Dust and the bacterioplankton.

Hill, Zubkov and Purdie (2010) examined the metabolic response of the bacterioplankton to atmospheric dust input into the North Atlantic. With large amounts of dust produced and deposited in the North Atlantic every year, it is thought that this may have a significant effect on microbial communities. With the large amount of nutrients associated with dust, deposition may create large special and temporal fluctuations in nutrient availability. With increasing desertification dust deposition may increase. Hill et al (2010) attempted to assess the metabolic reaction of key groups in oceanic bacterioplankton to dust deposition.

Sample were collected at 20m depth in the eastern part of the North Atlantic during January and February, and treated with either direct additions of dust or leachate within an hour of sampling. Dust was collected on polypropylene filters and collected. Dust leachate was created by quickly passing 100mL of deionised water through a dust loaded filter.  In samples treated by direct addition of dust the following amount was added: 0.3mgL^-1, 1.5mgL^-1 ,4.7mgL^-1 and a control. Leachate additions to each of the samples treated were 700µL of dH₂O containing 100nM inorganic N and 10nM of inorganic P. After treatment seawater samples were incubated at in situ temperature and ambient light levels for 24 hours, with subsamples for the measurement of ³⁵S-Met uptake taken at t=0,2,4,6 and 24 hours.  ³⁵S-Met uptake was measured using a liquid scintillation counter to determine the radioactivity after time series incubation (10, 20 and 30 minutes) with  50pM ³⁵S-Met. After measurements were taken the bacterioplankton samples were analysed using flow cytometry to determine the overall community composition, and determination of group specific ³⁵S-Met uptake.

Overall Hill et al (2010) found that the bacterioplankton as a whole appeared to be unaffected after addition of the dust leachate. However it appeared that the SAR11 increased the uptake of the ³⁵S-Met by 4 to 13% but that the Prochlorococcus uptake decreased by 3 – 28% compared to the controls. During the trials with direct addition of dust results showed an overall decrease in ³⁵S-Met uptake. During the trials where dust was added directly there appeared to be a decrease in ³⁵S-Met uptake with the SAR11 and Prochlorococcus showing a decrease in uptake of 21-82% and 20-68% respectively. Hill et al (2010) suggest that the difference between the individual groups and the bacterial community as a whole may be down to the presence of opportunistic bacteria which utilise the large influx of nutrients to produce an overall increase in productivity. In addition bacterial growth of particular groups may be inhibited by dust associated elements. Prochlorococcus would be an example of this by being sensitive to copper which may be present in high level in the dust.

Overall this study provides a good view of the effects dust deposition may have on two of the most abundant groups of marine bacterioplankton. I think this may be of particular importance with the increase in desertification and how this may impact the global marine bacterioplankton, and all the knock on effects that may have. 

Hill, P., G.; Zubkov, M., V.; Purdie, D., A.. (2010). Differential responses of Prochlorococcus and SAR11-dominated bacterioplankton groups to atmospheric dust inputs in the tropical Northeast Atlantic Ocean. FEMS. 306 , 82-89.