Calcium signalling in bacteria

A Divalent Metal Cation-Metabolite Interaction Model Reveals Cation Buffering and Speciation

I present the perspective that the divalent metalome and the metabolome can be modeled as a network of chelating interactions instead of separate entities. I review progress in understanding the complex cellular environment, in particular recent contributions to modeling metabolite-Mg2+ interactions. I then demonstrate a simple extension of these strategies based approximately on intracellular Escherichia coli concentrations. This model is composed of four divalent metal cations with a range of cellular concentrations and physical properties (Mg2+, Ca2+, Mn2+, and Zn2+), eight representative metabolites, and interaction constants. I applied this model to predict the speciation of divalent metal cations between free and metabolite-chelated species. This approach reveals potentially beneficial properties, including maintenance of free divalent metal cations at biologically relevant concentrations, buffering of free divalent metal cations, and enrichment of functional metabolite-chelated species. While currently limited by available interaction coefficients, this modeling strategy can be generalized to more complex systems. In summary, biochemists should consider the potential of cellular metabolites to form chelating interactions with divalent metal cations.

Dissecting the Ca2+ dependence of DesA1 function in Mycobacterium tuberculosis

Mycobacterium tuberculosis (M. tb) has a complex cell wall, composed largely of mycolic acids, that are crucial to its structural maintenance. The M. tb desaturase A1 (DesA1) is an essential Ca2+-binding protein that catalyses a key step in mycolic acid biosynthesis. To investigate the structural and functional significance of Ca2+ binding, we introduced mutations at key residues in its Ca2+-binding βγ-crystallin motif to generate DesA1F303A, E304Q, and F303A-E304Q. Complementation of a conditional ΔdesA1 strain of Mycobacterium smegmatis, with the Ca2+ non-binders F303A or F303A-E304Q, failed to rescue its growth phenotype; these complements also exhibited enhanced cell wall permeability. Our findings highlight the criticality of Ca2+ in DesA1 function, and its implicit role in the maintenance of mycobacterial cellular integrity.

Prevalence of STEC virulence markers and Salmonella as a function of abiotic factors in agricultural water in the southeastern United States

Fresh produce can be contaminated by enteric pathogens throughout crop production, including through contact with contaminated agricultural water. The most common outbreaks and recalls in fresh produce are due to contamination by Salmonella enterica and Shiga toxin-producing E. coli (STEC). Thus, the objectives of this study were to investigate the prevalence of markers for STEC (wzy, hly, fliC, eaeA, rfbE, stx-I, stx-II) and Salmonella (invA) in surface water sources (n = 8) from produce farms in Southwest Georgia and to determine correlations among the prevalence of virulence markers for STEC, water nutrient profile, and environmental factors. Water samples (500 mL) from eight irrigation ponds were collected from February to December 2021 (n = 88). Polymerase chain reaction (PCR) was used to screen for Salmonella and STEC genes, and Salmonella samples were confirmed by culture-based methods. Positive samples for Salmonella were further serotyped. Particularly, Salmonella was detected in 6/88 (6.81%) water samples from all ponds, and the following 4 serotypes were detected: Saintpaul 3/6 (50%), Montevideo 1/6 (16.66%), Mississippi 1/6 (16.66%), and Bareilly 1/6 (16.66%). Salmonella isolates were only found in the summer months (May-Aug.). The most prevalent STEC genes were hly 77/88 (87.50%) and stx-I 75/88 (85.22%), followed by fliC 54/88 (61.63%), stx-II 41/88 (46.59%), rfbE 31/88 (35.22%), and eaeA 28/88 (31.81%). The wzy gene was not detected in any of the samples. Based on a logistic regression analysis, the odds of codetection for STEC virulence markers (stx-I, stx-II, and eaeA) were negatively correlated with calcium and relative humidity (p < 0.05). A conditional forest analysis was performed to assess predictive performance (AUC = 0.921), and the top predictors included humidity, nitrate, calcium, and solar radiation. Overall, information from this research adds to a growing body of knowledge regarding the risk that surface water sources pose to produce grown in subtropical environmental conditions and emphasizes the importance of understanding the use of abiotic factors as a holistic approach to understanding the microbial quality of water.

Calcium isotope fractionation by intracellular amorphous calcium carbonate (ACC) forming cyanobacteria

The formation of intracellular amorphous calcium carbonate (ACC) by various cyanobacteria is a widespread biomineralization process, yet its mechanism and importance in past and modern environments remain to be fully comprehended. This study explores whether calcium (Ca) isotope fractionation, linked to ACC-forming cyanobacteria, can serve as a reliable tracer for detecting these microorganisms in modern and ancient settings. Accordingly, we measured stable Ca isotope fractionation during Ca uptake by the intracellular ACC-forming cyanobacterium Cyanothece sp. PCC 7425. Our results show that Cyanothece sp. PCC 7425 cells are enriched in lighter Ca isotopes relative to the solution. This finding is consistent with the kinetic isotope effects observed in the Ca isotope fractionation during biogenic carbonate formation by marine calcifying organisms. The Ca isotope composition of Cyanothece sp. PCC 7425 was accurately modeled using a Rayleigh fractionation model, resulting in a Ca isotope fractionation factor (Δ44Ca) equal to -0.72 ± 0.05‰. Numerical modeling suggests that Ca uptake by these cyanobacteria is primarily unidirectional, with minimal back reaction observed over the duration of the experiment. Finally, we compared our Δ44Ca values with those of other biotic and abiotic carbonates, revealing similarities with organisms that form biogenic calcite. These similarities raise questions about the effectiveness of using the Ca isotope fractionation factor as a univocal tracer of ACC-forming cyanobacteria in the environment. We propose that the use of Δ44Ca in combination with other proposed tracers of ACC-forming cyanobacteria such as Ba and Sr isotope fractionation factors and/or elevated Ba/Ca and Sr/Ca ratios may provide a more reliable approach.

Different lanthanide elements induce strong gene expression changes in a lanthanide-accumulating methylotroph

IMPORTANCE

Since its discovery, Ln-dependent metabolism in bacteria attracted a lot of attention due to its bio-metallurgical application potential regarding Ln recycling and circular economy. The physiological role of Ln is mostly studied dependent on presence and absence. Comparisons of how different (utilizable) Ln affect metabolism have rarely been done. We noticed unexpectedly pronounced changes in gene expression caused by different Ln supplementation. Our research suggests that strain RH AL1 distinguishes different Ln elements and that the effect of Ln reaches into many aspects of metabolism, for instance, chemotaxis, motility, and polyhydroxyalkanoate metabolism. Our findings regarding Ln accumulation suggest a distinction between individual Ln elements and provide insights relating to intracellular Ln homeostasis. Understanding comprehensively how microbes distinguish and handle different Ln elements is key for turning knowledge into application regarding Ln-centered biometallurgy.

Gypsum-Related Impact on Antibiotic-Loaded Composite Based on Highly Porous Hydroxyapatite-Advantages and Disadvantages

Highly porous hydroxyapatite is sometimes considered toxic and useless as a biomaterial for bone tissue regeneration because of the high adsorption of calcium and phosphate ions from cell culture media. This negatively affects the osteoblast's growth in such ion-deprived media and suggests "false cytotoxicity" of tested hydroxyapatite. In our recent study, we showed that a small addition of calcium sulfate dihydrate (CSD) may compensate for this adsorption without a negative effect on other properties of hydroxyapatite-based biomaterials. This study was designed to verify whether such CSD-supplemented biomaterials may serve as antibiotic carriers. FTIR, roughness, mechanical strength analysis, drug release, hemocompatibility, cytotoxicity against human osteoblasts, and antibacterial activity were evaluated to characterize tested biomaterials. The results showed that the addition of 1.75% gypsum and gentamicin caused short-term calcium ion compensation in media incubated with the composite. The combination of both additives also increased antibacterial activity against bacteria representative of bone infections without affecting osteoblast proliferation, hemocompatibility, and mechanical parameters. Thus, gypsum and antibiotic supplementation may provide advanced functionality for bone-regeneration materials based on hydroxyapatite of a high surface area and increasingly high Ca2+ sorption capacity.

The roles of calcium signaling and calcium deposition in microbial multicellularity

Calcium signaling is an essential mediator of signal-controlling gene expression in most developmental systems. In addition, calcium has established extracellular functions as a structural component of biogenic minerals found in complex tissues. In bacteria, the formation of calcium carbonate structures is associated with complex colony morphology. Genes promoting the formation of biogenic minerals are essential for proper biofilm development and protection against antimicrobial solutes and toxins. Here we review recent findings on the role of calcium and calcium signaling as emerging regulators of biofilm formation in beneficial bacteria, as well as essential mediators of biofilm formation and virulence in human pathogens. The presented analysis concludes that the new understanding of calcium signaling may help to improve the performance of beneficial strains for sustainable agriculture, microbiome manipulation, and sustainable construction. Unraveling the roles of calcium may also promote the development of novel therapies against biofilm infections that target calcium uptake, calcium sensors, and calcium carbonate deposition.

