To address this possibility, we determined the sensitivity of LAX12 and LAX16 to ampicillin, streptomycin, spectinomycin, chloramphenicol, tetracycline, nalidixic acid, rifampicin, erythromycin and acriflavin. Both mutants showed the same
susceptibility to the antibiotics tested as did MLA301, which suggested that the dysfunction in the mutants was distinct from a loss-of-function mutation in the antibiotic efflux system(s). Several amino acid exporters have been shown to transport not only their primary amino acid substrates but also other amino acids including their analogs (Zakataeva et al., 1999; Daßler et al., 2000; Franke et al., 2003; Livshits et al., 2003; Kutukova et al., 2005). We thus determined the intracellular amino acid levels in the parent MLA301 and the mutant LAX12 in the presence of l-alanyl-glycine, l-alanyl-l-leucine or l-alanyl-l-phenylalanine Fluorouracil nmr (1 mM each). LAX12 showed a Apoptosis Compound Library higher level of intracellular l-alanine than MLA301; however, the intracellular level of each of the other amino acids contained in the dipeptides, glycine, l-leucine and l-phenylalanine, was almost the same for MLA301 and LAX12 (data not shown). The results indicated that the l-alanine export system, the function of which has been lost in LAX12, does not share substrate specificity for glycine, l-leucine and l-phenylalanine. Because there is no evidence that previously
identified l-leucine and aromatic amino acid exporters transport l-alanine (Kutukova et al., 2005; Doroshenko et al., 2007), it is most
probable that the newly identified l-alanine export system is distinct from those amino acid exporters. To our knowledge, the l-alanine export system found in this study is the first documented system that exports l-alanine as a preferential substrate. The mutants obtained in this study should be useful for further characterization of the l-alanine efflux system(s) and identification of MycoClean Mycoplasma Removal Kit the gene(s) encoding l-alanine exporter(s). “
“Pseudomonas fluorescens BM07 is known to produce cold-induced exobiopolymer, which is mainly composed of water-insoluble hydrophobic polypeptides (up to 85%) and saccharides (8%), by decreasing the culture temperature down to as low as 10 °C. We screened for transposon insertion mutants of P. fluorescens BM07 that were unable to produce the exobiopolymer. Among the eight mutants that showed the deficiency of exobiopolymer and O-lipopolysaccharide, one mutant BM07-59 that had the highest polyhydroxyalkanoates (PHA) production was selected. The transposon inserted gene in BM07-59 was identified as galU. The disruption of the gene galU coded for the putative product, UDP-glucose pyrophosphorylase (GalU), resulted in 1.5-fold more accumulation of PHA compared with the wild-type strain from 70 mM fructose or galactose at 30 °C. Electrophoretic analysis of lipopolysaccharide showed that the mutant lacked the O-antigen lipopolysaccharide bands.