Eco-efficient novel enzymatic concepts for slime control in pulp and paper processing

Slime biofilms consist of microbial populations attached to a surface and embedded within matrix containing extracellular polysaccharides (EPS) which forms the major structural component of the biofilm. The presence of biofilm protects the contaminating micro-organisms against biocides to a certain extent. The enzymatic degradation mechanisms of these polysaccharides have not been largely studied, partly because of their branched and complex polymeric structure. In this work novel enzymes for slime EPS degradation have been isolated and their suitability for slime control in the paper industry is being established. Slime producing organisms were first isolated from different paper machine environments using chemical pulp, CTMP, mechanical pulp and recycled pulp as raw material. Bacteria were isolated from the paper machine slimes using the ability to form slimy colonies on glucose containing solid medium as criterion for slime production. Totally 43 bacterial isolates were obtained. Of the strains at least 14 belonged to the Enterohacteriaceae and 9 to the aerobic spore-forming bacteria (Bacillus, Paenibacillus. Brevibacillus). Bacteria belonging to the family Enterobacteriaceae have been found especially from the deposits in a mill in Finland but also in the Spanish mills. Non-enterobacterial gram-negative slime-producers isolated include Brevundimonas vesicularis, Methylobacterium sp. and Pseudomonas aeruginosa. Polysaccharides were produced in shake flasks using 35 strains isolated. The strains were cultivated for 5-6d with measurement of culture medium viscosity during the cultivation. Of the 35 strains used significant viscosity increase was observed by 12 strains. In most cases the type of nitrogen source (organic/inorganic) did not have significant effect on polysaccharide production. The slime polysaccharides were precipitated by ethanol whereafter their chemical composition was analysed by HPLC. A more detailed structural analysis of the produced polysaccharides was carried out using HPSEC and GC-MS. With the exception of one homogalactan, the polysaccharides produced were heteropolysaccharides with various monosaccharide compositions. The structure of selected EPS have been characterised using advanced analytical techniques. Microbial cultures capable of degrading the isolated bacterial polysaccharides were enriched from soil and compost samples by incubating the samples in medium containing the respective polysaccharide as the only carbon source. The methodology for screening of exopolysaccharide producing enzymes and their effect on biofilm structure has been proved in the case of Klebsiella pneurnoniae originally isolated from a paper machine biofilm. Degradation of polysaccharide was detected as reduction of culture medium viscosity. All the composts used for enrichment appeared to be good sources of cultures degrading polysaccharides of bacteria from paper machines. The polysaccharide-degrading cultures obtained were multi-species mixed populations. The most potential EPS degrading enzymes have been purified and their mode of action is being investigated. Due to the complex composition of slimes it is expected that these new enzymes can most efficiently be used in combinations of several effective enzymes, possibly also with synergistic use of dispersing agents.