Microbial growth in actual martian regolith in the form of Mars meteorite EETA79001

Studies to understand the growth of organisms on Mars are hampered by the use of simulants to duplicate martian mineralogy and chemistry. Even though such materials are improving, no terrestrial simulant can replace a real martian sample. Here we report the use of actual martian regolith, in the form of Mars meteorite EETA79001 sawdust, to demonstrate its ability to support the growth of four microorganisms, E. coli. Eucapsis sp., Chr20-20201027-1, and P. halocryophilus, for up to 23 days under terrestrial conditions using regolith:water ratios from 4:1 to 1:10. If the EETA79001 sawdust is widely representative of regolith on the martian surface, our results imply that microbial life under appropriate conditions could have been present on Mars in the past and/or today in the subsurface, and that the regolith does not contain any bactericidal agents. The results of our study have implications not only for putative martian microbial life but also for building bio-sustainable human habitats on Mars.

Salinization and sedimentation drive contrasting assembly mechanisms of planktonic and sediment-bound bacterial communities in agricultural streams

Agriculture is the most dominant land use globally and is projected to increase in the future to support a growing human population but also threatens ecosystem structure and services. Bacteria mediate numerous biogeochemical pathways within ecosystems. Therefore, identifying linkages between stressors associated with agricultural land use and responses of bacterial diversity is an important step in understanding and improving resource management. Here, we use the Mississippi Alluvial Plain (MAP) ecoregion, a highly modified agroecosystem, as a case study to better understand agriculturally associated drivers of stream bacterial diversity and assembly mechanisms. In the MAP, we found that planktonic bacterial communities were strongly influenced by salinity. Tolerant taxa increased with increasing ion concentrations, likely driving homogenous selection which accounted for ~90% of assembly processes. Sediment bacterial phylogenetic diversity increased with increasing agricultural land use and was influenced by sediment particle size, with assembly mechanisms shifting from homogenous to variable selection as differences in median particle size increased. Within individual streams, sediment heterogeneity was correlated with bacterial diversity and a subsidy-stress relationship along the particle size gradient was observed. Planktonic and sediment communities within the same stream also diverged as sediment particle size decreased. Nutrients including carbon, nitrogen, and phosphorus, which tend to be elevated in agroecosystems, were also associated with detectable shifts in bacterial community structure. Collectively, our results establish that two understudied variables, salinity and sediment texture, are the primary drivers of bacterial diversity within the studied agroecosystem, whereas nutrients are secondary drivers. Although numerous macrobiological communities respond negatively, we observed increasing bacterial diversity in response to agricultural stressors including salinization and sedimentation. Elevated taxonomic and phylogenetic bacterial diversity likely increases the probability of detecting community responses to stressors. Thus, bacteria community responses may be more reliable for establishing water quality goals within highly modified agroecosystems that have experienced shifting baselines.

Biochemical and metabolic signatures are fundamental to drought adaptation in PGPR Enterobacter bugandensis WRS7

Drought alone causes more annual loss in crop yield than the sum of all other environmental stresses. There is growing interest in harnessing the potential of stress-resilient PGPR in conferring plant resistance and enhancing crop productivity in drought-affected agroecosystems. A detailed understanding of the complex physiological and biochemical responses will open up the avenues to stress adaptation mechanisms of PGPR communities under drought. It will pave the way for rhizosphere engineering through metabolically engineered PGPR. Therefore, to reveal the physiological and metabolic networks in response to drought-mediated osmotic stress, we performed biochemical analyses and applied untargeted metabolomics to investigate the stress adaptation mechanisms of a PGPR Enterobacter bugendensis WRS7 (Eb WRS7). Drought caused oxidative stress and resulted in slower growth rates in Eb WRS7. However, Eb WRS7 could tolerate drought stress and did not show changes in cell morphology under stress conditions. Overproduction of ROS caused lipid peroxidation (increment in MDA) and eventually activated antioxidant systems and cell signalling cascades, which led to the accumulation of ions (Na+, K+, and Ca2+), osmolytes (proline, exopolysaccharides, betaine, and trehalose), and modulated lipid dynamics of the plasma membranes for osmosensing and osmoregulation, suggesting an osmotic stress adaption mechanism in PGPR Eb WRS7. Finally, GC-MS-based metabolite profiling and deregulated metabolic responses highlighted the role of osmolytes, ions, and intracellular metabolites in regulating Eb WRS7 metabolism. Our results suggest that understanding the role of metabolites and metabolic pathways can be exploited for future metabolic engineering of PGPR and developing bio inoculants for plant growth promotion under drought-affected agroecosystems.

Microbially Induced Calcium Carbonate Precipitation by Sporosarcina pasteurii: a Case Study in Optimizing Biological CaCO3 Precipitation

Current production of traditional concrete requires enormous energy investment that accounts for approximately 5 to 8% of the world's annual CO2 production. Biocement is a building material that is already in industrial use and has the potential to rival traditional concrete as a more convenient and more environmentally friendly alternative. Biocement relies on biological structures (enzymes, cells, and/or cellular superstructures) to mineralize and bind particles in aggregate materials (e.g., sand and soil particles). Sporosarcina pasteurii is a workhorse organism for biocementation, but most research to date has focused on S. pasteurii as a building material rather than a biological system. In this review, we synthesize available materials science, microbiology, biochemistry, and cell biology evidence regarding biological CaCO3 precipitation and the role of microbes in microbially induced calcium carbonate precipitation (MICP) with a focus on S. pasteurii. Based on the available information, we provide a model that describes the molecular and cellular processes involved in converting feedstock material (urea and Ca2+) into cement. The model provides a foundational framework that we use to highlight particular targets for researchers as they proceed into optimizing the biology of MICP for biocement production.

Production and characterization of lipopeptide biosurfactant from a new strain of Pseudomonas antarctica 28E using crude glycerol as a carbon source

Pseudomonas is a cosmopolitan genus of bacteria found in soil, water, organic matter, plants and animals and known for the production of glycolipid and lipopeptide biosurfactants. In this study bacteria (laboratory collection number 28E) isolated from soil collected in Spitsbergen were used for biosurfactant production. 16S rRNA sequencing and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF) revealed that this isolate belongs to the species Pseudomonas antarctica. In the present study, crude glycerol, a raw material obtained from several industrial processes, was evaluated as a potential low-cost carbon source to reduce the costs of lipopeptide production. Among several tested glycerols, a waste product of stearin production, rich in nitrogen, iron and calcium, ensured optimal conditions for bacterial growth. Biosurfactant production was evidenced by a reduction of surface tension (ST) and an increase in the emulsification index (E24%). According to Fourier-transform infrared spectroscopy (FTIR) and electrospray ionization mass spectrometry (ESI-MS), the biosurfactant was identified as viscosin. The critical micelle concentration (CMC) of lipopeptide was determined to be 20 mg L-1. Interestingly, viscosin production has been reported previously for Pseudomonas viscosa, Pseudomonas fluorescens and Pseudomonas libanensis. To the best of our knowledge, this is the first report on viscosin production by a P. antarctica 28E. The results indicated the potential of crude glycerol as a low-cost substrate to produce a lipopeptide biosurfactant with promising tensioactive and emulsifying properties.

l-Asparaginase producing novel Streptomyces sp. HB2AG: optimization of process parameters and whole genome sequence analysis

l-asparaginase (ASNase) is a key enzyme widely used as an anti-cancer drug and is also used in the pharmaceutical and food processing industries. This enzyme's applications are determined by its source and nature. The production of the enzyme through the fermentation process is also crucial for economic feasibility. Searching for a new potent microbial strain is necessary for increased ASNase synthesis. In this work, a potent strain was isolated from the sediment of Chilika Lake and selected for its high ASNase production potential. It was recognized following Bergey's manual of determinative and phylogenetic analysis was carried out by 16S rDNA sequencing. The isolated organism was Streptomyces sp. HB2AG. Additionally, a genome-wide analysis of HB2AG was performed. The result showed that the HB2AG genome possesses a chromosome with 6,099,956 bp and GC content of 74.0%. The whole genome analysis of the strain HB2AG revealed the presence of ASNase (ansA, ansB) and Asparagine synthase (asnB) in the HB2AG genome. Optimization of media composition is crucial for microbial growth and obtaining the desired end product. The current effort focuses on the Taguchi orthogonal design to determine optimum factor combinations that would allow the strain to produce maximum ASNase enzyme. Results showed that compared to unoptimized media, approximately 1.76-fold higher ASNase production was observed in Sea Water Luria Bertani (SWLB) media, pH-5, 0.5% (w/v) of lactose, 0.5% (w/v) of casein, 2.5% (w/v) NaCl, 1 mM Ca2+ and 0.1% Tween 80.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03620-0.

