Bacteria beneficially used to degrade and remove organic waste

Bacteria possess an extraordinary capacity to adapt and
survive within diverse environments. Viable bacteria can be recovered from
habitats ranging from moderate environments such as rivers, oceans and soil,
through living hosts, to extreme environments such as beneath Greenlandic
glaciers (Loveland-Curtze et al., 2009)
and deep inside ice cores, thermal springs (Brock and Freeze 1969), deep sea
hydrothermal vents (Kashefi and Lovley 2003), and even radioactive waste
(Fredrickson et al., 2004). It is
currently thought that there are approximately 4-6 x1030 prokaryotic
cells worldwide (Whitman et al., 1998),
comprising over a third of the world’s biomass.

In their natural environment, bacteria are thought to
survive preferentially in structures known as biofilms. These are complex
three-dimensional constructions, consisting of bacterial cells enveloped in a
slime known as the extracellular matrix, and commonly attached to a surface.

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Once a biofilm has formed on a surface, it is very difficult to remove, as
bacteria growing in these structures are typically up to 1000-fold more
tolerant to stresses, including antimicrobial compounds, than free-living
cells. The recalcitrance of biofilms to removal is of great economic relevance
in industrial, environmental and medical settings. Biofilm fouling is a common
occurrence in industrial plants, resulting in release of toxic metabolites and
corrosion. The metabolic activities of biofilms are not always toxic however,
and biofilms are beneficially used to degrade and remove organic waste
substances, for example from drinking water during sewage treatment.

Biofilms are also clinically relevant, as it is thought
that up to 65% of all infections in developed countries are due to biofilm
development (Costerton et al., 1999;
Costerton et al., 2003; Lewis 2007;
Potera 1999). These infections are wide-ranging, from colonisation of the lungs
of patients with cystic fibrosis or chronic obstructive lung disease, to
chronic wound infections, and infections of medical implants. Biofilm
infections have serious consequences on the patients’ prognosis, because
bacteria in biofilms are also notoriously recalcitrant to antibiotics.

An important contributor to the recalcitrance of bacteria
in biofilms is the presence of large numbers of dormant or slowly replicating
cells called persisters. Persister cells are present in all bacterial
populations, and due to their slow replication rates are much more recalcitrant
to antimicrobial agents, surviving otherwise lethal antibiotic treatment (Balaban
et al., 2004; Sufya et al., 2003). Once the antibiotic is
removed, persister cells can re-seed bacterial populations, resulting in
recurrent infections. Due to much higher numbers of persisters in biofilms as
opposed to planktonic cultures, biofilms are correspondingly more recalcitrant.

Therefore, if a biofilm infection is not properly diagnosed, this can
subsequently lead to ineffective therapeutic intervention and result in poor
clearance of the microcolony, and this in turn can lead to complications
through the release of bacteria from the biofilm causing bacteraemia and
recurrent symptoms.

Biofilms are a
remarkably successful microbial survival mechanism. A biofilm is a colony of
bacteria that has transitioned from a planktonic (free-swimming) state to a
fixed, surface attached sessile state (Branda et al., 2005). The surface to which the biofilm attaches may be
biotic or abiotic. The process of biofilm formation takes place in a number of
distinct stages, brought about through differential expression of bacterial
genes in response to their environment (O’Toole and Wong., 2016).


The components
of a biofilm vary depending on the environment, but biofilms are generally
comprised of living bacteria and macromolecule
such as polysaccharides, proteins, nucleic acid, glycoproteins and
phospholipids arranged within an intricate matrix that provides a
protective structure as well as a system of channels allowing for the diffusion
of water, nutrients and metabolic waste (Chadha., 2014, Hooshangi and Bentley.,
2008, Costerton et al., 1999). 


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