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The work in this paper has identified two new factors, bacillithiol and sporulene, as modulators of the resistance and germination of spores of two Bacillus subtilis strains, and by extension, probably spores of other Bacillota. Since spores of some species can give rise to cells that can cause food spoilage and/or disease, new knowledge about spore resistance and germination could have applied utility.

50 I. 50 II. 52 III. 53 IV. 66 V. 71 VI. 72 VII. 74 75 References 75 SUMMARY: Cryptospores, recovered from Ordovician through Devonian rocks, differ from trilete spores in possessing distinctive configurations (i.e. hilate monads, dyads, and permanent tetrads). Their affinities are contentious, but knowledge of their relationships is essential to understanding the nature of the earliest land flora. This review brings together evidence about the source plants, mostly obtained from spores extracted from minute, fragmented, yet exceptionally anatomically preserved fossils. We coin the term ‘cryptophytes’ for plants that produced the cryptospores and show them to have been simple terrestrial organisms of short stature (i.e. millimetres high). Two lineages are currently recognized. Partitatheca shows a combination of characters (e.g. spo‐rophyte bifurcation, stomata, and dyads) unknown in plants today. Lenticulatheca encompasses discoidal sporangia containing monads formed from dyads with ultrastructure closer to that of higher plants, as exemplified by Cooksonia. Other emerging groupings are less well characterized, and their precise affinities to living clades remain unclear. Some may be stem group embryophytes or tracheophytes. Others are more closely related to the bryophytes, but they are not bryophytes as defined by extant representatives. Cryptophytes encompass a pool of diversity from which modern bryophytes and vascular plants emerged, but were competitively replaced by early tracheophytes. Sporogenesis always produced either dyads or tetrads, indicating strict genetic control. The long‐held consensus that tetrads were the archetypal condition in land plants is challenged.

Throughout the life cycle of mushrooms, countless spores are released from the fruiting bodies. The spores have significant implications in the food and medicine industries due to pharmacological effects attributed to their bioactive ingredients. Moreover, high concentration of mushroom spores can induce extrinsic allergic reactions in mushroom cultivation workers. Therefore, it is important to study the bioactive ingredients of medicinal mushroom spores and molecular mechanisms of spore formation to develop healthcare products utilizing medicinal mushroom spores and breed sporeless/low- or high-spore-producing strains. This review summarizes the bioactive compounds of mushroom spores, the influence factors and molecular mechanisms of spore formation. Many bioactive compounds extracted from mushroom spores have a wide range of pharmacological activities. Several exogenous factors such as temperature, humidity, light, nutrients, and culture matrix, and endogenous factors such as metabolism-related enzymes activities and expression levels of genes related to sporulation individually or in combination affect the formation, size, and discharge of spores. The future research directions are also discussed for supplying references to analyze the bioactive compounds of spores and the molecular mechanisms of spore formation in mushrooms.

The primary objective of this study was to identify the molecular signals present in arbuscular mycorrhizal (AM) germinated spore exudates (GSEs) responsible for activating nuclear Ca2+ spiking in the Medicago truncatula root epidermis. Medicagotruncatula root organ cultures (ROCs) expressing a nuclear-localized cameleon reporter were used as a bioassay to detect AM-associated Ca2+ spiking responses and LC-MS to characterize targeted molecules in GSEs. This approach has revealed that short-chain chitin oligomers (COs) can mimic AM GSE-elicited Ca2+ spiking, with maximum activity observed for CO4 and CO5. This spiking response is dependent on genes of the common SYM signalling pathway (DMI1/DMI2) but not on NFP, the putative Sinorhizobium meliloti Nod factor receptor. A major increase in the CO4/5 concentration in fungal exudates is observed when Rhizophagus irregularis spores are germinated in the presence of the synthetic strigolactone analogue GR24. By comparison with COs, both sulphated and nonsulphated Myc lipochito-oligosaccharides (LCOs) are less efficient elicitors of Ca2+ spiking in M.truncatula ROCs. We propose that short-chain COs secreted by AM fungi are part of a molecular exchange with the host plant and that their perception in the epidermis leads to the activation of a SYM-dependent signalling pathway involved in the initial stages of fungal root colonization.