Identification of lthB, a Gene Encoding a Putative Glycosyltransferase Family 8 Protein Required for Leptothrix Sheath Formation

The bacterium Leptothrix cholodnii generates cell chains encased in sheaths that are composed of woven nanofibrils. The nanofibrils are mainly composed of glycoconjugate repeats, and several glycosyltransferases (GTs) are required for its biosynthesis. However, only one GT (LthA) has been identified to date. In this study, we screened spontaneous variants of L. cholodnii SP6 to find those that form smooth colonies, which is one of the characteristics of sheathless variants. Genomic DNA sequencing of an isolated variant revealed an insertion in the locus Lcho_0972, which encodes a putative GT family 8 protein. We thus designated this protein LthB and characterized it using deletion mutants and antibodies. LthB localized adjacent to the cell envelope. ΔlthB cell chains were nanofibril free and thus sheathless, indicating that LthB is involved in nanofibril biosynthesis. Unlike the ΔlthA mutant and the wild-type strain, which often generate planktonic cells, most ΔlthB organisms presented as long cell chains under static conditions, resulting in deficient pellicle formation, which requires motile planktonic cells. These results imply that sheaths are not required for elongation of cell chains. Finally, calcium depletion, which induces cell chain breakage due to sheath loss, abrogated the expression of LthA, but not LthB, suggesting that these GTs cooperatively participate in glycoconjugate biosynthesis under different signaling controls. IMPORTANCE In recent years, the regulation of cell chain elongation of filamentous bacteria via extracellular signals has attracted attention as a potential strategy to prevent clogging of water distribution systems and filamentous bulking of activated sludge in industrial settings. However, a fundamental understanding of the ecology of filamentous bacteria remains elusive. Since sheath formation is associated with cell chain elongation in most of these bacteria, the molecular mechanisms underlying nanofibril sheath formation, including the intracellular signaling cascade in response to extracellular stimuli, must be elucidated. Here, we isolated a sheathless variant of L. cholodnii SP6 and thus identified a novel glycosyltransferase, LthB. Although mutants with deletions of lthA, encoding another GT, and lthB were both defective for nanofibril formation, they exhibited different phenotypes of cell chain elongation and pellicle formation. Moreover, LthA expression, but not LthB expression, was influenced by extracellular calcium, which is known to affect nanofibril formation, indicating the functional diversities of LthA and LthB. Such molecular insights are critical for a better understanding of ecology of filamentous bacteria, which, in turn, can be used to improve strategies to control filamentous bacteria in industrial facilities.

High Cell-Density Cultivation of Methylococcus capsulatus Bath for Efficient Methane-Derived Mevalonate Production

The engineered Methylococcus capsulatus Bath presents a promising approach for converting methane, a potent greenhouse gas, into valuable chemicals. High cell-density culture (HCDC) is necessary for high-titer growth-associated bioproducts, but it often requires time-consuming and labor-intensive optimization processes. In this study, we aimed to achieve efficient HCDC of M. capsulatus Bath by measuring the residual nutrient levels during bioreactor operations and analyzing the specific uptake of each medium component. By controlling the concentrations of nutrients, particularly calcium and phosphorus via intermittent feeding, we achieved a high cell density of 28.2 g DCW/L and a significantly elevated production of mevalonate at a concentration of 1.8 g/L from methane. Our findings demonstrate that the methanotroph HCDC approach presented herein offers a promising strategy for promoting sustainable development, with an exceptional g-scale production titer for value-added synthetic biochemicals.

The Activity of Calcium Glycerophosphate and Fluoride against Cariogenic Biofilms of Streptococcus mutans and Candida albicans Formed In Vitro

This study evaluated the effects of calcium glycerophosphate (CaGP), with or without fluoride (F), on dual-species biofilms of Streptococcus mutans and Candida albicans. The biofilms were treated three times with 0.125, 0.25, and 0.5% CaGP solutions, with or without 500 ppm F (NaF). Additionally, 500 and 1100 ppm F-solutions and artificial saliva served as controls. After the final treatment, the microbial viability and biofilm structure, metabolic activity, total biomass production, and the composition of the extracellular matrix composition were analyzed. Regardless of the presence of F, 0.25 and 0.5% CaGP promoted a higher biomass production and metabolic activity increase than the controls (p < 0.05). F-free CaGP solutions reduced bacterial cell population significantly more than the 500 ppm F group or the negative control (p < 0.05). All the groups reduced the proteins, and 0.5% CaGP combined with F led to the highest reduction in the carbohydrate and nucleic acids content of the extracellular matrix (p < 0.05). It can be concluded that CaGP alone affected the number of bacterial cells and, when combined with F, reduced its production of biomass, metabolic activity, and the expression of the extracellular matrix components.

The elements of life: A biocentric tour of the periodic table

Living systems are built from a small subset of the atomic elements, including the bulk macronutrients (C,H,N,O,P,S) and ions (Mg,K,Na,Ca) together with a small but variable set of trace elements (micronutrients). Here, we provide a global survey of how chemical elements contribute to life. We define five classes of elements: those that are (i) essential for all life, (ii) essential for many organisms in all three domains of life, (iii) essential or beneficial for many organisms in at least one domain, (iv) beneficial to at least some species, and (v) of no known beneficial use. The ability of cells to sustain life when individual elements are absent or limiting relies on complex physiological and evolutionary mechanisms (elemental economy). This survey of elemental use across the tree of life is encapsulated in a web-based, interactive periodic table that summarizes the roles chemical elements in biology and highlights corresponding mechanisms of elemental economy.

Characterization of the glmS Ribozymes from Listeria Monocytogenes and Clostridium Difficile

The glmS ribozyme regulates the expression of the essential GlmS enzyme being involved in cell wall biosynthesis. While >450 variants of the glmS ribozyme were identified by in silico approaches and homology searches, only a few have yet been experimentally investigated. Herein, we validate and characterize the glmS ribozymes of the human pathogens Clostridium difficile and Listeria monocytogenes. Both ribozymes, as their previous characterized homologs rely on glucosamine-6-phosphate as co-factor and the presence of divalent cations for exerting the cleavage reaction. The observed EC₅₀ values in turn were found to be in the submicromolar range, at least an order of magnitude lower than observed for glmS ribozymes from other bacteria. The glmS ribozyme of L. monocytogenes was further shown to bear unique properties. It discriminates between co-factors very stringently and other than the glmS ribozyme of C. difficile retains activity at low temperatures. This finding illustrates that albeit being highly conserved, glmS ribozymes have unique characteristics.

A New Face of the Old Gene: Deletion of the PssA, Encoding Monotopic Inner Membrane Phosphoglycosyl Transferase in Rhizobium leguminosarum, Leads to Diverse Phenotypes That Could Be Attributable to Downstream Effects of the Lack of Exopolysaccharide

The biosynthesis of subunits of rhizobial exopolysaccharides is dependent on glycosyltransferases, which are usually encoded by large gene clusters. PssA is a member of a large family of phosphoglycosyl transferases catalyzing the transfer of a phosphosugar moiety to polyprenol phosphate; thus, it can be considered as priming glycosyltransferase commencing synthesis of the EPS repeating units in Rhizobium leguminosarum. The comprehensive analysis of PssA protein features performed in this work confirmed its specificity for UDP-glucose and provided evidence that PssA is a monotopic inner membrane protein with a reentrant membrane helix rather than a transmembrane segment. The bacterial two-hybrid system screening revealed interactions of PssA with some GTs involved in the EPS octasaccharide synthesis. The distribution of differentially expressed genes in the transcriptome of the ΔpssA mutant into various functional categories indicated complexity of cell response to the deletion, which can mostly be attributed to the lack of exopolysaccharide and downstream effects caused by such deficiency. The block in the EPS biosynthesis at the pssA step, potentially leading to an increased pool of UDP-glucose, is likely to be filtered through to other pathways, and thus the absence of EPS may indirectly affect the expression of proteins involved in these pathways.

