Optimization of sample preparation and green color imaging using the mNeonGreen fluorescent protein in bacterial cells for photoactivated localization microscopy

mNeonGreen fluorescent protein is capable of photo-switching, hence in principle applicable for super-resolution imaging. However, difficult-to-control blinking kinetics that lead to simultaneous emission of multiple nearby mNeonGreen molecules impedes its use for PALM. Here, we determined the on- and off- switching rate and the influence of illumination power on the simultaneous emission. Increasing illumination power reduces the probability of simultaneous emission, but not enough to generate high quality PALM images. Therefore, we introduce a simple data post-processing step that uses temporal and spatial information of molecule localizations to further reduce artifacts arising from simultaneous emission of nearby emitters. We also systematically evaluated various sample preparation steps to establish an optimized protocol to preserve cellular morphology and fluorescence signal. In summary, we propose a workflow for super-resolution imaging with mNeonGreen based on optimization of sample preparation, data acquisition and simple post-acquisition data processing. Application of our protocol enabled us to resolve the expected double band of bacterial cell division protein DivIVA, and to visualize that the chromosome organization protein ParB organized into sub-clusters instead of the typically observed diffraction-limited foci. We expect that our workflow allows a broad use of mNeonGreen for super-resolution microscopy, which is so far difficult to achieve.

Discovery of a dual protease mechanism that promotes DNA damage checkpoint recovery

The DNA damage response is a signaling pathway found throughout biology. In many bacteria the DNA damage checkpoint is enforced by inducing expression of a small, membrane bound inhibitor that delays cell division providing time to repair damaged chromosomes. How cells promote checkpoint recovery after sensing successful repair is unknown. By using a high-throughput, forward genetic screen, we identified two unrelated proteases, YlbL and CtpA, that promote DNA damage checkpoint recovery in Bacillus subtilis. Deletion of both proteases leads to accumulation of the checkpoint protein YneA. We show that DNA damage sensitivity and increased cell elongation in protease mutants depends on yneA. Further, expression of YneA in protease mutants was sufficient to inhibit cell proliferation. Finally, we show that both proteases interact with YneA and that one of the two proteases, CtpA, directly cleaves YneA in vitro. With these results, we report the mechanism for DNA damage checkpoint recovery in bacteria that use membrane bound cell division inhibitors.

A repetitive mutation and selection system for bacterial evolution to increase the specific affinity to pancreatic cancer cells

It is difficult to target and kill cancer cells. One possible approach is to mutate bacteria to enhance their binding to cancer cells. In the present study, Gram-negative Escherichia coli and Gram-positive Bacillus subtilis were randomly mutated, and then were positively and negatively selected for binding cancer vs normal cells. With repetitive mutation and selection both bacteria successfully evolved to increase affinity to the pancreatic cancer cell line (Mia PaCa-2) but not normal cells (HPDE: immortalized human pancreatic ductal epithelial cells). The mutant E. coli and B. subtilis strains bound to Mia PaCa-2 cells about 10 and 25 times more than to HPDE cells. The selected E. coli strain had mutations in biofilm-related genes and the regulatory region for a type I pilus gene. Consistent with type I pili involvement, mannose could inhibit the binding to cells. The results suggest that weak but specific binding is involved in the initial step of adhesion. To test their ability to kill Mia PaCa-2 cells, hemolysin was expressed in the mutant strain. The hemolysin released from the mutant strain was active and could kill Mia PaCa-2 cells. In the case of B. subtilis, the initial binding to the cells was a weak interaction of the leading pole of the motile bacteria. The frequency of this interaction to Mia PaCa-2 cells dramatically increased in the evolved mutant strain. This mutant strain could also specifically invade beneath Mia PaCa-2 cells and settle there. This type of mutation/selection strategy may be applicable to other combinations of cancer cells and bacterial species.

Transcription and translation of the sigG gene is tuned for proper execution of the switch from early to late gene expression in the developing Bacillus subtilis spore

