Bacteria from the cactus surface and cucumber seedling growth

From the epidermis to bacterial cultures

The surface of Tacinga inamoena cladodes provides a habitat for epiphytic microorganisms. Two strains were obtained from plants growing in the Brazilian Caatinga. These were Brevibacillus sp. UPT4 from Serra do Umbuzeiro near Paulo Afonso and Pantoea sp. SPM1 from Serra Branca in Jeremoabo. A paper published in 2026 assessed their characteristics in culture and then their effects on young cucumber plants. The cactus species identifies the origin of the microbiological material here. [Pereira et al. 2026, pp. 415–417]

What the laboratory tests showed

In a medium containing tryptophan, both strains produced a colour signal interpreted by the authors as production of indole-3-acetic acid, a member of the auxin group. The concentration measured was 58,93 µg/ml for Brevibacillus and 53,19 µg/ml for Pantoea. The test uses Salkowski reagent and provides a screening assessment of indole compounds. Growth in a medium without added nitrogen indicated potential associated with nitrogen fixation, while Pantoea tested positive for potassium release from the medium. [Pereira et al. 2026, pp. 416–417, Table 1]

In culture, both strains grew at a reduced water activity of 0,957. Pantoea tolerated NaCl concentrations up to 8%, and Brevibacillus up to 4%. These parameters describe the bacteria in a defined laboratory medium. Their effects on the plant were assessed in the next stage of the experiment. [Pereira et al. 2026, pp. 416–417, Table 1]

Twenty experimental units

Cucumber seeds were inoculated with an individual strain or a mixture of both strains. The control received only a xanthan gum solution, used to help the inoculum adhere. Each of the four treatments had five replicates. The plants grew in pots containing 2 kg of soil in a greenhouse in Paulo Afonso in December 2024. They were watered daily to maintain adequate moisture, and measurements were taken 25 days after emergence. This was a growth trial with an adequate water supply. [Pereira et al. 2026, p. 417]

Shoot elongation and root development

Following treatment with Brevibacillus sp. UPT4, shoot length was 56,59% greater than in the control, stem diameter 20,20% greater, and root length 43,40% greater. The strain mixture increased shoot length by 38,52% and stem diameter by 13,58%. The Pantoea strain alone primarily altered traits of the underground part. All three inoculated treatments increased root volume by 92,86–117,86% relative to the control. [Pereira et al. 2026, pp. 418–419, Fig. 2–3]

The value of 194,86%, highlighted in the abstract, refers to the relative increase in the proportion of root dry biomass in the dry biomass of the whole seedling following treatment with Pantoea. This index describes biomass allocation between roots and shoots. The change in root proportion can be large even when the change in total plant mass is much smaller. Length, volume, root mass and proportions between organs were analysed separately. [Pereira et al. 2026, pp. 418–420, Fig. 4]

Significance for research on biological preparations

The result establishes a direction for further testing of the two strains as potential components of biological preparations. The confirmed scope covers early cucumber development in a single greenhouse experiment. Effectiveness in field soil, persistence of colonisation, the safety of the particular strain and effects on yield require further assessment. Research can also investigate whether the metabolic traits measured actually mediate the root response. The paper connects the biology of cactus-associated microorganisms with a separate agricultural application. [Pereira et al. 2026, pp. 420–421]