The Influence of Calcium on the Growth, Morphology and Gene Regulation in Gemmatimonas phototrophica

The bacterium Gemmatimonas phototrophica AP64 isolated from a freshwater lake in the western Gobi Desert represents the first phototrophic member of the bacterial phylum Gemmatimonadota. This strain was originally cultured on agar plates because it did not grow in liquid medium. In contrast, the closely related species G. groenlandica TET16 grows both on solid and in liquid media. Here, we show that the growth of G. phototrophica in liquid medium can be induced by supplementing the medium with 20 mg CaCl₂ L^-1. When grown at a lower concentration of calcium (2 mg CaCl₂ L^-1) in the liquid medium, the growth was significantly delayed, cells were elongated and lacked flagella. The elevated requirement for calcium is relatively specific as it can be partially substituted by strontium, but not by magnesium. The transcriptome analysis documented that several groups of genes involved in flagella biosynthesis and transport of transition metals were co-activated after amendment of 20 mg CaCl₂ L^-1 to the medium. The presented results document that G. phototrophica requires a higher concentration of calcium for its metabolism and growth compared to other Gemmatimonas species.

Effect of nutrients deficiency on biofilm formation and single cell protein production with a purple non-sulphur bacteria enriched culture

Purple non-sulphur bacteria (PNSB) are of interest for biorefinery applications to create biomolecules, but their production cost is expensive due to substrate and biomass separation costs. This research has utilized fuel synthesis wastewater (FSW) as a low-cost carbon-rich substrate to produce single-cell protein (SCP) and examines PNSB biofilm formation using this substrate to achieve a more efficient biomass-liquid separation. In this study, PNSB were grown in Ca, Mg, S, P, and N-deficient media using green shade as biofilm support material. Among these nutrient conditions, only N-deficient and control (nutrient-sufficient) conditions showed biofilm formation. Although total biomass growth of the control was 1.5 times that of the N-deficient condition and highest overall, the total biofilm-biomass in the N-deficient condition was 2.5 times greater than the control, comprising 49% of total biomass produced. Total protein content was similar between these four biomass samples, ranging from 35.0 ± 0.2% to 37.2 ± 0.0%. The highest protein content of 44.7 ± 1.3% occurred in the Mg-deficient condition (suspended biomass only) but suffered from a low growth rate. Overall, nutrient sufficient conditions are optimal for overall protein productivity and dominated by suspended growth, but where fixed growth systems are desired for cost-effective harvesting, N-deficient conditions provide an effective means to maximize biofilm production without sacrificing protein content.

Endosymbiotic selective pressure at the origin of eukaryotic cell biology

The dichotomy that separates prokaryotic from eukaryotic cells runs deep. The transition from pro- to eukaryote evolution is poorly understood due to a lack of reliable intermediate forms and definitions regarding the nature of the first host that could no longer be considered a prokaryote, the first eukaryotic common ancestor, FECA. The last eukaryotic common ancestor, LECA, was a complex cell that united all traits characterising eukaryotic biology including a mitochondrion. The role of the endosymbiotic organelle in this radical transition towards complex life forms is, however, sometimes questioned. In particular the discovery of the asgard archaea has stimulated discussions regarding the pre-endosymbiotic complexity of FECA. Here we review differences and similarities among models that view eukaryotic traits as isolated coincidental events in asgard archaeal evolution or, on the contrary, as a result of and in response to endosymbiosis. Inspecting eukaryotic traits from the perspective of the endosymbiont uncovers that eukaryotic cell biology can be explained as having evolved as a solution to housing a semi-autonomous organelle and why the addition of another endosymbiont, the plastid, added no extra compartments. Mitochondria provided the selective pressures for the origin (and continued maintenance) of eukaryotic cell complexity. Moreover, they also provided the energetic benefit throughout eukaryogenesis for evolving thousands of gene families unique to eukaryotes. Hence, a synthesis of the current data lets us conclude that traits such as the Golgi apparatus, the nucleus, autophagosomes, and meiosis and sex evolved as a response to the selective pressures an endosymbiont imposes.

Protection of the DNA from Selected Species of Five Kingdoms in Nature by Ba(II), Sr(II), and Ca(II) Silica-Carbonates: Implications about Biogenicity and Evolving from Prebiotic Chemistry to Biological Chemistry

The origin of life on Earth is associated with the Precambrian era, in which the existence of a large diversity of microbial fossils has been demonstrated. Notwithstanding, despite existing evidence of the emergence of life many unsolved questions remain. The first question could be as follows: Which was the inorganic structure that allowed isolation and conservation of the first biomolecules in the existing reduced conditions of the primigenial era? Minerals have been postulated as the ones in charge of protecting theses biomolecules against the external environment. There are calcium, barium, or strontium silica-carbonates, called biomorphs, which we propose as being one of the first inorganic structures in which biomolecules were protected from the external medium. Biomorphs are structures with different biological morphologies that are not formed by cells, but by nanocrystals; some of their morphologies resemble the microfossils found in Precambrian cherts. Even though biomorphs are unknown structures in the geological registry, their similarity with some biological forms, including some Apex fossils, could suggest them as the first "inorganic scaffold" where the first biomolecules became concentrated, conserved, aligned, and duplicated to give rise to the pioneering cell. However, it has not been documented whether biomorphs could have been the primary structures that conserved biomolecules in the Precambrian era. To attain a better understanding on whether biomorphs could have been the inorganic scaffold that existed in the primigenial Earth, the aim of this contribution is to synthesize calcium, barium, and strontium biomorphs in the presence of genomic DNA from organisms of the five kingdoms in conditions emulating the atmosphere of the Precambrian era and that CO₂ concentration in conditions emulating current atmospheric conditions. Our results showed, for the first time, the formation of the kerogen signal, which is a marker of biogenicity in fossils, in the biomorphs grown in the presence of DNA. We also found the DNA to be internalized into the structure of biomorphs.

Sheep Milk Symbiotic Ice Cream: Effect of Inulin and Apple Fiber on the Survival of Five Probiotic Bacterial Strains during Simulated In Vitro Digestion Conditions

We conducted a study to determine the survival of bacterial cells under in vitro digestion. For this purpose, ice cream mixes were prepared: control, with 4% inulin, 2.5% inulin and 1.5% apple fiber and 4% apple fiber. Each inoculum (pH = 4.60 ± 0.05), containing 9 log cfu g^-1 bacteria, at 5% (w/w) was added to the ice cream mixes (Lacticaseibacilluscasei 431, Lactobacillus acidophilus LA-5, Lacticaseibacillus paracasei L-26, Lacticaseibacillusrhamnosus, Bifidobacterium animalis ssp. lactis BB-12) and fermentation was carried out to pH 4.60 ± 0.05. The in vitro digestion method simulated the stages of digestion that occur in the mouth, stomach and small intestine under optimal controlled conditions (pH value, time and temperature). At each stage of digestion, the survival rate of probiotic bacteria was determined using the plate-deep method. As expected, in the oral stage, there was no significant reduction in the viability of the probiotic bacteria in any ice cream group compared to their content before digestion. In the stomach stage, Bifidobacterium animalis ssp. lactis BB-12 strain had the highest viable counts (8.48 log cfu g^-1) among the control samples. Furthermore, a 4% addition of inulin to ice cream with Bifidobacterium BB-12 increased gastric juice tolerance and limited strain reduction by only 16.7% compared to the number of bacterial cells before digestion. Regarding ice cream samples with Bifidobacterium BB-12, replacing part of the inulin with apple fiber resulted in increased survival at the stomach stage and a low reduction in the bacterial population of only 15.6% compared to samples before digestion. At the stomach stage, the positive effect of the addition of inulin and apple fiber was also demonstrated for ice cream samples with Lacticaseibacilluscasei 431 (9.47 log cfu g^-1), Lactobacillus acidophilus LA-5 (8.06 log cfu g^-1) and Lacticaseibacillus paracasei L-26 (5.79 log cfu g^-1). This study showed the highest sensitivity to simulated gastric stress for ice cream samples with Lacticaseibacillusrhamnosus (4.54 log cfu g^-1). Our study confirmed that the 4% addition of inulin to ice cream increases the survival rate of L. casei and Bifidobacterium BB-12 in simulated intestinal juice with bile by 0.87 and 2.26 log cfu g^-1, respectively. The highest viable count in the small intestine stage was observed in ice cream with L. acidophilus. The addition of inulin increased the survival of L. rhamnosus by 10.8% and Bifidobacterium BB-12 by about 22% under conditions of simulated in vitro digestion compared to their control samples. The survival rates of L. casei and L. paracasei were also highly affected by the 4% addition of apple fiber, where the increase under gastrointestinal passage conditions was determined to range from 7.86-11.26% compared to their control counterparts. In comparison, the lowest survival rate was found in the control ice cream with L. rhamnosus (47.40%). In our study at the intestinal stage, only five ice cream groups: a sample with 4% inulin and L. acidophilus, a control sample with Bifidobacterium BB12, a sample with 2.5% inulin and 1.5% apple fiber with Bifidobacterium BB12, a control sample with L. rhamnosus, a sample with 4% fiber and L. rhamnosus reported bacterial cell counts below 6 log cfu g^-1 but higher than 5 log cfu g^-1. However, in the remaining ice cream groups, viable counts of bacterial cells ranged from 6.11 to 8.88 log cfu g^-1, ensuring a therapeutic effect. Studies have clearly indicated that sheep milk ice cream could provide a suitable matrix for the delivery of probiotics and prebiotics and contribute to intestinal homeostasis. The obtained results have an applicative character and may play an essential role in developing new functional sheep milk ice cream.

