Studies on Hirsutella citriformis Speare are scarce. Among these, some reports have focused on phenotypic identification, based on its morphological structure and morphometric characteristics. This fungus is known to control economically important citrus crop pests. In recent years, H. citriformis has received increased attention as a control agent for the Asian citrus psyllid Diaphorina citri Kuwayama (Hemiptera: Liviidae), which causes the Huanglongbing (HLB) disease. Unfortunately, formal H. citriformis strains characterization is marginal, which mainly involves the role of biologically active exudates (metabolites) produced during their growth. Information regarding their mode of action and biocontrol potential is limited. However, epizootics reports of this fungus, under suitable environmental conditions for its development (25 °C to 28 °C and ~80% relative humidity), have demonstrated its parasitization efficacy. Therefore, it becomes challenging to determine whether H. citriformis strains may be developed as commercial products. In this review, we showed relevant information on isolation and bioassay strategies of H. citriformis to evaluate potential biocontrol strains under laboratory and field conditions in America.

Hirsutella citriformis Speare is the only entomopathogenic fungus that has been applied to control the hemipteran Diaphorina citri Kuwayama. However, the use of available commercial products under field conditions is limited due to conidia’s shelf life and short environmental persistence. We have previously reported the citrus psyllid D. citri adults’ biocontrol potential using H. citriformis strains. The aim of the present study was to evaluate different formulations based on H. citriformis (OP-Hir-3, OP-Hir-10, and OP-Hir-12 strains) conidia and gums as additives to improve D. citri adults’ biocontrol, under laboratory, greenhouse, and field conditions, using Hirsutella gums as conidia stabilizers to improve their viability under environmental drought conditions and as insecticide. Laboratory bioassay results showed that the highest (p < 0.05) D. citri mortality was achieved using FOP-Hir-10GH (63.5%), followed by the Hirsutella gum control (42.2%). Under greenhouse conditions, adults’ mortality reached up to 84.6% with FOP-Hir-12 and 49.0% with Hirsutella gum. In addition, we applied H. citriformis formulations under field conditions in a commercial citrus grove located in Tecomán, Colima, México, at 21.5 °C and 73.3% relative humidity (RH) in March and 25.7 °C and 72.5% RH in October 2022 and observed 67.3% and 94.0% mortality of D. citri adults, respectively. Hirsutella gum alone showed significant insecticidal activity against D. citri adults. In conclusion, this study demonstrated that Hirsutella gum functioned as additive to H. citriformis conidia formulations, improving D. citri adults’ mortality and showing potential for this pest biocontrol in citrus orchards.

Cancer is a complex disease due to its high variability and resistance to conventional treatments. The search for new therapies has prompted the study of less invasive natural sources, such as endophytic bacteria from medicinal plants. Bacillus subtilis is known to produce bioactive metabolites with promising pharmacological properties. This study evaluated the antitumor activity of the endophyte B. subtilis from Ibervillea sonorae against murine L5178Y-R lymphoma cells within in vitro and in vivo models. B. subtilis methanol extract was fractionated in hexane, chloroform, and methanol, with the chloroform partition showing the highest tumor cell growth inhibition (IC₅₀ = 34.62 ± 0.180 µg/mL) and the highest selectivity index (SI = 15.53) when compared with the hexane and methanol partitions. The in vivo study showed that mice treated with 10 mg/kg of the chloroform partition significantly (p < 0.01) reduced the tumor volume and weight without affecting tumor-free body weight. The maximum tolerated dose test indicated that 10 mg/kg was safe and well tolerated. These results indicate that B. subtilis may be a promising source of selective antitumor compounds.

