How environmental conditions cause the formation of different Flavobacteria communities in the North Atlantic Ocean

A review of Gómez-Pereira, R. P. et al (2010) Distinct Flavobacterial communities in contrasting water masses of North Atlantic Ocean, The ISME Journal. 4, 472-487.

Flavobacteria are one of the most abundant groups of picoplankton found in the marine environment, yet quantitative research about the population of the numerous clades and their distribution patterns is still very much unknown. These microbes have been found to occupy a variety of marine systems, including open ocean waters as well as coastal sediments and hydrothermal vents and are thought to thrive in more productive conditions such as in areas where phytoplankton and algal blooms are high. However, they have also been found in oligotrophic marine surface waters, which also suggests their capability to adapt to various conditions even those where there is minimal life and nutrients. Sequence-based studies have shown the presence of different clades, for example some that are dominant during an algal bloom and others which dominate the area before or after the bloom. Findings like these stress the importance for further research to be done to found out about the clades, their population, distribution patterns and also the association and dynamics between Flavobacterial and phytoplankton communities.

This study intends to further the understanding of these microbes by conducting quantitative analysis in an area where algal blooms are present, specifically in the North Antlantic ocean, between the east Greenland current where there is a high concentration of chlorophyll a and the North Atlantic subtropical gyre (NAST), which in contrast is an oligotrophic area with little primary production. These two strong gradients will act as environmental barriers and will influence the distribution of the picoplankton groups, particularly different clades of flavobacteria and will allow for good analysis of their distribution.

A transect was formed encompassing 9 water masses and each station was sampled at 12 depths, from 10m to 250m or 500m. It measured the chlorophyll a, total picoplankton, analysed the nutrients present and observed the thermal and optical properties. 16s rRNA gene libraries were also constructed from the 20m samples and specific primers were used to help identify the different phylotypes.

It was predicted that from the transect laid out, common Flavobacteria would be present in each, however individual clades will prevail in each of the areas, and that there will be a higher abundance in the northern areas due to the lower temperature and high nutrient and phytoplankton levels, which will allow them to thrive.

The results found that as predicted, flavobacteria favoured colder, nutrient rich areas, but that clades had been found which preferred the oligotrophic conditions in warmer waters such as in the NAST area. Cluster analysis of clade abundance showed flavobacterial communities were generally homogeneous within the specific water masses but varied between them. Furthermore, 16s rRNA analysis confirmed only little overlap (2-5%) between the bodies of water where characteristics such as nutrient level and temperature varied greatly and larger overlaps of phylotypes (25-40%) in areas where these characteristics were a lot more similar.

Chlorophyll a was also found to be a factor in the diversity of clades, as through CARD-FISH quantification, it was found that in areas were sharp decreases in chlorophyll a were detected, reduction in specific populations of Flavobacteria (VIS3, VIS4 and VIS6) were also found. Rare clades, such as VIS1 and VIS2 were only found in low frequencies (<0.5% relative abundance) and all showed preferences to different enviormenatl conditions, such as iron-fertilised waters or temprerature. Due to their low numbers in all the areas, it has still not been established what role they play in the ecological function in the marine environment.

Considering the results, and in addition to previous studies concerning Flavobacteria distribution, it can be seen that picoplankton, and thus Flavobacteria populations have pronounced seasonal, latitudinal and depth distribution patterns, therefore also showing differential distribution patterns.

The study has provided quite specific results for many of the clades found in the samples, adding to the limited data and helping establish the various adaptions, environmental preferences and roles of the different clades found, thus furthering our knowledge of the distribution and biogeography of flavobacteria in the North Atlantic.

However, apart from the previous studies which were used to provide further data, the study was conducted only throughout September. To further their work, the populations could be sampled repeatedly across the year, for example every month or season. Conditions throughout the transect will change throughout the year and this can have a big impact on the populations and distributions of the clades. By looking at more samples, the data will be more representative of the flavobacterial phylotypes and could provide interesting correlations between populations and environmental changes. It would also allow more research to be done concerning the rare clades, as it would be possible to look at how the population size varies throughout each season, to establish whether they always remain small in number or whether preferred conditions and thus populations blooms occur periodically and how this would affect their role in their ecosystem.