Molecular identification of yeast, lactic and acetic acid bacteria species during spoilage of tchapalo, a traditional sorghum beer from Côte d'Ivoire.

Yeasts, lactic and acetic acid bacteria are responsible of microbial spoilage of alcoholic beverages. However species involved in deterioration of sorghum beer produced in Côte d'Ivoire has not been investigated. This study was carried out to identify species of yeast, LAB and AAB during spoilage of tchapalo in order to define the best strategy for beer preservative. Thus, a total of 210 yeasts, LAB and AAB were isolated from samples of tchapalo stored at ambient temperature and at 4 °C for 3 days. Based on PCR-RFLP of the ITS region and the sequencing of D1/D2 domain, yeast isolates were assigned to seven species (Saccharomyces cerevisiae, Candida tropicalis, Rhodotorula mucilaginosa, Trichosporon asahii, Kluyveromyces marxianus, Meyerozyma guilliermondii and Trichosporon coremiiforme). During the storage at ambient temperature and at 4 °C, S. cerevisiae was the predominant species (> 76%). Excepted R. mucilaginosa, occurrence of non-Saccharomyces species was sporadic. LAB species detected in fresh samples using molecular methods were Pediococcus acidilactici, Lactobacillus paracasei, Lb. curvatus, Lb. fermentum and Weisssella paramesenteroides. P. acidilactici was the dominant species (47.8%) followed by Lb. paracasei (17.5%). W. paramesenteroides and Lb. fermentum were not detected during the spoilage at ambient temperature while at 4 °C W. paramesenteroides and Lb. paracasei have not been detected. For AAB, the species found were Acetobacter pasteurianus sub paradoxus and Acetobacter cerevisiae. These species were common to all samples during spoilage and A. pasteurianus sub paradoxus was the most frequently detected.

Mutational analysis of glucose transport regulation and glucose-mediated virulence gene repression in Listeria monocytogenes.

Listeria monocytogenes transports glucose/mannose via non-PTS permeases and phosphoenolpyruvate:carbohydrate phosphotransferase systems (PTS). Two mannose class PTS are encoded by the constitutively expressed mpoABCD and the inducible manLMN operons. The man operon encodes the main glucose transporter because manL or manM deletion significantly slows glucose utilization, whereas mpoA deletion has no effect. The PTS(Mpo) mainly functions as a constitutively synthesized glucose sensor controlling man operon expression by phosphorylating and interacting with ManR, a LevR-like transcription activator. EIIB(Mpo) plays a dual role in ManR regulation: P~EIIB(Mpo) prevailing in the absence of glucose phosphorylates and thereby inhibits ManR activity, whereas unphosphorylated EIIB(Mpo) prevailing during glucose uptake is needed to render ManR active. In contrast to mpoA, deletion of mpoB therefore strongly inhibits man operon expression and glucose consumption. A ΔptsI (EI) mutant consumes glucose at an even slower rate probably via GlcU-like non-PTS transporters. Interestingly, deletion of ptsI, manL, manM or mpoB causes elevated PrfA-mediated virulence gene expression. The PTS(Man) is the major player in glucose-mediated PrfA inhibition because the ΔmpoA mutant showed normal PrfA activity. The four mutants showing PrfA derepression contain no or only little unphosphorylated EIIAB(Man) (ManL), which probably plays a central role in glucose-mediated PrfA regulation.