Biofilm formation is a concerning issue for many industrial processes, especially for water treatment membranes, because it leads to fouling and poor performance of the system. Combinations of physical and chemical cleaning methods are commonly used to remove the deposited biofilms. However, there is little understanding of the interactions between chemical cleaning agents and the biofilm. Therefore, companies perform a series of iterations whereby a certain cleaning product or process is applied to the surface with the hope of dislodging the biofilm. This leads to indiscriminate use of cleaning agents and inconsistent results of biofilm removal. The goal of this project is to give insights to the impact of representative cleaning agents on individual biofilm components and ultimately, to design an efficient microbial cleaning strategy for biofouled surfaces, which will help to ensure a safe and sustainable operation of water supply and enhance the performance of membrane-based water treatment processes.

In this study, the interaction between a homogeneous layer of a single biofilm component (polysaccharides, proteins, nucleic acids) and different cleaning solutions (base, oxidizer, surfactant, chelating agent) was evaluated by comparing permeate flux of an ultrafiltration membrane and frequency shift measured by a quartz crystal microbalance. The efficacy of cleaning agents towards model biofilm component mixtures designed to mimic gram-negative and gram-positive bacterial biofilms and an actual bacterial biofilm component extracted from Pseudomonas aeruginosa (a gram-negative bacteria) were tested. The presence of calcium in the feed solution hindered the ability of the cleaning solutions to completely remove the foulants except when a chelating agent was used. The usage of a base and an oxidizer showed the best performance yet did not fully removed the model biofilm component mixtures or the bacterial biofilm component. Overall, it was determined that the presence of proteins in biofilms determines their susceptibility to cleaning.

The molecular mechanisms responsible for the sexual differentiation of the zebra finch song system remain mysterious. Androgen receptors are expressed in a sexually dimorphic fashion in the zebra finch song system: males have more cells expressing androgen receptors, and this sex difference appears very early in development (day 9 posthatch). Estrogen administration to hatchling females up-regulates androgen receptor expression in their song system and profoundly masculinizes their song system's morphology. Co-administering flutamide, an androgen receptor blocker, with estrogen impedes estrogen's masculinizing effects on the song system, suggesting that androgens are required for masculine development. Accordingly, to investigate further the role of androgens in the sexual differentiation of the zebra finch song system, we sought to block androgen activity in males by administering large, sustained doses of flutamide from just before androgen receptors are expressed in the song system (day 7) through to the day of sacrifice (days 61-63). Flutamide profoundly reduced the size of the testes, demonstrating that this drug and mode of administration could have a large impact on tissues. In contrast, flutamide had only a minor impact on the song system: the number of RA neurons was slightly reduced, and the corrected HVC volume showed a trend toward demasculinization. Other brain measures (uncorrected HVC, and corrected and uncorrected volumes of Area X, lMAN, RA, and Rotundus; neuron size in lMAN, HVC, and RA; and number of HVC and LMAN neurons) were not significantly affected. The present results do not support an important role for androgen in masculinizing the song circuit after posthatch day 7. (c) 2007 Elsevier Ireland Ltd. All rights reserved.

Background

Methods

Results

Conclusions