The Microbes Behind the Scene.
Bacteria that cause for biodegradable plastic usually are the dominant hydrocarbon degraders in landfill environments. They also posses diverse metabolic pathways that are not present in fungi which allows them to utilize most recalcitrant petroleum hydrocarbons.
Bacterial degradation of aromatic compounds can be divided into three steps:
modification and conversion of the many different compounds into a few central aromatic intermediates (ring-fission substrates); this step is refered as peripheral pathway and involves considerable modification of the ring and/or perhaps elimination of substituent groups;
oxidative ring cleavage by dioxygenases, which are responsible for the oxygenolytic ring cleavage of dihdyroxylated aromatic compounds (catechol, protocatechuate, gentisate); further degradation of the non-cyclic, non-aromatic ring-fission products to intermediates of central metabolic pathways.
Long-chain hydrocarbons (C10-C18) can be used rapidly by many high G+C Gram-positive bacteria. Only a few bacteria can oxidize C2-C8 hydrocarbons. Degradation of n-alkanes requires activation of the inert substrates by molecular oxygen with help of oxygenases by three possible ways that are associated with membranes:
Monooxygenase attacks at the end producing alkan-1-ol:
R-CH3 + O2 + NAD(P)H + H+ → R-CH2OH _ NAD(P)+ + H2
Dioxygenase attack produces the hydroperoxides, which are reduced to yield also alkan-1-ol:
R-CH3 + O2 → R-CH2OOH + NAD(P)H + H+ → R-CH2OH + NAD(P)+ + H2O
Rarely, subterminal oxidation at C2 by monooxygenase yields secondary alcohols.
It is important to keep in mind that many strains within one species of bacteria usually exist. Usually, only some of strains are capable of hydrocarbon degradation.
Some sulfate-reducing bacteria produce hydrogen sulfide, which can cause sulfide stress cracking. Acidithiobacillus bacteria produce sulfuric acid; Acidothiobacillus thiooxidans frequently damages sewer pipes. Ferrobacillus ferrooxidans directly oxidizes iron to iron oxides and iron hydroxides; the rusticles forming on RMS Titanic wreck are caused by bacterial activity. Other bacteria produce various acids, both organic and mineral, or ammonia.
In presence of oxygen, aerobic bacteria like Acidithiobacillus thiooxidans, Thiobacillus thioparus, and Thiobacillus concretivorus, all three widely present in the environment, are the common corrosion-causing factors resulting in biogenic sulfide corrosion.
Without presence of oxygen, anaerobic bacteria, especially Desulfovibrio and Desulfotomaculum, are common. Desulfovibrio salixigens requires at least 2.5% concentration of sodium chloride, but D. vulgaris and D. desulfuricans can grow in both fresh and salt water. D. africanus is another common corrosion-causing microorganism. The Desulfotomaculum genus comprises sulfate-reducing spore-forming bacteria; Dtm. orientis and Dtm. nigrificans are involved in corrosion processes. Sulfate-reducers require reducing environment; an electrode potential lower than -100 mV is required for them to thrive. However, even a small amount of produced hydrogen sulfide can achieve this shift, so the growth, once started, tends to accelerate.
Layers of anaerobic bacteria can exist in the inner parts of the corrosion deposits, while the outer parts are inhabited by aerobic bacteria.
Some bacteria are able to utilize hydrogen formed during cathodic corrosion processes.
Bacterial colonies and deposits can form concentration cells, causing and enhancing galvanic corrosion. [1].
Bacterial corrosion may appear in form of pitting corrosion, for example in pipelines of the oil and gas industry.[1] Anaerobic corrosion is evident as layers of metal sulfides and hydrogen sulfide smell. On cast iron, a graphitic corrosion selective leaching may be the result, with iron being consumed by the bacteria, leaving graphite matrix with low mechanical strength in place.
Various corrosion inhibitors can be used to combat microbial corrosion. Formulae based on benzalkonium chloride are common in oilfield industry.
Microbial corrosion can also apply to plastics, concrete, and many other materials. Two examples are Nylon-eating bacteria and Plastic-eating bacteria.
List of bacterial genera important in biodegradable plastic.
cellular organisms – Bacteria
Actinobacteria
Micrococcaceae
Arthrobacter
Arthrobacter spp. were shown to degrade various aromatic hydrocarbons such as phenanthrene (Ref.) and others ( Ref.).
