Bacteria beneficially used to degrade and remove organic waste

Bacteria possess an extraordinary capacity to adapt andsurvive within diverse environments. Viable bacteria can be recovered fromhabitats ranging from moderate environments such as rivers, oceans and soil,through living hosts, to extreme environments such as beneath Greenlandicglaciers (Loveland-Curtze et al., 2009)and deep inside ice cores, thermal springs (Brock and Freeze 1969), deep seahydrothermal vents (Kashefi and Lovley 2003), and even radioactive waste(Fredrickson et al., 2004).

It iscurrently thought that there are approximately 4-6 x1030 prokaryoticcells worldwide (Whitman et al., 1998),comprising over a third of the world’s biomass. In their natural environment, bacteria are thought tosurvive preferentially in structures known as biofilms. These are complexthree-dimensional constructions, consisting of bacterial cells enveloped in aslime known as the extracellular matrix, and commonly attached to a surface.Once a biofilm has formed on a surface, it is very difficult to remove, asbacteria growing in these structures are typically up to 1000-fold moretolerant to stresses, including antimicrobial compounds, than free-livingcells. The recalcitrance of biofilms to removal is of great economic relevancein industrial, environmental and medical settings.

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Biofilm fouling is a commonoccurrence in industrial plants, resulting in release of toxic metabolites andcorrosion. The metabolic activities of biofilms are not always toxic however,and biofilms are beneficially used to degrade and remove organic wastesubstances, for example from drinking water during sewage treatment. Biofilms are also clinically relevant, as it is thoughtthat up to 65% of all infections in developed countries are due to biofilmdevelopment (Costerton et al., 1999;Costerton et al., 2003; Lewis 2007;Potera 1999).

These infections are wide-ranging, from colonisation of the lungsof patients with cystic fibrosis or chronic obstructive lung disease, tochronic wound infections, and infections of medical implants. Biofilminfections have serious consequences on the patients’ prognosis, becausebacteria in biofilms are also notoriously recalcitrant to antibiotics. An important contributor to the recalcitrance of bacteriain biofilms is the presence of large numbers of dormant or slowly replicatingcells called persisters.

Persister cells are present in all bacterialpopulations, and due to their slow replication rates are much more recalcitrantto antimicrobial agents, surviving otherwise lethal antibiotic treatment (Balabanet al., 2004; Sufya et al., 2003).

Once the antibiotic isremoved, persister cells can re-seed bacterial populations, resulting inrecurrent infections. Due to much higher numbers of persisters in biofilms asopposed to planktonic cultures, biofilms are correspondingly more recalcitrant.Therefore, if a biofilm infection is not properly diagnosed, this cansubsequently lead to ineffective therapeutic intervention and result in poorclearance of the microcolony, and this in turn can lead to complicationsthrough the release of bacteria from the biofilm causing bacteraemia andrecurrent symptoms. Biofilms are aremarkably successful microbial survival mechanism. A biofilm is a colony ofbacteria that has transitioned from a planktonic (free-swimming) state to afixed, surface attached sessile state (Branda et al., 2005). The surface to which the biofilm attaches may bebiotic or abiotic.

The process of biofilm formation takes place in a number ofdistinct stages, brought about through differential expression of bacterialgenes in response to their environment (O’Toole and Wong., 2016). The componentsof a biofilm vary depending on the environment, but biofilms are generallycomprised of living bacteria and macromoleculesuch as polysaccharides, proteins, nucleic acid, glycoproteins andphospholipids arranged within an intricate matrix that provides aprotective structure as well as a system of channels allowing for the diffusionof water, nutrients and metabolic waste (Chadha., 2014, Hooshangi and Bentley.,2008, Costerton et al.

, 1999).