The effects of the algae extract on industrially relevant E. coli
metabolism were evaluated by measuring total protein accumulation
by Bradford assay. E. coli cultures grown in algae extract exhibited a
17% greater peak protein density when compared with cultures grown
in the presence of yeast extract (Fig. 2). Interestingly, protein
production was not linked directly to cell concentration and most
protein production for both cultures took place early in the exponential
phase. It appears that the highest protein production rates occurred
simultaneouslywith highest specific growth rateswhen substrate levels
were greatest (substrate levels have already begun to drop off by the
middle of the exponential phase). As was the case in growth
measurements, protein production for algae extract continued longer
than in yeast extract. Cultures growth in algae extract maintained
positive protein production for 11.5 h after inoculation (Fig. 2). Cultures
grown in yeast extract exhibited a higher degree of self-digestion as
early as 9 h when protein concentrations began to fall. These trends in
prolonged protein production and the delay of self-digestion may also
be explained by the additional nutrients found in whole proteins that
were made available later in the growth process. This characteristic of
algae extract could prove very useful in some industrial applications
where prolonged protein expression is necessary to achieve maximum
production from batch cultures before encountering stationary phase,
especially when producing enzymes or secondary metabolites where
cells must remain viable for longer periods of time.