Dodecylamine rapidly kills of spores of multiple Firmicute species: properties of the killed spores and the mechanism of the killing

Recent progress in proteins regulating the germination of Bacillus subtilis spores

Bacterial spores can remain dormant for years, but they maintain the ability to recommence life through a process termed germination. Although spore germination has been reviewed many times, recent work has provided novel conceptual and molecular understandings of this important process. By using Bacillus subtilis as a model organism, here we thoroughly describe the signal transduction pathway and events that lead to spore germination, incorporating the latest findings on transcription and translation that are likely detected during germination. Then, we comprehensively review the proteins associated with germination and their respective functions. Notably, the typical germinant receptor GerA and the SpoVAF/FigP complex have been newly established as channels for ions release at early stage of germination. Moreover, given that germination is also affected by spore quality, such as molecular cargo, we collect the data about the proteins regulating sporulation to affect spore quality. Specifically, RocG-mediated glutamate catabolism during sporulation to ensure spore quality; GerE-regulated coat protein expression, and CotH-modified coat protein by phosphorylation to ensure normal coat assembly; and RNase Y-degraded RNA in newly released spores to promote dormancy. The latest progress in our understanding of these germination proteins provides valuable insights into the mechanism underlying germination.

Foodborne spore-forming bacteria: Challenges and opportunities for their control through the food production chain

Foodborne spore-forming bacteria represent a significant challenge within the food production chain due to their widespread occurrence and resistance to various processing methods. In addition to their role in food spoilage, these bacteria exhibit pathogenic properties, posing risks to public health. A comprehensive understanding of the impact of unit operations along the food production continuum, from farm or field to fork, is essential for ensuring both the safety and quality of food products. This chapter explores the factors influencing the growth, inactivation, and persistence of these bacteria, as well as the challenges and opportunities for their control. The discussion encompasses preventive measures, control strategies at the farm and field levels, and processing operations, including both thermal and non-thermal methods. Post-processing controls, such as storage and distribution practices, are also addressed. Furthermore, consumer behavior, education, and lessons learned from past outbreaks and product recalls contribute to a broader understanding of how to manage spore-forming bacteria within the food production chain. By assessing and quantifying the effects of each processing step, it becomes possible to implement effective control measures, thereby ensuring microbiological safety and enhancing the quality of food products.

Albusamides A-G: Hydroxylated Fatty Amine Derivatives from the Deep-Sea-Derived Actinomycete Streptomyces albus 228DD-066 and Their Cytotoxic Activity

A series of new hydroxylated fatty amine derivatives, albusamides A-G (1-7), along with four known compounds (8-11), which are reported for the first time from a natural source, were isolated from the culture broth of Streptomyces albus 228DD-066 derived from a deep-sea sediment sample gathered off the coast of Dokdo Island, Republic of Korea. Their structures were elucidated through the comprehensive analysis of 1D and 2D NMR spectra and HRESIMS, and absolute configurations were determined using the modified Mosher's method. Biological evaluations against solid and blood cancer cell lines revealed that these new metabolites have moderate to strong cytotoxic activity. Compound 3 exhibited high cytotoxic activity with GI50 values ranging from 0.4 to 0.6 μM against solid cancer cell lines and exhibited the strongest cytotoxicity (GI50 value = 0.2 μM) against the WSU-DLCL2 blood cancer cell line.

Preservation effects of photodynamic inactivation-mediated antibacterial film on storage quality of salmon fillets: Insights into protein quality

The preservation effects of a photodynamic inactivation (PDI)-mediated polylactic acid/5-aminolevulinic acid (PLA/ALA) film on the storage quality of salmon fillets were investigated. Results showed that the PDI-mediated PLA/ALA film could continuously generate reactive oxygen species by consuming oxygen to inactivate native pathogens and spoilage bacteria on salmon fillets. Meanwhile, the film maintained the content of muscle proteins and their secondary and tertiary structures, as well as the integrity of myosin by keeping the activity of Ca2+-ATPase, all of which protected the muscle proteins from degradation. Furthermore, the film retained the activity of total superoxide dismutase (T-SOD), suppressed the accumulation of lipid peroxides (e.g., MDA), which greatly inhibited four main types of protein oxidations. As a result, the content of flavor amino acids and essential amino acids in salmon fillets was preserved. Therefore, the PDI-mediated antimicrobial packaging film greatly preserves the storage quality of aquatic products by preserving the protein quality.

