Strategies to enhance stress tolerance in lactic acid bacteria across diverse stress conditions

Lactic acid bacteria (LAB) hold significant importance in diverse fields, including food technology, industrial biotechnology, and medicine. As basic components of starter cultures, probiotics, immunomodulators, and live vaccines, LAB cells resist a variety of stressors, including temperature fluctuations, osmotic and pH shocks, exposure to oxidants and ultraviolet radiation, substrate deprivation, mechanical damage, and more. To stay alive in these adversities, LAB employ a wide range of stress response strategies supported by various mechanisms, for example rearrangement of metabolism, expression of specialized biomolecules (e.g., chaperones and antioxidants), exopolysaccharide synthesis, and complex repair and regulatory systems. LAB can coordinate responses to various stressors using global regulators. In this review, we summarize current knowledge about stress response strategies used by LAB and consider mechanisms of response to specific stressful factors, supported by illustrative examples. In addition, we discuss technical approaches to increase the stress resistance of LAB, including pre-adaptation, genetic modification of strains, and adjustment of cultivation conditions. A critical analysis of the recent findings in this field augments comprehension of stress tolerance mechanisms in LAB, paving the way for prospective research directions with implications in fundamental and practical areas.

Experimental and computational studies of graphene oxide covalently functionalized by octylamine: electrochemical stability, hydrogen evolution, and corrosion inhibition of the AZ13 Mg alloy in 3.5% NaCl

Recently, carbon allotropes were shown to play a key role in energy harvesting and as hydrophobic coatings on metal alloys. We have designed octylamine-functionalized graphene oxide materials for energy harvesting and as an anti-corrosion coating for metal alloy protection in a 3.5% NaCl medium. The material has been characterized by different techniques to confirm the structure and composition of the modified graphene oxide sheet: FTIR spectroscopy, XRD, Raman spectroscopy, FESEM and TEM. The electrochemical stability and corrosion inhibition efficiency were studied by electrochemical methods. The electrochemical stability increased with an increase in the applied voltage up to 500 mV, and the corrosion inhibition efficiency was shown to be 73%. The coating stability studies showed a long stability time in the corrosion medium.

Octylamine-functionalized graphene oxide chemisorbed onto a Mg alloy surface by non-bonding electron.

Experimental and computational studies of a graphene oxide barrier layer covalently functionalized with amino acids on Mg AZ13 alloy in salt medium

Leucine functionalized graphene oxide chemisorbed on a 111 surface AZ13 magnesium alloy via edge functional groups.

Experimental and DFT studies of carbon nanotubes covalently functionalized with an imidazole derivative for electrochemical stability and green corrosion inhibition as a barrier layer on the nickel alloy surface in a sulphuric acidic medium

Nickel-based alloys are used for various applications such as in automobiles, superalloys and ship making. Their stability in acidic environments, however, is often not sufficient due to their native oxide films not withstanding harsh conditions. Carbon-based materials, in contrast, have shown high stability in acidic environments. In the present work, 4,5-diphenyl-imidazole-functionalized carbon nanotubes were investigated as a corrosion-inhibiting barrier layer on nickel alloy surfaces. We studied the corrosion inhibition efficiency of the imidazole-functionalized carbon nanotubes coated on nickel alloys. The materials were characterized using microscopy and spectroscopy methods. DFT studies were performed as well. The corrosion inhibition was evaluated using electrochemical methods. The imidazole-functionalized CNTs were shown to be crystalline and to have tubular structures. They displayed excellent corrosion inhibition on the nickel alloy surface.

(A) The electrostatic interaction of a functionalized carbon material with a 111 nickel surface, (B) the OPT structure of 4,5-DPM + CNT, and (C) 4,5-DPIM + CNT material chemisorbed on a 111 nickel alloy surface.

CMOS-compatible biosensor for L-carnitine detection

A CMOS-compatible ISFET with a Ta₂O₅ sensitive surface was developed. The structure was optimized for achieving high sensitivity using a subthreshold operation mode and by reducing the influence of the capacitances on the value of subthreshold swing. The developed ISFET was used as a basis for a biosensor for L-carnitine detection. To this end, carnitine acetyltransferase was immobilized on the ISFET sensitive surface. The immobilized enzyme was active (0.082 U/g _{model plate}). The complete microsystem, consisting of a packaged chip, an immobilized enzyme and a microfluidic channel, detected L-carnitine at a range of 0.2-100 μM with a LOD of 0.2 μM. The biosensor response was linear in the range of 0.2-50 μM of L-carnitine with sensitivity 18.0 ± 1.7 mV/μM. An experiment with artificial urine containing 1.3 μM L-carnitine showed that the proposed biosensor could be used on a real sample. Therefore, a new sensor specially optimized for biosensing CMOS-compatible ISFET structures and direct determination of L-carnitine with immobilized carnitine acetyltransferase was developed.

Structural isomerism of Ru(ii)-carbonyl complexes: synthesis, characterization and their antitrypanosomal activities

New complexes with the formula [RuCl(CO)(dppb)(N–N)]PF₆ were prepared by varying the CO position as well as the diimine ligand.

