Effect of shear on morphology and erythromycin production in Saccharopolyspora erythraea fermentations

Abstract

A complex medium was used to investigate the effects of shear on the S. erythraea fermentation at 7-l scale. Maximum biomass was 11.1 0.5 g l A1 at 1250 rpm (tip speed 4.45 ms A1 ), whereas it was 12.7 0.2 g l A1 at 350 rpm (tip speed 1.07 ms A1 ). Speci®c erythromycin production was not stirrer speed dependent in the range of 350 to 1000 rpm and decreased by 10% at stirrer speed of 1250 rpm. Morphological measurements using image analysis showed that the major axis of the mycelia (both freely dispersed and clumps) decreased after the end of the rapid growth phase to a relatively constant value (equilibrium size) dependent on the stirrer speed. The mechanical properties of the cell wall were examined by disruption of fermentation broth in homogeniser and it was shown that mechanical strength of the cell wall increased in a large extent during deceleration phase. IntroductionIn submerged cultures the provision of agitation to the broth is dictated by the requirement for adequate oxygen transfer rate and bulk mixing, often subjecting the ®la-mentous organisms to strong¯ow forces [1, 2, 3]. These forces may lead to physical damage, changes in morphology and variations in the rate of production of secondary metabolites [4,5,6,7]. In addition, changes in the morphology of the organism can affect the rheology of the culture [8,9,10], affecting mass transfer parameters in the fermenter [11,12] and the downstream processing such as micro®ltration.Over 60% of antibiotics of microbial origin are produced from actinomycetes ®lamentous organism, including b-lactams, polyketides, aminoglycosides and peptide antibiotics. While there are many reports for the effect of shear environment on fermentation of ®lamentous fungi in the stirred tank [4,6,7,13,14,15], there are very few quantitative studies in the case of the actinomycetes ®la-mentous organisms. Belmar-Campero and Thomas [16] studied the effect of stirrer speed in 5-l fermentation for S. clavuligerus. They found that increasing the agitation speed accelerated the fragmentation and subsequent regrowth. Martin et al. [17] reported a decrease in the mean mycelia diameter from 124 lm to 70 lm when the stirrer speed in a 3-l S. erythraea fermentation increased from 750 rpm to 1250 rpm.In the present work the effect of shear on morphology, growth and erythromycin production of S. erythraea in stirred tank bioreactor is investigated. In the majority of the reports in the literature it is impossible to distinguish the effect of mechanical shear forces from other effects such as oxygen transfer rates. In this study dissolved oxygen tension was kept above 60% of air saturation by adding oxygen to the air inlet when necessary. It has been reported that no signi®cant effects on growth, morphology, and productivity are to be expected from such a DOT level [16], therefore, differences in culture behaviour may be considered to be mainly due to mechanical forces. Materials and methods MicroorganismThe organism used was Saccharopolyspora erythraea CA340 kindly denoted by Abbott Laborat...

Viability, strength, and fragmentation of Saccharopolyspora erythraea in submerged fermentation

“…This is counterintuitive, since the agitation conditions were similar in both fermentations and one would expect weaker mycelia in the nitrate-limited fermentation to be more susceptible to breakage. Heydrian et al (1999), by subjecting S. erythraea grown in a complex medium (although the limiting component was not stated, it was almost certainly phosphorous) to high pressure homogenisation, reported that mycelial strength reached a maximum at the end of the growth phase, while observing the onset of fragmentation in the culture before the end of the growth phase. They also demonstrated that a wide range of agitation conditions do not in¯uence the size distributions or productivity achieved by mycelia during fermentation.…”

The inter-relationship between inoculum concentration, morphology, rheology and erythromycin productivity in submerged cultivation of Saccharopolyspora erythraea

“…The effect of various parameters such as shear, biomass concentration and medium components (Bushell et al, 1997a;Hamedi et al, 2004;Heydarian et al, 1999;Rostamza et al, 2008;Sarra et al, 1996) on the morphology of this actinomycete has been previously reported. To the knowledge of the authors, there is no report in the literature about the effect of inoculum size on the morphology, rheology and erythromycin production by this microorganism; furthermore, the relative erythromycin productivities of pellet and clump forms of this actinomycete have not been considered in any previous study.…”

“…The number and dimensions of pellets, clumps and free mycelia were determined manually. The morphological parameters measured in this study for these three growth forms are described in Table 1 ( Heydarian et al, 1999;Rodríguez Porcel et al, 2005). For each parameter, the values reported are the mean of between 100-300 measurements.…”

Estimation of hyphal tensile strength in production‐scale Aspergillus oryzae fungal fermentations

“…However, this is a non-trivial task and the vast majority of previous publications that have attempted to describe fragmentation have done so based solely on morphological measurements (Amanullah et al, 1999;Cui et al, 1997;Heydarian et al, 1999;Justen et al, 1996Justen et al, , 1998aJusten et al, , 1998bNielsen and Krabben, 1995;Smith et al, 1990;Wardell and Bushell, 1999). We took a similar approach in a previous study (Li et al, 2000), and determined fragmentation rates (k frag ) for the batches described here, using a ®rst-order model:…”

“…Heydarian et al, (1999) grew the ®lamentous bacterium S. erythraea in a fermentor and assessed relative tensile strength by viewing the size of fragments emerging from a single pass through a laboratory homogenizer. The assumption was made that larger fragments corresponded to greater tensile strength.…”