Improvement of Lignocellulolytic Enzyme Production Mediated by Calcium Signaling in Bacillus subtilis Z2 under Graphene Oxide Stress

An increase in exoenzyme production can be enhanced by environmental stresses such as graphene oxide (GO) stress, but the link between the two events is still unclear. In this work, the effect of GO as an environmental stress factor on exoenzyme (lignocellulolytic enzyme, amylase, peptidase, and protease) biosynthesis was investigated in Bacillus subtilis Z2, and a plausible mechanism by which cytosolic Ca²⁺ regulates lignocellulolytic enzyme production in B. subtilis Z2 subjected to GO stress was proposed. The filter paper-hydrolyzing (FPase [representing total cellulase]), carboxymethylcellulase (CMCase [representing endoglucanase]), and β-glucosidase activities and extracellular protein concentration of the wild-type strain under 10 μg/mL GO stress were 1.37-, 1.64-, 1.24-, and 1.16-fold those of the control (without GO stress), respectively. Correspondingly, the transcription levels of lignocellulolytic enzyme genes, cytosolic Ca²⁺ level, and biomass concentration of B. subtilis were all increased. With lignocellulolytic enzyme from B. subtilis used to hydrolyze alkali-pretreated rice straw, the released reducing sugar concentration reached 265.53 mg/g, and the removal rates of cellulose, hemicellulose, and lignin were 52.4%, 30.1%, and 7.5%, respectively. Furthermore, transcriptome data revealed that intracellular Ca²⁺ homeostasis played a key role in regulating the levels of gene transcription related to the synthesis of lignocellulolytic enzymes and exoenzymes. Finally, the use of Ca²⁺ inhibitors (LaCl₃ and EDTA) and deletion of spcF (a calmodulin-like protein gene) further demonstrated that the overexpression of those genes was regulated via calcium signaling in B. subtilis subjected to GO stress. IMPORTANCE To effectively convert lignocellulose into fermentable sugars, high lignocellulolytic enzyme loading is needed. Graphene oxide (GO) has been shown to promote exoenzyme (lignocellulolytic enzyme, amylase, peptidase, and protease) production in some microorganisms; however, the regulatory mechanism of the biosynthesis of lignocellulolytic enzymes under GO stress remains unclear. In this work, the lignocellulolytic enzyme production of B. subtilis under GO stress was investigated, and the potential mechanism by which B. subtilis enhanced lignocellulolytic enzyme production through the calcium signaling pathway under GO stress was proposed. This work revealed the role of calcium signaling in the production of enzymes under external environmental stress and provided a direction to facilitate lignocellulolytic enzyme production by B. subtilis.

Long-term nickel contamination increased soil fungal diversity and altered fungal community structure and co-occurrence patterns in agricultural soils

Nickel (Ni) contamination imposes deleterious effects on the stability of soil ecosystem. Soil fungal community as a crucial moderator of soil remediation and biochemical processes has attracted more and more research interests. In the present study, soil fungal community composition and diversity under long-term Ni contamination were investigated and fungal interaction networks were built to reveal fungal co-occurrence patterns. The results showed that moderate Ni contamination significantly increased fungal diversity and altered fungal community structure. Functional predictions based on FUNGuild suggested that the relative abundance of arbuscular mycorrhizal fungi (AMF) significantly increased at moderate Ni contamination level. Ni contamination strengthened fungal interactions. Keystone taxa at different Ni contamination levels, such as Penicillium at light contamination, were identified, which might have ecological significance in maintaining the stability of fungal community to Ni stress. The present study provided a deeper insight into the effect of long-term Ni contamination on fungal community composition and co-occurrence patterns, and was helpful to further explore ecological risk of Ni contamination in cultivated field.

Oralbiotica/Oralbiotics: The Impact of Oral Microbiota on Dental Health and Demineralization: A Systematic Review of the Literature

The oral microbiota plays a vital role in the human microbiome and oral health. Imbalances between microbes and their hosts can lead to oral and systemic disorders such as diabetes or cardiovascular disease. The purpose of this review is to investigate the literature evidence of oral microbiota dysbiosis on oral health and discuss current knowledge and emerging mechanisms governing oral polymicrobial synergy and dysbiosis; both have enhanced our understanding of pathogenic mechanisms and aided the design of innovative therapeutic approaches as ORALBIOTICA for oral diseases such as demineralization. PubMed, Web of Science, Google Scholar, Scopus, Cochrane Library, EMBEDDED, Dentistry & Oral Sciences Source via EBSCO, APA PsycINFO, APA PsyArticles, and DRUGS@FDA were searched for publications that matched our topic from January 2017 to 22 April 2022, with an English language constraint using the following Boolean keywords: ("microbio*" and "demineralization*") AND ("oral microbiota" and "demineralization"). Twenty-two studies were included for qualitative analysis. As seen by the studies included in this review, the balance of the microbiota is unstable and influenced by oral hygiene, the presence of orthodontic devices in the oral cavity and poor eating habits that can modify its composition and behavior in both positive and negative ways, increasing the development of demineralization, caries processes, and periodontal disease. Under conditions of dysbiosis, favored by an acidic environment, the reproduction of specific bacterial strains increases, favoring cariogenic ones such as Bifidobacterium dentium, Bifidobacterium longum, and S. mutans, than S. salivarius and A. viscosus, and increasing of Firmicutes strains to the disadvantage of Bacteroidetes. Microbial balance can be restored by using probiotics and prebiotics to manage and treat oral diseases, as evidenced by mouthwashes or dietary modifications that can influence microbiota balance and prevent or slow disease progression.

Study of the Ca2+-dependent gene expression of EuPrt, an extracellular metalloprotease produced by the psychro-tolerant bacterium Exiguobacterium undae Su-1

The effect of a Ca2+ ion on the gene expression of an on-demand type of metalloprotease from psychrotrophic Exiguobacterium undae Su-1 (EuPrt) was studied. We first established a modified mM9 medium for strain Su-1 to examine its effect in more detail. Then, when the strain was cultured in mM9 medium and 1.0 mM CaCl2 was added, we detected the mature EuPrt and its precursor proteins via Western blotting analysis and found the relative protease activity and its transcription increased by 50-fold and 7-fold, respectively, at the peak. Furthermore, the intracellular concentration of Ca2+ ions was analyzed using inductively coupled plasma atomic emission spectroscopy (ICP-AES) with other metal ions along the growth of strain Su-1. The intracellular concentration of Ca2+ ion was found to increase as much as 3-fold in response to the addition of an extracellular Ca2+ ions, indicating that euPrt gene expression is regulated by sensing its intracellular concentration.

Abiotic factors modulate interspecies competition mediated by the type VI secretion system effectors in Vibrio cholerae

Vibrio cholerae, the etiological pathogen of cholera, employs its type VI secretion system (T6SS) as an effective weapon to survive in highly competitive communities. Antibacterial and anti-eukaryotic functions of the T6SS depend on its secreted effectors that target multiple cellular processes. However, the mechanisms that account for effector diversity and different effectiveness during interspecies competition remain elusive. Here we report that environmental cations and temperature play a key role in dictating cellular response and effector effectiveness during interspecies competition mediated by the T6SS of V. cholerae. We found that V. cholerae could employ its cell-wall-targeting effector TseH to outcompete the otherwise resistant Escherichia coli and the V. cholerae immunity deletion mutant ∆tsiH when Mg²⁺ or Ca²⁺ was supplemented. Transcriptome and genetic analyses demonstrate that the metal-sensing PhoPQ two-component system is important for Mg²⁺-dependent sensitivity. Competition analysis in infant mice shows that TseH was active under in vivo conditions. Using a panel of V. cholerae single-effector active mutants, we further show that E. coli also exhibited variable susceptibilities to other T6SS effectors depending on cations and temperatures, respectively. Lastly, V. cholerae effector VasX could sensitize Pseudomonas aeruginosa to its intrinsically resistant antibiotic irgasan in a temperature-dependent manner. Collectively, these findings suggest that abiotic factors, that V. cholerae frequently encounters in natural and host environments, could modulate cellular responses and dictate the competitive fitness conferred by the T6SS effectors in complex multispecies communities.

