A Rigidity-Enhanced Antimicrobial Activity: A Case for Linear Cationic α-Helical Peptide HP(2–20) and Its Four Analogues

Linear cationic α-helical antimicrobial peptides are referred to as one of the most likely substitutes for common antibiotics, due to their relatively simple structures (≤40 residues) and various antimicrobial activities against a wide range of pathogens. Of those, HP(2–20) was isolated from Helicobacter pylori ribosomal protein. To reveal a mechanical determinant that may mediate the antimicrobial activities, we examined the mechanical properties and structural stabilities of HP(2–20) and its four analogues of same chain length by steered molecular dynamics simulation. The results indicated the following: the resistance of H-bonds to the tensile extension mediated the early extensive stage; with the loss of H-bonds, the tensile force was dispensed to prompt the conformational phase transition; and Young's moduli (N/m2) of the peptides were about 4∼8×109. These mechanical features were sensitive to the variation of the residue compositions. Furthermore, we found that the antimicrobial activity is rigidity-enhanced, that is, a harder peptide has stronger antimicrobial activity. It suggests that the molecular spring constant may be used to seek a new structure-activity relationship for different α-helical peptide groups. This exciting result was reasonably explained by a possible mechanical mechanism that regulates both the membrane pore formation and the peptide insertion

Pengaruh Jenis Sumber Nitrogen pada Produksi Biosurfaktan oleh Bakteri Halofil

Bakteri halofil merupakan bakteri yang membutuhkan NaCl untuk pertumbuhannya. Salah satu potensi bakteri halofil adalah dapat menghasilkan biosurfaktan yang aktif pada konsentrasi garam yang tinggi. Oleh karena itu, biosurfaktan tersebut dapat diaplikasikan dalam industri minyak terutama pada bidang enhanced oil recovery (EOR). Selain itu, biosurfaktan diketahui secara luas diaplikasikan dalam industri farmasi dan makanan. Sifatnya yang lebih ramah lingkungan dibandingkan dengan surfaktan sintetis menyebabkan ketertarikan untuk produksi biosurfaktan dalam skala besar semakin meningkat. Salah satu cara untuk meningkatkan produksi biosurfaktan adalah dengan melakukan optimasi sumber nitrogen pada medium produksi. Oleh karena itu penelitian ini bertujuan untuk mengetahui sumber nitrogen terbaik yang dapat digunakan untuk produksi biosurfaktan secara optimal. Penelitian ini menggunakan lima jenis sumber nitrogen antara lain urea, NH4Cl, NaNO3, (NH4)2SO4, dan KNO3 sedangkan jenis bakteri halofil yang digunakan adalah Halomonas elongata BK-AG18. Hasil penelitian ini menunjukkan bahwa urea merupakan sumber nitrogen terbaik yang digunakan untuk medium produksi biosurfaktan. Hal ini ditunjukkan dari hasil yang diperoleh dari diameter penyebaran minyak sebesar 3 cm

Removal of humic acid from peat water using untreated powdered eggshell as a low cost adsorbent

The main objective of this study is to investigate the possibility of powdered eggshell used as an adsorbent material for removal of humic acid from peat water. The influences of contact time, dose of eggshells, pH, and temperature were the factors considered in the removal processes of humic acid from peat water. In addition, adsorption isotherms of humic acid onto the powdered eggshell were also evaluated with the Langmuir and Freundlich approximations. Our results showed that the equilibrium of the process was eventually established after 60 min of the contact time, and also found that using 5 g of the powdered eggshell nearly 95 % of humic acid has been successfully removed from the peat water. The removal of humic acid gave better result when it was conducted at low pH, and it was almost unaffected the temperatures variation. The data was well fitted to Freundlich isotherm with the correlation coefficient of not <0.999, and could uptake the humic acid about 126.58 mg/g at pH 4.01, estimated from the Langmuir model. The kinetic experimental data proportionally correlated with the pseudo-second-order kinetic model with a rate constant in the range of 0.016-0.112 g mg -1 min -1 , while intra-particle-diffusion were the main rate determining step in the humic acid removal process. The powdered eggshell investigated in this study, thus, exhibited as a high potential adsorbent for the removal of humic acid from peat water