Magnesium and calcium ions: roles in bacterial cell attachment and biofilm structure maturation

Poly (acetyl, arginyl) glucosamine disrupts Pseudomonas aeruginosa biofilms and enhances bacterial clearance in a rat lung infection model

Pseudomonas aeruginosa is a common opportunistic pathogen that can cause chronic infections in multiple disease states, including respiratory infections in patients with cystic fibrosis (CF) and non-CF bronchiectasis. Like many opportunists, P. aeruginosa forms multicellular biofilm communities that are widely thought to be an important determinant of bacterial persistence and resistance to antimicrobials and host immune effectors during chronic/recurrent infections. Poly (acetyl, arginyl) glucosamine (PAAG) is a glycopolymer that has antimicrobial activity against a broad range of bacterial species, and also has mucolytic activity, which can normalize the rheological properties of cystic fibrosis mucus. In this study, we sought to evaluate the effect of PAAG on P. aeruginosa bacteria within biofilms in vitro, and in the context of experimental pulmonary infection in a rodent infection model. PAAG treatment caused significant bactericidal activity against P. aeruginosa biofilms, and a reduction in the total biomass of preformed P. aeruginosa biofilms on abiotic surfaces, as well as on the surface of immortalized cystic fibrosis human bronchial epithelial cells. Studies of membrane integrity indicated that PAAG causes changes to P. aeruginosa cell morphology and dysregulates membrane polarity. PAAG treatment reduced infection and consequent tissue inflammation in experimental P. aeruginosa rat infections. Based on these findings we conclude that PAAG represents a novel means to combat P. aeruginosa infection, and may warrant further evaluation as a therapeutic.

Environment in the lung of cystic fibrosis patients stimulates the expression of biofilm phenotype in Mycobacterium abscessus

Introduction. Pulmonary infections caused by organisms of the Mycobacterium abscessus complex are increasingly prevalent in populations at risk, such as patients with cystic fibrosis, bronchiectasis and emphysema.Hypothesis. M. abscessus infection of the lung is not observed in immunocompetent individuals, which raises the possibility that the compromised lung environment is a suitable niche for the pathogen to thrive in due to the overproduction of mucus and high amounts of host cell lysis.Aim. Evaluate the ability of M. abscessus to form biofilm and grow utilizing in vitro conditions as seen in immunocompromised lungs of patients.Methodology. We compared biofilm formation and protein composition in the presence and absence of synthetic cystic fibrosis medium (SCFM) and evaluated the bacterial growth when exposed to human DNA.Results. M. abscessus is capable of forming biofilm in SCFM. By eliminating single components found in the medium, it became clear that magnesium works as a signal for the biofilm formation, and chelation of the divalent cations resulted in the suppression of biofilm formation. Investigation of the specific proteins expressed in the presence of SCFM and in the presence of SCFM lacking magnesium revealed many different proteins between the conditions. M. abscessus also exhibited growth in SCFM and in the presence of host cell DNA, although the mechanism of DNA utilization remains unclear.Conclusions. In vitro conditions mimicking the airways of patients with cystic fibrosis appear to facilitate M. abscessus establishment of infection, and elimination of magnesium from the environment may affect the ability of the pathogen to establish infection.

The blueprint for building a biofilm the Clostridioides difficile way

Clostridioides difficile is an opportunistic pathogen that causes by a high rate of recurrent infections. Persistence in the gastrointestinal tract is thought to be mediated by sporulation and/or biofilm formation. There is an increase interest in C. difficile biofilm formation and recent findings have provided a framework to model surface-attached biofilm formation. For in vitro biofilm formation, C. difficile must undergo a metabolic reprogramming as it enters stationary phase. This helps maintain long-term viability and increases responsiveness to signals leading to biofilm formation. Metabolic reprogramming and biofilm formation requires several regulatory factors and these overlap with the sporulation cascade. Despite recent advances, further research is needed to answer outstanding questions in the field.

cAMP Receptor Protein Positively Regulates the Expression of Genes Involved in the Biosynthesis of Klebsiella oxytoca Tilivalline Cytotoxin