A cascade of alternative sigma factors directs developmental gene expression during spore formation by the bacterium Bacillus subtilis. As the spore develops, a tightly regulated switch occurs in which the early-acting sigma factor σ^F is replaced by the late-acting sigma factor σ^G. The gene encoding σ^G (sigG) is transcribed by σ^F and by σ^G itself in an autoregulatory loop; yet σ^G activity is not detected until σ^F-dependent gene expression is complete. This separation in σ^F and σ^G activities has been suggested to be due at least in part to a poorly understood intercellular checkpoint pathway that delays sigG expression by σ^F. Here we report the results of a careful examination of sigG expression during sporulation. Unexpectedly, our findings argue against the existence of a regulatory mechanism to delay sigG transcription by σ^F and instead support a model in which sigG is transcribed by σ^F with normal timing, but at levels that are very low. This low-level expression of sigG is the consequence of several intrinsic features of the sigG regulatory and coding sequence—promoter spacing, secondary structure potential of the mRNA, and start codon identity—that dampen its transcription and translation. Especially notable is the presence of a conserved hairpin in the 5’ leader sequence of the sigG mRNA that occludes the ribosome-binding site, reducing translation by up to 4-fold. Finally, we demonstrate that misexpression of sigG from regulatory and coding sequences lacking these features triggers premature σ^G activity in the forespore during sporulation, as well as inappropriate σ^G activity during vegetative growth. Altogether, these data indicate that transcription and translation of the sigG gene is tuned to prevent vegetative expression of σ^G and to ensure the precise timing of the switch from σ^F to σ^G in the developing spore.

Global changes in gene expression occur during normal cellular growth and development, as well as during cancer cell transformation and bacterial pathogenesis. In this study we have investigated the molecular mechanisms that drive the switch from early to late developmental gene expression during spore formation by the model bacterium Bacillus subtilis. At early times, gene expression in the developing spore is directed by the transcription factor σ^F; at later times σ^F is replaced by σ^G. An important, yet poorly understood aspect of this σ^F-to-σ^G transition is how σ^G activation is delayed until the early, σ^F-directed phase of gene expression is complete. Here we have carefully examined expression of the gene encoding σ^G, sigG, and found that its transcription and translation are ordinarily dampened by several features of its regulatory and coding sequences. Moreover, we have found that this “tuning” of sigG expression is required for proper timing of the switch to σ^G. These results reframe our understanding of how sigG is regulated during B. subtilis sporulation and, more broadly, advance our understanding of how global changes in gene expression can be precisely executed at the molecular/genetic level.

Synchronization in pairs of rotating active biomotors

Although synchronization is a well-known physical phenomenon, experimental studies of its emergence in living bacterial cells are still scarce. The difficulty in generating a controlled scenario to detect synchronization has limited the experimental outcomes so far. We present a realization based on holographic optical tweezers in which adhered pairs of self-propelled bacteria rotate in a plane. The separation distance between the bacteria determines the strength of the hydrodynamic coupling. Despite the noisy environment and autonomous dynamics of the living bacteria, we find evidence of phase locking and frequency entrainment in their rotation. The observation of higher order frequency synchronization is also discussed.

Paramagnetism in Bacillus spores: Opportunities for novel biotechnological applications

Spores of Bacillus megaterium, Bacillus cereus, and Bacillus subtilis were found to exhibit intrinsic paramagnetic properties as a result of the accumulation of manganese ions. All three Bacillus species displayed strong yet distinctive magnetic properties arising from differences in manganese quantity and valency. Manganese ions were found to accumulate both within the spore core as well as being associated with the surface of the spore. Bacillus megaterium spores accumulated up to 1 wt.% manganese (II) within, with a further 0.6 wt.% adsorbed onto the surface. At room temperature, Bacillus spores possess average magnetic susceptibilities in the range of 10-6 to 10-5 . Three spore-related biotechnological applications-magnetic sensing, magnetic separation and metal ion adsorption-were assessed subsequently, with the latter two considered as having the most potential for development.

The Photochemistry of Unprotected DNA and DNA inside Bacillus subtilis Spores Exposed to Simulated Martian Surface Conditions of Atmospheric Composition, Temperature, Pressure, and Solar Radiation

DNA is considered a potential biomarker for life-detection experiments destined for Mars. Experiments were conducted to examine the photochemistry of bacterial DNA, either unprotected or within Bacillus subtilis spores, in response to exposure to simulated martian surface conditions consisting of the following: temperature (-10°C), pressure (0.7 kPa), atmospheric composition [CO₂ (95.54%), N₂ (2.7%), Ar (1.6%), O₂ (0.13%), and H₂O (0.03%)], and UV-visible-near IR solar radiation spectrum (200-1100 nm) calibrated to 4 W/m² of UVC (200-280 nm). While the majority (99.9%) of viable spores deposited in multiple layers on spacecraft-qualified aluminum coupons were inactivated within 5 min, a detectable fraction survived for up to the equivalent of ∼115 martian sols. Spore photoproduct (SP) was the major lesion detected in spore DNA, with minor amounts of cyclobutane pyrimidine dimers (CPD), in the order TT CPD > TC CPD >> CT CPD. In addition, the (6-4)TC, but not the (6-4)TT, photoproduct was detected in spore DNA. When unprotected DNA was exposed to simulated martian conditions, all photoproducts were detected. Surprisingly, the (6-4)TC photoproduct was the major photoproduct, followed by SP ∼ TT CPD > TC CPD > (6-4)TT > CT CPD > CC CPD. Differences in the photochemistry of unprotected DNA and spore DNA in response to simulated martian surface conditions versus laboratory conditions are reviewed and discussed. The results have implications for the planning of future life-detection experiments that use DNA as the target, and for the long-term persistence on Mars of forward contaminants or their DNA. Key Words: Bacillus subtilis-DNA-Mars-Photochemistry-Spore-Ultraviolet. Astrobiology 18, 393-402.

