Synthesis of silver nanoparticles by cell-free extract (CFE) of Pseudomonas aeruginosa M6 isolated from a mangrove ecosystem was demonstrated using two physical methods, namely, boiling (conventional thermal treatment (CTT)) and microwave treatment (MWT) at pH 9. X-ray diffraction (XRD) analysis revealed the presence of smaller (10.4 nm), pure silver nanoparticles synthesized via CTT (C-NPs) and larger silver oxide nanoparticles in majority with negligible concentration of pure silver particles by MWT. Transmission electron microscopy (TEM) analysis showed that C-NPs are spherical in shape. Atomic force microscopy (AFM) analysis also confirmed the presence of large-sized, aggregated nanoparticles synthesized via MWT (M-NPs). Electrophoresis indicated the size and charge-based mobility in agarose gel (0.4%), wherein the C-NPs moved faster than M-NPs, because of their relatively smaller size. The zeta potential value of C-NPs and M-NPs was found to be −30.1 mV and −23.1 mV, respectively. Fourier transform infrared (FT-IR) results revealed that both C-NPs and M-NPs were capped with proteins, but with different conformations. Furthermore, TEM analysis of bacterial cells exposed to aqueous silver nitrate showed the presence of spherical silver nanoparticles accumulated in periplasmic space, indicating the possible involvement of periplasmic nitrate reductase in this process. In addition, both C-NPs and M-NPs have also shown good antibacterial and anticandidal activities. Thus, marine Pseudomonas aeruginosa M6 can be a potential source for the synthesis of silver nanoparticles.

No abstract

Complex inter-bacterial interactions largely influence the structure and function of the gut microbial community. Though several host-associated phenomena have often been shown to be involved in the stability, structure, and function of the gut microbial community, the implication of contact-dependent and contact-independent inter-bacterial interactions has been overlooked. Such interactions are tightly governed at multiple layers through several extracellular organelles, including contact-dependent inhibition (CDI), nanotubes, type VI secretion system (T6SS), and membrane vesicles (MVs). Recent advancements in molecular techniques have revealed that such extracellular organelles function beyond exhibiting competitive behavior and are also involved in manifesting cooperative behaviors. Cooperation between bacteria occurs through the sharing of several beneficial molecules including nucleic acids, proteins, metabolites, and nutrients among the members of the community, while competition occurs by means of multiple toxins. Intrinsic coordination between contact-dependent and contact-independent mechanisms collectively provides a fitness advantage and increased colonization resistance to the gut microbiota, where molecular trafficking plays a key role. This review is intended to provide a comprehensive view of the salient features of the different bacterial interactions and to highlight how microbiota deploy multifaceted organelles, for exerting both cooperative and competitive behaviors. We discuss the current knowledge of bacterial molecular trafficking and its impact on shaping the gut microbial community.

The bioprospecting proficient of novel pigmented probiotic strains with respect to aquaculture industry was unexplored hitherto. In this study, we investigated the probiotic potential of novel pigmented bacterial strains isolated from the indigenous soil sediments in their vicinal habitats, which were screened for their antimicrobial activity against aquatic pathogens using agar well diffusion assay. The strains namely Exiguobacterium acetylicum (S01), Aeromonas veronii (V03), and Chryseobacterium joostei (V04) were phenotypically identified and confirmed by 16S rRNA gene sequence analysis. Further characterization revealed that strains S01 and V03 survive relatively in lower pH and higher bile salt concentrations and possess good adherence ability and broad-spectrum antibiotic susceptibility. The isolate S01 exhibited the higher adhesion ability to hydrocarbons (82%) and mannose-specific adhesion (msa) gene expression. Additionally, the probiotic effects were evaluated in Artemia nauplii fed with algae supplemented with S01, V03, and V04 strains (2.7 × 10 cfu/mL) for 3 days under axenic environment. We observed a significant increase (p < 0.05) in the survival rate of Artemia nauplii treated with S01 (83 ± 5%) and V03 (55 ± 5%), whereas the survival rate was only 30 ± 0% in the untreated group. Moreover, the individual length (IL) was increased in treated group S01 (156.7 ± 2.2 μm), V03 (146.1 ± 3.4 μm), and V04 (134.4 ± 2.5 μm) compared with untreated group (116.0 ± 4.8 μm). Our results revealed that E. acetylicum S01 exhibits desirable functional probiotic attributes compared to A. veronii and C. joostei and it would be a promising probiotic strain, which can be efficiently used in the aquaculture applications.

No abstract

Cell‐to‐cell communication is essentially required in bacteria for the production of multiple virulence factors and successful colonization in the host. Targeting the virulence factors production without hampering the growth of the pathogens is a potential strategy to control pathogenesis. To accomplish this, a total of 43 mangrove isolates were screened for quorum quenching (QQ) activity against Pseudomonas aeruginosa (PA), in which eight bacteria have shown antibiofilm activity without hampering the growth of the PA. Prominent QQ activity was observed in Bacillus subtilis BR4. Previously, we found that BR4 produces stigmatellin Y, a structural analogue of PQS signal of PA, which could competitively bind with PqsR receptor and inhibits the quorum sensing (QS) system of PA. Further, stigmatellin Y containing ethyl acetate extract (S‐EAE) (100 µg ml−1) of BR4 significantly inhibits (p < 0.001) the biofilm formation of PA. Confocal laser scanning microscope (CLSM) and scanning electron microscope (SEM) analysis also fortified the QQ activity of BR4. Furthermore, S‐EAE of BR4 (500 µg ml−1) has significantly reduced the production of virulence factors, including protease, elastase, pyocyanin and extracellular polysaccharides substances. Furthermore, liquid chromatography–mass spectrometry (LC–MS)/MS analysis affirms that BR4 intercepts the PQS‐mediated QS system by reducing the synthesis of as many PQS signals, including precursor molecule (243.162313 Da) of PQS signal. Thus, S‐EAE of B. subtilis BR4 could be used as a promising therapeutic agent to combat QS system‐mediated pathogenesis of PA. Further therapeutic potentials of stigmatellin Y to be evaluated in clinical studies for the treatment of multidrug resistant PA.

No abstract

Objective: The focus of this study was to explore the nuance strategy to combat the virulence factors of the pathogens by probiotic Enterococcus durans LAB38.Methods: Probiotic attributes was determined by bile salt tolerance (0.5%) and Artemia gnotobiotic assay. Quorum sensing (QS) inhibitory activity of the supernatant and ethyl acetate (EA) extract of LAB38 was evaluated using the indicator strains, includes Chromobacterium violaceum CV026 (miniTn5 mutant of ATCC 31532), methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa (PA). Reporter strains, Vibrio harveyi BB170 (luxN mutant), BB886 (luxP mutant) and Escherichia coli pSB401 (pACYC184-derived) were used for bioluminescence-based target specificity analysis. Gas chromatography-mass spectrometry (GC-MS) analysis of EA extract was performed using standard protocol.Results: LAB38 has shown bile salt tolerance and positive probiotic effect toward Artemia salina. In addition, 100 µg/ml EA extract has significantly reduced the violacein production (37±1.4%) in CV026, biofilm formation in MRSA (94±0.9 %) and PA (22±0.08%). Further, 200 µg/ml of EA extract has shown inhibition against both autoinducer-1 (AI-1) and AI-2 mediated QS system. Bioluminescence inhibition is directly proportional to the time of exposure. GC-MS result revealed that bromine, sulfur containing molecule and azulene derivative were found in the EA extract. Conclusion:This is the first report on probiotic E. durans for quorum quenching activity. Hence, the bacterium could be used for future therapeutics application.