The germination stability of Paenibacillus alkaliterreae (PA) spores under various temperature, salinity, and pH conditions was studied for their potential use in bioconcrete crack remediation.The operating range of PA spore germination and biomineralization of CaCO3 was within 25–37°C, salinity 0.5–4% (w/v), and pH 6–10.Self-healing of concrete was studied using extracellular polymeric substance (EPS)-coated spores and uncoated free spores under wet and wet–dry cycle curing of concrete prisms.EPS-coated spores showed self-healing in terms of an area repair ratio of 88 ± 2.8%, compared with 72 ± 2.7% in free spores.The mechanical properties of both bioconcrete combinations comprising EPS-coated and uncoated spores were significantly higher compared with conventional concrete. Microbially induced biomineralization (MIBM) is a trending biotechnological application with the potential to be used in the engineering of built environment; however, it is limited by premature germination of spores due to stresses during concrete mixing. We investigated the germination dynamics of Paenibacillus alkaliterreae (PA) spores under variable temperature, pH, and salinity levels to identify the operating ranges conducive for spore germination and biomineralization in an outdoor environment. To prevent premature germination, the spores were covered with a protective coating of extracellular polymeric substance (EPS). The spores germinated and biomineralized CaCO3 across environmental conditions of 25–37°C, 0.5–4% NaCl, and pH 6–10. EPS-coated spores achieved 88 ± 2.8% self-healing in 28 days compared with 72 ± 2.7% in free spores. Chemical and morphological characterization confirmed that the bioconcrete comprised CaCO3 biomineral in the form calcite, which improved the strength, durability, and quality of this bioconcrete over conventional concrete. [Display omitted] Our work on microbially enhanced mineralization in bioconcrete by bacterial extracellular polymeric substance (EPS)-coated spores is currently at Technology Readiness Level (TRL) 3, with experimental proof of concept at laboratory conditions. We observed certain challenges of this microbe-mediated self-healing of concrete, including low scalability and high cost. To overcome these limitations, further research into, and development of, mineral bioengineering with large-scale biomanufacturing of minerals by optimization or strain engineering of potent biomineral producing strains are needed to achieve self-healing of concrete on a shorter timescale. Commercialization of this technology would require the criteria to be met related to regulatory policies of using microbial spores in concrete structures. This can be achieved by assessing the environmental impact and sensitivity analysis of this bio-based technological solution. The current study attempts to mitigate the huge carbon footprint generated by the construction industry during cement production. This was achieved by using EPS-coated bacterial spores to make bioconcrete structures. These spores led to microbially enhanced biomineralization that resulted in self-healing of bioconcrete and improved mechanical properties.

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.

The bacterial spore, the hardiest known life form, can survive in a metabolically dormant state for many years and can withstand high temperatures, radiation, and toxic chemicals. The molecular basis of spore dormancy and resistance is not understood, but the physical state of water in the different spore compartments is thought to play a key role. To characterize this water in situ, we recorded the water ²H and ¹⁷O spin relaxation rates in D₂O-exchanged Bacillus subtilis spores over a wide frequency range. The data indicate high water mobility throughout the spore, comparable with binary protein-water systems at similar hydration levels. Even in the dense core, the average water rotational correlation time is only 50 ps. Spore dormancy therefore cannot be explained by glass-like quenching of molecular diffusion but may be linked to dehydration-induced conformational changes in key enzymes. The data demonstrate that most spore proteins are rotationally immobilized, which may contribute to heat resistance by preventing heat-denatured proteins from aggregating irreversibly. We also find that the water permeability of the inner membrane is at least 2 orders of magnitude lower than for model membranes, consistent with the reported high degree of lipid immobilization in this membrane and with its proposed role in spore resistance to chemicals that damage DNA. The quantitative results reported here on water mobility and transport provide important clues about the mechanism of spore dormancy and resistance, with relevance to food preservation, disease prevention, and astrobiology.

