Antimicrobial peptide (AMP) from Zingiber zerumbet rhizomes with inhibitory effect on Pythium myriotylum secretory proteases and zoospore viability.

Protease mediated proteolysis has been widely implicated in virulence of necrotrophic fungal pathogens. This is counteracted in plants by evolving new and effective antimicrobial peptides (AMP) that constitute important components of innate immune system. Peptide extraction from rhizome of Zingiber zerumbet was optimized using ammonium sulphate (50-80% w/v) and acetone (60 and 100% v/v) with maximal protein recovery of 1.2 ± 0.4 mg/g obtained using 100% acetone. Evaluation of inhibitory potential of Z. zerumbet rhizome protein extract to prominent hydrolases of necrotrophic Pythium myriotylum revealed maximal inhibition of proteases (75.8%) compared to other hydrolytic enzymes. Protein was purified by Sephacryl S200HR resin resulting in twofold purification and protease inhibition of 84.4%. Non-reducing polyacrylamide gel electrophoresis (PAGE) of the fractions yielded two bands of 75 kDa and 25 kDa molecular size. Peptide mass fingerprint of the protein bands using matrix assisted laser desorption/ionization (MALDI)-time of flight (TOF) mass spectroscopy (MS) and subsequent MASCOT searches revealed peptide match to methylesterase from Arabidopsis thaliana (15%) and to hypothetical protein from Oryza sativa (98%) respectively. Further centrifugal filter purification using Amicon Ultra (10,000 MW cut-off) filter, yielded a prominent band of 25 kDa size. Concentration dependent inhibition of zoospore viability by Z. zerumbet AMP designated as ZzAMP was observed with maximal inhibition of 89.5% at 4 µg protein and an IC50 value of 0.59 µg. Studies are of particular relevance in the context of identifying the molecules involved in imparting below ground defense in Z. zerumbet as well in development of AMPs as potential candidate molecules for control of necrotrophic pathogens of agricultural relevance.

Soil fertility and the impact of exotic invasion on microbial communities in Hawaiian forests.

Exotic plant invasions into Hawaiian montane forests have altered many important nutrient cycling processes and pools. Across different ecosystems, researchers are uncovering the mechanisms involved in how invasive plants impact the soil microbial community-the primary mediator of soil nutrient cycling. We examined whether the invasive plant, Hedychium gardnerianum, altered microbial community composition in forests dominated by a native tree, Metrosideros polymorpha, under varying soil nutrient limitations and soil fertility properties within forest plots of the Hawaii long-term substrate age gradient (LSAG). Microbial community lipid analysis revealed that when nutrient limitation (as determined by aboveground net primary production [ANPP]) and soil fertility were taken into account, plant species differentially altered soil microbial community composition. Microbial community characteristics differed under invasive and native plants primarily when N or P was added to the older, highly weathered, P-limited soils. Long-term fertilization with N or P at the P-limited site led to a significant increase in the relative abundance of the saprophytic fungal indicator (18:2 omega 6c,9c) under the invasive plant. In the younger, N-limited soils, plant species played a minor role in influencing soil microbial community composition. We found that the general rhizosphere microbial community structure was determined more by soil fertility than by plant species. This study indicates that although the aggressive invasion of a nutrient-demanding, rapidly decomposable, and invasive plant into Hawaiian forests had large impacts on soil microbial decomposers, relatively little impact occurred on the overall soil microbial community structure. Instead, soil nutrient conditions were more important determinants of the overall microbial community structure within Hawaii's montane forests.