| dc.description.abstract | Interaction of surfactants with bacteria has immense implication on various aspects. Pulmonary surfactants were used as carbon sources by Pseudomonas aeruginosa in cystic fibrosis infected patients; enteric microbiota are in constant contact with surface-active bile acid and ingested dietary emulsifiers. Biodegradation of discharged man-made surfactants renders them harmless again, or even more harmful. To gain understanding on bacterial-surfactant interactions, this study begins with effects of non-ionic surfactants on the outer most part of bacteria, the outer membrane. Ethoxylate surfactants chosen were octylphenol polyethoxylate (OPEOn), octaethylene glycol monododecyl, polyethylene glycol (PEG) 400 and 1000, Tween 60 and 80. The model strain used in this study is a Gram-negative bacteria, Pseudomonas nitroreducens strain TX1. It is a close relative to P. aeruginosa, an important human pathogen. Strain TX1 is a highly efficient degrader of industrial surfactants such as octylphenol polyethoxylates, Triton X-100. In addition to the wild type strain, two transposon insertion mutants, ΔcbrA & ΔcbrB, whose functions closely relate to carbon source utilization and motility were used to shed light on how TX1 interact and catabolize OPEOn. In liquid culture, calculation of relation of turbidity and light microscopy cell count found that, at the same turbidity, succinate-grown wildtype cultures had higher cell numbers under light microscopy compared with OPEOn-grown cultures. Coupled with the observation that succinate-grown culture forms aggregate, while that of OPEOn-grown culture did not, it was suggested that surfactant such as OPEOn prevents cells from forming aggregates. On solid media, old colonies that became hyper-adherent were observed when TX1 grows on OPEOn. Cells clings to together, as well as on to the agar surface, rendering it difficult for it to be scraped from the agar surface without leaving messy residues. The hyper-adherent phenomena of TX1 grown on non-ionics surfactant may help elucidate how the Pseudomonas species switch between motile and a sessile, biofilm-forming stage, which is of great bacterial physiological implication regarding pathogenesis of P. aeruginosa in cystic fibrosis infection and the interaction among gut bacteria and that with mucus membrane in the presence of ethoxylate surfactants. To further observe morphology, scanning electron microscopy and atomic force microscopy (AFM) were used. Although not much difference on the cell surface were noticed with both methodologies, cell dimension statistics by AFM showed OPEOn-containing medium resulted in shorter and thinner cells at log phase. In stationary phase, wildtype cells were always shortened in succinate and OPEOn media. As a result, in log phase, surface area to volume ratio of succinate and OPEOn grown cells increase from 12 to 14, respectively, when surfactant is present. An intriguing discovery was that, the OPEOn-grown cells had a rounder cross-section as observed by AFM, while succinate-grown cells are flatter. Since fatty acids were the major constituents of membrane lipids which in turn make up the cell envelope, total cell fatty acid contents and compositions were analyzed for wildtype and the two mutants grown on individual ethoxylate surfactants as sole carbon source or supplemented along side with glucose. It was shown that raise in hydroxylated fatty acids, such as 10:0 3OH, 12:1 3OH, 14:0 3OH was a general finding from strain TX1 grown in the presence of ethoxylate surfactants with or without glucose. As a result, when cell grows on ethoxylate surfactants such as OPEOn, saturated fatty acids in total fatty acid increase to 48%, from 37% of succinate-grown cells, suggesting increase in membrane rigidity. This is the first study to demonstrate higher saturated fatty acid content could be used to correlate with a rounder, rather than flatter Gram-negative bacterial cell cross-section. In conclusion, increase in surface-area-to-volume ratio and a rounder cell cross-section may facilitate material exchange with the extracellular environment, while general increase in saturated fatty acids counteract against the membrane-disrupting action of surfactant by granting rigidity to cell membrane. | en_US |