Cyclic di-AMP Acts as an Extracellular Signal That Impacts Bacillus subtilis Biofilm Formation and Plant Attachment

There is a growing appreciation for the impact that bacteria have on higher organisms. Plant roots often harbor beneficial microbes, such as the Gram-positive rhizobacterium Bacillus subtilis, that influence their growth and susceptibility to disease. The ability to form surface-attached microbial communities called biofilms is crucial for the ability of B. subtilis to adhere to and protect plant roots. In this study, strains harboring deletions of the B. subtilis genes known to synthesize and degrade the second messenger cyclic di-adenylate monophosphate (c-di-AMP) were examined for their involvement in biofilm formation and plant attachment. We found that intracellular production of c-di-AMP impacts colony biofilm architecture, biofilm gene expression, and plant attachment in B. subtilis We also show that B. subtilis secretes c-di-AMP and that putative c-di-AMP transporters impact biofilm formation and plant root colonization. Taken together, our data describe a new role for c-di-AMP as a chemical signal that affects important cellular processes in the environmentally and agriculturally important soil bacterium B. subtilis These results suggest that the "intracellular" signaling molecule c-di-AMP may also play a previously unappreciated role in interbacterial cell-cell communication within plant microbiomes.IMPORTANCE Plants harbor bacterial communities on their roots that can significantly impact their growth and pathogen resistance. In most cases, however, the signals that mediate host-microbe and microbe-microbe interactions within these communities are unknown. A detailed understanding of these interaction mechanisms could facilitate the manipulation of these communities for agricultural or environmental purposes. Bacillus subtilis is a plant-growth-promoting bacterium that adheres to roots by forming biofilms. We therefore began by exploring signals that might impact its biofilm formation. We found that B. subtilis secretes c-di-AMP and that the ability to produce, degrade, or transport cyclic di-adenylate monophosphate (c-di-AMP; a common bacterial second messenger) affects B. subtilis biofilm gene expression and plant attachment. To our knowledge, this is the first demonstration of c-di-AMP impacting a mutualist host-microbe association and suggests that c-di-AMP may function as a previously unappreciated extracellular signal able to mediate interactions within plant microbiomes.

Cell death as a trigger for morphogenesis

The complex morphologies observed in many biofilms play a critical role in the survival of these microbial communities. Recently, the formation of wrinkles has been the focus of many studies aimed at finding fundamental information on morphogenesis during development. While the underlying genetic mechanisms of wrinkling are not well-understood, recent discoveries have led to the counterintuitive idea that wrinkle formation is triggered by localized cell death. This work examines the hypothesis that the material properties of a biofilm both power and control wrinkle formation within biofilms in response to localized cell death. Using an agent-based model and a high-performance platform (Biocellion), we built a model that qualitatively reproduced wrinkle formation in biofilms due to cell death. Through the use of computational simulations, we determined important relationships between cellular level mechanical interactions and changes in colony morphology. These simulations were also used to identify significant cellular interactions that are required for wrinkle formation. These results are a first step towards more comprehensive models that, in combination with experimental observations, will improve our understanding of the morphological development of bacterial biofilms.

The novel antibiotic rhodomyrtone traps membrane proteins in vesicles with increased fluidity

The acylphloroglucinol rhodomyrtone is a promising new antibiotic isolated from the rose myrtle Rhodomyrtus tomentosa, a plant used in Asian traditional medicine. While many studies have demonstrated its antibacterial potential in a variety of clinical applications, very little is known about the mechanism of action of rhodomyrtone. Preceding studies have been focused on intracellular targets, but no specific intracellular protein could be confirmed as main target. Using live cell, high-resolution, and electron microscopy we demonstrate that rhodomyrtone causes large membrane invaginations with a dramatic increase in fluidity, which attract a broad range of membrane proteins. Invaginations then form intracellular vesicles, thereby trapping these proteins. Aberrant protein localization impairs several cellular functions, including the respiratory chain and the ATP synthase complex. Being uncharged and devoid of a particular amphipathic structure, rhodomyrtone did not seem to be a typical membrane-inserting molecule. In fact, molecular dynamics simulations showed that instead of inserting into the bilayer, rhodomyrtone transiently binds to phospholipid head groups and causes distortion of lipid packing, providing explanations for membrane fluidization and induction of membrane curvature. Both its transient binding mode and its ability to form protein-trapping membrane vesicles are unique, making it an attractive new antibiotic candidate with a novel mechanism of action.

