Phenotypic Switching in Biofilm-Forming Marine Bacterium Paenibacillus lautus NE3B01

Influence of phenotypic variation of Paenibacillus polymyxa E681 on growth promotion in cucumbers

The goal of the current study is to better understand how bacteria may adapt to survive under adverse environmental conditions by altering and improving their phenotypes. In this study, we report the consequences of phenotypic variation in Paenibacillus polymyxa E681 (E681), a plant growth-promoting rhizobacterium (PGPR), isolated from winter barley root that has a variety of advantageous effects on crop plants. In our previous study, two different types of bacterial cells in E681 were distinguished. We used the term F-type for the variant that doesn't produce endospores and B-type for the endospore-producing wild type. Under the circumstances of our experiment, the cucumber rhizosphere soil and the surface of the seeds produced phenotypic variance. On tryptic soy agar (TSA) plates, the B-type spontaneously converted into the F-type, but the reverse was not reversible. Intriguingly, the plant growth promotion test displayed that cucumber seedlings treated with F-type cells had characteristics resembling those of the untreated control. Whereas, growth promotion of cucumber seedlings treated with B-type depends on temperature conditions. In particular, an increased growth promotion was observed at a low temperature of 20°C. The phenotypic change from B-type to F-type did not occur at 20°C for 6 days in the growth curve analysis of E681, but it did occur on the fourth and second days at 30 and 37°C, respectively. Therefore, before using PGPR strains as a bacterial inoculant for sustainable agriculture, it is imperative to resolve phenotypic variance in these strains.

A crucial review on polycyclic aromatic Hydrocarbons - Environmental occurrence and strategies for microbial degradation

Over the last century, contamination of polycyclic aromatic hydrocarbons (PAHs) has risen tremendously due to the intensified industrial activities like petrochemical, pharmaceutical, insecticides and fertilizers applications. PAHs are a group of organic pollutants with adverse effects on both humans and the environment. These PAHs are widely distributed in various ecosystems including air, soil, marine water and sediments. Degradation of PAHs generally occurs through processes like photolysis, adsorption, volatilization, chemical degradation and microbial degradation. Microbial degradation of PAHs is done by the utilization of diverse microorganisms like algae, bacteria, fungi which are readily compatible with biodegrading/bio transforming PAHs into H₂O, CO₂ under aerobic, or CH₄ under anaerobic environment. The rate of PAHs degradation using microbes is mainly governed by various cultivation conditions like temperature, pH, nutrients availability, microbial population, chemical nature of PAHs, oxygen and degree of acclimation. Several microbial species including Selenastrum capricornutum, Ralstonia basilensis, Acinetobacter haemolyticus, Pseudomonas migulae, Sphingomonas yanoikuyae and Chlorella sorokiniana are known to degrade PAHs via biosorption and enzyme-mediated degradation. Numerous bacterial mediated PAHs degradation methods are studied globally. Among them, PAHs degradation by bacterial species like Pseudomonas fluorescence, Pseudomonas aeruginosa, Rhodococcus spp., Paenibacillus spp., Mycobacterium spp., and Haemophilus spp., by various degradation modes like biosurfactant, bioaugmentation, biostimulation and biofilms mediated are also investigated. In contrarily, PAHs degradation by fungal species such as Pleurotus ostreatus, Polyporus sulphureus, Fusarium oxysporum occurs using the activity of its ligninolytic enzymes such as lignin peroxidase, laccase, and manganese peroxidase. The present review highlighted on the PAHs degradation activity by the algal, fungal, bacterial species and also focused on their mode of degradation.

Structural and mechanical characterization of biofilm-associated bacterial polymer in the emulsification of petroleum hydrocarbon

The marine bacterium Pseudomonas furukawaii PPS-19 isolated from the oil-polluted site of Paradip port, Odisha, India, was found to form a strong biofilm in 2% (v/v) crude oil. Confocal Laser Scanning Microscopy (CLSM) revealed biofilm components along with multi-layered dense biofilm of rod-shaped cells with 64.7 µm thickness. Scanning electron micrographs showed similar biofilm architecture covered with a gluey matrix of extracellular polymeric substances (EPS) in the presence of 2% (v/v) crude oil. The architecture of purified EPS was also studied through FESEM that exposed its porous and three-dimensional flakes-like structure. The structural characterization by FTIR revealed that EPS was composed of primary alkane, amines, halide, hydroxyl groups, uronic acid, and saccharides. The XRD profile exhibited an amorphous phase of the EPS with a crystallinity index of 0.336. The EPS showed three-step thermal decomposition and thermal stability up to 600 °C, as confirmed by TGA and DSC thermogram. EPS produced by marine bacterium P. furukawaii PPS-19 could act as bioemulsifier and showed the highest emulsifying activity of 66.23% on petrol. The emulsifying ability of the EPS was superior to the commercial polymer xanthan. The emulsion also showed high stability with time and temperature exposure. The marine bacterium P. furukawaii PPS-19 and the EPS complex showed 89.52% degradation of crude oil within 5 days. These properties demonstrated the potential of biofilm-forming marine bacterium as bioemulsifier for its application in the bioremediation of oil-polluted sites.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02795-8.

