Microbial community structure, pigment composition, and nitrogen source of red snow in Antarctica

Abstract

"Red snow" refers to red-colored snow, caused by bloom of cold-adapted phototrophs, so-called snow algae. The red snow found in Langhovde, Antarctica, was investigated from several viewpoints. Various sizes of rounded red cells were observed in the red snow samples under microscopy. Pigment analysis demonstrated accumulation of astaxanthin in the red snow. Community structure of microorganisms was analyzed by culture-independent methods. In the analyses of small subunit rRNA genes, several species of green algae, fungus, and various phylotypes of bacteria were detected. The detected bacteria were closely related to psychrophilic or psychrotolerant heterotrophic strains, or sequences detected from low-temperature environments. As predominant lineage of bacteria, members of the genus Hymenobacter were consistently detected from samples obtained in two different years. Nitrogen isotopic compositions analysis indicated that the red snow was significantly 15N-enriched. Based on an estimation of trophic level, it was suggested that primary nitrogen sources of the red snow were supplied from fecal pellet of seabirds including a marine top predator of Antarctica.

Figure 1

Map of the sampling site in Langhovde, Antarctica. The sampling site is indicated with an asterisk

Figure 2

Microphotograph of the fresh red snow sample obtained in 2006. Bar indicates 50 µm

Figure 3

Chromatogram showing the result of pigment analysis on the sample obtained in 2006. 1–3 non-esterified astaxanthin, 4 lutein, 5 chlorophyll b, 6–11 astaxanthin esters, 12 pheophytin a

Figure 4

DGGE profile of eukaryotic SSU rRNA genes obtained from the red snow sample collected in 2006 and phylogenetic affiliations of the DGGE bands

Figure 5

DGGE profile of 16S rRNA genes. Underlined bands were inferred to have originated from chloroplast of eukaryotic phototrophs

Figure 6

Phylogenetic affiliations of the bacterial OTUs obtained from the clone library. Numbers on nodes are percentage values of bootstrap resampling (values larger than 50 are shown)

Figure 7

Stepwise ¹⁵N-enrichment along trophic levels and a hypothesis of linkage between seabirds in the food web and transportation of ¹⁵N-enriched fecal pellet via aerial pathway as a trigger of red snow

Figure 8

Seabird as a predator and prey in the food web at Langhovde: a a south polar skua preying on a snow petrel near sampling site. b a snow petrel in the nest at Yukidori valley. Note that accumulated fecal pellet in front of the nest. c a kill site on a snow field at Yukidori valley. Note that the color of red is from fresh blood of a dead seabird, not from snow algal aggregate. d a kill site on the moss mat. The blue peg (No. 19) stands for a site number of moss vegetation monitoring [20]