Impact of sporulation temperature on germination of Bacillus subtilis spores under optimal and adverse environmental conditions

Bacillus subtilis spores are important food spoilage agents and are occasionally involved in food poisoning. In foods that are not processed with intense heat, such bacterial spores are controlled by a combination of different hurdles, such as refrigeration, acidification, and low water activity (aw), which inhibit or delay germination and/or growth. Sporulation temperature has long been regarded as a relevant factor for the assessment of germination in chemically defined media, but little is known about its impact on food preservation environments. In this study, we compared germination dynamics of B. subtilis spores produced at optimal temperature (37 °C) with others incubated at suboptimal (20 °C) and supraoptimal (43 °C) temperatures in a variety of nutrients (rich-growth medium, L-alanine, L-valine, and AGFK) under optimal conditions as well as under food-related stresses (low aw, pH, and temperature). Spores produced at 20 °C had a lower germination rate and efficiency than those incubated at 37 °C in all the nutrients, while those sporulated at 43 °C displayed a higher germination rate and/or efficiency in response to rich-growth medium and mostly to L-alanine and AGFK under optimal environmental conditions. However, differences in germination induced by changes in sporulation temperature decreased when spores were activated by heat, mainly due to the greater benefit of heat for spores produced at 20 °C and 37 °C than at 43 °C, especially in AGFK. Non-heat-activated spores produced at 43 °C still displayed superior germination fitness under certain stresses that had considerably impaired the germination of the other two populations, such as reduced temperature and aw. Moreover, they presented lower temperature and pH boundaries for the inhibition of germination in rich-growth medium, while requiring a higher NaCl concentration threshold compared to spores obtained at optimal and suboptimal temperature. Sporulation temperature is therefore a relevant source of variability in spore germination that should be taken into account for the accurate prediction of spore behaviour under variable food preservation conditions with the aim of improving food safety and stability.

Comparative study on the impact of equally stressful environmental sporulation conditions on thermal inactivation kinetics of B. subtilis spores

Control of bacterial spores continues to be one of the main challenges for the food industry due to their wide dissemination and extremely high resistance to processing methods. Furthermore, the large variability in heat resistance in spores that contaminate foods makes it difficult to establish general processing conditions. Such heterogeneity not only derives from inherent differences among species and strains, but also from differences in sporulation environments that are generally ignored in spores encountered in foods. We evaluated heat inactivation kinetics and the thermodependency of resistance parameters in B. subtilis 168 spores sporulated at adverse temperatures, water activity (aw), and pH, applying an experimental approach that allowed us to quantitatively compare the impact of each condition. Reduction of incubation temperature from the optimal temperature dramatically reduced thermal resistance, and it was the most influential factor, especially at the highest treatment temperatures. These spores were also more sensitive to chemicals presumably acting in the inner membrane. Reducing sporulation aw increased heat resistance, although the magnitude of that effect depended on the solute and the treatment temperature. Thus, changes in sporulation environments varied 3D100°C values up to 10.4-fold and z values up to 1.7-fold, highlighting the relevance of taking such a source of variability into account when setting heat processing conditions. UV-C treatment and sodium hypochlorite efficiently inactivated all spore populations, including heat-resistant ones produced at low aw.

