Fifty three fungi isolated from soils of different microhabitats of eastern Himalayan range (3,400~3,600 msl) were screened for mycosynthesis of silver nanaoparticles (AgNPs) and their efficacy as antimicrobials were assessed in combination with commonly used antibiotics. Three isolates Aspergillus terreus SP5, Paecilomyces lilacinus SF1 and Fusarium sp. MP5 identified based on morphological and 18S rRNA gene sequences were found to synthesize AgNPs. These nanoparticles were characterized by visual observation followed by UV-visible spectrophotometric analysis. The AgNPs synthesized by Aspergillus terreus SP5, Paecilomyces lilacinus SF1 and Fusarium sp. MP5 showed absorbance maxima at 412, 419, and 421 nm respectively in the visible region. Transmission electron microscopy micrograph showed formation of spherical AgNPs of 5~50 nm size. The antimicrobial activity of the mycosynthesized nanoparticles were investigated alone and in combination with commonly used antibiotics for analysis of growth inhibition zone against test organisms, namely, Staphylococcus aureus MTCC96, Streptococcus pyogenes MTCC1925, Salmonella enterica MTCC735 and Enterococcus faecalis MTCC2729. The mycosynthesized nanoparticles showed potent antibacterial activity and interestingly their syngergistic effect with erythromycin, methicillin, chloramphenicol and ciprofloxacin was significantly higher as compared to inhibitions by AgNPs alone. The present study indicates that silver nanoparticles synthesized using soil borne indigenous fungus of high altitudes show considerable antimicrobial activity, deserving further investigation for potential applications.

Three endophytic fungi Aspergillus tamarii PFL2, Aspergillus niger PFR6 and Penicllium ochrochloron PFR8 isolated from an ethno-medicinal plant Potentilla fulgens L. were used for the biosynthesis of silver nanoparticles. Scanning and transmission electron microscopic analysis were performed to study the structural morphology of the biosynthesized silver nanoparticles. The electron microscopy study revealed the formation of spherical nanosized silver particles with different sizes. The nanoparticles synthesized using the fungus A. tamarii PFL2 was found to have the smallest average particle size (3.5 ±3 nm) as compared to the nanoparticles biosynthesized using other two fungi A. niger PFR6 and P. ochrochloron PFR8 which produced average particle sizes of 8.7 ±6 nm and 7.7 ±4.3 nm, respectively. The energy dispersive X-ray spectroscopy (EDS) technique in conjunction with scanning electron microscopy was used for the elemental analysis of the nanoparticles. The selected area diffraction pattern recorded from single particle in the aggregates of nanoparticles revealed that the silver particles are crystalline in nature.

In the present study, silver nanoparticles (AgNPs) with an average particle size of 5.5 ± 3.1 nm were biosynthesized using an endophytic fungus Cryptosporiopsis ericae PS4 isolated from the ethno-medicinal plant Potentilla fulgens L. The nanoparticles were characterized using UV-visible spectrophotometer, transmission electron microscopy (TEM), scanning electron microscopy (SEM), selective area electron diffraction (SAED), and energy dispersive X-ray (EDX) spectroscopy analysis. Antimicrobial efficacy of the AgNPs was analyzed singly and in combination with the antibiotic/antifungal agent chloramphenicol/fluconazole, against five pathogenic microorganisms--Staphylococcus aureus MTCC96, Salmonella enteric MTCC735, Escherichia coli MTCC730, Enterococcus faecalis MTCC2729, and Candida albicans MTCC 183. The activity of AgNPs on the growth and morphology of the microorganisms was studied in solid and liquid growth media employing various susceptibility assays. These studies demonstrated that concentrations of AgNPs alone between 10 and 25 μM reduced the growth rates of the tested bacteria and fungus and revealed bactericidal/fungicidal activity of the AgNPs by delaying the exponential and stationary phases. Examination using SEM showed pits and ruptures in bacterial cells indicating fragmented cell membrane and severe cell damage in those cultures treated with AgNPs. These experimental findings suggest that the biosynthesized AgNPs may be a potential antimicrobial agent.

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Very few studies have addressed the phylogenetic diversity of fungi from Northeast India under the Eastern Himalayan range. In the present study, an attempt has been made to study the phylogenetic diversity of culturable soil fungi along the altitudinal gradients of eastern Himalayas. Soil samples from 24 m above sea level to 2,000 m above sea level altitudes of North-East India were collected to investigate soil micro-fungal community structure and diversity. Molecular characterization of the isolates was done by PCR amplification of 18S rDNA using universal primers. Phylogenetic analysis using BLAST revealed variation in the distribution and richness of different fungal biodiversity over a wide range of altitudes. A total of 107 isolates were characterized belonging to the phyla Ascomycota and Zygomycota, corresponding to seven orders (Eurotiales, Hypocreales, Calosphaeriales, Capnodiales, Pleosporales, Mucorales, and Mortierellales) and Incertae sedis. The characterized isolates were analysed for richness, evenness and diversity indices. Fungal diversity had significant correlation with soil physico-chemical parameters and the altitude. Eurotiales and Hypocreales were most diverse and abundant group of fungi along the entire altitudinal stretch. Species of Penicillium (D = 1.44) and Aspergillus (D = 1.288) were found to have highest diversity index followed by Talaromyces (D = 1.26) and Fusarium (D = 1.26). Fungal distribution showed negative correlation with altitude and soil moisture content. Soil temperature, pH, humidity and ambient temperature showed positive correlation with fungal distribution.