Satish V. Patil

Is there a common water-activity limit for the three domains of life?

Archaea and Bacteria constitute a majority of life systems on Earth but have long been considered inferior to Eukarya in terms of solute tolerance. Whereas the most halophilic prokaryotes are known for an ability to multiply at saturated NaCl (water activity (aw) 0.755) some xerophilic fungi can germinate, usually at high-sugar concentrations, at values as low as 0.650–0.605 aw. Here, we present evidence that halophilic prokayotes can grow down to water activities of <0.755 for Halanaerobium lacusrosei (0.748), Halobacterium strain 004.1 (0.728), Halobacterium sp. NRC-1 and Halococcus morrhuae (0.717), Haloquadratum walsbyi (0.709), Halococcus salifodinae (0.693), Halobacterium noricense (0.687), Natrinema pallidum (0.681) and haloarchaeal strains GN-2 and GN-5 (0.635 aw). Furthermore, extrapolation of growth curves (prone to giving conservative estimates) indicated theoretical minima down to 0.611 aw for extreme, obligately halophilic Archaea and Bacteria. These were compared with minima for the most solute-tolerant Bacteria in high-sugar (or other non-saline) media (Mycobacterium spp., Tetragenococcus halophilus, Saccharibacter floricola, Staphylococcus aureus and so on) and eukaryotic microbes in saline (Wallemia spp., Basipetospora halophila, Dunaliella spp. and so on) and high-sugar substrates (for example, Xeromyces bisporus, Zygosaccharomyces rouxii, Aspergillus and Eurotium spp.). We also manipulated the balance of chaotropic and kosmotropic stressors for the extreme, xerophilic fungi Aspergillus penicilloides and X. bisporus and, via this approach, their established water-activity limits for mycelial growth (∼0.65) were reduced to 0.640. Furthermore, extrapolations indicated theoretical limits of 0.632 and 0.636 aw for A. penicilloides and X. bisporus, respectively. Collectively, these findings suggest that there is a common water-activity limit that is determined by physicochemical constraints for the three domains of life.

Plant Extract: A Promising Biomatrix for Ecofriendly, Controlled Synthesis of Silver Nanoparticles

Uses of plants extracts are found to be more advantageous over chemical, physical and microbial (bacterial, fungal, algal) methods for silver nanoparticles (AgNPs) synthesis. In phytonanosynthesis, biochemical diversity of plant extract, non-pathogenicity, low cost and flexibility in reaction parameters are accounted for high rate of AgNPs production with different shape, size and applications. At the same time, care has to be taken to select suitable phytofactory for AgNPs synthesis based on certain parameters such as easy availability, large-scale nanosynthesis potential and non-toxic nature of plant extract. This review focuses on synthesis of AgNPs with particular emphasis on biological synthesis using plant extracts. Some points have been given on selection of plant extract for AgNPs synthesis and case studies on AgNPs synthesis using different plant extracts. Reaction parameters contributing to higher yield of nanoparticles are presented here. Synthesis mechanisms and overview of present and future applications of plant-extract-synthesized AgNPs are also discussed here. Limitations associated with use of AgNPs are summarised in the present review.

Cationic Antimicrobial Peptides and Biogenic Silver Nanoparticles Kill Mycobacteria without Eliciting DNA Damage and Cytotoxicity in Mouse Macrophages

ABSTRACT With the emergence of multidrug-resistant mycobacterial strains, better therapeutic strategies are required for the successful treatment of the infection. Although antimicrobial peptides (AMPs) and silver nanoparticles (AgNPs) are becoming one of the popular antibacterial agents, their antimycobacterial potential is not fully evaluated. In this study, we synthesized biogenic-silver nanoparticles using bacterial, fungal, and plant biomasses and analyzed their antibacterial activities in combination with AMPs against mycobacteria. Mycobacterium smegmatis was found to be more susceptible to AgNPs compared to M. marinum. We found that NK-2 showed enhanced killing effect with NP-1 and NP-2 biogenic nanoparticles at a 0.5-ppm concentration, whereas LLKKK-18 showed antibacterial activity only with NP-2 at 0.5-ppm dose against M. smegmatis. In case of M. marinum NK-2 did not show any additive activity with NP-1 and NP-2 and LLKKK-18 alone completely inhibited the bacterial growth. Both NP-1 and NP-2 also showed increased killing of M. smegmatis in combination with the antituberculosis drug rifampin. The sizes and shapes of the AgNPs were determined by transmission electron microscopy and dynamic light scattering. AgNPs showed no cytotoxic or DNA damage effects on macrophages at the mycobactericidal dose, whereas treatment with higher doses of AgNPs caused toxicity and micronuclei formation in cytokinesis blocked cells. Macrophages actively endocytosed fluorescein isothiocyanate-labeled AgNPs resulting in nitric oxide independent intracellular killing of M. smegmatis. Apoptosis and cell cycle studies showed that treatment with higher dose of AgNPs arrested macrophages at the G1-phase. In summary, our data suggest the combined effect of biogenic-AgNPs and antimicrobial peptides as a promising antimycobacterial template.

