Visualization of SpoVAEa protein dynamics in dormant spores of Bacillus cereus and dynamic changes in their germinosomes and SpoVAEa during germination

Bacillus cereus spores, like most Bacillus spores, can survive for years depending on their specific structure, and germinate when their surroundings become suitable. Spore germination proteins play an important role in the initiation of germination. Because germinated spores lose the extreme resistance of the dormant state, more information related to the function of germination proteins could be useful to develop new strategies to control B. cereus spores. Prior work has shown that: i) the channel protein SpoVAEa exhibits high frequency movement in the outer leaflet of the inner membrane (IM) in dormant spores of B. subtilis; ii) the dynamics of germinosome formation in developing spores of B. cereus indicate that the formation of germinosome foci is slower than foci formation of germinant receptor GerR and scaffold protein GerD. However, the dynamics of movement of SpoVAEa in B. cereus spores, and the complete behavior of the germinosome in germinated spores of B. cereus are still unclear. In this study, we found that the SpoVAEa fluorescent foci in dormant spores of B. cereus redistribute at a lower frequency than in B. subtilis, and likely colocalize with GerD in dormant spores. Our results further indicate that: i) overexpression of GerR(A-C-B)-SGFP2 and SpoVAEa-SGFP2 with GerD-mScarlet-I from a plasmid leads to more heterogeneity and lower efficiency of spore germination in B. cereus; ii), germinosome foci composed of GerR(A-C-B)-SGFP2 and GerD-mScarlet-I were lost prior to the phase transition in germination; and iii) GerD-mScarlet-I foci spread out but continued to exist beyond the phase transition of B. cereus spores.

Comparison of Synergistic Effect of Nisin and Monolaurin on the Inactivation of Three Heat Resistant Spores Studied by Design of Experiments in Milk

Spore forming bacteria are special problems for the dairy industry. Heat treatments are insufficient to kill the spores. This is a continuously increasing problem for the industry, but we should be able to control it. In this context, we investigated the combined effect of nisin, monolaurin, and pH values on three heat resistant spores in UHT milk and distilled water and to select an optimal combination for the maximum spore inactivation. The inhibitory effect of nisin (between 50 and 200 IU/ml), monolaurin (ranging from 150 to 300 µg/ml), and pH (between 5 and 8) was investigated using a central composite plan. Results were analyzed using the response surface methodology (RSM). The obtained data showed that the inactivation of Bacillus spores by the combined effect of nisin-monolaurin varies with spore species, acidity, and nature of the medium in which the bacterial spores are suspended. In fact, Terribacillus aidingensis spores were more resistant, to this treatment, than Paenibacillus sp. and Bacillus sporothermodurans ones. The optimum process parameters for a maximum reduction of bacterial spores (∼3log) were obtained at a concentration of nisin >150 IU/ml and of monolaurin >200 µg/ml. The current study highlighted the presence of a synergistic effect between nisin and monolaurin against heat bacterial spores. So, such treatment could be applied by the dairy industry to decontaminate UHT milk and other dairy products from bacterial spores.

Moderate high-pressure superdormancy in Bacillus spores: properties of superdormant spores and proteins potentially influencing moderate high-pressure germination

Resistant bacterial spores are a major concern in industrial decontamination processes. An approach known as pressure-mediated germination-inactivation strategy aims to artificially germinate spores by pressure to mitigate their resistance to inactivation processes. The successful implementation of such a germination-inactivation strategy relies on the germination of all spores. However, germination is heterogeneous, with some ‘superdormant’ spores germinating extremely slowly or not at all. The present study investigated potential underlying reasons for moderate high-pressure (150 MPa, 37°C) superdormancy of Bacillus subtilis spores. The water and dipicolinic acid content of superdormant spores was compared to that of the initial dormant spore population. The results suggest that water and dipicolinic acid content are not major drivers of moderate high-pressure superdormancy. Proteomic analysis was used to identify proteins that were quantified at significantly different levels in superdormant spores. Subsequent validation of the germination capacity of deletion mutants revealed that the presence of protein YhcN is required for efficient moderate high-pressure germination and that proteins MinC, cse60, and SspK may also play a role, albeit a minor one. Importance Spore-forming bacteria are ubiquitous in nature, and as a consequence, inevitably enter the food chain or other processing environments. Their presence can lead to significant spoilage or safety related issues. Intensive treatment is usually required to inactivate them; however, this harms important quality attributes. A pressure-mediated germination-inactivation approach can balance the need for effective spore inactivation and retention of sensitive ingredients. However, superdormant spores are the bottleneck preventing the successful and safe implementation of such a strategy. In-depth understanding of moderate high-pressure germination and the underlying causes of superdormancy is necessary to advance the development of mild high pressure-based spore control technologies. The approach used in this work allowed the identification of proteins that have not yet been associated to reduced germination at moderate high-pressure. This research paves the way for further studies on the germination and superdormancy mechanisms in spores, assisting the development of mild spore inactivation strategies.

Bacterial biosilicification: A new insight into the global silicon cycle

Biosilicification is the process by which organisms incorporate soluble, monomeric silicic acid, Si(OH)4, in the form of polymerized insoluble silica, SiO2. Biosilicifying eukaryotes, including diatoms, siliceous sponges, and higher plants, have been the targets of intense research to study the molecular mechanisms underlying biosilicification. By contrast, prokaryotic biosilicification has been less well studied, partly because the biosilicifying capability of well-known bacteria was not recognized until recently. This review summarizes recent findings on bacterial extracellular and intracellular biosilicification, the latter of which has been demonstrated only recently in bacteria. The topics discussed herein include bacterial (and archaeal) extracellular biosilicification in geothermal environments, encapsulation of Bacillus spores within a silica layer, and silicon accumulation in marine cyanobacteria. The possible contribution of bacterial biosilicification to the global silicon cycle is also discussed.

Sterilization effects of UV laser irradiation on Bacillus atrophaeus spore viability, structure, and proteins

Bacillus spores are highly resistant to toxic chemicals and extreme environments. Because some Bacillus species threaten public health, spore inactivation techniques have been intensively investigated. We exposed Bacillus atrophaeus spores...