In this article we will discuss about the biodeterioration of various materials.
1. Biodeterioration of Stored Plant Food Material:
The stored (unprocessed) plant material (fruits, seeds, etc.) are usually decayed due to post harvest attack of bacteria and fungi. This kind of spoilage is called biodeterioration. However, loss of plant materials before harvest is covered in plant pathology.
The microbes can damage the plant materials partially as well as completely that definitely down the grade or the quality of the products. A large number of bacteria such as Erwinia sp., Corynebacterium sp. and fungi such as Phytophthora sp., Streptomyces sp., Curvularia sp., Aspergillus sp. etc. are commonly found to be associated with food materials.
The storage fungi are usually developed from dormant spores/ mycelium that cause post harvest spoilage resulting into deterioration of food, fruits, seeds, etc. during storage.
Now- a-days deterioration is mostly checked by altering storage conditions by chilling, using inert gases and by treatment with low dosages of gamma-radiation. The most affected products are soft fruits and salad vegetables; whereas grains, oilseeds and legumes are durable products and root vegetables and apples are of semi-perishable nature.
2. Biodeterioration of Leather:
Leather is a product of animal hides. Besides its wool and animal glues, there is other animal product which is attacked by microorganisms since leather contains keratins, animal fats and proteins. Therefore, it is rapidly deteriorated by lipolytic and proteolytic microorganisms which secrete lipases and proteases.
Leather production from animal hides involves soaking process which is carried out in water where several bacilli (B. sublitis, B. megaterium. B. punilis) attack it. They secrete several extracellular enzymes that may remain active long after the death of their producer organism.
During leather deterioration microbial damage may cause tensile strength and colouration. Since finished leather is quite acidic, hence fungi such as Rhizopus, Mucor, Cunninghamella and Aspergillus deteriorate quite fairly, whereas bacteria are secondary colonizers.
Wool, fur, and feathers mainly contain cystein rich proteins (keratin) that is degraded by keratinophilic fungi such as Trichophyton sp., Chryosporium sp. and Streptomyces sp. They damage, colour, impart odour and affect the tensile strength. Biodeterioration of these items now-a-days is checked by incorporating biocide (bromopol i.e. 2-bromo-nitropropane-1, 3-diol) during processing of the above items for clothing.
3. Biodeterioration of Stone and Building Materials:
Old ancient monuments, natural rocks, etc. are all attacked by various microorganisms such as large number of cyanobacteria, especially Pleurococcus, Oscillatoria, etc., lichens, fungi, including Botrytis, Penicillium, and Trichoderma sp.
They use concrete, brick and mortar of building material as nutrients. Various biocides in washes, bleaching compounds, phenolics and organo-tin compounds are being used to save the building materials.
Actually, microbes colonize the site which may cause excessive expansion and contraction associated with wetting and drying of colonies. Entrapment of water within the colonies and crack can lead to enhanced damage. In addition, hyphal penetration into the surface layers of these materials can result in crack formation which may be promoted by excretion of corrosive metabolites.
Several organic acids solubilize calcium carbonate while oxalic and citric acids solubilize silicates. Desulfovibrio desulfuricans reduce sulphur compounds and produces H2S which is then oxidized to sulphuric acid by Thiobacillus thiooxidans.
Various nitrifying bacteria, Nitrobacter, Nitrosomonas, also solubilise calcium associated with building material. They oxidize ammonia to nitrite leading in the formation of soluble form of calcium i.e. calcium nitrite. Besides, a large number of pseudomonads corrode steel and iron structures used in building construction.
4. Biodeterioration of Paper and Other Cellulosic Materials:
Plant cells are composed of cellulose, hemicellulose, lignin and pectic substances. Therefore, the plant cell biomass derives paper and card. Besides, it is used to thicken cosmetics, paints, etc.
Although, a large number of factors are responsible for the microbial spoilage of paper, etc. Deterioration of paper occurs by various cellulolytic fungi such as Trichoderma chaetomium and Aspergillus, and bacteria such as Cellulomonas, etc.
These microorganisms secrete cellulases (endo- β-glucanases, exo-β-glucanases, and β-glucosidase) convert cellulose into glucose. Besides, some microorganisms also secrete enzyme xylanases that deteriorate hemicellulose present in paper. However, many other microbial activities have major effect on material strength.
5. Biodeterioration of Fuels and Lubricants:
Fuels and lubricants are the products of petroleum. Fuels and lubricants are attacked only if water is present. Lubricants deteriorate more quickly as they consist of an emulsion of soil finely dispersed in water, in the presence of emulsifying agent.
These hydrocarbons are shorter carbon chain length (petrol, gasoline) less susceptible to biodeterioration in comparison to those having long chain length such as diesel oil and kerosene. Further they also contain phenolic substances.
A large number of fungal species e.g. Aspergillus, Hormoconis (formly Cladosporium resinae) often found to be associated with oil sludge. These soil fungi degrade linear and branched alkanes to aromatic rings. Biodeterioration of these hydrocarbons containing materials may be controlled by adding biocides (organoboron, isothiazolones, etc.).
6. Biodeterioration of Metals:
Microorganisms are known to corrode metals. They make biofilm by colonization/ concentration of cells, which release corrosive metabolic products resulting in removal of hydrogen by sulphate reducing bacteria.