Bacterial antibiotic resistance constitutes a major public healthcare issue and deaths caused by antimicrobial resistance are expected to soon exceed the number of cancer-related fatalities. In order to fight resistance, new antibiotics have to be developed that are not affected by existing microbial resistance strategies. Thus, antibiotics with novel or multiple targets are urgently needed. Rhodomyrtone displays excellent antibacterial activity, has been safely used in traditional Asian medicine for a long time, and resistance against this promising antibiotic candidate could not be detected in multiple passaging experiments. Here we demonstrate that rhodomyrtone possesses a completely novel mechanism of action, which is opposed to that of existing cell envelope-targeting drugs, minimizing the risk of cross-resistance, and in fact rhodomyrtone is highly active against e.g. vancomycin-resistant Staphylococcus aureus. Thus, rhodomyrtone is an extremely interesting compound for further antibacterial drug development.

Screening lactic acid bacteria to manufacture two-stage fermented feed and pelleting to investigate the feeding effect on broilers

Bacillus subtilis var. natto N21 (BS) and different lactic acid bacteria were applied to produce two-stage fermented feeds. Broilers were fed these feeds to select the best fermented feed. The selected fermented feed was pelleted and investigated for its effects on growth performance, carcass traits, intestinal microflora, serum biochemical constituents, and apparent ileal nutrient digestibility. Trial 1 involved three hundred thirty-six 1-d-old broilers with equal numbers of each sex, randomly assigned into control, BS + Bacillus coagulans L12 (BBC), BS + Lactobacillus casei (BLC), BS + Lactobacillus acidophilus (BLA), BS + Lactobacillus acidophilus L15 (BLA15), BS + Lactobacillus delbruekckii (BLD), and BS + Lactobacillus reuteri P24 (BLR24) groups with 3 replicates per group. Trial 2 involved two hundred forty 1-d-old broilers with equal numbers of each sex, randomly assigned into control, BBC, and pelleted BS + Bacillus coagulans L12 fermented feed (PBBC) groups with 4 replicates per group. Trial 3 involved sixteen 21-d-old male broilers randomly assigned into control and PBBC groups with 4 replicates per group for a nutrient digestibility trial. The feed conversion ratio (FCR) in the BBC group was better than the control (P < 0.05), and the production efficiency factor (PEF) was the best. However, weight gain (WG), feed intake (FI), and PEF were the lowest in the BLD group (P < 0.05). The WG during 0 to 21 d and 0 to 35 d in the PBBC groups were higher than the control (P < 0.05). The relative weight of the proventriculus + gizzard in the BBC and PBBC groups were higher than the control (P < 0.05). The digestible amino acid content in the PBBC group increased significantly (P < 0.05). Bacillus coagulans L12 is the best lactic acid bacteria for second stage fermentation. PBBC improved broiler growth performance, which may be due to the higher digestible amino acid content, it has the potential to become a commercial feed.

Antibacterial Activity, Cytotoxicity, and the Mechanism of Action of Bacteriocin from Bacillus subtilis GAS101

OBJECTIVE

The aim of this study was to purify and characterize bacteriocin from the soil isolate Bacillus subtilis GAS101, and to determine its antimicrobial as well as antibiofilm potential. The purified bacteriocin was further analyzed and evaluated for mammalian cell cytotoxicity and the possible mode of action.

MATERIAL AND METHODS

Bacteriocin from B. subtilis GAS101 (an animal husbandry soil isolate) was partially purified and checked for antimicrobial and antibiofilm activity against gram-positive and gram-negative bacteria. The molecular weight of bacteriocin was determined using tricine SDS-PAGE gel. The stability of bacteriocin was investigated at various temperatures and pH levels, and its sensitivity towards 8 enzymes and 6 chemicals was determined. Cytotoxicity analysis was performed on a Vero cell line by a tetrazolium dye-based assay. Scanning electron microscopy (SEM) of bacteriocin-treated bacteria was carried out to determine the possible mode of action.

RESULTS

Bacteriocin from B. subtilis GAS101 was a potential inhibitor of both the indicator organisms (Staphylococcus epidermidis and Escherichia coli), and had a molecular weight of approximately 6.5 kDa. An in situ gel assay showed a zone of inhibition corresponding to the estimated protein band size. Bacteriocin was stable and showed antibacterial activity in broad ranges of temperature (30-121°C) and pH (2-12). It was sensitive to 4 proteolytic enzymes, which indicated its proteinaceous nature. Bacteriocin showed > 70% cell viability on the mammalian Vero cell line. SEM depicted that the bacteriocin was able to disrupt the bacterial cell membrane as its probable mode of action.