Micrococcus
Isolated from oil-biodegrading consortia in marine environment ( Ref.).
Brevibacteriaceae
Brevibacterium
These bacteria were isolated from petroleum-degrading consortia ( Ref.).
Dermabacteraceae
Brachybacterium
B. phenoliresistens was isolated from an oil-contaminated coastal sand sample ( Ref.).
Dietziaceae
Dietzia
Marine hydrocarbon-utilizing bacteria ( Ref.).
Cellulomonadaceae
Cellulomonas
Sediment hydrocarbon-utilizing bacteria ( Ref.).
Intrasporangiaceae
Janibacter
Implicated in degradation of polycyclic hydrocarbons (PAHs) ( Ref.).
Terrabacter
Implicated in degradation of polycyclic hydrocarbons (PAHs) in marine sediments ( Ref.).
Corynebacteriaceae
Mycobacterium
Some species can utilize polycyclic hydrocarbons (PAH) and other pollutants ( Ref.).
Corynebacterium
Isolated from oil-degrading consortia ( Ref.).
Gordoniaceae
Gordonia
Some strains also utilize oil ingredients ( Ref.).
Nocardioidaceae
Nocardioides
Most species are free-living in soil and water. Some species can utilize polycyclic hydrocarbons (PAH) and other pollutants ( Ref.).
Rhodococcus
Some species can utilize polycyclic hydrocarbons (PAH) and other pollutants ( Ref.).
Nocardiaceae
Nocardia
( Ref.).
Smaragdicoccus
( Ref.).
Cyanobacteria
Cyanobacteria can play important role in oil-degrading consoria by not only oxydizing oil components but also by providing microbial community with nitrogen ( Ref.).
Bacteroidetes/
Chlorobi group
Flavobacteria
Chryseobacterium
Were isolated from stable carbazole-degrading consortium with Achromobacter (Guo W et al, 2008) and other oil-degrading bacterial communities (Ref.).
Flavobacterium
Some strains are capable of degrading polycyclic aromatic hydrocarbons and heterocyclics (Ref.).
Yeosuana
A marine bacterium, Y. aromativorans GW1-1T, capable of degrading benzo[a]pyrene (BaP) (Ref.).
Deinococcus-Thermus
Thermaceae
Thermus
Aerobic rods found in warm water (40-79 C°) such as hot springs, hot water tanks, and thermally polluted rivers; can degrade crude oil (Ref.).
Thermotogae
Thermotogaceae
Petrotoga
(Ref.).
Firmicutes
Bacillaceae
Endospore-producing; mostly saprophytes from soil, but a few are insect or animal parasites or pathogens.
Bacillus
Common in soil; several species (B. subtilis, B. cereus and others) were shown to use naphthalene, pyrene and other aromatics (Ref.).
Geobacillus
Endospore-forming, thermophilic bacteria capable of utilizing long-chain alkanes (Ref.).
Staphylococcaceae
Staphylococcus
Some species are opportunistic pathogens of humans and animals. Pathways of utilization of phenanthrene and other aromatic compounds by these organisms was studied (Ref.).
Proteobacteria
Alphaproteobacteria
Comprised mostly of two major phenotypes: purple non-sulfur bacteria and aerobic bacteriochlorophyll-containing bacteria.
Sphingomonadaceae
Sphingomonas
Degrade a broad range of substituted aromatic compounds ( Ref.).
Sphingobium
Degrade a range aromatic compounds ( Ref.).
Rhodobacteraceae
Paracoccus
Hydrocarbon-utilizing bacteria ( Ref.).
Stappia
Alkaliphilic and halophilic hydrocarbon-utilizing bacteria ( Ref.).
Roseobacter
Marine hydrocarbon-utilizing bacteria ( Ref.).
Rhodospirillaceae
Thalassospira
A polycyclic aromatic hydrocarbon-degrading marine bacterium ( Ref.).
Tistrella
A phenanthrene-degrading marine bacterium ( Ref.).
Brucellaceae
Ochrobactrum
A polycyclic aromatic hydrocarbon-degrading marine bacterium ( Ref.).
Rickettsiales
SAR11 cluster
Candidatus Pelagibacter
Betaproteobacteria
Comprised of chemoheterotrophs and chemoautotrophs which derive nutrients from decomposition of organic material.
Alcaligenaceae
Achromobacrer
Were isolated from stable carbazole-degrading consortium with Chryseobacterium (Guo W et al, 2008) and other oil-degrading bacterial communities (Ref.).