Mitochondrial Calcium: Effects of Its Imbalance in Disease

Calcium is used in many cellular processes and is maintained within the cell as free calcium at low concentrations (approximately 100 nM), compared with extracellular (millimolar) concentrations, to avoid adverse effects such as phosphate precipitation. For this reason, cells have adapted buffering strategies by compartmentalizing calcium into mitochondria and the endoplasmic reticulum (ER). In mitochondria, the calcium concentration is in the millimolar range, as it is in the ER. Mitochondria actively contribute to buffering cellular calcium, but if matrix calcium increases beyond physiological demands, it can promote the opening of the mitochondrial permeability transition pore (mPTP) and, consequently, trigger apoptotic or necrotic cell death. The pathophysiological implications of mPTP opening in ischemia-reperfusion, liver, muscle, and lysosomal storage diseases, as well as those affecting the central nervous system, for example, Parkinson’s disease (PD), Alzheimer’s disease (AD), Huntington’s disease (HD), and amyotrophic lateral sclerosis (ALS) have been reported. In this review, we present an updated overview of the main cellular mechanisms of mitochondrial calcium regulation. We specially focus on neurodegenerative diseases related to imbalances in calcium homeostasis and summarize some proposed therapies studied to attenuate these diseases.

Mucoid Pseudomonas aeruginosa Can Produce Calcium-Gelled Biofilms Independent of the Matrix Components Psl and CdrA

Biofilms are aggregates of microorganisms embedded in an extracellular matrix comprised largely of exopolysaccharides (EPSs), nucleic acids, and proteins. Pseudomonas aeruginosa is an opportunistic human pathogen that is also a model organism for studying biofilms in the laboratory. Here, we define a novel program of biofilm development used by mucoid (alginate-overproducing) P. aeruginosa in the presence of elevated calcium. Calcium cations cross-link negatively charged alginate polymers, resulting in individual cells being suspended in an alginate gel. The formation of this type of structurally distinct biofilm is not reliant on the canonical biofilm EPS components Psl and Pel or the matrix protein CdrA. We also observed that mucoid P. aeruginosa biofilm cells do not have the typical elevated levels of the secondary messenger cyclic di-GMP (c-di-GMP), as expected of biofilm cells, nor does the overproduction of alginate rely on high c-di-GMP. This contrasts with nonmucoid biofilms in which the production of the matrix components Psl, Pel, and CdrA is positively regulated by elevated c-di-GMP. We further demonstrate that calcium-gelled alginate biofilms impede the penetration of the antibiotic tobramycin, thus protecting the biofilm community from antibiotic-mediated killing. Finally, we show that bacterial aggregates with a dispersed cell arrangement like laboratory-grown calcium-alginate biofilm structures are present in explanted cystic fibrosis (CF) lung samples. Our findings illustrate the diverse nature of biofilm formation and structure in P. aeruginosa. IMPORTANCE The opportunistic pathogen Pseudomonas aeruginosa produces a complex biofilm matrix comprised of exopolysaccharides (EPSs), nucleic acids, and proteins. P. aeruginosa biofilm formation canonically depends on a variable combination of the exopolysaccharides Psl and Pel and the matrix protein CdrA. We demonstrate that mucoid P. aeruginosa, which overproduces the EPS alginate, possesses an entirely alternate and calcium-dependent method of biofilm formation. These mucoid biofilm structures do not require Psl, Pel, or CdrA, and they display a unique organization of individually suspended cells similar to bacterial aggregates observed in cystic fibrosis airways. Furthermore, calcium-gelled mucoid biofilms impede the penetration and killing action of the antibiotic tobramycin, illustrating their potential clinical significance. Our findings highlight the compositional and structural variety of P. aeruginosa biofilm aggregates.

Synergistic Effects of Fluconazole Combined with Doxycycline Against Dual-Species Cultures of Candida albicans and Staphylococcus epidermidis and the Mechanisms of Action

Bacterial and fungal coinfections have posed great clinical challenges in recent years, and combination therapy may be a useful way to treat these mixed infections. The objective of this study was to find an effective drug combination to treat dual-species cultures of fungi and bacteria. In this study, we focused on poorly investigated mixed cultures of Candida albicans and Staphylococcus epidermidis. In this research, we investigated the effects of fluconazole (FLC) and doxycycline (DOX) against dual-species cultures of C. albicans and S. epidermidis. Both the fractional inhibitory concentration index model and ΔE model revealed a synergistic antimicrobial effect between FLC and DOX against the four groups of dual-species cultures. Mechanistic studies revealed that the synergism of FLC and DOX against dual-species cultures may be associated with the inhibition of biofilms and calcium dysregulation. Fluconazole+doxycycline appears to be a potential drug combination for the treatment of bacterial and fungal coinfections. These findings are of great significance for overcoming clinical bacterial and fungal coinfections and might provide novel insights into drug discovery for combination therapy.

Diversity and Potential Function of Prokaryotic and Eukaryotic Communities from Different Mangrove Sediments

Mangrove trees generally play important roles in protecting intertidal ecosystems. The mangrove root-associated sediments provide a repertoire of microbial communities that contribute to pivotal ecological functions in the system. In the present study, we used the high-throughput sequencing and PICRUSt-predicted functional information (based on 16S/18S rDNA profiles) to investigate the bacterial, archaeal, and fungal communities in two mangrove systems, located in the estuary of the Jiulong River (China), with different contaminated conditions and frequencies of human activity. Diverse distribution patterns for microbial communities were observed in six sediment samples collected from the two survey areas, which were found to be related mainly to the substrates in mangrove sediments. The sediments were predominated by relatively higher ratios of heterotrophic bacteria that participated in the degradation of organic matters, including phylum of Chloroflexi, Acidobacteriota, Desulfobacterota, and Proteobacteria. In addition, Crenarchaeota and Ascomycota presented the highest abundances of archaea and fungi, respectively. The relatively high concentrations of calcium, nitrogen, magnesium, and phosphorus in mangrove sediments correlated significantly with the microbial communities. In addition, although the potential functions were similar in the two sites based on COG and KEGG pathways, the abundances of enzymes involved in the degradation processes of cellulose and hemicellulose and the metabolism of nitrogen and sulfur presented distinctions. These results provide insights into the environmental conditions shaping microbial assemblies of the mangrove sediments under the impacts of human activities; for instance, a more abundant amount of calcium was found in urban areas in this study.

Subversion of Phytomyxae Cell Communication With Surrounding Environment to Control Soilborne Diseases; A Case Study of Cytosolic Ca2+ Signal Disruption in Zoospores of Spongospora subterranea

Ca2+ signaling regulates physiological processes including chemotaxis in eukaryotes and prokaryotes. Its inhibition has formed the basis for control of human disease but remains largely unexplored for plant disease. This study investigated the role of Ca2+ signaling on motility and chemotaxis of Spongospora subterranea zoospores, responsible for root infections leading to potato root and tuber disease. Cytosolic Ca2+ flux inhibition with Ca2+ antagonists were found to alter zoospore swimming patterns and constrain zoospore chemotaxis, root attachment and zoosporangia infection. LaCl3 and GdCl3, both Ca2+ channel blockers, at concentrations ≥ 50 μM showed complete inhibition of zoospore chemotaxis, root attachment and zoosporangia root infection. The Ca2+ chelator EGTA, showed efficient chemotaxis inhibition but had relatively less effect on root attachment. Conversely the calmodulin antagonist trifluoperazine had lesser effect on zoospore chemotaxis but showed strong inhibition of zoospore root attachment. Amiloride hydrochloride had a significant inhibitory effect on chemotaxis, root attachment, and zoosporangia root infection with dose rates ≥ 150 μM. As expected, zoospore attachment was directly associated with root infection and zoosporangia development. These results highlight the fundamental role of Ca2+ signaling in zoospore chemotaxis and disease establishment. Their efficient interruption may provide durable and practical control of Phytomyxea soilborne diseases in the field.

