EXERCISE 19
Bacterial Growth
and Productivity
Earlier discussions emphasized that dead organic
matter, called detritus, exists as a spectrum from
dissolved organic compounds, organic colloids,
and larger particles of organic matter. Dissolved
organic matter is in much greater abundance, by
about five to ten times, than is particulate organic
matter. All microflora must degrade particulate
organic matter enzymatically to the dissolved
form prior to assimilation for further metabolic
breakdown and eventual mineralization to
inorganic solutes and gases.
The rates of growth by bacteria and their productivity are known poorly from aquatic ecosystems. Much of this lack of progress resulted
from the slow application oflaboratory methodology to heterogeneous natural communities of
bacteria. Often methods were developed for
isolated strains at high laboratory concentrations.
A number of methods have been developed
recently that permit examination of growth and
productivity of in situ communities of bacteria.
These methods are evolving as more is learned
about metabolic constraints and variations.
Natural variance is high in microbial communities, and many organisms are metabolically
inactive. The methods used to examine bacteria
are labor intensive. We describe methods here
in considerable detail because they require
rigorous application in order to obtain meaningful results. Conversion of rates of biomass change
or genetic replication to actual rates of carbon
flux in bacterial secondary productivity is
difficult and is undergoing intensive study by
many researchers. A spectrum of conversion
factors is given for different environmental
conditions in order to indicate the range of
probable in situ values.
We stress the importance of these evaluations
of in situ metabolism and growth rates of bacteria.
Much ofthe understanding about biogeochemical
cycling in aquatic ecosystem has been limited
severely by poor or inadequate techniques for
evaluation of bacterial metabolism and its
limitations by environmental parameters. The
methods presented here are not perfect, and they
are laborious. Certainly they will improve with
time. However, these methods offer means to
examine in situ rates of bacterial growth and
productivity and, importantly, means to evaluate
in situ effects of experimental manipulations of
environmental conditions.
BACTERIAL ENUMERATION AND BIOMASS DETERMINATION
Evaluation of the species composition and relative numbers of heterotrophic
bacteria by direct enumeration or by plating on culture media may give useful
255
Bacterial Growth
and Productivity
Earlier discussions emphasized that dead organic
matter, called detritus, exists as a spectrum from
dissolved organic compounds, organic colloids,
and larger particles of organic matter. Dissolved
organic matter is in much greater abundance, by
about five to ten times, than is particulate organic
matter. All microflora must degrade particulate
organic matter enzymatically to the dissolved
form prior to assimilation for further metabolic
breakdown and eventual mineralization to
inorganic solutes and gases.
The rates of growth by bacteria and their productivity are known poorly from aquatic ecosystems. Much of this lack of progress resulted
from the slow application oflaboratory methodology to heterogeneous natural communities of
bacteria. Often methods were developed for
isolated strains at high laboratory concentrations.
A number of methods have been developed
recently that permit examination of growth and
productivity of in situ communities of bacteria.
These methods are evolving as more is learned
about metabolic constraints and variations.
Natural variance is high in microbial communities, and many organisms are metabolically
inactive. The methods used to examine bacteria
are labor intensive. We describe methods here
in considerable detail because they require
rigorous application in order to obtain meaningful results. Conversion of rates of biomass change
or genetic replication to actual rates of carbon
flux in bacterial secondary productivity is
difficult and is undergoing intensive study by
many researchers. A spectrum of conversion
factors is given for different environmental
conditions in order to indicate the range of
probable in situ values.
We stress the importance of these evaluations
of in situ metabolism and growth rates of bacteria.
Much ofthe understanding about biogeochemical
cycling in aquatic ecosystem has been limited
severely by poor or inadequate techniques for
evaluation of bacterial metabolism and its
limitations by environmental parameters. The
methods presented here are not perfect, and they
are laborious. Certainly they will improve with
time. However, these methods offer means to
examine in situ rates of bacterial growth and
productivity and, importantly, means to evaluate
in situ effects of experimental manipulations of
environmental conditions.
BACTERIAL ENUMERATION AND BIOMASS DETERMINATION
Evaluation of the species composition and relative numbers of heterotrophic
bacteria by direct enumeration or by plating on culture media may give useful
255