Institute of Microbial Technology

Cherry tomatoes, consumed worldwide, have a short shelf life and are highly susceptible to significant pre- and postharvest losses, largely due to fungal pathogens like Alternaria alternata and Fusarium oxysporum. With the growing demand for nutritious food products free from synthetic preservatives, biopreservation has emerged as a safe and reliable method for controlling fungal growth in food. Biopreservation using lactic acid bacteria (LAB), known for producing antimicrobial metabolites, presents a promising approach at both the farm and industrial scales. This study investigates the antifungal potential of Lactobacillus fermentum O1.1, an isolate obtained from orange peel, against A. alternata and F. oxysporum. The growth performance of this isolate was assessed in various plant-based media, including watermelon rind (WMR), banana peel, and orange peel, in addition to MRS medium. Among these, WMR was found to be the most supportive medium for its growth. The cell-free supernatant (CFS) of Lb. fermentum O1.1 grown in WMR medium exhibited maximum inhibition of F. oxysporum (79.1%) and A. alternata (68%). Furthermore, cherry tomatoes infected with A. alternata and treated with the WMR-based CFS showed a reduced disease incidence (DI) of 16.78 ± 0.05%, compared to 40.17 ± 4.53% DI with the MRS-based CFS. Similarly, tomatoes infected with F. oxysporum and treated with the WMR-based CFS demonstrated a DI of 10.34 ± 4.86%, in contrast to 45.67 ± 4.53% DI with the MRS-based CFS. At room temperature (25 ± 2 °C), the WMR-based CFS extended the shelf life of cherry tomatoes from 2 to 5 days and decreased fungal susceptibility, with a reduction in DI by 16.78 ± 0.05% and 10.34 ± 4.86%, respectively. These findings suggest that Lb. fermentum O1.1 has significant potential as a biopreservative agent against fungal spoilage in cherry tomatoes.

Prions represent epigenetic regulator proteins that can self-propagate their structure and confer their misfolded structure and function on normally folded proteins. Like the mammalian prion PrPSc, prions also occur in fungi. While a few prions, like Swi1, affect gene expression, none are shown to affect heterochromatin structure and function. In fission yeast and metazoans, histone methyltransferase Clr4/Suv39 causes H3-Lys9 methylation, which is bound by the chromodomain protein Swi6/HP1 to assemble heterochromatin. Earlier, we showed that sng2-1 mutation in the Cut4 subunit of anaphase-promoting complex abrogates heterochromatin structure due to defective binding and recruitment of Swi6. Here, we demonstrate that the Cut4p forms a non-canonical prion form, designated as [SNG2], which abrogates heterochromatin silencing. [SNG2] exhibits various prion-like properties, e.g. non-Mendelian inheritance, requirement of Hsp proteins for its propagation, de novo generation upon cut4 overexpression, reversible curing by guanidine, cytoplasmic inheritance and formation of infectious protein aggregates, which are dissolved upon overexpression of hsp genes. Interestingly, [SNG2] prion imparts an enhanced tolerance to stress conditions, supporting its role in promoting cell survival under environmental stress during evolution.

Diabetes mellitus (DM) is a major risk factor for tuberculosis (TB), though the underlying mechanisms linking DM and TB remain ambiguous. Macrophages are a key player in the innate immune response and their phagocytic ability is enhanced in response to microbial infections. Upon infection or inflammation, they also repel invading pathogens by generating; reactive oxygen species (ROS), reactive nitrogen species (RNS), pro-inflammatory cytokines (IL-1β and IL-6), and anti-inflammatory cytokines (IL-10). However, the robustness of these innate defensive capabilities of macrophages when exposed to hyperglycemia remains unclear. In our current work, we explored the production of these host defense molecules in response to challenge with Mycobacterium tuberculosis (Mtb) infection and lipopolysaccharide (LPS) stimulation. Utilizing peritoneal macrophages from high-fat diet + streptozotocin induced diabetic mice and hyperglycemic THP-1-derived macrophages as model systems; we found that LPS stimulation and Mtb infection were ineffective in stimulating the production of ROS, RNS, and pro-inflammatory cytokines in cells exposed to hyperglycemia. On the contrary, an increase in production of anti-inflammatory cytokines was observed. To confirm the mechanism of decreased anti-bacterial activity of the diabetic macrophage, we explored activation status of these compromised macrophages and found decreased surface expression of activation (TLR-4) and differentiation markers (CD11b and CD11c). We postulate that this could be the cause for higher susceptibility for Mtb infection among diabetic individuals.