CONCLUSION

Thermostable and pH-tolerant bacteriocin from B. subtilis GAS101, of about 6.5 kDa, showed broad-spectrum antimicrobial and antibiofilm activity.

FRET Analysis of the Chemotaxis Pathway Response

Most motile bacteria follow spatial gradients of chemical and physical stimuli in their environment. In Escherichia coli and other bacteria, the best characterized chemotaxis is in gradients of amino acids or sugars, but other physiological stimuli such as pH, osmolarity, redox potentials, and temperature are also known to elicit tactic responses. These multiple environmental stimuli are integrated and processed within a highly sophisticated chemotaxis network to generate coordinated chemotaxis behavior, which features high sensitivity, a wide dynamic range, and robustness against variations in background stimulation, protein levels, and temperature. Although early studies relied on behavioral analyses to characterize chemotactic responses in vivo, or on biochemical assays to study the pathway in vitro, we describe here a method to directly measure the intracellular pathway response using Förster resonance energy transfer (FRET). In E. coli, the most commonly used form of the FRET assay relies on the interaction between the phosphorylated response regulator CheY and its phosphatase CheZ to quantify activity of the histidine kinase CheA. We further describe a FRET assay for Bacillus subtilis, which employs CheY and the motor-associated phosphatase FliY as a FRET pair. In particular, we highlight the use of FRET to quantify pathway properties, including signal amplification, dynamic range, and kinetics of adaptation.

Effect of probiotics on the basis of Bacillus subtilis and Bifidobacterium longum on the biochemical parameters of the animal organism

For the purpose of safe modulation of the intestinal microflora, probiotics have been increasingly used in recent years. In the present work, the effect of the probiotic sporobacterin (Bacillus subtilis 534) (I group) and soybean-bifidum (Bifidobacterium longum) (II group) on male rats of the Wistar line was evaluated. In assessing nonspecific immunity in vitro, there was an increase in the level of baseline level in the first and second groups (by 8.3 and 12.2% more control). The influence of probiotic preparations on the intestinal normoflora was assessed using PCR. Bifidumbacterin increased the normal microflora, in particular, Escherichia coli 1.55 times, Lactobacillus 1.26 times, Enterococcus 1.3 times as much control; the level of conditionally pathogenic microflora, in particular, Proteus spp. decreased by 1.3 times in comparison with the control. Sporobacterin also contributed to an increase in the amount of E. coli (1.55 times) and Lactobacillus (0.9 times). When a culture of Bifidobacterium longum was introduced, a selective reduction in the loss of chemical elements was observed against the background of the diet used. At the end of the experiment, the content of calcium in the body tissues of animals of group II exceeded this indicator in group I by 3.9%, phosphorus by 17.6%, copper by 28.5%, and zinc by 15.2%. The totality of the results obtained by us indicates that inclusion of Bifidumbacterium longum in the diet of animals makes the use of this preparation in the correction of mineral imbalance and improves the microflora of the intestines of animals by reducing the number of representatives of opportunistic microflora against the background of an increase in the number of basic representatives of normal microbiocenosis. Also, the use of probiotic drugs as additives leads to a slight increase in the level of nonspecific immunity, which increases the natural resistance of the organism.

Extract from the fermented soybean product Natto inhibits Vibrio biofilm formation and reduces shrimp mortality from Vibrio harveyi infection

Many bacteria, including Vibrio pathogens of shrimp, need to colonize and/or form biofilms in hosts or the environment to cause disease. Thus, one possible control strategy for shrimp Vibriosis is biofilm inhibition. With this objective, an extract from the Japanese fermented soybean product, Natto was tested with the luminescent shrimp pathogen Vibrio harveyi (VH) for its ability to inhibit or degrade biofilm and to interfere with cell growth in broth. Natto is a traditional fermentation product of Bacillus subtilis var Natto (BSN1). Using 96 well microtiter plates coated with 0.4% chitosan, we found that biofilm formation by VH was inhibited, while growth in parallel broth cultures was not. When an extract from Natto prepared using BSN1 was mixed with feed for the whiteleg shrimp Penaeus vannamei before immersion challenge with V. harveyi at 10⁶ cfu/ml, survival was significantly higher (p≤0.05) than for control shrimp given feed without these additives. Further work done to test whether d-amino acids were involved in biofilm formation as previously reported for B. subtilis, Staphylococus aureus and Pseudomonas aeruginosa gave negative results. In conclusion, we discovered that Natto extract can inhibit Vibrio biofilm formation and that it or BSN1 alone added to shrimp feed can significantly reduce shrimp mortality in immersion challenges with pathogenic VH. This shows some promise for possible application against Vibriosis in shrimp since Natto is generally regarded as safe (GRAS) for human consumption.

