Impact of Higher Alginate Expression on Deposition of Pseudomonas aeruginosa in Radial Stagnation Point Flow and Reverse Osmosis Systems

Abstract

Extracellular polymeric substances (EPS) have major impact on biofouling of reverse osmosis (RO) membranes. On one hand, EPS can reduce membrane permeability and on the other, EPS production by the primary colonizers may influence their deposition and attachment rate and subsequently affect the biofouling propensity of the membrane. The role of bacterial exopolysaccharides in bacterial deposition followed by the biofouling potential of an RO membrane was evaluated using an alginate overproducing (mucoid) Pseudomonas aeruginosa. The mucoid P. aeruginosa PAOmucA22 was compared with its isogenic nonmucoid prototypic parent PAO1 microscopically in a radial stagnation point flow (RSPF) system for their bacterial deposition characteristics. Then, biofouling potential of PAO1 and PAOmucA22 was determined in a crossflow rectangular plate-and-frame membrane cell, in which the strains were cultivated on a thin-film composite, polyamide, flat RO membrane coupon (LFC-1) under laminar flow conditions. In the RSPF system, the observed deposition rate of the mucoid strain was between 5- and 10-fold lower than of the wild type using either synthetic wastewater medium (with ionic strength of 14.7 mM and pH 7.4) or 15 mM KCl solution (pH of 6.2). The slower deposition rate of the mucoid strain is explained by 5- to 25-fold increased hydrophilicity of the mucoid strain as compared to the isogenic wild type, PAO1. Corroborating with these results, a significant delay in the onset of biofouling of the RO membrane was observed when the mucoid strain was used as the membrane colonizer, in which the observed time for the induced permeate flux decline was delayed (ca. 2-fold). In conclusion, the lower initial cell attachment of the mucoid strain decelerated biofouling of the RO membrane. Bacterial deposition and attachment is a critical step in biofilm formation and governed by intimate interactions between outer membrane proteins of the bacteria and the surface. Shielding these interactions by a hydrated and hydrophilic alginate capsule is shown to dramatically lessen the biofouling potential of the membrane colonizers.

The role of cell-surface interactions in bacterial initial adhesion and consequent biofilm formation on nanofiltration/reverse osmosis membranes

“…These areas include: (j) the choice of micro-organisms used when studying the fundamentals of biofouling on RO/NF systems in research laboratories should ideally use micro-organisms isolated from aquatic systems and isolates from membrane autopsies. For years several key studies adding to significant contributions on membrane biofouling in RO/NF systems employed model organisms that have little relevance to water environments, such as Pseudomonas aeruginosa [22,67,73,129], a known clinical strain responsible for nosocomial and chronic wound types of infection; (k) an understanding of the succession and dynamics of surface colonization, which may partly depend on the effects of transient attachment periods and/or competition between species, should be further developed. Siboni et al [132] analyzed the community dynamics in early stage biofilm formation in the marine environment.…”

“…This theory has been applied in investigations of bacterial adhesion on membranes, in controlled environments, by taking into account the membrane contact angle, roughness and surface charge, as well as the bacteria cell wall properties [19][20][21]. It should be noted, however, that these theories should be applied with caution; for example, bacterial cell properties can change due to a change in EPS expression, consequently affecting their adhesion [22]. Furthermore, the presence of bacterial appendages, even negatively charged ones, can pierce the electrostatic energy barrier between the negatively charged surface of the bacteria and the negative charge of the adhering surface [23].…”

“…In the particular case of NF and RO membrane surfaces, increase in levels of bacterial adhesion is correlated with increased bacterial cell wall hydrophobicity [30]. Herzberg et al [22] showed that hydrophobicity of the cells varies with the growth stage and with the amount of alginate they produce by comparing a mucoid strain with a wild strain of P. aeruginosa in their exponential and stationary phase. The mucoid strain with higher alginate expression in the stationary phase was found to be more hydrophilic, and deposited less onto a quartz surface.…”

Composition and Variability of Biofouling Organisms in Seawater Reverse Osmosis Desalination Plants

“…At present, little is known of the bacteria in seawater that cause biofouling. The Pseudomonas species that is commonly used as a model organism for membrane fouling studies (22)(23)(24) is neither the initiator nor the dominant bacteria in the RO membrane biofilm according to the recent studies of total bacterial community of the RO biofilm (6,39). In fact, most of the model organisms are easily cultivable bacteria, which do not reflect the natural microbial community on May 7, 2018 by guest http://aem.asm.org/ in water for treatment, because more than 99% of those bacteria are not cultivable on nutrient-rich artificial medium (14,31).…”

Bacterial adhesion onto nanofiltration and reverse osmosis membranes: Effect of permeate flux

“…In one recent study (Walker et al (2005)) it was shown that the adhesion profile of Escherichia coli was dependent on its growth phase, which was determined by the charge distribution resulting from electrostatic repulsion forces. Differences in biofouling of RO membranes have also been showed to depend on the growth stage of the bacterial species studied (Herzberg et al (2009)). Differences were caused by the bacterial cell properties such as zeta potential.…”