Microscopic techniques to evaluate the biofilm formation ability of a marine bacterium Pseudomonas aeruginosa PFL-P1 on different substrata

Biofilm formation in bacteria is strongly affected by the nature of substrata. Different substrata such as glass, polystyrene, steel, ceramic, and rubber were used to assess the biofilm forming ability of a marine bacterium Pseudomonas aeruginosa PFL-P1 using a scanning electron microscope (SEM), atomic force microscope (AFM), and confocal laser scanning microscope (CLSM). The bacterium formed dense biofilms with varied aggregation on different substrata. SEM study revealed small rod-shaped cells with diverse arrangements within the biofilms on all the substrata under study. The AFM study revealed the highest roughness of 545 nm on the ceramic substratum. The biofilms formed on ceramic substratum were characterized with maximum roughness (742 nm), maximum peak height (1,480 nm), and maximum arithmetic mean height (611 nm), significantly higher than all the other substrata (p < .05). AFM studies confirmed that P. aeruginosa PFL-P1 exhibited biofilm heterogeneity on all the substrata. The CLSM study indicated a higher fraction of nucleic acids to α-polysaccharides ratio in the biofilms. COMSTAT analysis revealed the highest biofilm biomass of ~18 μm³ /μm² on the ceramic substratum. The maximum biofilm thickness of ~50 μm in the native state on the ceramic substratum was significantly higher than glass (p = .0015), polystyrene (p = .0001), steel (p = .0035), and rubber substrata (p = .0001). The higher surface roughness of ceramic substratum is accountable for more area for colonization, as evident from higher biomass and thickness of the biofilm. This study provides insight into the substratum properties, which modulate the biofilm forming ability in bacteria.

Effect of C/N substrates for enhanced extracellular polymeric substances (EPS) production and Poly Cyclic Aromatic Hydrocarbons (PAHs) degradation

Extracellular Polymeric Substances (EPS) influenced Poly Cyclic Aromatic Hydrocarbons (PAHs) degrading Klebsiella pneumoniae was isolated from the marine environment. To increase the EPS production by Klebsiella pneumoniae, several physicochemical parameters were tweaked such as different carbon sources (arabinose, glucose, glycerol, lactose, lactic acid, mannitol, sodium acetate, starch, and sucrose at 20 g/L), nitrogen sources (ammonium chloride, ammonium sulphate, glycine, potassium nitrate, protease peptone and urea at 2 g/L), different pH, carbon/nitrogen ratio, temperature, and salt concentration were examined. Maximum EPS growth and biodegradation of Anthracene (74.31%), Acenaphthene (67.28%), Fluorene (62.48%), Naphthalene (57.84%), and mixed PAHs (55.85%) were obtained using optimized conditions such as glucose (10 g/L) as carbon source, potassium nitrate (2 g/L) as the nitrogen source at pH 8, growth temperature of 37 °C, 3% NaCl concentration and 72 h incubation period. The Klebsiella pneumoniae biofilm architecture was studied by confocal laser scanning microscopy (CLSM) and scanning electron microscope (SEM). The present study demonstrates the EPS influenced PAHs degradation of Klebsiella pneumoniae.

Molecular changes associated with spontaneous phenotypic variation of Paenibacillus polymyxa, a commonly used biocontrol agent, and temperature-dependent control of variation