Effects of Bacterial Fermentation on the Biochemical Constituents and Antioxidant Potential of Fermented and Unfermented Soybeans Using Probiotic Bacillus subtilis (KCTC 13241)

Fermented soybeans, cheonggukjang (CKJ), are considered to be more wholesome than soybeans in Korea. To select the best soybean cultivar for making functional CKJ, a comparison was made between the biological activities of four soybean cultivars in their unfermented soybean (UFS) and CKJ states. Changes in 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity, 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) assays, superoxide dismutase (SOD)-like activity, total phenolic compounds, total amino acids, and isoflavones were investigated. The levels of DPPH, ABTS, SOD-like activity, and total phenolic compounds increased in CKJ among all cultivars. The isoflavone aglycone and total amino acids showed the highest amount in CKJ prepared from soybean cultivar Aga 3. These results suggest that the improved antioxidant activity of CKJ in all cultivars might occur because of the higher levels of aglycones and total phenolic compounds achieved during fermentation. Moreover, CKJ prepared from soybean cultivar Aga 3 showed higher antioxidant activity than the other cultivars and so can be considered for the commercial production of functional foods in the future.

Effects of Bacillus subtilis on some physiological and biochemical parameters of Triticum aestivum L. (wheat) under salinity

Endophytic strain Bacillus subtilis (B. subtilis) 10-4, producing indole-3-acetic acid (IAA) and siderofores but not active in phosphate solubilization, exerted a protective effect on Triticum aestivum L. (wheat) plant grown under salinity (2% NaCl) stress. Exposure to salt stress resulted in an essential increase of proline (Pro) and malondialdehyde (MDA) level in the seedlings. At the same time the seedlings inoculated with B. subtilis 10-4 were characterized by decreased level of stress-induced Pro and MDA accumulation. It was revealed that both B. subtilis 10-4 and salinity caused increase in the content of endogenous salicylic acid (SA) in wheat seedlings as compared to SA content in the control, while B. subtilis 10-4 suppressed stress-induced SA accumulation. Water storage capacity (WSC) in leaf tissues was increased and stress-induced hydrolysis of statolite starch in root cap cells of the germinal roots was reduced by B. subtilis 10-4. The obtained data indicated that the activation of the defense reactions induced by B. subtilis 10-4 induced defense reactions may be connected with their ability to decrease the level of stress-induced oxidative and osmotic stress in seedlings and with the increase of endogenous SA level that can make a significant contribution to the implementation of the protective effect of B. subtilis 10-4 and is manifested in the improvement of plant growth, WSC of leaves and slowing down of the process of statolite starch hydrolysis under salinity.

Bacteria and bacterial envelope components enhance mammalian reovirus thermostability

Enteric viruses encounter diverse environments as they migrate through the gastrointestinal tract to infect their hosts. The interaction of eukaryotic viruses with members of the host microbiota can greatly impact various aspects of virus biology, including the efficiency with which viruses can infect their hosts. Mammalian orthoreovirus, a human enteric virus that infects most humans during childhood, is negatively affected by antibiotic treatment prior to infection. However, it is not known how components of the host microbiota affect reovirus infectivity. In this study, we show that reovirus virions directly interact with Gram positive and Gram negative bacteria. Reovirus interaction with bacterial cells conveys enhanced virion thermostability that translates into enhanced attachment and infection of cells following an environmental insult. Enhanced virion thermostability was also conveyed by bacterial envelope components lipopolysaccharide (LPS) and peptidoglycan (PG). Lipoteichoic acid and N-acetylglucosamine-containing polysaccharides enhanced virion stability in a serotype-dependent manner. LPS and PG also enhanced the thermostability of an intermediate reovirus particle (ISVP) that is associated with primary infection in the gut. Although LPS and PG alter reovirus thermostability, these bacterial envelope components did not affect reovirus utilization of its proteinaceous cellular receptor junctional adhesion molecule-A or cell entry kinetics. LPS and PG also did not affect the overall number of reovirus capsid proteins σ1 and σ3, suggesting their effect on virion thermostability is not mediated through altering the overall number of major capsid proteins on the virus. Incubation of reovirus with LPS and PG did not significantly affect the neutralizing efficiency of reovirus-specific antibodies. These data suggest that bacteria enhance reovirus infection of the intestinal tract by enhancing the thermal stability of the reovirus particle at a variety of temperatures through interactions between the viral particle and bacterial envelope components.