High spatial resolution imaging of subcellular macro and trace element distribution during phagocytosis

The bioavailability of trace elements in the course of evolution had an essential influence on the emergence of life itself. This is reflected in the co-evolution between eukaryotes and prokaryotes. In this study, the influence and cellular distribution of bioelements during phagocytosis at the host-pathogen interface was investigated using high-resolution nanoscale secondary ion mass spectrometry (NanoSIMS) and quantitative inductively coupled plasma mass spectrometry (ICP-MS). In the eukaryotic murine macrophages (RAW 264.7 cell line), the cellular Fe / Zn ratio was found to be balanced, whereas the dominance of iron in the prokaryotic cells of the pathogen Salmonella enterica Serovar Enteritidis was about 90% compared to zinc. This confirms the evolutionary increased zinc requirement of the eukaryotic animal cell. Using NanoSIMS, the Cs+ primary ion source allowed high spatial resolution mapping of cell morphology down to subcellular level. At a comparable resolution, several low abundant trace elements could be mapped during phagocytosis with a RF plasma O- primary ion source. An enrichment of copper and nickel could be detected in the prokaryotic cells. Surprisingly, an accumulation of cobalt in the area of nuclear envelope was observed indicating an interesting but still unknown distribution of this trace element in murine macrophages.

Well-designed oxidized Sb/g-C3N4 2D/2D nanosheets heterojunction with enhanced visible-light photocatalytic disinfection activity

2D/2D heterojunction photocatalysts with excellent photocatalytic activity highlight considerable potential in water disinfection. Here, an oxidized Sb/g-C₃N₄ 2D/2D nanosheets heterojunction (Sb-SbO_x/CNS) was constructed based on a facile one-step liquid-phase exfoliation method using concentrated sulfuric acid. By doing so, bulk Sb and g-C₃N₄ were exfoliated simultaneously and then, intercalated each other. Compared with CNS and Sb-SbO_x, the obtained Sb-SbO_x/CNS demonstrated better photocatalytic disinfection activity towards Escherichia coli K-12 (E. coli K-12) under visible light irradiation. The 5% oxidized Sb/g-C₃N₄ 2D/2D nanosheets heterojunction (5.0% Sb-SbO_x/CNS) exhibited the best photocatalytic performance and admirable cycling stability, which was ascribed to the unique structure where the interfacial charge separation was strengthened by the strong coupling effect between Sb-SbO_x and CNS. Meanwhile, the fundamental mechanism of photocatalytic disinfection was also proposed. The photogenerated ROS (reactive oxygen species) violently attacked the E. coli K-12 membrane, creating massive and irreparable holes on the cell membrane. The leakage of cations (K⁺, Na⁺, Ca²⁺ and Mg²⁺), adenosine triphosphate, total soluble sugar and protein accelerated the destruction of E. coli K-12. Trapping experiments suggested that the photocatalytic disinfection process against E. coli K-12 was dominated by h⁺ generated on 5.0% Sb-SbO_x/CNS. This work offers a new promising way to modify the 2D/2D heterojunction featuring efficient photocatalytic disinfection performance.

3D Bio-Printability of Hybrid Pre-Crosslinked Hydrogels

Maintaining shape fidelity of 3D bio-printed scaffolds with soft biomaterials is an ongoing challenge. Here, a rheological investigation focusing on identifying useful physical and mechanical properties directly related to the geometric fidelity of 3D bio-printed scaffolds is presented. To ensure during- and post-printing shape fidelity of the scaffolds, various percentages of Carboxymethyl Cellulose (CMC) (viscosity enhancer) and different calcium salts (CaCl₂ and CaSO₄, physical cross-linkers) were mixed into alginate before extrusion to realize shape fidelity. The overall solid content of Alginate-Carboxymethyl Cellulose (CMC) was limited to 6%. A set of rheological tests, e.g., flow curves, amplitude tests, and three interval thixotropic tests, were performed to identify and compare the shear-thinning capacity, gelation points, and recovery rate of various compositions. The geometrical fidelity of the fabricated scaffolds was defined by printability and collapse tests. The effect of using multiple cross-linkers simultaneously was assessed. Various large-scale scaffolds were fabricated (up to 5.0 cm) using a pre-crosslinked hybrid. Scaffolds were assessed for the ability to support the growth of Escherichia coli using the Most Probable Number technique to quantify bacteria immediately after inoculation and 24 h later. This pre-crosslinking-based rheological property controlling technique can open a new avenue for 3D bio-fabrication of scaffolds, ensuring proper geometry.

Bacterial aggregation assisted by anionic surfactant and calcium ions

We identify factors leading to aggregation of bacteria in the presence of a surfactant using absorbance and microscopy. Two marine bacteria, Marinobacter hydrocarbonoclasticus SP17 and Halomonas titanicae Bead 10BA, formed aggregates of a broad size distribution in synthetic sea water in the presence of an anionic surfactant, dioctyl sodium sulfosuccinate (DOSS). Both DOSS at high concentrations and calcium ions were necessary for aggregate formation, but DOSS micelles were not required for aggregation. Addition of proteinase K but not DNase1 eliminated aggregate formation over two hours. Finally, swimming motility also enhanced aggregate formation.

Apoptosis-like bacterial death modulated by photoactive hyperthermia nanomaterials and enhanced wound disinfection application

Photothermal therapy (PTT) is considered as an efficient therapeutic strategy for wound disinfection. However, there is a dilemma that on the one hand, the high PTT temperature for killing bacteria (>58 °C) could cause serious injury to normal tissue, however, low-temperature results in unsatisfactory treatment efficiency. To settle the issue, we have proposed a novel approach to gently kill bacteria in an apoptosis-like mode via PTT, in which the bacteria can maintain intact membranes but cannot proliferate. This is different from the typical necrosis-like mode of bacterial cell death requiring higher temperatures. We found that PTT prefers to trigger the gradual efflux of Ca²⁺/Mg²⁺ ions from the bacterial intracellular content rather than directly destroy the outer membranes, but can cause the dynamic variation of the membrane surface micromorphology. Hence, the microbial viability of E. coli can be dynamically changed from the live state to an apoptosis-like state (45-55 °C), then to apoptosis/necrosis (ca. 58 °C), and finally to necrosis (>61 °C). Based on this strategy, we can kill bacteria through an apoptosis-like mode. Better healing efficacy of mice wounds was achieved at a PTT temperature of 50 °C as compared to that at 58 °C, which sheds light on the wound disinfection and healing applications in clinics with a mild PTT strategy.

Calcium Signaling Mechanisms Across Kingdoms

Calcium (Ca²⁺) is a unique mineral that serves as both a nutrient and a signal in all eukaryotes. To maintain Ca²⁺ homeostasis for both nutrition and signaling purposes, the toolkit for Ca²⁺ transport has expanded across kingdoms of eukaryotes to encode specific Ca²⁺ signals referred to as Ca²⁺ signatures. In parallel, a large array of Ca²⁺-binding proteins has evolved as specific sensors to decode Ca²⁺ signatures. By comparing these coding and decoding mechanisms in fungi, animals, and plants, both unified and divergent themes have emerged, and the underlying complexity will challenge researchers for years to come. Considering the scale and breadth of the subject, instead of a literature survey, in this review we focus on a conceptual framework that aims to introduce to readers to the principles and mechanisms of Ca²⁺ signaling. We finish with several examples of Ca²⁺-signaling pathways, including polarized cell growth, immunity and symbiosis, and systemic signaling, to piece together specific coding and decoding mechanisms in plants versus animals. Expected final online publication date for the Annual Review of Cell and Developmental Biology, Volume 37 is October 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

E. coli RNase I exhibits a strong Ca2+-dependent inherent double-stranded RNase activity

Since its initial characterization, Escherichia coli RNase I has been described as a single-strand specific RNA endonuclease that cleaves its substrate in a largely sequence independent manner. Here, we describe a strong calcium (Ca2+)-dependent activity of RNase I on double-stranded RNA (dsRNA), and a Ca2+-dependent novel hybridase activity, digesting the RNA strand in a DNA:RNA hybrid. Surprisingly, Ca2+ does not affect the activity of RNase I on single stranded RNA (ssRNA), suggesting a specific role for Ca2+ in the modulation of RNase I activity. Mutation of a previously overlooked Ca2+ binding site on RNase I resulted in a gain-of-function enzyme that is highly active on dsRNA and could no longer be stimulated by the metal. In summary, our data imply that native RNase I contains a bound Ca2+, allowing it to target both single- and double-stranded RNAs, thus having a broader substrate specificity than originally proposed for this traditional enzyme. In addition, the finding that the dsRNase activity, and not the ssRNase activity, is associated with the Ca2+-dependency of RNase I may be useful as a tool in applied molecular biology.

