Two Soil Bacteria Compounds Strike Candida at Two Vulnerable Points at Once

A pair of small molecules harvested from a humble soil bacterium is drawing fresh attention to one of medicine’s most stubborn problems: fungal infections that refuse to yield to existing drugs. In a new study published in The Journal of Antibiotics, researchers Jyoti Shukla and Ashok K. Dubey of Netaji Subhas University of Technology in New Delhi report that two compounds previously isolated from Streptomyces chrestomyceticus strain ADP4 attack Candida albicans, the most common cause of serious fungal disease in humans, through a rare double-pronged mechanism. One compound, a chrestosyl cyclohexyl ketone known as 1PB1, and its chemical cousin, a chrestosyl amino decalin known as 45R, simultaneously sabotage the fungus’s membrane-building machinery and a cell wall enzyme that helps it grow and remodel itself. Because the two compounds hit separate cellular targets at the same time, the findings suggest a strategy that could be harder for the fungus to resist than the single-target drugs that dominate the current clinic.

The clinical backdrop is grim. Candida albicans lives harmlessly on the skin and mucous membranes of most healthy people, but in patients whose immune defenses are compromised it turns opportunistic, causing infections that range from thrush and invasive candidiasis to deadly bloodstream sepsis. Treatment options have narrowed rather than widened over the decades: the azole antifungals, which include fluconazole, have been used so widely that resistant strains now circulate in hospitals worldwide, and the newer echinocandins, though valuable, are expensive and have their own limitations. Resistance in Candida typically emerges through mutations in the drug’s protein target, overexpression of that target, or efflux pumps that simply expel the drug from the cell before it can act. A compound that must be defeated twice, at two biologically distinct targets, presents a far taller order for the pathogen’s evolutionary toolkit.

The first of the two targets examined in the study is CYP51, also known as lanosterol 14-alpha-demethylase, a cytochrome P450 enzyme that sits at the heart of ergosterol biosynthesis. Ergosterol is the fungal equivalent of cholesterol: it lodges in the cell membrane and governs the membrane’s fluidity, integrity and the function of embedded proteins. Without it, the fungal cell membrane becomes leaky and disorganized, and the cell cannot survive. The azole class works by blocking CYP51, which is precisely why resistance to azoles usually maps onto mutations in this enzyme or its gene. A molecule that inhibits CYP51 by a different binding mode, or that is structurally unrelated to azoles, could in principle evade the resistance mutations that have eroded fluconazole’s effectiveness.

Using molecular docking, Shukla and Dubey found that both compounds lodge themselves into the CYP51 active site with convincing affinity. The computed binding energy was minus 7.4 kilocalories per mole for 1PB1 and minus 7.6 kilocalories per mole for 45R, scores that fall into the range typically considered indicative of stable ligand-protein complexes. But docking alone is only a hypothesis. The researchers then treated Candida albicans cultures with each compound and profiled the cells’ sterol content by gas chromatography-mass spectrometry. The telltale signature of CYP51 inhibition appeared: lanosterol, the enzyme’s substrate, accumulated in the treated cells because the blocked enzyme could no longer convert it downstream. The consequence was visible in the ergosterol assays, which showed that ergosterol production fell by roughly 69.92 percent, give or take 2.3 percent, in cells exposed to 1PB1 and by 55.48 percent, give or take 1.79 percent, in cells exposed to 45R. In plain terms, both compounds starved the fungus of the lipid that its membranes depend on.

The second target is less conventional and, in some ways, more intriguing. Exo-beta-1,3-glucanase is a cell wall enzyme that clips beta-glucan, the sugar polymer that gives the fungal wall much of its structural strength. Unlike beta-1,3-glucan synthase, the target of the echinocandin class, exo-glucanase participates in the trimming and remodeling of wall glucan, processes the fungus relies on during growth, cell division and the transition between its yeast and hyphal forms, which is central to its virulence. Because it is a wall-associated enzyme rather than a membrane-bound one, and because it has not been the focus of a major drug class, exo-beta-1,3-glucanase represents a comparatively fresh angle of attack against the pathogen.

