Bacillus pantothenticus spores activated by dimethylformamide and dimethylsulphoxide

High-throughput, single-cell analysis of macrophage interactions with fluorescently labeled Bacillus anthracis spores

The engulfment of Bacillus anthracis spores by macrophages is an important step in the pathogenesis of inhalational anthrax. However, from a quantitative standpoint, the magnitude to which macrophages interact with and engulf spores remains poorly understood, in part due to inherent limitations associated with commonly used assays. To analyze phagocytosis of spores by RAW264.7 macrophage-like cells in a high-throughput, nonsubjective manner, we labeled B. anthracis Sterne 7702 spores prior to infection with an Alexa Fluor 488 amine-reactive dye in a manner that did not alter their germination, growth kinetics, and heat resistance. Using flow cytometry, large numbers of cells exposed to labeled spores were screened to concurrently discriminate infected from uninfected cells and surface-associated from internalized spores. These experiments revealed that spore uptake was not uniform, but instead, highly heterogeneous and characterized by subpopulations of infected and uninfected cells, as well as considerable variation in the number of spores associated with individual cells. Flow cytometry analysis of infections demonstrated that spore uptake was independent of the presence or absence of fetal bovine serum, a germinant that, while routinely used in vitro, complicates the interpretation of the outcome of infections. Two commonly used macrophage cell lines, RAW264.7 and J774A.1 cells, were compared, revealing significant disparity between these two models in the rates of phagocytosis of labeled spores. These studies provide the experimental framework for investigating mechanisms of spore phagocytosis, as well as quantitatively evaluating strategies for interfering with macrophage binding and uptake of spores.

Heat activation/shock temperatures for Bacillus anthracis spores and the issue of spore plate counts versus true numbers of spores

Assessing true numbers of viable anthrax spores is complex. Optimal heat activation conditions vary with species, media and germinants. Published time/temperature combinations for Bacillus anthracis spores range from 60 degrees C for <or=90 min to boiling for 1 min. Results presented here indicate that temperatures are best kept to <or=70 degrees C and holding times need not exceed 15-30 min. Under conditions of 60 degrees C for 90 min, 62-23 degrees C for 15 min and 70 degrees C for 15 or 30 min, although the ratio of heated:unheated counts ranged from <1 to >1, post-heating counts were less than their pre-heating counterparts on between 71% and 88% of occasions. A high probability was found of viable spore counts differing significantly from counts determined microscopically, with differences of almost 1 log possible. Viable counts were lower than microscopic counts in 15 of 18 tests.

Spore germination in Dictyostelium discoideum. II. Effects of dimethyl sulfoxide on post-activation lag as evidence for the multistate model of activation

Mutant spores of Dictyostelium discoideum, strain SG-10, differ from wild type spores in their ability to spontaneously germinate, to be activated with 5% Dimethyl Sulfoxide (DMSO), and to be deactivated with 0.2 M sucrose. Both heat-activated wild type and mutant spores began to swell after a lag of 60-75 min at ambient temperature. Suspension of heat activated spores in 5% DMSO resulted in blockage of spore swelling and a concomitant severe inhibition of respiration; removal of 5% DMSO allowed resumption of respiration and the spores began to swell after a lag of only 15 min. It was concluded that 5% DMSO allowed the early reactions (M) to proceed but blocked the later reactions (R) of post-activation lag. Treatment of one day old spores with 20% DMSO solution for 30-120 min quantitatively activated the population. The post-activation lag time was directly dependent on the time of 20% DMSO treatment. Spores activated with 20% DMSO treatment could be deactivated by incubation at 0 degrees C; the spores most quickly deactivated at 0 degrees C were those within 10 min of swelling. Mitochondrial transport inhibitors such as azide and cyanide caused deactivation in an analogous manner. It is hypothesized that spores proceed to the second portion of the lag phase called (R) before the environment determines if dormancy is reimposed or if germination will proceed. The sensitive strain (SG-10) showed a greater degree of "damage" than the wild type after supraoptimal treatment with 40% DMSO. The spores became more resistant with age to the "damaging" action of 40% DMSO. All the observed effects of DMSO treatment were compatible with our multistate model of activation which suggests that the early portion of the lag phase (M) may involve a relative uncoupling of oxidative phosphorylation while the later portion (R) may require tight coupling.

Water vapor, aqueous ethyl alcohol, and heat activation of Bacillus megaterium spore germination

Dormant spores of Bacillus megaterium were activated for germination on glucose by heating them in aqueous suspension (but not if heated dry), by treating them with aqueous ethyl alcohol at 30 C, or by exposing them to water vapor at room temperature. The degree of water vapor activation depended upon the relative humidity, the time, and the temperature of exposure. Activation increased the extent and rate of glucose-induced germination and decreased the average microlag. Extended water vapor treatment also activated spores for germination induced by KI and by l-alanine. Spores activated by any of the three treatments were deactivated by treatment at 66 C, either for 18 hr in 100% ethyl alcohol or for 40 hr over P(2)O(5). Deactivated spores were reactivated by heat, by 5 m ethyl alcohol, or by water vapor. It is postulated that heating and ethyl alcohol may change the structure of liquid water, so that it is more like water vapor and can more readily penetrate to and hydrate a critical (enzymatic?) spore site, leading to activation.