204
and degradation products are being metabolized (McGenity et al. 2012). Studies on
the microbial response to the DwH spill elucidated a dramatic shift in microbial
community composition (Gutierrez et al. 2013a; Joye et al. 2014) and the development of a multifunctional microbial assemblage containing primary oil-degrading
and exopolysaccharide-producing prokaryotes (Arnosti et al. 2016). Such exopolysaccharides released in the presence of oil, e.g., by Halomonas spp., exhibit amphiphilic properties, which allows these macromolecules to interface with hydrophobic
substrates, such as hydrocarbons (Gutierrez et al. 2013b).
The presence of oil droplets leads to the formation of micron-scale aggregates
(20–100 μm), where microbial cells surround droplets of oil (Doyle et al. 2018).
Such microaggregates promote the development of diverse, interacting bacterial
communities (Doyle et al. 2018). The proximity of the cells to each other and
reduced diffusion within the aggregate would allow direct exchange of substrates,
efficient use of exoenzymes, and quorum sensing. The formation of such structures,
which function as floating biofilms, allows the degradation of complex hydrocarbon
mixtures, which requires the nonredundant capabilities of a diverse oil-degrading
community (Dombrowski et al. 2016). The formation of such microbial microagglomerations is a function of oil concentration (Doyle et al. 2018). As degradation
of oil products proceeds, the substrates change leading to a succession of bacterial
communities. The microbial community of the deep plume (1000 m) that formed
during DwH responded to the addition of specific substrates resembling bacterial
EPS and oil degradation products, suggesting that similar bacterial transformations
of oil degradation by-products also contributed to microbial activity inside the deepwater plume (Ziervogel et al. 2014). Experiments show the formation of microscopic bacterial oil aggregates at depth, similar to those observed in surface waters
(Baelum et al. 2012).
The relationship between such microscopic bacteria, oil droplet agglomerations,
and large (cm-sized) mucus-rich MOS that formed at the surface during the DwH
and also consisted of exudates produced from oil carbon and bacteria (Passow et al.
2012; Passow and Ziervogel 2016) is currently unresolved. Two pathways from
small bacteria-oil aggregates to large bacterial marine snow may be envisioned.
First, possibly the specific conditions during DwH resulted directly in the formation
of such exceptionally large bacterial MOS. Second, the bacterial microagglomerations are incorporated into marine snow-sized aggregates that form from detritus,
feces, or algae. The importance of the synthesis of bacterial EPS and a diverse,
shifting bacterial community, for the formation of MOS, was also confirmed by
experiments conducted with water from the Faroe-Shetland Channel (Suja et al.
2017), emphasizing that MOS formation is a more general phenomenon.
Likely different factors drive the formation of the different types of MOS. Thus
when predicting the likelihood of the formation of MOS, the type of MOS needs to
be considered. But all MOS appears to sink eventually (after aging in some cases),
and once MOS reaches the seafloor, it severely impacts the benthic microbial community (Yang et al. 2016a, b), as well as larger organisms (Baguley et al. 2015,
Reuscher et al. 2017, Washburn et al. 2017, Schwing et al. 2018). Resuspension of
MOS from the seafloor reactivates microbial degradation and activities (Ziervogel
et al. 2016) and redistributes MOS horizontally (Diercks et al. 2018).
A. Quigg et al.
and degradation products are being metabolized (McGenity et al. 2012). Studies on
the microbial response to the DwH spill elucidated a dramatic shift in microbial
community composition (Gutierrez et al. 2013a; Joye et al. 2014) and the development of a multifunctional microbial assemblage containing primary oil-degrading
and exopolysaccharide-producing prokaryotes (Arnosti et al. 2016). Such exopolysaccharides released in the presence of oil, e.g., by Halomonas spp., exhibit amphiphilic properties, which allows these macromolecules to interface with hydrophobic
substrates, such as hydrocarbons (Gutierrez et al. 2013b).
The presence of oil droplets leads to the formation of micron-scale aggregates
(20–100 μm), where microbial cells surround droplets of oil (Doyle et al. 2018).
Such microaggregates promote the development of diverse, interacting bacterial
communities (Doyle et al. 2018). The proximity of the cells to each other and
reduced diffusion within the aggregate would allow direct exchange of substrates,
efficient use of exoenzymes, and quorum sensing. The formation of such structures,
which function as floating biofilms, allows the degradation of complex hydrocarbon
mixtures, which requires the nonredundant capabilities of a diverse oil-degrading
community (Dombrowski et al. 2016). The formation of such microbial microagglomerations is a function of oil concentration (Doyle et al. 2018). As degradation
of oil products proceeds, the substrates change leading to a succession of bacterial
communities. The microbial community of the deep plume (1000 m) that formed
during DwH responded to the addition of specific substrates resembling bacterial
EPS and oil degradation products, suggesting that similar bacterial transformations
of oil degradation by-products also contributed to microbial activity inside the deepwater plume (Ziervogel et al. 2014). Experiments show the formation of microscopic bacterial oil aggregates at depth, similar to those observed in surface waters
(Baelum et al. 2012).
The relationship between such microscopic bacteria, oil droplet agglomerations,
and large (cm-sized) mucus-rich MOS that formed at the surface during the DwH
and also consisted of exudates produced from oil carbon and bacteria (Passow et al.
2012; Passow and Ziervogel 2016) is currently unresolved. Two pathways from
small bacteria-oil aggregates to large bacterial marine snow may be envisioned.
First, possibly the specific conditions during DwH resulted directly in the formation
of such exceptionally large bacterial MOS. Second, the bacterial microagglomerations are incorporated into marine snow-sized aggregates that form from detritus,
feces, or algae. The importance of the synthesis of bacterial EPS and a diverse,
shifting bacterial community, for the formation of MOS, was also confirmed by
experiments conducted with water from the Faroe-Shetland Channel (Suja et al.
2017), emphasizing that MOS formation is a more general phenomenon.
Likely different factors drive the formation of the different types of MOS. Thus
when predicting the likelihood of the formation of MOS, the type of MOS needs to
be considered. But all MOS appears to sink eventually (after aging in some cases),
and once MOS reaches the seafloor, it severely impacts the benthic microbial community (Yang et al. 2016a, b), as well as larger organisms (Baguley et al. 2015,
Reuscher et al. 2017, Washburn et al. 2017, Schwing et al. 2018). Resuspension of
MOS from the seafloor reactivates microbial degradation and activities (Ziervogel
et al. 2016) and redistributes MOS horizontally (Diercks et al. 2018).
A. Quigg et al.