Klebsiella oxytoca is a resident of the human gut. However, certain K. oxytoca toxigenic strains exist that secrete the nonribosomal peptide tilivalline (TV) cytotoxin. TV is a pyrrolobenzodiazepine that causes antibiotic-associated hemorrhagic colitis (AAHC). The biosynthesis of TV is driven by enzymes encoded by the aroX and NRPS operons. In this study, we determined the effect of environmental signals such as carbon sources, osmolarity, and divalent cations on the transcription of both TV biosynthetic operons. Gene expression was enhanced when bacteria were cultivated in tryptone lactose broth. Glucose, high osmolarity, and depletion of calcium and magnesium diminished gene expression, whereas glycerol increased transcription of both TV biosynthetic operons. The cAMP receptor protein (CRP) is a major transcriptional regulator in bacteria that plays a key role in metabolic regulation. To investigate the role of CRP on the cytotoxicity of K. oxytoca, we compared levels of expression of TV biosynthetic operons and synthesis of TV in wild-type strain MIT 09-7231 and a Δcrp isogenic mutant. In summary, we found that CRP directly activates the transcription of the aroX and NRPS operons and that the absence of CRP reduced cytotoxicity of K. oxytoca on HeLa cells, due to a significant reduction in TV production. This study highlights the importance of the CRP protein in the regulation of virulence genes in enteric bacteria and broadens our knowledge on the regulatory mechanisms of the TV cytotoxin.

Functions of elements in soil microorganisms

The soil microbial community fulfils various functions, such as nutrient cycling and carbon (C) sequestration, therefore contributing to maintenance of soil fertility and mitigation of global warming. In this context, a major focus of research has been on C, nitrogen (N) and phosphorus (P) cycling. However, from aquatic and other environments, it is well known that other elements beyond C, N, and P are essential for microbial functioning. Nonetheless, for soil microorganisms this knowledge has not yet been synthesised. To gain a better mechanistic understanding of microbial processes in soil systems, we aimed at summarising the current knowledge on the function of a range of essential or beneficial elements, which may affect the efficiency of microbial processes in soil. This knowledge is discussed in the context of microbial driven nutrient and C cycling. Our findings may support future investigations and data evaluation, where other elements than C, N, and P affect microbial processes.

Biodegradation and physiological response mechanism of Bacillus aryabhattai to cyclotetramethylenete-tranitramine (HMX) contamination

This study aims to reveal the biodegradation and interaction mechanism of cyclotetramethylenete-tranitramine (HMX) by a newly isolated bacteria. In this study, a bacterial strain (Bacillus aryabhattai) with high efficiency for HMX degradation was used as the test organism to analyze the changes in growth status, cell function, and mineral metabolism following exposure to different stress concentrations (0 and 5 mg L^-1) of HMX. Non-targeted metabonomics was used to reveal the metabolic response of this strain to HMX stress. The results showed that when the HMX concentration was 5 mg L^-1, the removal rate of HMX within 24 h of inoculation with Bacillus aryabhatta was as high as 90.5%, the OD₆₀₀ turbidity was 1.024, and the BOD₅ was 225 mg L^-1. Scanning electron microscope (SEM) images showed that the morphology of bacteria was not obvious Variety, Fourier transform infrared spectroscopy (FTIR) showed that the cell surface -OH functional groups drifted, and ICP-MS showed that the cell mineral element metabolism was disturbed. Non-targeted metabonomics showed that HMX induced the differential expression of 254 metabolites (133 upregulated and 221 downregulated). The main differentially expressed metabolites during HMX stress were lipids and lipid-like molecules, and the most significantly affected metabolic pathway was purine metabolism. At the same time, the primary metabolic network of bacteria was disordered. These results confirmed that Bacillus aryabhattai has a high tolerance to HMX and can efficiently degrade HMX. The degradation mechanism involves the extracellular decomposition of HMX and transformation of the degradation products into intracellular purines, amino sugars, and nucleoside sugars that then participate in cell metabolism.

