12 Measuring Bacterial Biomass Production and Growth Rates from Leucine Incorporation in Natural Aquatic Environments

The rate of biomass production is a fundamental property of all organisms in nature, but it is an especially important parameter of microbes in natural aquatic environments. An estimate of microbial production can be used as a general index of microbial activity and specifically to calculate growth rates. Since many processes scale with it, biomass production can be used to obtain a first-order estimate of rates of several processes mediated by microbes. For example, in the case of heterotrophic bacteria, the organisms to be discussed here, biomass production can be used to estimate use of dissolved organic material (DOM) if coupled with an estimate of the growth efficiency. That is, DOM uptake equals bacterial biomass production divided by the growth efficiency (expressed as a fraction, not a percentage). Biomass production is the increase in biomass per unit time per unit w)lume or per area and is a function of both biomass (B), usually expressed as carbon mass per volume (e.g. lagC l~), and the specific growth rate (i a) (e.g. h ') (Ducklow, 2000). in the absence of any mortality (grazers and viruses), bacterial biomass increases exponentially (although not necessarily very quickly) which can be described by