The ability of fractions of dissolved organic @entity505 ( @entity4420 ) of different molecular weights (MW) to support bacterial growth was studied in batch culture experiments. Natural pelagic bacteria were inoculated into particle-free (0.2-mum filtered) water, taken from 10 oligotrophic lakes of differing humic content, and either used without further treatments or ultrafiltered to remove @entity4420 of >10,000 MW or >1,000 MW. Stationaryphase abundance of bacteria in the cultures was used as an estimate of bacterial carrying capacity. High-MW @entity4420 (>10,000) comprised an increasing fraction of total @entity4420 with increasing total @entity4420 and humic content of the lakes. High-MW @entity4420 was generally more available to bacteria (i.e., more bacteria were produced per unit of organic @entity505 initially present) than low-MW (<10,000) @entity4420 . The availability to bacteria of this high-MW @entity4420 decreased with increasing humic content. However, although less available in humic lakes than in clearwater lakes, the higher abundance of high-MW @entity4420 made it quantitatively more important as a bacterial substrate; i.e., a larger fraction of the total bacterial yield of the cultures was due to high-MW @entity4420 compounds in humic lakes than in clearwater lakes. On the average, 48% of bacterial growth occurred at the expense of @entity4420 of <10,000 MW. @entity4420 of <1,000 MW was responsible for an average of 22% of bacterial growth, with no significant correlation to humic content and @entity4420 concentration of lakes. The @entity4420 which supports bacterial growth, as well as the total @entity4420 , is of different quality in humic and clearwater lakes.

Bacterioplankton growth on fractions of dissolved organic XXXX of different molecular weights from humic and clear waters.

@entity505 :: ('MESH:D002244', 'Chemical') :: ['carbon'] @entity4420 :: ('CHEBI:16973', 'Chemical') :: ['DOC']
@entity505 :: (MESH:D002244,Chemical) :: ['carbon']
