Beyond growth rate 0.6: Corynebacterium glutamicum cultivated in highly diluted environments

Fast growth of industrial microorganisms, such as Corynebacterium glutamicum, is a direct amplifier for the productivity of any growth coupled or decoupled production process. Recently, it has been shown that C. glutamicum when grown in a novel picoliter bioreactor (PLBR) exhibits a 50% higher growth rate compared to a 1 L batch cultivation [Grünberger et al. (2012) Lab Chip]. We here compare growth of C. glutamicum with glucose as substrate at different scales covering batch cultivations in the liter range down to single cell cultivations in the picoliter range. The maximum growth rate of standard batch cultures as estimated from different biomass quantification methods is mu = 0.42 ± 0.03 h(-1) even for microtiter scale cultivations. In contrast, growth in a microfluidic perfusion system enabling analysis of single cells reproducibly reveals a higher growth rate of mu = 0.62 ± 0.02 h(-1). When in the same perfusion system cell-free supernatant from exponentially grown shake flask cultures is used the growth rate of single cells is reduced to mu = 0.47 ± 0.02 h(-1). Likewise, when fresh medium is additionally supplied with 5 mM acetate, a growth rate of mu = 0.51 ± 0.01 h(-1) is determined. These results prove that higher growth rates of C. glutamicum than known from typical batch cultivations are possible, and that growth is definitely impaired by very low concentrations of byproducts such as acetate.