Burkholderia thailandensis, although normally avirulent for mammals, can infect macrophages in vitro and has occasionally been reported to cause pneumonia in humans. It is therefore used as a model organism for the human pathogen B. pseudomallei, to which it is closely related phylogenetically. We characterized the B. thailandensis clinical isolate CDC2721121 (BtCDC272) at the genome level and studied its response to environmental cues associated with human host colonization, namely, temperature and oxygen limitation. Effects of the different growth conditions on BtCDC272 were studied through whole genome transcription studies and analysis of proteins associated with the bacterial cell surface. We found that growth at 37°C, compared to 28°C, negatively affected cell motility and flagella production through a mechanism involving regulation of the flagellin-encoding fliC gene at the mRNA stability level. Growth in oxygen-limiting conditions, in contrast, stimulated various processes linked to virulence, such as lipopolysaccharide production and expression of genes encoding protein secretion systems. Consistent with these observations, BtCDC272 grown in oxygen limitation was more resistant to phagocytosis and strongly induced the production of inflammatory cytokines from murine macrophages. Our results suggest that, while temperature sensing is important for regulation of B. thailandensis cell motility, oxygen limitation has a deeper impact on its physiology and constitutes a crucial environmental signal for the production of virulence factors.

A Lactobacillus sakei strain named FLEC01 was isolated from human feces and characterized genotypically. Comparison of the genetic features of this strain with those of both the meat-borne L. sakei strain 23K and another human isolate, LTH5590, showed that they belong to different but closely related clusters. The three L. sakei strains did not persist and only transited through the gastrointestinal tracts (GITs) of conventional C3H/HeN mice. In contrast, they all colonized the GITs of axenic mice and rapidly reached a population of 10 9 CFU/g of feces, which remained stable until day 51. Five days after mice were fed, a first subpopulation, characterized by small colonies, appeared and reached 50% of the total L. sakei population in mice. Fifteen to 21 days after feeding, a second subpopulation, characterized by rough colonies, appeared. It coexisted with the two other populations until day 51, and its cell shapes were also affected, suggesting a dysfunction of the cell division or cell wall. No clear difference between the behaviors of the meat-borne strain and the two human isolates in both conventional and axenic mice was observed, suggesting that L. sakei is a food-borne bacterium rather than a commensal one and that its presence in human feces originates from diet. Previous observations of Escherichia coli strains suggest that the mouse GIT environment could induce mutations to increase their survival and colonization capacities. Here, we observed similar mutations concerning a food-grade grampositive bacterium for the first time.Although initially characterized from rice wine (28), the lactic acid bacterium species Lactobacillus sakei is considered the main representative flora of meat products, representing the major population of many fermented meat products and of raw meat stored under vacuum-packaged conditions (10,12,13). L. sakei is naturally present in many fish and meat products that are traditionally processed without the use of starter cultures (33). In addition, when small-scale facilities producing traditional dry fermented sausage were searched, L. sakei was detected only in the meat matrix, suggesting that meat is contaminated by this species mainly during the early processing steps (certainly by hide or feces of the animals) and not later on or by contact with the environment or materials within the facilities (2).L. sakei shows high degrees of phenotypic and genomic diversity (11-13) that may explain the difficult detection and misidentification of it in the past. For instance, although the human gut microbiota has been intensively investigated by different microbial and molecular methods for many years, the presence of L. sakei in the feces of healthy humans was reported only recently (16,17,26,39). The presence of the meat-borne species L. sakei in human feces, similar to that of several other lactobacilli, could be correlated to human diet, including raw and fermented meat (or fish), for millennia (37). Considering its relatively high concentration in human feces (10 6 per g) that was p...

We recently showed that Lactobacillus sakei, a natural meat-borne lactic acid bacterium, can colonize the gastrointestinal tracts (GIT) of axenic mice but that this colonization in the intestinal environment selects L. sakei mutants showing modified colony morphology (small and rough) and cell shape, most probably resulting from the accumulation of various mutations that confer a selective advantage for persistence in the GIT. In the present study, we analyzed such clones, issued from three different L. sakei strains, in order to determine which functions were modified in the mutants. In the elongated filamentous cells of the rough clones, transmission electron microscopy (TEM) analysis showed a septation defect and dotted and slanted black bands, suggesting the presence of a helical structure around the cells. Comparison of the cytoplasmic and cell wall/membrane proteomes of the meat isolate L. sakei 23K and of one of its rough derivatives revealed a modified expression for 38 spots. The expression of six oxidoreductases, several stress proteins, and four ABC transporters was strongly reduced in the GIT-adapted strain, while the actin-like MreB protein responsible for cell shaping was upregulated. In addition, the expression of several enzymes involved in carbohydrate metabolism was modified, which may correlate with the observation of modified growth of mutants on various carbon sources. These results suggest that the modifications leading to a better adaptation to the GIT are pleiotropic and are characterized in a rough mutant by a different stress status, a cell wall modification, and modified use of energy sources, leading to an improved fitness for the colonization of the GIT.Lactobacilli are Gram-positive bacteria known mostly for their importance in the food industry or their potential beneficial effects on consumers. Their presence in the human gastrointestinal tract (GIT) has frequently been reported, and, although in small amounts (31), 16 different Lactobacillus species have been isolated at least once from human feces (35). Most of those species are probably not autochthonous but rather persisting species introduced in the GIT after food ingestion.Lactobacillus sakei is known as a food-borne bacterium, frequently isolated from fresh or fermented meat but also found in fish or vegetal fermented products (6, 30). The importance of L. sakei in the meat industry significantly increased in recent years because of its technological properties that are optimal for sausage fermentation (5, 9) and its potential use as a bioprotective culture for the biopreservation of various meat products (3, 5, 36). L. sakei has been detected in human feces (20, 37), and some human strains have been isolated (7, 10). The estimated amount of this species in the fecal samples (10 6 CFU/g of feces) does not permit a conclusion about whether its presence is strictly food related or not. In addition, although the physiological functions involved in the adaptation to and growth of L. sakei in its preferred environment (meat esse...