessment, and it identifies a robust thermophilic producer in Priestia megaterium AMD 2024 that can serve as a platform for further engineering. As industries everywhere search for biologically based alternatives to petrochemical processes, studies like this one show that some of the most promising feedstocks are already piling up behind seafood processing plants, waiting for the right microbe to come along.

For the researchers, the message is straightforward: chitinase production no longer needs to depend on expensive purified substrates or energy-intensive conditions. A waste product that once cost money to throw away can, with the right bacterium and the right experimental design, become the foundation of a sustainable enzyme industry serving agriculture, manufacturing, and cosmetics alike. The 2.93-fold boost achieved through response surface methodology is not merely a laboratory curiosity; it is the kind of quantitative improvement that makes the difference between a process that stays in a paper and one that attracts investment. And with the enzyme shown to be safe for human skin cells, the path from shrimp shell heap to shelf-ready product has never looked shorter.

Subject of Research: Microbial production and statistical optimization of chitinase from shrimp shell waste using thermophilic bacteria

Article Title: Harnessing shrimp shell waste: enhanced chitinase production through optimization techniques for ecofriendly solutions using bacteria

Article References: Abd-Elhalim, B. T., & Ashour, M. A. (2026). Harnessing shrimp shell waste: enhanced chitinase production through optimization techniques for ecofriendly solutions using bacteria. Biotechnology for Biofuels and Bioproducts, 19(1), Article 73. https://doi.org/10.1186/s13068-026-02808-9

Image Credits: AI Generated

DOI: 10.1186/s13068-026-02808-9

Keywords: chitinase, shrimp shell waste, Priestia megaterium, response surface methodology, Plackett-Burman design, central composite design, thermophilic bacteria, biowaste valorization, partial purification, cytotoxicity, circular economy, green biotechnology