Actually, microbial concentrations of the cells appear from an oxygen gradient that develops as a microbial colony, in contact with the metal, utilizes the available oxygen. These colonies have both oxygen-accessible (border) and oxygen-limited zone (centre), which are having negative and positive charge particles respectively.
This leads to metal ion formation by producing insoluble hydroxides. Iron corrosion occurs mainly due to a bacterium, Gallionella (chemolithotroph) that oxidizes ferrous ions to ferric ions and forms insoluble ferric hydroxide deposits at the site of microbial attack.
Various organic and inorganic acids are of microbial origin for example H. resinae produces sulphuric acid to sulphide. The organism comes in contact of steel/iron resulting in corrosion and breakage/leakage of water pipe lines.
7. Biodeterioration of Plastics:
These are polymeric materials made up of polyethylene, polystyrene, polyvinyl chloride (PVC) and polyesters. Many plastics are resistant to microbial attack but addition of various other materials makes the plastics prone to microbial attack.
Streptomyces rubireticuli and Penicillium sp. are reported to deteriorate PVC and polyamides (nylon), respectively. Polyesters, polycaprolactone and polybutylene adipate are degraded by bacteria and fungi.
8. Biodeterioration of Cosmetics and Pharmaceutical Products:
Cosmetics are being manufactured in the form of lotions, creams, liquids, solids and powder forms. Some are stickers and used externally for cleaning and decorative proposes.
They consist of large quantity of water, animal, plant/mineral oils, natural gums thickening agents, carbohydrates, aroma and flavouring agents in addition to protein hydro lysates, milk, beer, egg, plant extracts, etc. These product formulations are good sources of nutrients for microbes.
Although, preservatives are added but due to complex nature of formulations, preservatives become less effective. Sometimes, creams and lotions are contaminated with pseudomonads, although with low levels of this group of organisms do not harm the individual but is applied to patients with skin infection/damage, situation may become worst.
Some of the deteriorated cosmetics impart foul odours due to production of organic acids, fatty acids, amines, ammonia, and hydrogen sulfide. Production of ammonia or acid leads to alter the pH, which may change the consistency and colour of the products by developing lumps and slime. Sometimes gas bubbles are also generated. Such products later on become unstable and form separate oil and water phases.
Various lipids (oils, fats) are susceptible to microbial attack when dispersed in aqueous formulations after degradation. They give rise to glycerol and fatty acids. The fatty acids may further break down via β-oxidation to form odorous ketones. Many other additive chemicals particularly glycerol and sorbitol are used in toothpaste, etc.
These allow various microbes to grow and secrete amylases, cellulases, etc. responsible for degradation of such carbon containing microbial nutrients. Shampoo and detergents often contain sodium dodecyl sulfate which act as substrates for enzyme alkyl sulphatases. The species of Pseudomonas, Citrobacter and Aerobacter secrete enzymes that breakdown the finished items and may generate unpleasant odour, particularly H2S.
Pharma products are both sterile (injectable, intravenous infusions, etc.) and non-sterile forms (tablets, capsules, powders, suspensions, syrups). Many non-sterile pharma products contain low amount of active principles besides a large quantity of additive substances.
Similar to cosmetic and lotions, they many contain preservatives. The presence of low levels of pathogenic microorganisms, higher level of opportunistic pathogens besides contamination with toxic microbial metabolites leads to deterioration.
Various disinfectants contain ammonia compounds, reported to be contaminated with pseudomonads, for example Pseudomonas aeruginosa contaminates eye drops, washes and mascara, etc. Some injectables contain Gram-negative bacteria, fungi, etc. which produced endotoxins (pyrogens) that directly induce fever. For safe practices use of ultrapure water is recommended in the manufacture of intravenous drugs and infusions.
The active ingredients may also become ineffective due to microbial contamination. It leads to breakdown of antibiotics (for e.g. penicillin is attacked by β-lactamases). Such enzymes are secreted by various groups of microorganisms. Similarly, Aspirin is broken down by Acinetobacter iwoffii, Atropine is degraded by Pseudomonas and Corynebacterium spp., and Cladosporium herbarum causes spoilage of hydrocortisone.
Safe-practices:
Microbial quality control is a necessary step to check the deterioration of crude and finished materials. It is conducted to monitor microbial contamination of raw materials, to monitor and confirm the efficacy of operations such as sterilization, to control the pathogenic microorganisms (by their absence), and to evaluate the expected storage period.
The assessment is carried out by total microbial count and/or estimation of groups, e.g. conforms, or the detection of specific microorganisms. Further microbial activity within a product may also be confirmed from changes occurring to the pH, viscosity, stability, etc. As stated, spoilage may also occur due to the presence of dangerous metabolite products of microbial origin. Some of the fungi are responsible for the mycotoxins production.
Similarly, presence of endotoxins (pyrogens) can be deducted readily via the Limulus test (amoebocyte lysate assay.) The detection of microbial enzymes is often important as they too can persist after cell death. Many hydrolysate enzymes (cellulase) can pose to product storage life.
On the other hand, to test the efficacy of preservatives challenge test examine their effectiveness by utilizing biodeteriogens, or a group of standard organisms such as P. aeruginosa. Staphylococcus aureus, Candida albicans and Aspergillus niger. Soil burial tests are useful techniques for solid building, furnishing and clothing materials.
