A method for measuring low-weight carboxylic acids from biosolid compost.

Concentration of low-weight carboxylic acids (LWCA) is one of the important parameters that should be taken into consideration when compost is applied as soil improver for plant cultivation, because high amounts of LWCA can be toxic to plants. The present work describes a method for analysis of LWCA in compost as a useful tool for monitoring compost quality and safety. The method was tested on compost samples of two different ages: 3 (immature) and 6 (mature) months old. Acids from compost samples were extracted at high pH, filtered, and freeze-dried. The dried sodium salts were derivatized with a sulfuric acid-methanol mixture and concentrations of 11 low-weight fatty acids (C1-C10) were analyzed using headspace gas chromatography. The material was analyzed with two analytical techniques: the external calibration method (tested on 11 LWCA) and the standard addition method (tested only on formic, acetic, propionic, butyric, and iso-butyric acids). The two techniques were compared for efficiency of acids quantification. The method allowed good separation and quantification of a wide range of individual acids with high sensitivity at low concentrations. Detection limit for propionic, butyric, caproic, caprylic, and capric acids was 1 mg kg(-1) compost; for formic, acetic, valeric, enanthoic and pelargonic acids it was 5 mg kg(-1) compost; and for iso-butyric acid it was 10 mg kg(-1) compost. Recovery rates of LWCA were higher in 3-mo-old compost (57-99%) than in 6-mo-old compost (29-45%). In comparison with the external calibration technique the standard addition technique proved to be three to four times more precise for older compost and two times for younger compost. Disadvantages of the standard addition technique are that it is more time demanding and laborious.

Permeabilizing action of polyethyleneimine on Salmonella typhimurium involves disruption of the outer membrane and interactions with lipopolysaccharide.

Polyethyleneimine (PEI), a polycationic polymer substance used in various bioprocesses as a flocculating agent and to immobilize enzymes, was recently shown to make Gram-negative bacteria permeable to hydrophobic antibiotics and to detergents. Because this suggests impairment of the protective function of the outer membrane (OM), the effect of PEI on the ultrastructure of Salmonella typhimurium was investigated. Massive alterations in the OM of PEI-treated and thin-sectioned bacteria were observed by electron microscopy. Vesicular structures were seen on the surface of the OM, but no liberation of the membrane or its fragments was evident. Since a potential mechanism for the action of PEI could be its binding to anionic LPSs on the OM surface, the interaction of PEI with isolated LPSs was assayed in vitro. The solubility of smooth-type LPSs of Salmonella, regardless of the sugar composition of their O-specific chains, was not affected by PEI, nor was that of Ra-LPS (lacking O-specific chains but having a complete core oligosaccharide). PEI strongly decreased the solubility of rough-type LPSs of the chemotypes Rb2 and Re, whereas it had only a weak effect on the abnormally cationic Rb2-type pmrA mutant LPS, suggesting that the negative charge to mass ratio of LPS plays a critical role in the interaction.

Polyethyleneimine is an effective permeabilizer of gram-negative bacteria.

The effect of the polycation polyethyleneimine (PEI) on the permeability properties of the Gram-negative bacterial outer membrane was investigated using Escherichia coli, Pseudomonas aeruginosa and Salmonella typhimurium as target organisms. At concentrations of less than 20 micrograms ml-1, PEI increased the bacterial uptake of 1-N-phenylnaphthylamine, which is a hydrophobic probe whose quantum yield is greatly increased in a lipid environment, indicating increased hydrophobic permeation of the outer membrane by PEI. The effect of PEI was comparable to that brought about by the well-known permeabilizer EDTA. Permeabilization by PEI was retarded but not completely inhibited by millimolar concentrations of MgCl2. PEI also increased the susceptibility of the test species to the hydrophobic antibiotics clindamycin, erythromycin, fucidin, novobiocin and rifampicin, without being directly bactericidal. PEI sensitized the bacteria to the lytic action of the detergent SDS in assays where the bacteria were pretreated with PEI. In assays where PEI and SDS were simultaneously present, no sensitization was observed, indicating that PEI and SDS were inactivating each other. In addition, a sensitizing effect to the nonionic detergent Triton X-100 was observed for P. aeruginosa. In conclusion, PEI was shown to be a potent permeabilizer of the outer membrane of Gram-negative bacteria.