Bacterial diversity in the bacterioneuston (sea surface microlayer): the bacterioneuston through the looking glass

Abstract

The bacterioneuston is defined as the community of bacteria present within the neuston or sea surface microlayer. Bacteria within this layer were sampled using a membrane filter technique and bacterial diversity was compared with that in the underlying pelagic coastal seawater using molecular ecological techniques. 16S rRNA gene libraries of approximately 500 clones were constructed from both bacterioneuston and the pelagic water samples and representative clones from each library were sequenced for comparison of bacterial diversity. The bacterioneuston was found to have a significantly lower bacterial diversity than the pelagic seawater, with only nine clone types (ecotaxa) as opposed to 46 ecotaxa in the pelagic seawater library. Surprisingly, the bacterioneuston clone library was dominated by 16S rRNA gene sequences affiliated to two groups of organisms, Vibrio spp. which accounted for over 68% of clones and Pseudoalteromonas spp. accounting for 21% of the library. The dominance of these two 16S rRNA gene sequence types within the bacterioneuston clone library was confirmed in a subsequent gene probing experiment. 16S rRNA gene probes specific for these groups of bacteria were designed and used to probe new libraries of 1000 clones from both the bacterioneuston and pelagic seawater DNA samples. This revealed that 57% of clones from the bacterioneuston library hybridized to a Vibrio sp.-specific 16S rRNA gene probe and 32% hybridized to a Pseudoalteromonas sp.-specific 16S rRNA gene probe. In contrast, the pelagic seawater library resulted in only 13% and 8% of 16S rRNA gene clones hybridizing to the Vibrio sp. and Pseudoalteromonas sp. probes respectively. Results from this study suggest that the bacterioneuston contains a distinct population of bacteria and warrants further detailed study at the molecular level.

The sea-surface microlayer is a gelatinous biofilm

“…More recent evidence published in The ISME Journal supports the observations made in the North Sea by Franklin et al (2005) and shows distinct bacterioneuston communities are also present in estuarine surface microlayers (Cunliffe et al, 2008). Denaturing gradient gel electrophoresis comparison of bacterial and archaeal 16S rRNA genes from surface microlayer and subsurface water samples at two sites along the estuary showed that bacteria form distinct surface microlayer-specific community structures.…”

“…Franklin et al (2005) showed that the bacterioneuston at a site in the North Sea was distinctly different compared with subsurface water just 0.4 m below the surface. The bacterioneuston was dominated by two genera, Vibrio and Pseudoalteromonas.…”

“…The bacterioneuston was dominated by two genera, Vibrio and Pseudoalteromonas. Both organisms have physiological characteristics that are indicative of adaptations for biofilm survival (Franklin et al, 2005). If the seasurface microlayer is a gelatinous film, then organisms that have biofilm capabilities will have a selective advantage.…”

Phylogenetic and functional gene analysis of the bacterial and archaeal communities associated with the surface microlayer of an estuary

“…Samples were collected in December 2005 using the sampling protocol as previously described (Franklin et al, 2005) from two sites; site 1 (grid reference, 55108 0 14.47 00 N: 1131 0 09.91 00 N; salinity, 21.2 psu±3.1) and site 2 (grid reference, 55107 0 16.09 00 N: 1129 0 44.12 00 N; salinity, 31.4 psu ± 0.5). Forty-seven millimetre diameter polycarbonate membranes (Millipore, Watford, UK) were placed onto the surface of the water for 10 s using sterile forceps (sample depth E40 mm).…”

“…The SML is a unique ecosystem, often referred to as the bacterioneuston. A recent study of the bacterial communities in the SML of the coastal North Sea showed greatly reduced diversity in the SML compared to subsurface waters (Franklin et al, 2005).…”