Growth Inhibition of Aspergillus Spp. by Endophytic Bacteria

Aspergillus spp. (A. Niger, A. flavus, and A. fumigatus) contaminate food commodities through production of secondary metabolites (mycotoxins) and aspergillosis, and thus pose severe hazard to human and animal health. Hence, the inhibition of mycotoxin-producing fungi on agricultural storage commodities needs to be considered. The aims of this study were to evaluate endophytic bacteria isolated from rice tissues that inhibit Aspergillus spp. growth, as well as to characterize the selected isolates morphologically and biochemically. Dual culture and disk diffusion method tests on 155 endophytic bacteria obtained three isolates, i.e. FB-Endo 65, FB-Endo 73, and FB-Endo 95, which showed inhibition zone from 13 to 17 mm against Aspergillus spp. growth. The inhibition zone and quantity of antifungal compounds increased positively with the length of incubation periods from 0 to 6 days. Antifungal compounds from the three isolates were insoluble in ethyl acetate, but soluble in methanol. The methanol soluble substance(s) from FB-Endo 73 showed higher inhibition zone than that of the other isolates. This result indicated that all three isolates produced strong antifungal activity. Morphological and biochemical identifications of the isolates revealed that all isolates belonged to the genus Bacillus sp. Further studies include identification and production methods of antifungal compounds of those endophytic bacteria and their application on stored seeds

Homochiral growth through enantiomeric cross-inhibition

The stability and conservation properties of a recently proposed polymerization model are studied. The achiral (racemic) solution is linearly unstable once the relevant control parameter (here the fidelity of the catalyst) exceeds a critical value. The growth rate is calculated for different fidelity parameters and cross-inhibition rates. A chirality parameter is defined and shown to be conserved by the nonlinear terms of the model. Finally, a truncated version of the model is used to derive a set of two ordinary differential equations and it is argued that these equations are more realistic than those used in earlier models of that form.Comment: 20 pages, 6 figures, Orig. Life Evol. Biosph. (accepted

Medium alkalization due to carbon metabolism is largely responsible for inhibition of bacterial growth by Vibrio cholerae supernatants

Vibrio cholerae is the causative agent of the diarrheal disease cholera. Many Vibrio species secrete antimicrobial factors, though the identity of such a factor has not been determined for any V. cholerae strain. Such an antimicrobial factor could be relevant to pathogenesis of cholera, which disrupts the intestinal microbiome. In this study, we investigated the antimicrobial effects of supernatant from 72 hour old cultures of V. cholerae C6706 on Shigella flexneri CFS100. Inhibition of S. flexneri growth was found to be dependent on the alkaline pH of the supernatant. A 1:1 mixture of pH-adjusted supernatant and LB was found to inhibit S. flexneri growth at alkaline but not neutral pH, as was pH-adjusted LB alone. In minimal medium, elevation of supernatant pH by V. cholerae was dependent on nutritional factors, and this elevation of medium pH also correlated with increased S. flexneri growth inhibition. Though medium alkalization in LB is often attributed to amino acid catabolism and the consequent production of ammonia, supplementation of V. cholerae cultures in minimal medium with amino acids had a weaker effect on alkalization and inhibition than did supplementation with selected carbon sources. This suggests that some feature of carbon metabolism causes medium alkalization and the resultant antimicrobial activity. Several V. cholerae mutants in potentially relevant pathways were screened for alkalization and S. flexneri growth inhibition, but none had any effect.Complicating this picture is the finding that V. cholerae grown under microaerobic conditions produce a less alkaline supernatant with stronger S. flexneri growth inhibition. The significance of this is unknown.Molecular Bioscience

Designing probiotic therapies with broad-spectrum activity against a wildlife pathogen

Host-associated microbes form an important component of immunity that protect against infection by pathogens. Treating wild individuals with these protective microbes, known as probiotics, can reduce rates of infection and disease in both wild and captive settings. However, the utility of probiotics for tackling wildlife disease requires that they offer consistent protection across the broad genomic variation of the pathogen that hosts can encounter in natural settings. Here we develop multi-isolate probiotic consortia with the aim of effecting broad-spectrum inhibition of growth of the lethal amphibian pathogen Batrachochytrium dendrobatidis (Bd) when tested against nine Bd isolates from two distinct lineages. Though we achieved strong growth inhibition between 70 and 100% for seven Bd isolates, two isolates appeared consistently resistant to inhibition, irrespective of probiotic strategy employed. We found no evidence that genomic relatedness of the chytrid predicted similarity of inhibition scores, nor that increasing the genetic diversity of the bacterial consortia could offer stronger inhibition of pathogen growth, even for the two resistant isolates. Our findings have important consequences for the application of probiotics to mitigate wildlife diseases in the face of extensive pathogen genomic variation

Inhibition of Fructose-1,6-bisphosphatase by Aminoimidazole Carboxamide Ribotide Prevents Growth of Salmonella enterica purH Mutants on Glycerol

The enzyme fructose-1,6-bisphosphatase (FBP) is key regulatory point in gluconeogenesis. Mutants of Salmonella enterica lacking purH accumulate 5-amino-4-imidazole carboxamide ribotide (AICAR) and are unable to utilize glycerol as sole carbon and energy sources. The work described here demonstrates this lack of growth is due to inhibition of FBP by AICAR. Mutant alleles of fbp that restore growth on glycerol encode proteins resistant to inhibition by AICAR and the allosteric regulator AMP. This is the first report of biochemical characterization of substitutions causing AMP resistance in a bacterial FBP. Inhibition of FBP activity by AICAR occurs at physiologically relevant concentrations and may represent a form of regulation of gluconeogenic flux in Salmonella enterica

Reducing the Amount of Microbiological Growth Using Ultrasonic Treatment

This thesis explored the possibility of using ultrasonic treatment to reduce the amount of microbiological growth in a sample of contaminated mill wastewater. It was found that ultrasonic treatment reduces microbiological growth through the mechanism of cavitation. percent inhibition increases with both time of treatment and applied power. The most economical conditions were high power and a short treatment time. The increase in cell volume had an inverse effect on the percent inhibition. The increase in consistency of the treated solution also had an inverse effect on the percent inhibition and 6% was the maximum treatable consistency. Ultrasonic treatment was compared to three popular biocides at a 90% inhibition level. The biocides used were Methylene Bis(Thiocyanate), Isothiazolin, and a Thiadiazine type. Dosages to achieve 90% inhibition were 154 ppm., 161 ppm, and 127 ppm. respectively. The 90% inhibition level was reached with 0.0158 kW hrs. of energy, using ultrasonic treatment. This energy was scaled up to 8.030% HP day/ton. Further studies are recommended in the areas of cell geometry, determination of the maximum power efficiency, and the development of a dynamic model to test ultrasonic treatment in a situation oriented more towards the paper mill environment