Mimicking biofilm formation and development: Recent progress in in vitro and in vivo biofilm models

Biofilm formation in living organisms is associated to tissue and implant infections, and it has also been linked to the contribution of antibiotic resistance. Thus, understanding biofilm development and being able to mimic such processes is vital for the successful development of antibiofilm treatments and therapies. Several decades of research have contributed to building the foundation for developing in vitro and in vivo biofilm models. However, no such thing as an "all fit" in vitro or in vivo biofilm models is currently available. In this review, in addition to presenting an updated overview of biofilm formation, we critically revise recent approaches for the improvement of in vitro and in vivo biofilm models.

Biological and Physiochemical Methods of Biofilm Adhesion Resistance Control of Medical-Context Surface

The formation of biofilms on medical-context surfaces gives the EPS embedded bacterial community protection and additional advantages that planktonic cells would not have such as increased antibiotic resistance and horizontal gene transfer. Bacterial cells tend to attach to a conditioning layer after overcoming possible electrical barriers and go through two phases of attachments: reversible and irreversible. In the first, bacterial attachment to the surface is reversible and occurs quickly whilst the latter is permanent and takes place over a longer period of time. Upon reaching a certain density in the bacterial community, quorum sensing causes phenotypical changes leading to a loss in motility and the production of EPS. This position paper seeks to address the problem of bacterial adhesion and biofilm formation for the medical surfaces by comparing inhabiting physicochemical interactions and biological mechanisms. Several physiochemical methodologies (e.g. ultrasonication, alternating magnetic field and chemical surface coating) and utilizing biological mechanisms (e.g. quorum quenching and EPS degrading enzymes) were suggested. The possible strategical applications of each category were suggested and evaluated to a balanced position to possibly eliminate the adhesion and formation of biofilms on medical-context surfaces.

Impact of Rocky Desertification Control on Soil Bacterial Community in Karst Graben Basin, Southwestern China

Microorganisms play critical roles in belowground ecosystems, and karst rocky desertification (KRD) control affects edaphic properties and vegetation coverage. However, the relationship between KRD control and soil bacterial communities remains unclear. 16S rRNA gene next-generation sequencing was used to investigate soil bacterial community structure, composition, diversity, and co-occurrence network from five ecological types in KRD control area. Moreover, soil physical-chemical properties and soil stoichiometry characteristics of carbon, nitrogen and phosphorus were analyzed. Soil N and P co-limitation decreased in the contribution of the promotion of KRD control on edaphic properties. Though soil bacterial communities appeared strongly associated with soil pH, soil calcium, soil phosphorus and plant richness, the key factor to determine their compositions was the latter via changed edaphic properties. The co-occurrence network analysis indicated that soil bacterial network complexity in natural ecosystem was higher than that in additional management ecosystem. Candidatus Udaeobacter, Chthoniobacterales, and Pedosphaeraceae were recognized as the key taxa maintaining karst soil ecosystems in KRD control area. Our results indicate that natural recovery is the suitable way for restoration and rehabilitation of degraded ecosystems, and thus contribute to the ongoing endeavor to appraise the interactions among soil-plant ecological networks.

Mycobacterium tuberculosis Calcium Pump CtpF Modulates the Autophagosome in an mTOR-Dependent Manner

Calcium is a very important second messenger, whose concentration in various cellular compartments is under tight regulation. A disturbance in the levels of calcium in these compartments can play havoc in the cell, as it regulates various cellular processes by direct or indirect mechanisms. Here, we have investigated the functional importance of a calcium transporting P2A ATPase, CtpF of Mycobacterium tuberculosis (Mtb) in the pathogen's interaction with the host. Among its uncanny ways of dealing with the host with umpteen strategies for survival and persistence in humans, CtpF is identified as a new player. The levels of ctpF are upregulated in macrophage stresses like hypoxia, high nitric oxide levels and acidic pH. Using confocal microscopy and fluorimetry, we show that CtpF effluxes calcium in macrophages in early stages of Mtb infection. Downregulation of ctpF expression by conditional knockdown resulted in perturbation of host calcium levels and consequent decreased activation of mTOR. We present a mechanism how calcium efflux by the pathogen inhibits mTOR-dependent autophagy and enhances bacterial survival. Our work highlights how Mtb engages its metal efflux pumps to exploit host autophagic process for its proliferation.