Alcaligenes
Implicated in degradation polycyclic aromatic hydrocarbons (PAH) from oil and other pollutants (Ref.).
Comamonadaceae
Acidovorax
Has been found in consortia utilizing heterocyclic aromatics (Ref.)
Polaromonas
Has been shown to utilize naphthalene, benzene, toluene (Ref.)
Burkholderiaceae
Burkholderia
Found in consortia of microorganisms degrading polycyclic hydrocarbons (PAH) and other environmental pollutants ( Ref.).
Ralstonia
Free-living forms are known to utilize polycyclic hydrocarbons (PAHs) ( Ref.).
Rhodocyclaceae
Azoarcus
Gram-negative, facultatively anaerobic bacteria including species which are often associated with grasses and which fix nitrogen as well as species which anaerobically degrade toluene and other mono-aromatic hydrocarbons ( Ref.).
Thauera
Gram-negative, rod-shaped bacteria able to anaerobically oxidize and degrade toluene ( Ref.).
Delta-
proteobacteria
Represented by morphologically diverse, anaerobic sulfidogens; some members of this group are considered bacterial predators, having bacteriolytic properties.
Geobacteraceae
Geobacter
Anaerobic, metal-reducing bacteria in the family Geobacteraceae. They have the ability to oxidize a variety of organic compounds, including aromatic hydrocarbons ( Ref.).
Desulfobacteraceae
Desulfobacterium
Anaerobic, metabolizes C12-C20 alkanes ( Ref.).
Desulfobacula
Anaerobic, metabolizes toluene and benzene ( Ref.).
Desulfotignum
A Gram-negative, sulphate-reducing bacterium ( Ref.).
Epsilon-
proteobacteria
Consists of chemoorganotrophs usually associated with the digestive system of humans and animals.
Gamma-
proteobacteria
Comprised of facultatively anaerobic and fermentative gram-negative bacteria.
Piscirickettsiaceae
Cycloclasticus
Marine bacteria; play a major role in degrading polycyclic hydrocarbons (PAH) from crude oil in marine environment ( Ref.).
Pseudomonadaceae
Pseudomonas
Numerous strains are most studied oil biodegraders; many strains are patented and are included in commercial bioremediation mixtures ( Ref.).
Alteromonadaceae
Marinobacter
Implicated in degrading polycyclic hydrocarbons (PAH) and other environmental pollutants ( Ref.).
Pseudoalteromonadaceae
Pseudoalteromonas
Marine oil-degrading bacteria ( Ref.).
Pasteurellaceae
Pasteurella
Was shown to degrade fluoranthene ( Ref.).
Shewanellaceae
Shewanella
Marine organisms frequenly isolated from oil-contaminated sites ( Ref.).
Moraxellaceae
Acinetobacter
Abilities for bioremediation of oil were documented ( Ref.).
Moraxella
Plasmid-mediated degradation of hydroxylated, methoxylated, and carboxylated benzene derivatives in Moraxella spp. were documented ( Ref.).
Halomonadaceae
Halomonas
Synonym Deleya; isolated from oil-contaminated soils ( Ref.).
Alcanivoracaceae
Alcanivorax
Present in un-polluted sea water in low numbers; principal carbon and energy sources are linear-chain alkanes and their derivatives ( Ref.).
Oceanospirillaceae
Thalassolituus
Marine hydrocarbonoclastic alkane-degrading bacteria ( Ref.).
Oleispira
Marine hydrocarbonoclastic bacteria ( Ref.).
Neptunomonas
Marine hydrocarbonoclastic bacteria ( Ref.).
Oleiphilaceae
Oleiphilus
Marine obligate hydrocarbon-degrading bacteria ( Ref.).
Xanthomonadaceae
Rhodanobacter
Rhodanobacter spp. is capable of utilizing benzo[a]pyrene (BaP) ( Ref.).
Stenotrophomonas
S. maltophilia is capable of utilizing various polycyclic aromatic hydrocarbons (PAH) ( Ref.).
Xanthomonas
Produce a yellow pigment; some species are pathogenic to plants. Biodegradation of complex polycyclic aromatic hydrocarbons was studied ( Ref.).
Arenimonas
Was isolated on nutrient agar from a soil sample collected from an oil-contaminated site ( Ref.).
Zetaproteobacteria