[The Effect of Introduction of the Heterologous Gene Encoding the N-acyl-homoserine Lactonase (aiiA) on the Properties of Burkholderia cenocepacia 370]

To study the role of Quorum Sensing (QS) regulation in the control of the cellular processes of Burkholderia cenocepacia 370, plasmid pME6863 was transferred into its cells. The plasmid contains a heterologous gene encoding for AiiA N-acyl-homoserine lactonase, which degrades the signaling molecules of the QS system of N-acyl-homoserine lactones (AHL). An absence or reduction of AHL in the culture was revealed with the biosensors Chromobacterium violaceum CV026 and Agrobacterium tumifaciens NT1/pZLR4, respectively. The presence of the aiiA gene, which was cloned from Bacillus sp. A24 in the cells of B. cenocepacia 370, resulted in a lack of hemolytic activity, which reduced the extracellular proteolytic activity and decreased the cells' ability to migration in swarms on the surface of the agar medium. The introduction of the aiiA gene did not affect lipase activity, fatty acids synthesis, HCN synthesis, or biofilm formation. Hydrogen peroxide was shown to stimulate biofilm formation by B. cenocepacia 370 in concentrations that inhibited or weakly suppressed bacterial growth. The introduction of the aiiA gene into the cells did not eliminate this effect but it did reduce it.

[The ability of the natural ketones to interact with bacterial quorum sensing systems]

The effect of the natural ketones emitted by bacteria (2-nonanone, 2-heptanone, 2-undecanone) on the functioning of the Quorum Sensing (QS) systems was studied. In this work, three lux-reporter strains containing the components of the LasI/LasR, RhlI/RhlR, LuxI LuxR QS systems were used as biosensors for the N-acyl-homoserine lactones. It was shown that at concentrations of ketones that exhibited little or no bactericidal action the ketones could modulate the QS-response by suppressing the expression of the lux-operon reporter to a greater extent than the cell viability of these strains.

[Formation of the Pseudomonas aeruginosa PAO1 biofilms in the presence of hydrogen peroxide; the effect of the AiiA gene]

In the natural ecosystems, most bacteria exist as specifically organized biofilms attached to various surfaces; the biofilms have a complex architecture and are surrounded by an exopolymeric matrix. The bacteria in the biofilms are extremely resistant to antibacterial agents. The ability of the pathogenic bacteria to produce biofilms causes serious problems in medicine. Therefore, the study of the action of different compounds with antibacterial activity is of great interest. In this work, we studied the effect of the hydrogen peroxide (H2O2) on the formation of biofilms by Pseudomonas aeruginosa PAO1. It was shown that H2O2 in concentrations that do not suppress bacterial growth (or suppress it only weakly) stimulates the formation of the biofilms. At higher concentrations, H2O2 inhibits the formation of the biofilms. In order to determine if the stimulation of the biofilm formation depends on Quorum Sensing (QS) regulation, the plasmid pME6863 containing the heterologous gene aiiA encoding the N-acyl-homoserine lactonase AiiA was introduced into P. aeruginosa PAO1. The synthesis by cells of this enzyme degrading N-acyl-homoserine lactones (AHL), signaling molecules of the QS systems, led to the absence of the stimulation of the biofilm formation by the action of H2O2. This fact indicates that the stimulation of the biofilm formation in the presence of H2O2 depends on the functioning of the QS systems of the gene expression regulation of P. aeruginosa PAO1.

[Recurrent model of the dependence of a recessive lethal mutation on fitness components and its solution]

Experimental modeling and subsequent analysis of microevolutionary processes often involves estimation of fitness components, such as male mating competitiveness, female fecundity, progeny viability, meiotic drive upon the formation of sexual products, and so on. In this connection, we have developed a new method for estimating the relationship among fitness components and their effect on selection on frequencies of the mutant individuals in several generations, which can be applied to the case of rapid elimination of a lethal mutation from the population. The method of estimating unknown fitness components is based on the known estimates of other components and a relationship among the known and unknown components calculated from the frequency dynamics. Using the new method, a biological explanation of non-uniqueness of the admissible solutions. The method employs analysis of the form of the admissible solution region (at preset confidence intervals for the observed frequencies) in the space of the possible values.

On the aromaticity of square planar Ga4(2-) and In4(2-) in gaseous NaGa4- and NaIn4- clusters

We investigated the electronic structure and chemical bonding of two bimetallic clusters NaGa4- and NaIn4-. Photoelectron spectra of the anions were obtained and compared with ab initio calculations. We found that the ground state of the two anions contains a square planar dianion interacting with a Na+ cation. The Ga4(2-) and In4(2-) dianions both possess two delocalized pi electrons and are considered to be aromatic, similar to that recently found in Al4(2-). Using calculations for a model compound, we showed that a recently synthesized Ga4-organometallic compound also contains an aromatic -Ga4(2-)- unit, analogous to the gaseous clusters.

Observation of all-metal aromatic molecules

Aromaticity is a concept invented to account for the unusual stability of an important class of organic molecules: the aromatic compounds. Here we report experimental and theoretical evidence of aromaticity in all-metal systems. A series of bimetallic clusters with chemical composition MAl4- (M = Li, Na, or Cu), was created and studied with photoelectron spectroscopy and ab initio calculations. All the MAl4- species possess a pyramidal structure containing an M+ cation interacting with a square Al4(2-) unit. Ab initio studies indicate that Al4(2-) exhibits characteristics of aromaticity with two delocalized pi electrons (thus following the 4n + 2 electron counting rule) and a square planar structure and maintains its structural and electronic features in all the MAl4- complexes. These findings expand the aromaticity concept into the arena of all-metal species.