A novel biomaterial: bacterial cellulose and its new era applications

Bacterial cellulose (BC) is a promising natural polymer that is produced by bacteria and that has unique and desirable structural, physical, and chemical properties. From the time when the remarkable properties of BC were found 15 years ago compared with plant cellulose, interest has grown in BC and it has become an article of trade in diverse applications. Following this trend, this paper reviews the progress of relevant studies, including general information about cellulose, production by microorganisms as well as BC cultivation, and its properties. The applications reviewed in the present article comprise biological and nonbiological fields. The latest use of BC in the biomedical, environmental, agricultural, electronic, food, and industrial fields is discussed with its applications in composite form. The present article attempts to amass the assorted uses of BC under one umbrella. Thus, recent advances in BC applications in different fields are thoroughly reviewed. This article concludes with the need for future research of BC to make it commercialized as vital biomaterial.

Physical, structural, mechanical and thermal characterization of bacterial cellulose by G. hansenii NCIM 2529

The present study aims to investigate the physico mechanical, structural and thermal properties of the bacterial cellulose (BC) produced under shaking condition. Formation of characteristic cellulose sphere has been characterized by light and scanning electron microscopy. The purity of bacterial cellulose was confirmed by thin layer chromatography of hydrolyzed product and elemental analysis by Energy Dispersive Spectroscopy and Fourier transform infrared spectroscopy. High crystallinity bacterial cellulose (81%) composed by high Iα confirmed by X-ray diffraction and solid state C13 nuclear magnetic resonance spectroscopy. The Z-average particle size was 1.44 μm with high porosity of 181.81%. The water holding and absorption capacity was determined. Tensile strength reveals a Youngs modulus of 15.71 ± 0.15 MPa and tensile strength of up to 14.94 MPa. The thermal behavior evaluated by thermogravimetry and differential scanning calorimetry shows the thermal stability of bacterial cellulose. The results demonstrated unique characteristics of bacterial cellulose produced at shaking condition.

Towards an understanding of bacterial metabolites prodigiosin and violacein and their potential for use in commercial sunscreens

To exploit the microbial ecology of bacterial metabolite production and, specifically, to: (i) evaluate the potential use of the pigments prodigiosin and violacein as additives to commercial sunscreens for protection of human skin, and (ii) determine antioxidant and antimicrobial activities (against pathogenic bacteria) for these two pigments.

Bacterial cellulose of Gluconoacetobacter hansenii as a potential bioadsorption agent for its green environment applications

Bacterial cellulose (BC) is an interesting biopolymer produced by bacteria having superior properties. BC produced by Gluconoacetobacter hansenii (strain NCIM 2529) under shaking condition and explored for its applications in dye removal and bioadsorption of protein and heavy metals. Purity of BC was confirmed by Fourier transform infrared spectroscopy and scanning electron microscopy (SEM) analysis. BC removed azo dye and Aniline blue (400 mg/L) with 80% efficiency within 60 min. The adsorption and elution of Bovine serum albumin (BSA) and heavy metals like lead, cadmium and nickel (Pb2+, Cd2+ and Ni2+) was achieved with BC which confirms the exclusion ability with reusability. The BSA adsorption quantity was increased with increase in protein concentration with more than 90% adsorption and elution ratio. The effect of pH and temperature on BSA adsorption has been investigated. Bioadsorption (82%) and elution ratio (92%) of BC for Pb2+ was more when compared with Cd2+ (41 and 67%) and Ni2+ (33 and 85%), respectively. BC was also explored as soil conditioner to increase the water-holding capacity and porosity of soil. The results elucidated the significance of BC as renewable effective ecofriendly bioadsorption agent.

Amoebicidal activity of phytosynthesized silver nanoparticles and their in vitro cytotoxicity to human cells

Acanthamoeba causes infections in humans and other animals and it is important to develop treatment therapies. Jatropha curcas, Jatropha gossypifolia and Euphorbia milii plant extracts synthesized stable silver nanoparticles (AgNPs) that were relatively stable. Amoebicidal activity of J. gossypifolia, J. curcas and E. milii leaf extracts showed little effect on viability of Acanthamoeba castellanii trophozoites. Plant-synthesized AgNPs showed higher amoebicidal activity. AgNPs synthesized by J. gossypifolia extract were able to kill 74-27% of the trophozoites at concentrations of 25-1.56 μg mL(-1) . AgNPs were nontoxic at minimum inhibitory concentration with peripheral blood mononuclear cells. These results suggest biologically synthesized nanoparticles as an alternative candidate for treatment of Acanthamoeba infections.

Phytolatex synthesized gold nanoparticles as novel agent to enhance sun protection factor of commercial sunscreens

To study the potential of phytolatex (latex of Jatropha gossypifolia) fabricated gold nanoparticles as promising candidate in sunscreen formulations for enhancement in sun protection factor.

Antimicrobial activity of prodigiosin is attributable to plasma-membrane damage

Abstract The bacterial pigment prodigiosin has various biological activities; it is, for instance, an effective antimicrobial. Here, we investigate the primary site targeted by prodigiosin, using the cells of microbial pathogens of humans as model systems: Candida albicans, Escherichia coli, Staphylococcus aureus. Inhibitory concentrations of prodigiosin; leakage of intracellular K+ ions, amino acids, proteins and sugars; impacts on activities of proteases, catalases and oxidases; and changes in surface appearance of pathogen cells were determined. Prodigiosin was highly inhibitory (30% growth rate reduction of C. albicans, E. coli, S. aureus at 0.3, 100 and 0.18 μg ml−1, respectively); caused leakage of intracellular substances (most severe in S. aureus); was highly inhibitory to each enzyme; and caused changes to S. aureus indicative of cell-surface damage. Collectively, these findings suggest that prodigiosin, log Poctanol–water 5.16, is not a toxin but is a hydrophobic stressor able to disrupt the plasma membrane via a chaotropicity-mediated mode-of-action.