Extracellular polysaccharide (EPS) from Klebsiella oxytoca was chemically modified to increase net negative charge in order to expand the efficiency of metal binding. Chlorosulfonic acid (CSA) or a complex of dimethylformamide and sulfur trioxide (DMF–SO3) was used to introduce sulfate substituents onto the native polymer. Additionally, sequential treatment with divinylsulfone (DVS) and glycine or DVS and iminodiacetic acid (IDA) was used to introduce carboxyl residues. Native EPS exhibited a molecular mass distribution of 1500–1700 kDa and removed 38% and 19%, respectively, of lead and cadmium ions. Modification with CSA resulted in a reduction of molecular mass to 450–600 kDa and a removal from solution of lead and cadmium of 75% and 66%, respectively. Modification of EPS with the DMF–SO3 complex, while it did not affect the molecular mass of the polymer, resulted in decreased levels of lead and cadmium removal. Covalent substitution of EPS with DVS–glycine resulted in an increase of molecular mass to 3000 kDa and lead and cadmium removals of 46% and 47%, respectively. Modification of EPS with DVS–IDA increased molecular mass to 2200 kDa and demonstrated lead and cadmium removals of 57% each. Immobilization of native EPS and of the CSA and DVS–IDA modifications to oxirane–acrylic beads resulted in significant increases in metal binding per gram of bound polymer. This suggests a method for metal ion recovery using chelate desorption.

Although gravitational deposition is generally regarded to be important during biofilm development because it provides a mechanism by which bacteria can come into contact with a surface, this process is usually neglected in most biofilm studies. The purpose of this study was to develop a better understanding of the effect of gravitational deposition by comparing the development of biofilms on the upper and lower surfaces of a capillary glass tube biofilm reactor under various hydrodynamic conditions. Pure cultures of Pseudomonas fluorescens and Shewanella oneidensis MR-1 were used for the test. Results demonstrated that gravitational deposition significantly influences biofilm development under slow laminar flow conditions, which may be attributable to the effect of gravity on both attachment and detachment during the initial reversible attachment phase and the later development phase. Additionally, it was shown that hydrodynamic conditions have the potential to reduce the impact of gravitational deposition on biofilm development, and that this became less significant with an increase in flow rate. These results will be useful for comparing biofilm development in different biofilm systems.

Photodynamic therapy (PDT) offers potential as a non-invasive treatment of periodontal disease. In this study, microcosm biofilms were grown in vitro under conditions designed to mimic subgingival plaques typically found in patients with periodontitis. To investigate potential PDT modalities, biofilms were exposed to light from a helium/neon laser in conjunction with a photosensitizer, toluidine blue O (TBO), at varying output and concentration, respectively. To determine cytotoxic effects, viability profiling was undertaken on whole biofilms using standard plating methods, and on horizontal cross-sections of biofilms using confocal laser-scanning microscopy (CLSM) in conjunction with a differential viability stain. A light energy dose of 94.5 J in combination with 81.7 μM TBO was found to be optimal, achieving significant kills of over 97%. CLSM enabled visualization of the effects of PDT in three dimensions. Viability profiling of the CLSM images revealed that lethal photosensitization was most effective in the upper layers of biofilm. PDT was found to reduce the viability of subgingivally modelled plaques in vitro by a magnitude similar to that of chlorhexidine digluconate, which is commonly used to treat periodontal disease. The findings of this study indicate that PDT may be an effective alternative to conventional modalities in the treatment of periodontal disease.