SummaryThe insecticidal toxin complexes (Tcs) are produced by several Enterobacteriaceae associated with insects, such as Photorhabdus luminescens , Serratia entomophila and Xenorhabdus nematophilus. Genome sequences revealed tc -like genes in Yersinia spp., but insecticidal activity of this genus associated with the toxins has not been described. Through the search for genes upregulated at low growth temperatures in Yersinia enterocolitica strain W22703, a genomic island of 19 kb termed tc -PAI Ye with homologues of the toxin genes tcaA , tcaB , tcaC and tccC was identified. Southern blot and polymerase chain reaction (PCR) analysis of 34 strains demonstrated that the tc -PAI Ye is present in biovars 2, 3 and 4, but neither in biovars 1A and 1B, nor in five Yersinia species apathogenic in humans. Using the luxCDABE operon as reporter, the expression of the toxin genes was shown to be completely repressed in cells cultured at 37 °°°° C, and to increase by 4.6 orders of magnitude when the growth temperature was decreased gradually to 10 °°°° C. These data provide the first indication that temperature is a critical parameter for induction or repression of tc gene transcription. Whole-cell extracts of Y. enterocolitica strain W22703 cultivated at 10 °°°° C, but not at 30 °°°° C, led to insect mortality when fed to Manduca sexta larvae, in contrast to an insertional tcaA mutant. Overall the results suggest that the tc -PAI Ye could play an important role in the transmission and survival of pathogenic Y. enterocolitica strains outside mammalian hosts.

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ture for increasing cell density or biomass in the reactor, and hence the volumetric productivity. In this study, Lactococus lactis was chosen for immobilization in a fixed-bed reactor because of its importance for starter cultures.The aim was to demonstrate a proof of concept; for continuous cultivation of L. lactis in fixed bed reactors and to investigate strategies for scale-up (see Fig.).Among several macroporous carriers Sponceram (donated by ZellWerk, Eichstädt) and SIRAN (QVF) showed the best performance. The procedure for immobilization is simple and does not require extra equipment. During continuous cultivation in a 100 mL-fixed-bed reactor at perfusion rates up to 4.6 h -1 (more than four times higher as the max. growth rate) the volumetric lactate productivity was about 30 times higher than in batch culture. Compared to literature data the values obtained were significantly higher as well. This implies that probably the perfusion rates used in the previous works were too low, resulting in a lower volumetric productivity. For scale-up a 1.5 L radial-flow bioreactor was run with a perfusion rate of 2 d -1 corresponding to a medium throughput of 50 L per day for up to two weeks. The volume specific productivity for lactate and cell release was even higher as in the small scale system. Therefore, this small and compact reactor system can replace suspension reactors which are 50 to 100 times larger. Further scale-up should be possible.