Revista Chilena de Historia Natural 84 (3): 433-450, 2011
RESEARCH ARTICLE
Ecomicrobiology and microbial assimilative capacity of the oligotrophic Andean
Lake Laja, Chile
A strong socio-economic development pressure in South Chile will more and
more cause an impact to the present lakes and rivers. Nevertheless, our knowledge concerning the ecological structure and
the microbial self-purification capabilities of these lacustrine water bodies is scant but essential for a future sustainable
development of land and water use. We studied Lake Laja, a lake already heavily impacted by water diversions for
hydropower generation and irrigation. Typical for the Andean region Lake Laja is an oligotrophic water body, limited by
nitrogen nutrients. Only very low chlorophyll a and particulate organic carbon (POC) concentrations and a small abundance
and biomass of bacteria (mainly ultramicrobacteria) and heterotrophic flagellates were encountered. Weak trophic
interrelations were derived from a high bacteria-to-heterotrophic flagellate ratio. For the ten investigated extracellular
enzymes (alkaline phosphatase, leucine-, arginine-, glycine- and tyrosine-aminopeptidase, α-, β-D-glucosidase, α-, β -D-
galactosidase, N-acetyl- β –D- glucosaminidase), with the exception of α -D-glucosidase, a broad range of organic matter
degradation activities was proven. Probably, due to the N-limitation, organic nitrogen hydrolysing extracellular enzymes
reached activities on average of 45 % compared to other studies in oligotrophic waters. The possible effect of N-limitation
on extracellular enzyme activities was more pronounced by cell specific extracellular enzymatic activity rates, which
exceeded those of other oligotrophic water bodies on average by factor 2. The overall activities of all microbial
extracellular enzymes studied proved to be dominated by the dissolved free external enzymes (up to 98 %) over the
ectoenzymes which are associated with particulate organic matter (bacterial cell walls, particles, and aggregates). It is
concluded that future socio-economic changes, dealing with watershed human intervention (accelerating inorganic and
organic loads) as well as global change (temperature and precipitation changes) could lead to significant changes in the
ecology of Lake Laja.
Key words:
bacterioplankton, extracellular enzymes, heterotrophic flagellates, N-limitation,
phytoplankton
