Bacterial role in the decomposition of marine-derived material (penguin guano) in the terrestrial maritime Antarctic

Bacterial decomposition of Adélie Penguin (Pygoscelis adeliae) guano was followed during 42 days exposure in a rookery in Admiralty Bay, King George Island, South Shetland Islands, Antarctica. Bacterial abundance, both total counts (TC) determined by epifluorescence microscopy, and colony forming units (CFU) determined on nutrient media, was enhanced by an air temperature of between 7 and 11 °C, while temperatures above and below this negatively affected abundance. Optimal temperatures for guano decomposition ranged from 3 to 11 °C. Increasing wind velocity positively influenced photoautotrophic bacteria (TAC: total autotrophic bacteria count); photoautotrophs were enumerated during epifluorescence microscopy by their autofluorescence. Guano dry weight attained the lowest value of 74% of initial dry weight after 20 days in situ exposure. Changes in guano resulted from decomposition of the component fats, proteins, chitin, nitrogen and carbon, as well as of mineral recycling (Ca, P, Mg, and others). All transformations accompanied bacterial growth, with TC and CFU both attaining 1011 cells g−1 d wt of guano. Total bacterial biomass (TBB) increased from 594 μg C g−1 dry weight in fresh guano, to 9101 μg C g−1 dry weight after 42 days exposure in situ. Mean cell volume (MCV) also increased from 0.236 to 0.343 μm3. Photoautotrophic bacteria were numerically the smallest TC fraction throughout the incubation, with TAC to TC ratio ranging from 0.01 to 0.22%. Culturable bacteria abundance in guano increased dramatically from 0.28% of TC (in fresh guano) to 26% (3-h day), and 90% (42nd day) of TC. Within the total CFU population, copiotrophic bacteria were ca. two orders of magnitude more abundant than oligotrophic bacteria. Chitinolytic bacteria in guano were detected only late in the incubation; by 42 days, >40% of the initial chitin content remained. This material may comprise a significant fraction of the soil in the penguin rookery. Bacteria cultivated from the penguin guano displayed high morphophysiological diversity.