The underlying mechanism of bacterial spore germination: An update review

Bacterial spores are highly resilient and universally present on earth and can irreversibly enter the food chain to cause food spoilage or foodborne illness once revived to resume vegetative growth. Traditionally, extensive thermal processing has been employed to efficiently kill spores; however, the relatively high thermal load adversely affects food quality attributes. In recent years, the germination-inactivation strategy has been developed to mildly kill spores based on the circumstance that germination can decrease spore-resilient properties. However, the failure to induce all spores to geminate, mainly owing to the heterogeneous germination behavior of spores, hampers the success of applying this strategy in the food industry. Undoubtedly, elucidating the detailed germination pathway and underlying mechanism can fill the gap in our understanding of germination heterogeneity, thereby facilitating the development of full-scale germination regimes to mildly kill spores. In this review, we comprehensively discuss the mechanisms of spore germination of Bacillus and Clostridium species, and update the molecular basis of the early germination events, for example, the activation of germination receptors, ion release, Ca-DPA release, and molecular events, combined with the latest research evidence. Moreover, high hydrostatic pressure (HHP), an advanced non-thermal food processing technology, can also trigger spore germination, providing a basis for the application of a germination-inactivation strategy in HHP processing. Here, we also summarize the diverse germination behaviors and mechanisms of spores of Bacillus and Clostridium species under HHP, with the aim of facilitating HHP as a mild processing technology with possible applications in food sterilization. Practical Application: This work provides fundamental basis for developing efficient killing strategies of bacterial spores in food industry.

Resistance properties and the role of the inner membrane and coat of Bacillus subtilis spores with extreme wet heat resistance

AIMS

A protein termed 2Duf greatly increases wet heat resistance of Bacillus subtilis spores. The current work examines the effects of 2Duf on spore resistance to other sporicides, including chemicals that act on or must cross spores' inner membrane (IM), where 2Duf is likely present. The overall aim was to gain a deeper understanding of how 2Duf affects spore resistance, and of spore resistance itself.

METHODS AND RESULTS

2Duf's presence increased spore resistance to chemicals that damage or must cross the IM to kill spores. Spore coat removal decreased 2Duf-spore resistance to chemicals and wet heat, and 2Duf-spores made at higher temperatures were more resistant to wet heat and chemicals. 2Duf-less spores lacking coats and Ca-dipicolinic acid were also extremely sensitive to wet heat and chemicals that transit the IM to kill spores.

CONCLUSIONS

The new work plus previous results lead to a number of important conclusions as follows. (1) 2Duf may influence spore resistance by decreasing the permeability of and lipid mobility in spores' IM. (2) Since wet heat-killed spores that germinate do not accumulate ATP, wet heat may inactivate some spore IM protein essential in ATP production which is stabilized in a more rigid IM. (3) Both Ca-dipicolinic acid and the spore coat play an important role in the permeability of the spore IM, and thus in many spore resistance properties.

SIGNIFICANCE AND IMPACT OF THE STUDY

The work in this manuscript gives a new insight into mechanisms of spore resistance to chemicals and wet heat, to the understanding of spore wet heat killing, and the role of Ca-dipicolinic acid and the coat in spore resistance.

What's new and notable in bacterial spore killing!

Spores of many species of the orders Bacillales and Clostridiales can be vectors for food spoilage, human diseases and intoxications, and biological warfare. Many agents are used for spore killing, including moist heat in an autoclave, dry heat at elevated temperatures, UV radiation at 254 and more recently 222 and 400 nm, ionizing radiation of various types, high hydrostatic pressures and a host of chemical decontaminants. An alternative strategy is to trigger spore germination, as germinated spores are much easier to kill than the highly resistant dormant spores—the so called “germinate to eradicate” strategy. Factors important to consider in choosing methods for spore killing include the: (1) cost; (2) killing efficacy and kinetics; (3) ability to decontaminate large areas in buildings or outside; and (4) compatibility of killing regimens with the: (i) presence of people; (ii) food quality; (iii) presence of significant amounts of organic matter; and (iv) minimal damage to equipment in the decontamination zone. This review will summarize research on spore killing and point out some common flaws which can make results from spore killing research questionable.