Features of sporeforming bacteria.

Sporeformers are certain bacteria which can transform themselves from vegetative (= growing) form to spores (= resting form). Best-known examples of these bacteria are aerobic sporeformers ("bacillus-type", inc. Bacillus sp. , Paenibacillus sp. and other Gram-positive, aerobic sporeformers) and anaerobic sporeformers (most common species belong to the genus Clostridium). These bacteria are very common in all environments, especially in soils.

Spores of bacteria are not intended in the reproduction of organisms (like fungal spores) but to keep bacteria alive in conditions where they cannot be metabolically active. Sporulation is caused by the lack of nutrients, and germination of spores takes place whenever environmental conditions turn better for the growth of the bacterial cells.

These bacteria are a problem for paper industry because their spores tolerate dryness, cleaning agents and biocides very well. Their main sources are mineral pigments and starches, especially when these raw materials are delivered to the mills as dry powders. Whenever they are slurried, an effective biocide program shall be applied in the total system of their storage and dosing into the machines.

Another problems are analytical ones. Spores can be detected after a simple pasteurization of the samples (vegetative cells get killed, only spores stay alive) but this procedure kills also vegetative sporeformes. An analysis called "Sporeforming bacteria" does therefore not show potential sporeformers which are in vegetative growth phase. In addition, germination of spores, like every other chances in the properties of bacteria, takes certain time. This slows the growth of spores on nutrient media significantly. Fastest germination times can be achieved by PMEU incubator but the outgrowth of spores into vegetative cells may take much longer periods on the agar plates.

Evaluation of biocides should also be done with equipments like PMEU which show the different effects of biocides in the original samples.

Last but not least: if the growth of certain aerobic sporeformers has been very active, starch-degrading enzymes can stay active after biocidic treatments. Amylases can be found even after heat treatments because many of them are thermotolerant ones.

Sporeforming bacteria of paper industry have been studied very actively in Helsinki University, Dep. of Applied Chemistry and Microbiology. IM recommends to read scientific articles, written by the research group of Professor Mirja Salkinoja-Salonen, in magazines like "Applied and Environmental Microbiology" and "Industrial Microbiology and Biotechnology".

This group of bacteria is always a target of HACCP activities of paper mills, especially when products with high hygiene quality are manufactured. Studies to understand their features is therefore continuing also in future.