Title

Corrosion control using regenerative biofilms and biofilm inhibition using plant-derived chemicals

Date of Completion

January 2005

Keywords

Engineering, Chemical

Degree

Ph.D.

Abstract

Bacteria form biofilms on any surface and dominate as sessile cells in most ecosystems. Deleterious biofilms cause problems in both industry (e.g., corrosion of metals) and in medicine (e.g., infections on human organs), which makes it necessary to develop novel strategies to control corrosion and deleterious biofilms. ^ Two strategies are being investigated to control biocorrosion and deleterious biofilms. First, regenerative beneficial biofilms are used to protect metals. Biofilms producing gramicidin S [a 10-residue, cyclic peptide with the structure of cyclo(-Val-Orn-Leu-D-Phe-Pro-)2] were able to protect mild steel 1010 by inhibiting corrosion-causing, sulfate-reducing bacteria (SRB) in the aggressive, cooling service water of the AmerGen Three-Mile-Island (TMI) nuclear plant. A gramicidin-S-producing Bacillus brevis 18-3 biofilm protected mild steel by inhibiting both D. orientis and L. discophora SP-6 simultaneously. ^ Another strategy is to discover natural compounds that can inhibit biofilms without causing resistance to antibiotics. A new biofilm inhibitor, ursolic acid, inhibits biofilms of multiple bacteria without affecting growth and is effective in various media. As predicted by the DNA microarrays studying the gene expression profiles of E. coli K12 ATCC25404 grown with and without ursolic acid, removing motAB counteracts the inhibition of ursolic acid (which induces expression of motAB to make cells too motile). It was also discovered that sulfur metabolism (through cysB) affects biofilm formation in the absence of ursolic acid. ^ Mutant with both hha (a gene encoding for an environmental-response regulator of the pathogenic hemolysin operon) and its contiguous gene ybaJ deleted (ΔhhaybaJ) were tested for biofilm formation. It appears Hha and YbaJ increase biofilm formation by decreasing motility when a conjugative plasmid (R1drd 19) is present and that YbaJ plays the most important role in this regulation of motility. When hha/ybaJ is deleted, there is less conjugation, more motility and less biofilm. ^ In addition to ursolic acid, palmitoleic acid and asiatic acid also show biofilm inhibition without affecting growth rates. It is first presented here that a synergic effect is found for palmitoleic acid and the hha/ybaJ mutant in terms of biofilm inhibition. Analogs of ursolic acid showed comparable biofilm inhibition ability with asiatic acid possesses even stronger inhibition ability. ^