No abstract

No abstract

The influence of the growth rate on outer membrane protein composition and enterobactin production was studied with Klebsiella pneumoniae grown under conditions of iron limitation in chemostats. More enterobactin was produced at fast (D = 0.4 h-1) and slow (D = 0.1 h-1) growth rates in continuous cultures than in either logarithmic-or stationary-phase batch cultures. When the growth rate was controlled under conditions of carbon limitation and the iron level was reduced to 0.5 ,M, the iron-regulated outer membrane proteins and enterobactin were induced at the fast growth rate. At the slow growth rate, although the iron-regulated outer membrane proteins were barely visible, a significant level of enterobactin was still produced. These results suggest that under conditions of either carbon or iron limitation, the growth rate can influence the induction of the high-affinity iron uptake system of K. pneumoniae. Other outer membrane proteins, including a 39-kilodalton peptidoglycan-associated protein, were found to vary with the growth rate and nutrient limitation.Iron is an important microbial nutrient which is often not readily available to microorganisms. In aerobic environments at a neutral pH, it predominates as highly insoluble ferric hydroxide polymers (7). During many infections, the withholding of iron by transferrin and lactoferrin constitutes an important component of nonspecific mammalian defense mechanisms (13,17,39,40). The ability to obtain iron is therefore an important virulence factor and, in response to iron deprivation, many microorganisms produce lowmolecular-weight iron-chelating agents (or siderophores) and membrane receptor proteins (17,31,32,39,40). These high-affinity iron uptake systems are expressed by some bacteria growing in vivo during infections in both animals (18, 35) and humans (5,24,36). We recently showed that Klebsiella pneumoniae grown in batch cultures in irondepleted media or in serum induced at least six new ironregulated outer membrane (OM) proteins (IRMPs) together with the iron chelator enterobactin (enterochelin) (41).During infections, bacterial growth rates appear to be slow (4,11,37), and nutrients as well as or other than iron may be growth limiting (6,37,39 siderophore enterobactin by K. pneumoniae. In the carbonlimited chemostat, the medium iron content was lowered to concentrations close to but above the concentration which would be rate limiting. MATERIALS AND METHODSOrganisms and growth conditions. K. pneumoniae DL1, an encapsulated clinical isolate (41), was grown aerobically in continuous cultures at 37°C in glass chemostats at a working volume of 50 ml maintained at a dilution rate of either D = 0.1 h'-(doubling time, 6.9 h) or D = 0.4 h'-(doubling time, 1.7 h). For each experiment, the chemostat was allowed to equilibrate by passing five complete changes of medium through the vessel. Bacteria were also grown to the stationary phase in batch cultures. The simple salts medium (SSM) used for all cultures was that described by Williams et al. (41). This medium wa...

Environmental awareness and ever-growing restrictive regulations over contamination have increased the need for more environmentally-friendly lubricants. Due to their superior biodegradability and lower toxicity, vegetable oils are a good alternative to replace currently-used mineral oils. However, vegetable oils show low oxidation and thermal stability and poor anti-wear properties. Most of these drawbacks can be attenuated through the use of additives. In the last decade, ionic liquids have emerged as high-performance fluids and lubricant additives due to their unique characteristics. In this study, the tribological behavior of two phosphonium-based ionic liquids is investigated as additives of coffee bean oil in steel-steel contact. Coffee bean oil-ionic liquid blends containing 1, 2.5, and 5 wt% of each ionic liquid are studied using a block-on-flat reciprocating tribometer and the test results are compared to commercially-available, fully-formulated lubricant. Results showed that the addition of the ionic liquids to the coffee bean oil reduces wear volume of the steel disks, and wear values achieved are comparable to that obtained when the commercially-available lubricant is used.

Assimilation and uptake of iron in anaerobic cultures of Escherichia coli were supported by iron supplied as ferrienterobactin, ferrichrome, and ferrous ascorbate; however, as in the aerobic cultures, ferrichrome A was a poor iron source. Albomycin inhibited both aerobically and anaerobically grown cells. The siderophore outer membrane receptor proteins FepA and FhuA were produced under anaerobic iron-deficient conditions. Anaerobic transport of ferrienterobactin and ferrichrome was inhibited by KCN and dinitrophenol. The Km for ferrienterobactin uptake in anaerobically grown cells was 0.8 ,uM, and the Vmax was 38 pmol/min per mg, compared with 0.1 ,uM and 80 pmol/min per mg, respectively, in aerobically grown cells.