Introductory Microbiology

Gross, Trevor; Faull, J. L.; Ketteridge, Steve; Springham, Derek

doi:10.1007/978-1-4899-7194-4

Cited by 5 publications

(3 citation statements)

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“…To obtain dependable counts of microorganisms in a sample of soil or compost, a plate should have only 30 to 300 colonies (Ross 1983). It sometimes required a repeat to fulfill this condition because the population of antagonists will only be a fraction of the total count on a given plate.…”

Section: Discussionmentioning

confidence: 99%

A novel method for the identification and enumeration of microorganisms with potential for suppressing fungal plant pathogens

Rupela

Gopalakrishnan

Krajewski

et al. 2003

Biology and Fertility of Soils

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This paper describes a method that allowed counting of both the total culturable and antagonistic microorganisms in a given source such as compost. Fusarium solani, used as the test fungus, was spreadplated on quarter-strength (1/4) potato dextrose agar (PDA), its surface was exposed in a laminar flow for 4 h and then another layer (2-3 mm thick) of 1/4 PDA was poured over it, on which an appropriate dilution of a compost sample was spread-plated. Microorganisms in the compost samples appeared first, and were counted as total culturable organisms. Plates were further incubated until F. solani grew through the upper layer of PDA (generally in 4-8 days) and covered the whole plate including most of the microbial colonies, except for a few which had a halo around them. These were counted as antagonistic, and they were isolated and purified for further studies. The population of bacteria in the six specific compost samples (called Biodynamic or BD preparations by organic farmers) ranged from 3.45 log 10 (in BD502) to 8.59 log 10 (in BD504) per gram of materials. The population of antagonistic bacteria was counted for three of the six compost samples, and ranged from 3.24 log 10 (in BD502) to 6.90 log 10 (in BD500). Of the 67 bacterial isolates showing a halo that were assembled from different sources, 17 suppressed at least 1 of the 4 plant pathogenic fungi against which these were evaluated using the dual culture method.

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Section: Discussionmentioning

confidence: 99%

A novel method for the identification and enumeration of microorganisms with potential for suppressing fungal plant pathogens

Rupela

Gopalakrishnan

Krajewski

et al. 2003

Biology and Fertility of Soils

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“…It is well-known that during metabolism the allosteric feedback inhibition of the enzyme, catalyzing the initial step of the pathway, by the end product molecule significantly modulates the entire reaction . A recent single-molecule experiment studied the conversion of Amplex Red to resorufin by the horseradish peroxidase (HRP) enzyme in the presence of hydrogen peroxide (H 2 O 2 ) inside a lipid vesicle .…”

Section: Introductionmentioning

confidence: 99%

“…8,9 It is well-known that during metabolism the allosteric feedback inhibition of the enzyme, catalyzing the initial step of the pathway, by the end product molecule significantly modulates the entire reaction. 10 A recent single-molecule experiment studied the conversion of Amplex Red to resorufin by the horseradish peroxidase (HRP) enzyme in the presence of hydrogen peroxide (H 2 O 2 ) inside a lipid vesicle. 11 Notably, the uncharged Amplex Red molecules from the bulk medium penetrated through the phospholipid bilayer and entered into the reaction vesicle, whereas the charged product molecules were unable to come out of the enclosed area which led to the gradual accumulation of resorufin that in turn bound to the enzyme molecule at an allosteric site and inhibited the catalytic progress of the reaction.…”

Section: Introductionmentioning

confidence: 99%

Kinetics of Allosteric Inhibition of Single Enzyme by Product Molecules

2020

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Single-molecule experiment probed the catalytic conversions of Amplex Red to resorufin by horseradish peroxidase in which the product molecules were found to act as the allosteric inhibitor for the individual enzyme. While broad distributions of the initial reaction velocities and the number of product molecules required to cease the reaction unraveled the underlying dynamic disorder in the reaction pathway, bulk experimental measurements established the particularity of noncompetitive inhibition of the enzyme species. In this work, to rationalize the observed phenomena, we present a stochastic kinetic model of the enzymatic reaction taking into account the inhibitions of the enzyme and enzyme−substrate complex in the circumstance of their structural fluctuations. Starting from a chemical master equation that can further be reduced into a set of ordinary differential equations for the case of singleenzyme kinetics, we derived an analytical expression for the turnover time distribution, the first moment of which yielded the mean turnover time. The inverse of the latter showed excellent agreement with the bulk data of the initial enzymatic velocities measured in the presence of varying inhibitor concentrations. This supports the observed nature of inhibition which we further confirmed by constructing double-reciprocal plots for the inhibited kinetics. In addition, we successfully recovered ensemble data from another experiment that redesigned the aforesaid single-molecule catalysis to investigate the effects of molecular crowders on reaction velocity; the latter was greatly alleviated with increasing the molecular weight of the crowders. On the other hand, the calculated randomness parameter, determined from the higher moment of the turnover time distribution, clearly inferred dynamic disorder in the catalytic turnovers. Our work under a unified framework provides a robust theoretical description for the experimental kinetic study and eradicates the necessity of assuming an alternative mode of inhibition in analyzing the data, not consistent with the experiments, considered earlier.

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