Shapiro, L. P.. University of Oregon, firstname.lastname@example.org
Berardesco, G. P.. Northwestern University, email@example.com
Johnson, M. D.. University of Maryland, firstname.lastname@example.org
ANALYSIS OF BACTERIA LIVING IN ASSOCIATION WITH MARINE PHYTOPLANKTON BY DIRECT PCR AMPLIFICATION AND DGGE ANALYSIS
We have observed a close physical association between certain marine phytoplankton and bacteria that appear adhered to the phytoplankters' surface, within the zone of the phycosphere. Initially, we identified the bacteria following isolation and culturing of phytoplankton along with their attached bacteria. DNA was extracted from the culture, and we used denaturing gradient gel electrophoresis (DGGE) to separate PCR-amplified 16s rDNA fragments. Phylotypes unique to the bacteria that were physically attached to phytoplankton were then reamplified and sequenced.
More recently, we have been able to identify phylotypes of associated bacteria resulting from isolations of single chains of diatoms or repeated isolations of 6-10 conspecific phytoplankton cells from a single water sample, followed directly by PCR-amplification and DGGE analysis, with no intervening culturing of the phytoplankton and bacteria. In this way, we feel that we have avoided any bias resulting from culturing.
We have examined bacteria attached to several species of Thalassiosira, Pseudo-nitzschia, Chaetocerus, Asterionellopsis, Dinophysis and Alexandrium, and have identified several alpha-proteobacteria species, an actinomycete species, a Mycobacterium species, a Comomonas species, and a unique, deeply branching alpha-proteobacteria sequence.
This direct PCR procedure represents a significant technological advance since it can reveal much more of the natural diversity than the traditional culture methods and can be used to monitor changes that occur in the associated bacterial populations during culturing of the phytoplankter, and during changes in culture conditions.
Day: Tuesday, Feb. 2
Location: Sweeney Center