A model of cell-wall dynamics during sporulation in Bacillus subtilis

To survive starvation, Bacillus subtilis forms durable spores. After asymmetric cell division, the septum grows around the forespore in a process called engulfment, but the mechanism of force generation is unknown. Here, we derived a novel biophysical model for the dynamics of cell-wall remodeling during engulfment based on a balancing of dissipative, active, and mechanical forces. By plotting phase diagrams, we predict that sporulation is promoted by a line tension from the attachment of the septum to the outer cell wall, as well as by an imbalance in turgor pressures in the mother-cell and forespore compartments. We also predict that significant mother-cell growth hinders engulfment. Hence, relatively simple physical principles may guide this complex biological process.

Assessing the Impact of Germination and Sporulation Conditions on the Adhesion of Bacillus Spores to Glass and Stainless Steel by Fluid Dynamic Gauging

The adhesion of spores of 3 Bacillus species with distinctive morphologies to stainless steel and borosilicate glass was studied using the fluid dynamic gauging technique. Marked differences were observed between different species of spores, and also between spores of the same species prepared under different sporulation conditions. Spores of the food-borne pathogen B. cereus were demonstrated to be capable of withstanding shear stresses greater than 1500 Pa when adhered to stainless steel, in contrast to spores of Bacillus subtilis and Bacillus megaterium, which detached in response to lower shear stress. An extended DLVO model was shown to be capable of predicting the relative differences in spore adhesion between spores of different species and different culture conditions, but did not predict absolute values of force of adhesion well. Applying the model to germinating spores showed a significant reduction in adhesion force shortly after triggering germination, indicating a potential strategy to achieve enhanced removal of spores from surfaces in response to shear stress, such as during cleaning-in-place procedures.

PRACTICAL APPLICATION

Spore-forming bacteria are a concern to the food industry because they have the potential to cause food-borne illness and product spoilage, while being strongly adhesive to processing surfaces and resistant to cleaning-in-place procedures. This work is of significance to the food processors and manufacturers because it offers insight to the properties of spore adhesion and identifies a potential strategy to facilitate the removal of spores during cleaning procedures.

Experimental and theoretical studies on the morphogenesis of bacterial biofilms

Biofilm morphogenesis not only reflects the physiological state of bacteria but also serves as a strategy to sustain bacterial survival. In this paper, we take the Bacillus subtilis colony as a model system to explore the morphomechanics of growing biofilms confined in a defined geometry. We find that the growth-induced stresses may drive the occurrence of both surface wrinkling and interface delamination in the biofilm, leading to the formation of a labyrinthine network on its surface. The wrinkles are perpendicular to the boundary of the constraint region. The variation in the surface undulations is attributed to the spatial stress field, which is isotropic in the inner regime but anisotropic in the vicinity of the boundary. Our experiments show that the directional surface wrinkles can confer biofilms with anisotropic wetting properties. This study not only highlights the role of mechanics in sculpturing organisms within the morphogenetic context but also suggests a promising route toward desired surfaces at the interface between synthetic biology and materials sciences.

Laboratory Investigations on the Survival of Bacillus subtilis Spores in Deliquescent Salt Mars Analog Environments

Observed features such as recurring slope lineae suggest that liquid water may exist on the surface and near-subsurface of Mars today. The presence of this liquid water, likely in the form of a brine, has important implications for the present-day water cycle, habitability, and planetary protection policies. It is possible that this water is formed, at least partially, by deliquescence of salts, a process during which hygroscopic salts absorb water vapor from the atmosphere and form a saturated liquid brine. We performed laboratory experiments to examine the ability of Bacillus subtilis (B-168) spores, alone or mixed with calcium perchlorate salt (Ca(ClO₄)₂), to form liquid water via deliquescence under Mars-relevant conditions. Spore survival after exposure to these conditions was examined. An environmental chamber was used to expose the samples to temperature and relative humidity (RH) values similar to those found on Mars, and Raman microscopy was used to identify the phases of water and salt that were present and to confirm the presence of spores. We found that B-168 spores did not condense any detectable water vapor on their own during the diurnal cycle, even at 100% RH. However, when spores were mixed with perchlorate salt, the entire sample deliquesced at low RH values, immersing the spores in a brine solution during the majority of the simulated martian temperature and humidity cycle. After exposure to the simulated diurnal cycles and, in some cases, perchlorate brine, the impact of each environmental scenario on spore survival was estimated by standard plate assay. We found that, if there are deliquescent salts in contact with spores, there is a mechanism for the spores to acquire liquid water starting with only atmospheric water vapor as the H₂O source. Also, neither crystalline nor liquid Ca(ClO₄)₂ is sporicidal despite the low water activity. Key Words: Raman microscopy-Mars-Planetary protection-Salts-Water activity. Astrobiology 17, 997-1008.

