V. K. Plakunov

[Multi-Species Biofilms in Ecology, Medicine, and Biotechnology].

The structure, composition, and developmental patterns of multi-species biofilms are analyzed, as are the mechanisms of interaction of their microbial components. The main methodological approaches used for analysis of multi-species biofilms, including omics technologies, are characterized. Environmental communities (cyanobacterial mats and methanotrophic communities), as well as typical multi-species communities of medical importance (oral cavity, skin, and intestinal microbiomes), are described. A special section deals with the role of multi-species biofilms in such biotechnological processes as wastewater treatment, heavy metal removal, corrosion control, and environmental bioremediation.

Composition and functions of the extracellular polymer matrix of bacterial biofilms

The data on the composition and structure of the components comprising the extracellular polymer matrix of bacterial biofilms, the role of these components, and their functions in the biofilm are reviewed. The main biochemical mechanisms regulating the biosynthesis of biofilm matrix are discussed.

A universal method for quantitative characterization of growth and metabolic activity of microbial biofilms in static models

According to the results of worldwide research in medical microbiology, many microbial infections are caused by microorganisms organized as biofilms. Laboratory simulation of these communities in vitro is therefore necessary for investigation of the patterns of their formation and for testing the effect of antimicro-bial preparations. For these studies, the correlation between in vitro and in vivo activity of biocidal agents is of primary importance. Standard criteria of antimi-crobial activity used for planktonic cultures, such as the minimal inhibiting concentration (MIC), at which growth of planktonic cultures is suppressed completely (growth is not registered by optical techniques), or minimal bactericidal concentration (MBC), which causes the death of 99.9% of microorganisms (determined as the number of surviving cells), are not applicable to biofilm microbial communities. The properties of biofilm microbial populations, which contain high numbers of persister cells insensitive to antimi-crobial agents (Verstraeten et al., 2016), and of viable nonculturable cells (Lee et al., 2007; Li et al., 2014), prevent the application of these techniques. The new pharmacodynamic parameters proposed in order to overcome these difficulties include biofilm prevention/inhibiting concentration (MBPC or MBIC) (Sabaeifard et al., 2014), minimal biofilm bac-tericidal concentration (MBBC) (Macià et al., 2014), and minimal biofilm eradication concentration (MBEC) (Takei et al., 2013). Since they cannot be determined using the standard techniques for biofilm testing, new approaches are required, including the application of metabolic indicators (Peeters et al., 2008). Existing methods for the reconstruction and mod-eling of microbial biofilms belong to several major types (McBain, 2009; Coenye and Nelis, 2010; Leb-eaux et al., 2013): (1) closed or static models based on the application of microtiter plates (usually with 96 wells) and colony biofilms (Vandecandelaere et al., 2016); (2) open or dynamic systems with constant and (3) microcosms, i.e., multispecies biofilms formed on a surface similar to the one occurring in the environment and simulating the in situ situation (Rudney et al., 2012). Approaches based on microflu-idic techniques and combining the flow method with the possibility of continuous microscopic monitoring of the process of biofilm formation became popular Due to their relation to the topic of this article, we will discuss the most widespread models of the first type in more detail. The main shortcoming of microtiter plates (which are made of polystyrene, polypropylene, of polycar-bonate) is disordered growth of microbial biofilms. They may form at the bottom of the well, on its wall, or …

Regulation of biofilm formation by Pseudomonas chlororaphis in an in vitro system

The mutants of Pseudomonas chlororaphis 449 with completely or partially suppressed accumulation of N-acyl homoserine lactones exhibited the absence or a pronounced decrease of their capacity for stimulation of biofilm growth in the presence of azithromycin. Biofilms of the wild type strain preformed in the presence of the stimulatory azithromycin concentrations exhibited more intense staining with a polysaccharide-specific dye 1,9dimethyl methylene blue (DMMB) and were more resistant to heat shock. These findings indicate accumulation of the structural matrix polysaccharides, which play a protective role under conditions of thermal shock. Extremely low azithromycin concentrations (0.001–0.01 μg/mL) inhibit biofilm formation by P. chlororaphis 449 and P. chlororaphis 66 with suppression of the synthesis of DMMBstaining polysaccharides.