Glioblastoma is the most common and aggressive brain tumor in adults. However, due to the limitations of conventional treatments, as well as their side effects, there is a need to develop more effective and less harmful therapy strategies. There is evidence that plants endemic to northern Mexico possess biological activities that positively impact human health, particularly against cancer. Echinocereus engelmannii and Echinocereus pectinatus are cacti from the north of Mexico that produce bioactive compounds with antitumor activity. We obtained methanol extracts from previously isolated and fermented microorganisms associated with these cacti. Cell lines of extracts with cytotoxicity against glioblastoma cells U87, neuroblastoma cells SH-S5Y5, and Schwann neuronal cells (healthy control) were evaluated, using a colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazole bromide (MTT) reduction technique. The selective cytotoxicity extracts were analyzed using liquid chromatography tandem mass spectrometry (LC/MS²). We isolated 19 endophytic and soil-associated microorganisms from both cacti. Two of them were selected for their high percentages of tumor growth inhibition. The microorganism ES4 possessed the best activity with an IC₅₀ of 17.31 ± 1.70 µg/mL and a selectivity index of 3.11. We identified the bacterium Stenotrophomonas maltophilia by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) from the most active microorganisms against tumor growth. LC/MS² characterized the HS4 extract, and the most abundant group (50.0%) identified included carboxylic acids and derivatives, particularly bisgerayafolin A, Cyclo (Pro-Leu), maculosin, and tryptophan. In conclusion S. maltophilia extract inhibit the growth of glioma cells, showing greater sensitivity in the U87 cell line.

Biological control by beneficial microorganisms is known to significantly reduce the effect of pests on crops yield. Among the biocontrol strategies is the use of entomopathogenic fungi such as Hirsutella citriformis, which has been applied to infect and kill hemipteran insect pests, including Diaphorina citri Kuwayama (Hemiptera: Liviidae) and Bactericera cockerelli Sulc. (Hemiptera: Triozidae). These biological agents are applied in the form of conidia that are often combined with other inert materials to facilitate application, protect conidia, and improve their shelf life. The aim of this study was to implement strategies for developing formulations to increase conidia shelf life. We evaluated gum produced from one strain and conidia from two different H. citriformis strains. Conidia were formulated by evaluating different concentrations of Acacia and Hirsutella gums to enhance conidia viability during storage at 4 °C or 25 °C. Results indicated that formulations maintained conidia viability for at least 90 d after storage at 25 °C (≥70% viability) and at least 120 d after storage at 4 °C, which was significantly (p ≤ 0.05) higher than that of the control, without observing changes in pH values. We also demonstrated 100% formulation purity from days 0 to 120, among all treatments. In conclusion, evaluated formulations maintained H. citriformis conidia viability for at least three months, when stored at 4 °C.

Hirsutella citriformis Speare is the only entomopathogenic fungus involved in Diaphorina citri Kuwayama natural epizootics. The aim of the present study was to evaluate different protein sources as supplements to stimulate Hirsutella citriformis growth, improve conidiation on solid culture, and evaluate its produced gum for conidia formulation against D. citri adults. Hirsutella citriformis INIFAP-Hir-2 strain was grown on agar media enriched with wheat bran, wheat germ, soy, amaranth, quinoa, and pumpkin seed, in addition to oat with wheat bran and/or amaranth. The results demonstrated that 2% wheat bran significantly (p < 0.05) promoted mycelium growth. However, 4% and 5% wheat bran achieved the highest conidiation (3.65 × 10⁷ conidia/mL and 3.68 × 10⁷ conidia/mL, respectively). Higher conidiation (p < 0.05) was observed on oat grains supplemented with wheat bran, as compared with culturing on oat grains without supplements (7.25 × 10⁷ versus 5.22 × 10⁷ conidia/g), after a 14 d instead of 21 d incubation period. After supplementing synthetic medium or oat grains with wheat bran and/or amaranth, INIFAP-Hir-2 conidiation increased, whereas production time was reduced. After using Acacia and Hirsutella gums to formulate conidia produced on wheat bran and amaranth at 4%, field trial results showed that the highest (p < 0.05) D. citri mortality was achieved by Hirsutella gum-formulated conidia (80.0%), followed by the Hirsutella gum control (57.8%). Furthermore, Acacia gum-formulated conidia caused 37.8%, whereas Acacia gum and negative controls induced 9% mortality. In conclusion, Hirsutella citriformis gum used to formulate its conidia improved biological control against D. citri adults.