Abstract Bacterial spores formed upon metabolic stress have minimal metabolic activity and can remain dormant for years. Nevertheless, they can sense the environment and germinate quickly upon exposure to various germinants. Germinated spores can then outgrow into vegetative cells. Germination of spores of some anaerobes, especially Clostridioides difficile, is triggered by cholic acid and taurocholic acid. Elevated levels of these bile acids are thought to correlate with a perturbed gut microbiome, which cannot efficiently convert primary bile acids into secondary bile acids. That bile acids are germination-triggers suggests these bacteria have a life cycle taking place partially in the mammalian digestive tract where bile acids are plentiful; notably bile acids can be made by all vertebrates. Thus, spores survive in the environment until taken up by a host where they encounter an environment suitable for germination and then proliferate in the largely anaerobic large intestine; some ultimately sporulate there, regenerating environmentally resistant spores in the C. difficile life cycle. This review summarizes current literature on the effects of bile acids and their metabolites on spore germination in the gut and evidence that adaptation to bile acids as germinants is a consequence of a life cycle both inside and outside the digestive tract. The review summarizes current literature on effects of bile acids and their metabolites on clostridial spore germinant receptor proteins, their structural organization in germinosomes in spore membranes, and the occurrence of anaerobic spore forming bacteria in the gut together with the evidence that adaptation to bile acids as germinants is a consequence of a life cycle both inside and outside the digestive tract.

In disturbed or pioneer settings, spores and sclerotia of ectomycorrhizal fungi serve as the necessary inoculum for establishment of ectomycorrhizal-dependent trees. Yet, little is known about the persistence of these propagules through time. Here, live field soil was inoculated with known quantities of basidiospores from four pine-associated species of Rhizopogon; these samples were then buried in retrievable containers, and pine seedling bioassays of serially diluted spore samples were used to measure spore viability. In the first 4 yr, no evidence of loss of spore viability was found in the four Rhizopogon species tested, but all four species exhibited dormancy in which a maximum of 1-8% of their spores were initially receptive to pine roots. There were some differences between species in overall inoculum potential of their spores, but all species broke dormancy at a statistically similar rate. This result provides evidence for spore dormancy in a common ectomycorrhizal genus, but it also precludes our ability to estimate the longevity of the spores accurately. Nevertheless these results, coupled with the observed patterns of Rhizopogon spore banks, suggest that at least decade-long durations are likely. As this experiment progresses, the true longevity of the spores will eventually be revealed.

Living systems have inspired approaches to engineer cells as independent functional materials or integrate them within a natural or synthetic matrix to create engineered living materials (ELMs).To address the principal challenges arising from the ‘livingness’ of cells, bacterial spores have emerged as a game changer in the field, enabling users to ‘activate’ cells on demand and to treat ELMs with harsh conditions.The inherent physical properties of the structural components of the spores have led to diverse applications of spore-based materials.Emerging synthetic biology tools and better understanding of bacterial spores might contribute to expanding the relevance of spores in various fields, such as biosensing, biocatalysis, and data storage, among others. Inspired by biological functions of living systems, researchers have engineered cells as independent functional materials or integrated them within a natural or synthetic matrix to create engineered living materials (ELMs). However, the ‘livingness’ of cells in such materials poses serious drawbacks, such as a short lifespan and the need for cold-chain logistics. Bacterial spores have emerged as a game changer to bypass these shortcomings as a result of their intrinsic dormancy and resistance against harsh conditions. Emerging synthetic biology tools tailored for engineering spores and better understanding of their physical properties have led to novel applications of spore-based materials. Here, we review recent advances in such materials and discuss future challenges for the development of time- and cost-efficient spore-based materials with high performance. Inspired by biological functions of living systems, researchers have engineered cells as independent functional materials or integrated them within a natural or synthetic matrix to create engineered living materials (ELMs). However, the ‘livingness’ of cells in such materials poses serious drawbacks, such as a short lifespan and the need for cold-chain logistics. Bacterial spores have emerged as a game changer to bypass these shortcomings as a result of their intrinsic dormancy and resistance against harsh conditions. Emerging synthetic biology tools tailored for engineering spores and better understanding of their physical properties have led to novel applications of spore-based materials. Here, we review recent advances in such materials and discuss future challenges for the development of time- and cost-efficient spore-based materials with high performance.