10 - Biodeterioration and biodegradation


Microbial biodeterioration 

(not rodents, insects, birds, plants)


  • Environment dictates whether deterioration will occur and which species will be involved 


Methane can be oxidised into CO2 when nitrate levels are high











Single soil particle 


  • Mapping of O2 concentrations

  • 21% = same as air at sea level 

  • Centre is completely anoxic 

  • Each section is a different microbe environment 





  • Organisms responding to one another, setting up food webs, responding to and sharing nutrients








Progress of saprophytic activity



Succession 

Reasons: 

  • Exhaustion of nutrient sources 

  • Modification of nutrients for succeeding populations 

  • Metabolic end products act as substrates

  • Protected substrates become exposed 

  • Physical / chemical environment modified 

  • Breakdown in residual host defence 

  • Direct inhibition of succeeding populations 

  • Independent change in parameters 


Environment 



  • Water

  • Presence 

  • RH relative humidity 

  • Aw - water activity - ratio between water vapour and the water in an item - increases with temperature (%)

  • Most foods have a water activity of above 0.95


  • Temperature 

  • Growth 

  • Survival 


  • pH 

  • Buffering capacity 


  • Redox 

  • Eh - redox potential 


  • Nutrients 

  • Antimicrobial compounds 



Microbial communities / Consortia 


Modelling

All relevant to determine what can happen and what drives biodeterioration and biodegradation


  • Antagonism - can be due to already occupying a colonisable surface / produces a bacterium that competes against another organism 

  • Synergism - where microorganism support the growth of each other 

  • Commensalism - relationship between species in which one benefits and the other is unaffected 

  • Syntrophy / cross feeding -  cross feeding where one species lives off the products of another

  • Competition - populations of microorganisms inhabiting a common environment compete for nutrients and other resources of the environment 

  • Sometimes chemicals are secreted that are toxic or inhibitory to other competitors 

  • Successions - the initial microorganisms change the environment so that other microorganisms can thrive 





  •  Microorganisms prevent in intrusion of foreign strains










Biodeterioration 



  • Mechanical 

  • Chemical 

  • Assimilatory 

  • Dissimilatory 

  • Fouling and soiling



Major groups that undergo microbial based biodeterioration 

  • Crops ‘

  • Wood 

  • Animal products

  • Paints and coatings 

  • Rubber and plastics

  • Fuels and lubricants

  • Metals 

  • Stone 



Fodders

  • Crops that are grown for animal foods eg. hay

  • These undergo biodeterioration 


Problems with fodders: 

  • Moulding 

  • Aspergillosis (fungi) 

  • Mycotoxins - toxic to animals that eat them 

  • Farmers lungs - allergic reaction due to breathing in spores


Solutions

  • Drying - to do with the water activity of the fodder before storage 

  • Preservatives - non harmful to livestock but will prevent fungal growth 

  • Ventilation and building design 





Wood 

  • Tends to be stable long term because of its low moisture content (<20%) and low nitrogen (C:N ratio >350:1 content) 

  • Fungi is most important in the biodeterioration of wood (stainers and rotters) - white, brown and dry rot)



Animal products 

  • Hides, wool - controlled by microorganisms that produce lipases and proteases 

  • Prevention by curing, salting and drying of the animal products



Paints and coatings 

  • Solvent based - usually stable until applied 

  • Emulsion - fillers degradable to produce loss in viscosity 

  • Applied paints and coatings - fungal colonisation, algal growth - humidity, temperature and wind blown nutrients - leads to cracking and staining 




Chemical structure of oil-derived, non-biodegradable polymers:


  • The presence of an ester bond (C-O) provides a point of attack for hydrolytic enzymes 

  • But not all plastics with an ester bond are biodegradable (eg. PET, PEF)

  • However, hydrolytic enzymes such as cultinases are reported to degrade polymers such as PET in vitro 



Plastic recycling 

  • Plastics currently produced in a linear economy 

  • Needs to be turned circular - where plastics are reused, recycled and upcycled through their conversion to valubale products such as biodegradable polymers [PHAs - polyhydroxyalkanoates] - some bacteria make PHAs for themselves as carbohydrate stores


Fuels 

  • Fuel / water interface = blocked pipes 

  • Water / metal interface = corrosion 

→ Problems with:

  • Drainage 

  • Biocides 

  • Coatings 



Metals 

  • Concentration cell effect 

  • Iron oxidising bacteria 

  • Thiobacillus (plus fermentative bacteria)

  • Sulphate reducing bacteria 

Solutions 

  • Coatings of the metal

  • Cathodic protections



Buildings, monuments, sculptures 

  • Growth penetration 

  • Fungi send out hyphae - penetrate deep into various structure and weaken them 

  • Expansion of microbial cells 

  • Biofilms are like microbial tissues - can have mixtures of microbial communities that grow and develop together and expand 

  • Growth into cracks can break down the material 

  • Corrosive products - can break down things like limestone - sensitive to acids 

  • Thiobacillus 

  • Fermentative bacteria 

  • Ammonia oxidisers 


Above: green algal and cyanobacterial on mortar surfaces in the castle of Rappottenstein, 12th century (Austria) 

Above: Rosy stains characteristic for halophilic and halotolerant archaea and bacteria