SPATIAL AND TEMPORAL VARIATION OF NATURAL BACTERIOPLANKTON ASSEMBLAGES STUDIED BY TOTAL GENOMIC DNA CROSS-HYBRIDIZATION

Variations of the species compositions of marine bacterial communities are poorly understood, largely due to the general lack of cultivability of these organisms. With DNA hybridization, which uses total DNA directly extracted from natural bacteria and thus avoids growing pure cultures, we compared bacterioplankton assemblages from the oligotrophic Pacific Ocean (depths: 25, 100, 500, 1,000 m), the Caribbean Sea (< 20 m), and Long Island Sound (LIS; < 1 m). Comparisons were across depths, within depth, and across the three sampling locations. Temporal variations were studied with summer LIS samples taken a year apart. Deep Pacific samples (500 and 1,000 m) showed 30-90% similarity to each other, but differed from (similarities less-than-or-equal-to 5%) photic-zone (25 and 100 m) samples. The photic-zone samples showed only 15-45% similarity to each other. The 25-m samples were the most variable within depth (similarities > 50%). The three ocean-basin samples each had unique community DNA (similarities < 16%). The LIS community changed as much within 2 weeks as between successive summers (similarities down to 40-50%); however, the similarities (seven samples in this and a previous study) were never < 30%, suggesting a consistent subcommunity. We conclude that the total genomic DNAs of the bacterial communities varied significantly over time and space due to the different constituents of those communities, probably reflecting environmental factors.