IonoBiology: The functional dynamics of the intracellular metallome, with lessons from bacteria

Metal ions are essential for life and represent the second most abundant constituent (after water) of any living cell. While the biological importance of inorganic ions has been appreciated for over a century, we are far from a comprehensive understanding of the functional roles that ions play in cells and organisms. In particular, recent advances are challenging the traditional view that cells maintain constant levels of ion concentrations (ion homeostasis). In fact, the ionic composition (metallome) of cells appears to be purposefully dynamic. The scientific journey that started over 60 years ago with the seminal work by Hodgkin and Huxley on action potentials in neurons is far from reaching its end. New evidence is uncovering how changes in ionic composition regulate unexpected cellular functions and physiology, especially in bacteria, thereby hinting at the evolutionary origins of the dynamic metallome. It is an exciting time for this field of biology, which we discuss and refer to here as IonoBiology.

The potential application of supercritical CO2 in microbial inactivation of food raw materials and products

The purpose of this study was to review the possibility of using supercritical CO₂ as a green and sustainable technology for microbial inactivation of raw material for further application in the food industry. The history of the development of supercritical CO₂ microbial inactivation has been widely described in this article. The fundamental scientific part of the process like mechanism of bactericidal action of CO₂ or inactivation of key enzymes were characterized in detail. In summary, this study provides an overview of the latest literature on the use of supercritical carbon dioxide in microbial inactivation of food raw materials and products.

The Crystal Structure of the Ca2+-ATPase 1 from Listeria monocytogenes reveals a Pump Primed for Dephosphorylation

Many bacteria export intracellular calcium using active transporters homologous to the sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA). Here we present three crystal structures of Ca²⁺-ATPase 1 from Listeria monocytogenes (LMCA1). Structures with BeF₃^- mimicking a phosphoenzyme state reveal a closed state, which is intermediate between the outward-open E2P and the proton-occluded E2-P* conformations known for SERCA. It suggests that LMCA1 in the E2P state is pre-organized for dephosphorylation upon Ca²⁺ release, consistent with the rapid dephosphorylation observed in single-molecule studies. An arginine side-chain occupies the position equivalent to calcium binding site I in SERCA, leaving a single Ca²⁺ binding site in LMCA1, corresponding to SERCA site II. Observing no putative transport pathways dedicated to protons, we infer a direct proton counter transport through the Ca²⁺ exchange pathways. The LMCA1 structures provide insight into the evolutionary divergence and conserved features of this important class of ion transporters.

Genome-Wide Functional Screen for Calcium Transients in Escherichia coli Identifies Increased Membrane Potential Adaptation to Persistent DNA Damage

Calcium plays numerous critical roles in signaling and homeostasis in eukaryotic cells. Far less is known about calcium signaling in bacteria than in eukaryotic cells, and few genes controlling influx and efflux have been identified. Previous work in Escherichia coli showed that calcium influx was induced by voltage depolarization, which was enhanced by mechanical stimulation, which suggested a role in bacterial mechanosensation. To identify proteins and pathways affecting calcium handling in bacteria, we designed a live-cell screen to monitor calcium dynamics in single cells across a genome-wide knockout panel in E. coli The screen measured cells from the Keio collection of knockouts and quantified calcium transients across the population. Overall, we found 143 gene knockouts that decreased levels of calcium transients and 32 gene knockouts that increased levels of transients. Knockouts of proteins involved in energy production and regulation appeared, as expected, as well as knockouts of proteins of a voltage sink, F₁F_o-ATPase. Knockouts of exopolysaccharide and outer membrane synthesis proteins showed reduced transients which refined our model of electrophysiology-mediated mechanosensation. Additionally, knockouts of proteins associated with DNA repair had reduced calcium transients and voltage. However, acute DNA damage did not affect voltage, and the results suggested that only long-term adaptation to DNA damage decreased membrane potential and calcium transients. Our work showed a distinct separation between the acute and long-term DNA damage responses in bacteria, which also has implications for mitochondrial DNA damage in eukaryotes.IMPORTANCE All eukaryotic cells use calcium as a critical signaling molecule. There is tantalizing evidence that bacteria also use calcium for cellular signaling, but much less is known about the molecular actors and physiological roles. To identify genes regulating cytoplasmic calcium in Escherichia coli, we created a single-cell screen for modulators of calcium dynamics. The genes uncovered in this screen helped refine a model for voltage-mediated bacterial mechanosensation. Additionally, we were able to more carefully dissect the mechanisms of adaptation to long-term DNA damage, which has implications for both bacteria and mitochondria in the face of unrepaired DNA.

Evidence of Calcium Signaling and Modulation of the LmrS Multidrug Resistant Efflux Pump Activity by Ca2 + Ions in S. aureus

Calcium ions (Ca²⁺) play a pivotal role in eukaryote cell signaling and regulate many physiological functions. Although a similar role for Ca²⁺ in prokaryotes has been difficult to demonstrate, there is increasing evidence for Ca²⁺ as a cell regulator in bacteria. The purpose of this study was to investigate Ca²⁺ signaling and the effect of Ca²⁺ on the Staphylococcus aureus multidrug resistant efflux pump LmrS. We hypothesized that antibiotics act by increasing Ca²⁺ concentrations, which in turn enhance the efflux activity of LmrS. These Ca²⁺ transients were measured by luminometry in response to various antibiotics by using the photoprotein aequorin reconstituted within live bacterial cells. Efflux associated with LmrS was measured by the increase in fluorescence due to the loss of ethidium bromide (EtBr) from both S. aureus cells and from E. coli cells in which the lmrs gene of S. aureus was expressed. We found that addition of antibiotics to cells generated unique cytosolic Ca²⁺ transients and that addition of CaCl₂ to cells enhanced EtBr efflux whereas addition of Ca²⁺ chelators or efflux pump inhibitors significantly decreased EtBr efflux from cells. We conclude that antibiotics induce a Ca²⁺ mediated response through transients in cytosolic Ca²⁺, which then stimulates LmrS efflux pump.

Harnessing Environmental Ca2+ for Extracellular Protein Thermostabilization

Ca²⁺ is the third-most prevalent metal ion in the environment. EF hands are common Ca²⁺-binding motifs found in both extracellular and intracellular proteins of eukaryotes and prokaryotes. Cytoplasmic EF hand proteins often mediate allosteric control of signal transduction pathway components in response to intracellular Ca²⁺ concentration fluctuations by coupling Ca²⁺ binding to changes in protein structure. We show that an extracellular structural Ca²⁺-binding site mediates protein thermostabilization by such conformational coupling as well. Binding Ca²⁺ to the EF hand of the extracellular (periplasmic) Escherichia coli glucose-galactose binding protein thermostabilizes this protein by ∼17 K relative to its Ca²⁺-free form. Using statistical thermodynamic analysis of a fluorescent conjugate of ecGGBP that reports simultaneously on ligand binding and multiple conformational states, we found that its Ca²⁺-mediated stabilization is determined by conformational coupling mechanisms in two independent conformational exchange reactions. Binding to folded and unfolded states determines the maximum Ca²⁺-mediated stability. A disorder → order transition accompanies the formation of the Ca²⁺ complex in the folded state and dictates the minimum Ca²⁺ concentration at which the Ca²⁺-bound state becomes dominant. Similar transitions also encode the structural changes necessary for Ca²⁺-mediated control elements in signal transduction pathways. Ca²⁺-mediated thermostabilization and allosteric control, therefore, share a fundamental conformational coupling mechanism, which may have implications for the evolution of EF hands.

Comparison between a Conventional Anti-Biofouling Compound and a Novel Modified Low-Fouling Polyethersulfone Ultrafiltration Membrane: Bacterial Anti-Attachment, Water Quality and Productivity

In this work, the efficiency of a conventional chlorination pretreatment is compared with a novel modified low-fouling polyethersulfone (PES) ultrafiltration (UF) membrane, in terms of bacteria attachment and membrane biofouling reduction. This study highlights the use of membrane modification as an effective strategy to reduce bacterial attachment, which is the initial step of biofilm formation, rather than using antimicrobial agents that can enhance bacterial regrowth. The obtained results revealed that the filtration of pretreated, inoculated seawater using the modified PES UF membrane without the pre-chlorination step maintained the highest initial flux (3.27 ± 0.13 m³·m⁻²·h⁻¹) in the membrane, as well as having one and a half times higher water productivity than the unmodified membrane. The highest removal of bacterial cells was achieved by the modified membrane without chlorination, in which about 12.07 × 10⁴ and 8.9 × 10⁴ colony-forming unit (CFU) m⁻² bacterial cells were retained on the unmodified and modified membrane surfaces, respectively, while 29.4 × 10⁶ and 0.42 × 10⁶ CFU mL⁻¹ reached the filtrate for the unmodified and modified membranes, respectively. The use of chlorine disinfectant resulted in significant bacterial regrowth.