There has been a growing interest in deploying plant growth-promoting rhizobacteria (PGPR) as a biological control agent (BCA) to reduce the use of agrochemicals. Spontaneous phenotypic variation of PGPR, which causes the loss of traits crucial for biocontrol, presents a large obstacle in producing commercial biocontrol products. Here, we report molecular changes associated with phenotypic variation in Paenibacillus polymyxa, a PGPR widely used for biocontrol worldwide, and a simple cultural change that can prevent the variation. Compared to B-type (non-variant) cells of P. polymyxa strain E681, its phenotypic variant, termed as F-type, fails to form spores, does not confer plant growth-promoting effect, and displays altered colony and cell morphology, motility, antagonism against other microbes, and biofilm formation. This variation was observed in all tested strains of P. polymyxa, but the frequency varied among them. RNA-seq analysis revealed differential regulation of many genes involved in sporulation, flagella synthesis, carbohydrate metabolism, and antimicrobial production in F-type cells, consistent with their pleiotropic phenotypic changes. F-type cells's sporulation was arrested at stage 0, and the key sporulation gene spo0A was upregulated only in B-type cells. The phenotypic variation could be prevented by altering the temperature for growth. When E681 was cultured at 20 °C or lower, it exhibited no variation for 7 days and still reached ~ 10⁸ cfu/mL, the level sufficient for commercial-scale production of biocontrol products.

Staphylococcus aureus biofilm removal by targeting biofilm-associated extracellular proteins

Background & objectives:

Among cell surface proteins, biofilm-associated protein (Bap) promotes biofilm development in Staphylococcus aureus strains. The aim of this study was to investigate proteinase-mediated biofilm dispersion in different isolates of S. aureus.

Methods:

Biofilm assay was done in 96-well microtitre plate to evaluate the effect of proteinase K on biofilms of bovine mastitis S. Aureus isolates. Extracellular polymeric substances were extracted and evaluated for their composition (protein, polysaccharides and extracellular DNA), before and after the proteinase K treatment.

Results:

Biofilm assay showed that 2 µg/ml proteinase K significantly inhibited biofilm development in bap-positive S. aureus V329 as well as other S. aureus isolates (SA7, SA10, SA33, SA352), but not in bap-mutant M556 and SA392 (a weak biofilm-producing strain). Proteinase K treatment on S. aureus planktonic cells showed that there was no inhibition of planktonic growth up to 32 µg/ml of proteinase K. Proteinase K treatment on 24 h old preformed biofilms showed an enhanced dispersion of bap-positive V329 and SA7, SA10, SA33 and SA352 biofilms; however, proteinase K did not affect the bap-mutant S. aureus M556 and SA392 biofilms. Biofilm compositions study before and after proteinase K treatment indicated that Bap might also be involved in eDNA retention in the biofilm matrix that aids in biofilm stability. When proteinase K was used in combination with antibiotics, a synergistic effect in antibiotic efficacy was observed against all biofilm-forming S. aureus isolates.

Interpretation & conclusions:

Proteinase K inhibited biofilms growth in S. aureus bovine mastitis isolates but did not affect their planktonic growth. An enhanced dispersion of preformed S. aureus biofilms was observed on proteinase K treatment. Proteinase K treatment with antibiotics showed a synergistic effect against S. aureus biofilms. The study suggests that dispersing S. aureus by protease can be of use while devising strategies against S. aureus biofilms.

Characterization of Stenotrophomonas acidaminiphila NCW-702 biofilm for implication in the degradation of polycyclic aromatic hydrocarbons

AIMS

Biofilm formation and polycyclic aromatic hydrocarbons (PAHs) degradation by a marine bacterium Stenotrophomonas acidaminihila NCW-702 was investigated.

METHODS AND RESULTS

The biofilm structure was studied by confocal laser scanning microscopy (CLSM). Both planktonic and biofilm cultures were used for PAHs (phenanthrene and pyrene) degradation. In 7 days, Sten. acidaminiphila biofilm culture efficiently degraded 71·1 ± 3·1% and 40·2 ± 2·4% of phenanthrene and pyrene, respectively, whereas 38·7 ± 2·5% of phenanthrene and 29·7 ± 1% of pyrene degradation was observed in planktonic culture. The presence of phenolic intermediates in the culture supernatant during degradation process was evaluated by Folin-Ciocalteu reagent. The average thickness and diffusion distance of Sten. acidaminiphila NCW-702 biofilm was found to be 23·94 ± 2·62 μm and 2·68 ± 0·7 μm, respectively. Bacterial biofilms have numerous metabolic features that aid in the degradation of hydrophobic organic pollutants.

CONCLUSIONS

Biofilm of Sten. acidaminiphila NCW-702 was able to degrade PAHs more efficiently as compared to planktonic cells. The findings support the efficacy of biofilms over planktonic culture in bioremediation applications.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study provides a constructive application of bacterial biofilms for the bioremediation of hydrophobic organic contaminants. The biofilm mode remediation process has the advantage of reusability of bacterial biomass and is also a low cost process as compared to cell immobilization techniques.