Molecular investigation on the binding of Cd(II) by the binary mixtures of montmorillonite with two bacterial species

Bacteria-phyllosilicate complexes are commonly found in natural environments and are capable of immobilizing trace metals. However, the molecular binding mechanisms of heavy metals to these complex aggregates still remain poorly understood. This study investigated Cd adsorption on Gram-positive Bacillus subtilis, Gram-negative Pseudomonas putida and their binary mixtures with montmorillonite using surface complexation model, Cd K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy and isothermal titration calorimetry (ITC). We have shown that larger amounts of Cd are adsorbed by B. subtilis than by P. putida at pH<∼6, and Cd sorption that binding to phosphate groups plays a more important role in P. putida than in B. subtilis. This remind us that we should consider the microbe species when predict the biochemical behavior of trace metals in microbe-bearing environments. The observed Cd adsorption on the binary bacteria-clay composites was more than that predicted based on the component additivity approach. When taking bacteria-clay (1:1 mass ratio) as a representative example, an approximately 68%:32% metal distribution between the bacterial and mineral fraction was found. Both the EXAFS and ITC fits showed that the binding stoichiometry for Cd-carboxyl/phosphate was smaller in the binary mixtures than that in pure bacteria. We proposed that the significant deviations were possibly due to the physical-chemical interaction between the composite fractions that might reduce the agglomeration of the clay grains, increase the negative surface charges, and provide additional bridging of metals ions between bacterial cells and clays.

Impact of orientation and flexibility of peptide linkers on T. maritima lipase Tm1350 displayed on Bacillus subtilis spores surface using CotB as fusion partner

Fusion protein construction often requires peptide linkers for prolonged conformation, extended stability and enzyme activity. In this study a series of fusion between Thermotoga maritima lipase Tm1350 and Bacillus subtillis coat protein CotB, comprising of several peptide linkers, with different length, flexibility and orientations were constructed. Effects of temperature, pH and chemicals were examined, on the activity of displayed enzyme. The fusion protein with longer flexible linkers L9 [(GGGGS)₄] and L7 (GGGGS-GGGGS-EAAAK-EAAAK-GGGGS-GGGGS) possess 1.29 and 1.16-fold higher activity than the original, under optimum temperature and pH respectively. Moreover, spore surface displaying Tm1350 with L3 (EAAAK-GGGGS) and L9 ((GGGGS)₄) showed extended thermostably, maintaining 1.40 and 1.35-fold higher activity than the original respectively, at 80 °C after 5 h of incubation. The enzyme activity of linkers with different orientation, including L5, L6 and L7 was determined, where L7 maintained 1.05 and 1.27-fold higher activity than L5 and L6. Effect of 0.1% proteinase K, bromelain, 20% ethanol and 30% methanol was investigated. Linkers with appropriate Glycine residues (flexible) showed higher activity than Alanine residues (rigid). The activity of the displayed enzyme can be improved by maintaining orientation and flexibility of peptide linkers, to evaluate high activity and stability in industrial processes.

Role of tumbling in bacterial swarming

Typical wild-type bacteria swimming in sparse suspensions exhibit a movement pattern called "run and tumble," characterized by straight trajectories (runs) interspersed by shorter, random reorientation (tumbles). This is achieved by rotating their flagella counterclockwise, or clockwise, respectively. The chemotaxis signaling network operates in controlling the frequency of tumbles, enabling navigation toward or away from desired regions in the medium. In contrast, while in dense populations, flagellated bacteria exhibit collective motion and form large dynamic clusters, whirls, and jets, with intricate dynamics that is fundamentally different than trajectories of sparsely swimming cells. Although collectively swarming cells do change direction at the level of the individual cell, often exhibiting reversals, it has been suggested that chemotaxis does not play a role in multicellular colony expansion, but the change in direction stems from clockwise flagellar rotation. In this paper, the effects of cell rotor switching (i.e., the ability to tumble) and chemotaxis on the collective statistics of swarming bacteria are studied experimentally in wild-type Bacillus subtilis and two mutants-one that does not tumble and one that tumbles independently of the chemotaxis system. We show that while several of the parameters examined are similar between the strains, other collective and individual characteristics are significantly different. The results demonstrate that tumbling and/or flagellar directional rotor switching has an important role on the dynamics of swarming, and imply that swarming models of self-propelled rods that do not take tumbling and/or rotor switching into account may be oversimplified.