Structure of the O-specific polysaccharides from planktonic and biofilm cultures of Pseudomonas chlororaphis 449.

O-Specific polysaccharides were obtained from the lipopolysaccharides isolated from the planktonic and biofilm cultures of Pseudomonas chlororaphis 449 and studied by composition analysis and 1D and 2D (1)H and (13)C NMR spectroscopy. The following structure was established: -->4)-α-D-GalpNAc6Ac-(1-->3)-β-D-QuipNAc-(1-->6)-α-D-GlcpNAc-(1-->β-D-GlcpNAc-(1-->3) where the degree of non-stoichiometric 6-O-acetylation of GalNAc is ∼ 60% in the planktonic form or ∼ 10% in biofilm.

Substance P and Calcitonin Gene-Related Peptide: Key Regulators of Cutaneous Microbiota Homeostasis

Neurohormones diffuse in sweat and epidermis leading skin bacterial microflora to be largely exposed to these host factors. Bacteria can sense a multitude of neurohormones, but their role in skin homeostasis was only investigated recently. The first study focused on substance P (SP), a neuropeptide produced in abundance by skin nerve terminals. SP is without effect on the growth of Gram-positive (Bacillus cereus, Staphylococcus aureus, and Staphylococcus epidermidis) and Gram-negative (Pseudomonas fluorescens) bacteria. However, SP is stimulating the virulence of Bacillus and Staphylococci. The action of SP is highly specific with a threshold below the nanomolar level. Mechanisms involved in the response to SP are different between bacteria although they are all leading to increased adhesion and/or virulence. The moonlighting protein EfTu was identified as the SP-binding site in B. cereus and Staphylococci. In skin nerve terminals, SP is co-secreted with the calcitonin gene-related peptide (CGRP), which was shown to modulate the virulence of S. epidermidis. This effect is antagonized by SP. Identification of the CGRP sensor, DnaK, allowed understanding this phenomenon as EfTu and DnaK are apparently exported from the bacterium through a common system before acting as SP and CGRP sensors. Many other neuropeptides are expressed in skin, and their potential effects on skin bacteria remain to be investigated. Integration of these host signals by the cutaneous microbiota now appears as a key parameter in skin homeostasis.

Dynamics of biofilm formation on microscopic slides submerged in an anammox bioreactor

456 1 Anammox bacteria are microorganisms that perr form the process anaerobic ammonium oxidation with nitrite with release of molecular nitrogen. This group of microorganisms was discovered relatively recently. Anammox bacteria are responsible for formation of 30 to 80% dinitrogen gas in the nitrogen cycle [1]. Anamm mox bacteria are widely spread in natural ecosystems [2–4]. The anammox process occurs in marine sedii ments, at the oxic–anoxic interface within marine water column, in continental and shelf coastal waters, and in such freshwater ecosystems as wetlands and river sediments [5, 6]. Most importantly, the anammox process is closely associated with anthropogenic habii tats. It is applied in wastewater treatment bioreactors of different scale, from laboratory to industrial, including the reactors for nitrogennrich wastewater treatment. In all habitats anammox bacteria exhibit a strong tendency for attached growth and biofilm forr mation [7, 8]. This tendency is especially important in bioreactors, since anammox bacteria have an extremely low growth rate (doubling time is 11 days, according to Strous et al.) [9], and attached growth decreases the undesirable washout of anammox cells from the bioreactor. Resistance of anammox bacteria to high nitrite concentrations is greater in biofilms. In intact granular biofilms, the anammox process is not inhibited by nitrite concentration up to 400 mg NNNO 2 /L; in the case of homogenized biomass, the anammox process is already inhibited at 250 mg/L. Such differences are attributed to hindered subb strate diffusion into the deep layers of the granules. This suggestion was confirmed by microsensor meaa surements [10]. In order to provide conditions for immobilization, bioreactors for the cultivation of anammox bacteria are equipped with special carriers, usually polymeric [7, 8] or made of nonwoven fabric [11, 12]. The shape and size of the biofilm depend on the size and localization of the carriers and on the cull tivation conditions. Biofilms can be threeedimenn sional, spherical, or thin and flat [7, 8, 11]. In OLAND and SBR type reactors, which are not equipped with carriers and involve media stirring during cultivation, anammox bacteria form granules and flocs 1–2 and 0.5 mm in diameter, respectively [13, 14]. Apart from anammox bacteria, other microorganisms are present in biofilms. Normally, active living cells demonstrate distinct localization in the biofilm structure, similar to microbial mats. Stratification depends on the metaa bolic and nutritional requirements of a microbial group, as well as on its attitude towards oxygen. Coexx istence of …