Docking against this enzyme produced even stronger scores than for CYP51: minus 8.4 kilocalories per mole for 1PB1 and minus 8.1 kilocalories per mole for 45R. To verify that these predicted interactions translate into real enzymatic inhibition, the researchers ran in vitro enzyme assays. The results were striking. 1PB1 suppressed exo-beta-1,3-glucanase activity by a maximum of 94.6 percent, with an uncertainty of 4.7 percent, at a concentration of 52.7 micrograms per milliliter, while 45R achieved 91.77 percent inhibition, with an uncertainty of 1.7 percent, at 313.2 micrograms per milliliter. Nearly complete shutdown of a wall-remodeling enzyme, in a simple biochemical assay, is a potent result, and it places both compounds among the stronger exo-glucanase inhibitors described for this organism.

Static docking pictures can be misleading, however, because proteins and their bound ligands are constantly in motion. To address this, the team turned to molecular dynamics simulations, which track the atom-by-atom jostling of the protein-ligand complexes over simulated time. The simulations showed that the complexes formed by both compounds with both targets remained conformationally stable over the course of the trajectories, holding their bound poses far more securely than the corresponding unliganded, or apo, forms of the enzymes held their own structures. Stable dynamics are the computational equivalent of a firm handshake: they suggest that the binding observed in docking is not a fleeting artifact but a durable physical interaction capable of blocking the enzyme’s function in a living cell.

What makes the study noteworthy is not any single number but the convergence. A compound that inhibits only CYP51 can be defeated by the resistance mutations already widespread in clinical Candida populations. A compound that inhibits only a wall-remodeling enzyme might be dodged by compensatory changes in wall architecture. But a compound that must simultaneously be neutralized at CYP51 and at exo-beta-1,3-glucanase faces a double evolutionary barrier, and the combination of membrane destabilization and wall weakening may act synergistically on the fungal cell, which depends on both barriers staying intact. The dual-target profile also hints at the possibility of lower effective doses, since each partial hit reinforces the other. The work builds on the same group’s earlier characterization of ADP4 metabolites, which have previously shown anti-Candida and antibiofilm activity, and on a growing literature that mines Streptomyces species, the same bacterial genus that gave the world streptomycin and tetracycline, for molecules with antifungal potential.

Considerable distance remains between these results and a medicine on a pharmacy shelf. Docking scores are estimates, enzyme assays are conducted outside the cell, and the leap from a biochemical inhibition curve to a safe, absorbable, non-toxic drug in a human patient is long and statistically unforgiving. The compounds’ pharmacokinetics, their behavior in animal models of candidiasis, their toxicity toward human cells, and their activity against resistant clinical isolates all remain open questions. Nevertheless, the study adds two chemically distinctive scaffolds, a trimethyl cyclohexyl ketone and an amino decalin, to the short list of natural products with experimentally supported, dual mechanisms against Candida albicans. At a moment when fungal infections cause an estimated millions of severe cases each year and the antifungal pipeline runs thin, a soil bacterium offering molecules that hit the pathogen at two vulnerable points at once is exactly the kind of lead the field has been waiting for. The next challenge, as always in natural product drug discovery, will be turning a promising hit into a therapy.

Subject of Research: Dual-target antifungal compounds from Streptomyces chrestomyceticus ADP4 against Candida albicans

Article Title: New anti-fungal compounds 1PB1 and 45R from Streptomyces chrestomyceticus ADP4 target exo-β-1,3-glucanase and ergosterol biosynthesis in Candida albicans

Article References: Shukla, J., & Dubey, A. K. (2026). New anti-fungal compounds 1PB1 and 45R from Streptomyces chrestomyceticus ADP4 target exo-β-1,3-glucanase and ergosterol biosynthesis in Candida albicans. The Journal of Antibiotics. https://doi.org/10.1038/s41429-026-00958-4

Image Credits: AI Generated

DOI: 10.1038/s41429-026-00958-4

Keywords: antifungal compounds, Candida albicans, Streptomyces chrestomyceticus, CYP51, ergosterol biosynthesis, exo-beta-1,3-glucanase, molecular docking, molecular dynamics, natural products, drug resistance, The Journal of Antibiotics, dual mode of action