Effect of divalent ions on cariogenic biofilm formation

Background

Divalent cations are able to interact with exopolysaccharides (EPS) and thus are capable to modify the structure and composition of dental biofilm. At the moment, little is known about the adsorption of metals by cariogenic EPS; thus, the aim of the present study was to evaluate the effect of divalent ions (calcium, magnesium, and zinc) on the growth and biofilm formation of mutans streptococci and on the dissolution of hydroxyapatite as well as to investigate their binding to the bacterial EPS.

Results

S. mutans strains used in this study show the highest tolerance towards calcium of the ions tested. Growth parameters showed no differences to control condition for both strains up to 100 mM; revealing natural tolerance to higher concentration of calcium in the surroundings. Although excessive levels of calcium did not impair the growth parameters, it also did not have a positive effect on biofilm formation or its binding affinity to EPS. Magnesium-saturated environment proved to be counterproductive as strains were able to dissolve more Ca²⁺ from the tooth surface in the presence of magnesium, therefore releasing excessive amounts of Ca²⁺ in the environment and leading to the progression of the disease. Thus, this supports the idea of self-regulation, when more Ca²⁺ is released, more calcium is bound to the biofilm strengthening its structure and however, also less is left for remineralization. Zinc inhibited bacterial adhesion already at low concentrations and had a strong antibacterial effect on the strains as well as on calcium dissolution; leading to less biofilm and less EPS. Additionally, Zn²⁺ had almost always the lowest affinity to all EPS; thus, the unbound zinc could also still remain in the surrounding environment and keep its antimicrobial properties.

Conclusion

It is important to maintain a stable relationship between calcium, magnesium and zinc as excessive concentrations of one can easily destroy the balance between the three in cariogenic environment and lead to progression of the disease.

Quantification of Major Bacteria and Yeast Species in Kefir Consortia by Multiplex TaqMan qPCR

Kefir grains are complex microbial systems of several groups of microorganisms. The identification and quantification of the microbial composition of milk kefirs was described in several studies, which provided an insight into the microbial consortia in this complex ecosystem. Nevertheless, the current methods for identification and quantification are not appropriate for deeper studies on kefir consortia, e.g., population dynamics and microbial interactions in kefir grains. This requires another sensitive and reliable quantitative method. Therefore, this study aims to develop multiplexed qPCR assays to specifically detect and quantify, as an example, several microorganisms of the milk kefir microbial community. Primer-probe sets, which target species-specific genes in six bacteria and five yeasts, were designed, and their sensitivity and specificity to the target species was analyzed in simplex as well as four multiplex qPCR assays. The self-designed multiplex assays were applied for the detection of target bacteria and yeast species in milk kefirs, in both, grain and beverage fractions. Detection of all target microorganisms in simplex and multiplex qPCR was achieved by good linearity, efficiency, repeatability and reproducibility in all assays. When the designed assays were applied on six kefirs, all target microorganisms were detected in different samples, but not all in one kefir sample. The two ubiquitous lactobacilli Lactobacillus kefiranofaciens and Lb. kefiri were present in all six kefirs studied, but were associated with different other yeasts and bacteria. Especially on the yeast community a significant diversity was observed. In general, multiplex TaqMan qPCR as developed here was proven to have high potential for specific identification of target microorganisms in kefir samples and for the first time, eleven target bacteria and yeasts of kefir microbiota were rapidly detected and quantified. This study, thus, provides a fast and reliable protocol for future studies on kefir and other similar microbial ecosystems.

The role of magnesium in biomaterials related infections

Magnesium is currently increasing interest in the field of biomaterials. An extensive bibliography on this material in the last two decades arises from its potential for the development of biodegradable implants. In addition, many researches, motivated by this progress, have analyzed the performance of magnesium in both in vitro and in vivo assays with gram-positive and gram-negative bacteria in a very broad range of conditions. This review explores the extensive literature in recent years on magnesium in biomaterials-related infections, and discusses the mechanisms of the Mg action on bacteria, as well as the competition of Mg²⁺ and/or synergy with other divalent cations in this subject.