Controlling of microbial biofilms formation: Anti- and probiofilm agents

Controlling the formation and reconstruction of microbial biofilms is of ever increasing importance for the ecological, medical, and biotechnological aspects of biofilm studies. The goal of this review was to provide systematization and analysis of the results obtained in recent years on the modes and mechanisms of the stimulatory or inhibitory effect of extreme factors and biocidal agents on biofilm formation. Special attention is paid to controlling the formation of medically (infective diseases, implant biofouling) and technologically or biotechnologically important biofilms (bioremediation, biocorrosion, and biosynthesis of biologically active compounds).

Effect of two cosmetic compounds on the growth, biofilm formation activity, and surface properties of acneic strains of Cutibacterium acnes and Staphylococcus aureus

Increasing popularity of preservative‐free cosmetics necessitates in‐depth research, specifically as bacteria can react to local factors by important metabolic changes. In this respect, investigating the effect of cosmetic preparations on pathogenic strains of commensal species such as acneic forms of Cutibacterium acnes (former Propionibacterium acnes) and bacteria behaving both as commensals and opportunistic pathogens such as Staphylococcus aureus is of major interest. In this study, we studied the effect of commonly used cosmetics, Uriage™ thermal water (UTW) and a rhamnose‐rich polysaccharide (PS291®) on RT4 and RT5 acneic strains of C. acnes and a cutaneous strain of S. aureus. UTW affected the growth kinetic of acneic C. acnes essentially by increasing its generation time and reducing its biomass, whereas only the S. aureus final biomass was decreased. PS291 had more marginal effects. Both compounds showed a marked antibiofilm activity on C. acnes and S. aureus. For S. aureus that appeared essentially due to inhibition of initial adhesion. Cosmetics did not modify the metabolic activity of bacteria. Both C. acnes and S. aureus showed marked hydrophobic surface properties. UTW and PS291 had limited effect on C. acnes but increased the hydrophobic character of S. aureus. This work underlines the effect of cosmetics on cutaneous bacteria and the potential limitations of preservative‐free products.

Stimulation of Violacein Biosynthesis in Chromobacterium violaceum Biofilms in the Presence of Dimethyl Sulfoxide

The ever-increasing interest in microbial biofilm research stems primarily from high resistance of biofilm microorganisms to stresses and biocidal agents, which hampers disinfection of medical equipment and chemotherapy of infectious diseases. Many researchers concentrate therefore of the search for compounds with antibiofilm activity. At the same time, microbial biofilms may be of biotechnological importance, i.e., in wastewater treatment and in biosynthesis of biologically active compounds (Nozhevnikova et al., 2015). Search for probiofilm compounds stimulating growth of microbial biofilms and the biosynthetic processes occurring in them attracts, however, much less attention (Plakunov et al., 2017).