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Fang, A.

Publications and source records attributed to Fang, A..

10 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Shear stress enhances microcin B17 production in a rotating wall bioreactor, but ethanol stress does not

Stress, including that caused by ethanol, has been shown to induce or promote secondary metabolism in a number of microbial systems. Rotating-wall bioreactors provide a low stress and simulated microgravity environment which, however, supports only poor production of microcin B17 by Escherichia coli ZK650, as compared to production in agitated flasks. We wondered whether the poor production is due to the low level of stress and whether increasing stress in the bioreactors would raise the amount of microcin B17 formed. We found that applying shear stress by addition of a single Teflon bead to a rotating wall bioreactor improved microcin B17 production. By contrast, addition of various concentrations of ethanol to such bioreactors (or to shaken flasks) failed to increase microcin B17 production. Ethanol stress merely decreased production and, at higher concentrations, inhibited growth. Interestingly, cells growing in the bioreactor were much more resistant to the growth-inhibitory and production-inhibitory effects of ethanol than cells growing in shaken flasks.

NASA Center JSC↗
NASA NTRS2001

Induction of microcin B17 formation in Escherichia coli ZK650 by limitation of oxygen and glucose is independent of glucose consumption rate

We examined the consumption of glucose from the media in which Escherichia coli ZK650 was grown. This organism, which produces the polypeptide antibiotic microcin B17 best under conditions of limiting supplies of glucose and air, was grown with a low level of glucose (0.5 mg/ml) as well as a high level (5.0 mg/ml) under both high and low aeration. Glucose consumption rates were virtually identical under both high and low aeration. Thus, glucose consumption rate is not a regulating factor in microcin B17 formation.

NASA Discipline Cell Biology↗
NASA NTRS2001

Secondary metabolism in simulated microgravity

We have studied microbial secondary metabolism in a simulated microgravity (SMG) environment provided by NASA rotating-wall bioreactors (RWBs). These reactors were designed to simulate some aspects of actual microgravity that occur in space. Growth and product formation were observed in SMG in all cases studied, i.e., Bacillus brevis produced gramicidin S (GS), Streptomyces clavuligerus made beta-lactam antibiotics, Streptomyces hygroscopicus produced rapamycin, and Escherichia coli produced microcin B17 (MccB17). Of these processes, only GS production was unaffected by SMG; production of the other three products was inhibited. This was determined by comparison with performance in an RWB positioned in a different mode to provide a normal gravity (NG) environment. Carbon source repression by glycerol of the GS process, as observed in shaken flasks, was not observed in the RWBs, whether operated in the SMG or NG mode. The same phenomenon occurred in the case of MccB17 production, with respect to glucose repression. Thus, the negative effects of carbon source on GS and beta-lactam formation are presumably dependent on shear, turbulence, and/or vessel geometry, but not on gravity. Stimulatory effects of phosphate and the precursor L-lysine on beta-lactam antibiotic production, as observed in flasks, also occurred in SMG. An almost complete shift in the localization of produced MccB17 from cells to extracellular medium was observed when E. coli was grown in the RWB under SMG or NG. If a plastic bead was placed in the RWB, accumulation became cellular, as it is in shaken flasks, indicating that sheer stress favors a cellular location. In the case of rapamycin, the same type of shift was observed, but it was less dramatic, i.e., growth in the RWB under SMG shifted the distribution of produced rapamycin from 2/3 cellular:1/3 extracellular to 1/3 cellular:2/3 extracellular. Stress has been shown to induce or promote secondary metabolism in a number of other microbial systems. RWBs provide a low stress SMG environment, which, however, supports only poor production of MccB17, as compared to production in shaken flasks. We wondered whether the poor production in RWBs under SMG is due to the low level of stress, and whether increasing stress in the RWBs would raise the amount of MccB17 formed. We found that increasing shear stress by adding a single Teflon bead to the RWB improved MccB17 production. Although shear stress seems to have a marked positive effect on MccB17 production in SMG, addition of various concentrations of ethanol to RWBs (or to shaken flasks) failed to increase MccB17 production. Ethanol stress merely decreased production and, at higher concentrations, inhibited growth. Interestingly, cells growing in the RWB were much more resistant to the growth- and production-inhibitory effects of ethanol than cells growing in shaken flasks. With respect to S. hygroscopicus, addition of Teflon beads to the RWB reversed the inhibition of growth, but rapamycin production was still markedly inhibited, and the distribution did not revert back to a preferential cellular site.

NASA Discipline Cell Biology↗
NASA NTRS2000

Growth of Steptomyces hygroscopicus in rotating-wall bioreactor under simulated microgravity inhibits rapamycin production

Growth of Streptomyces hygroscopicus under conditions of simulated microgravity in a rotating-wall bioreactor resulted in a pellet form of growth, lowered dry cell weight, and inhibition of rapamycin production. With the addition of Teflon beads to the bioreactor, growth became much less pelleted, dry cell weight increased but rapamycin production was still markedly inhibited. Growth under simulated microgravity favored extracellular production of rapamycin, in contrast to a greater percentage of cell-bound rapamycin observed under normal gravity conditions.

NASA Center JSC↗
NASA NTRS2000

Relief from glucose interference in microcin B17 biosynthesis by growth in a rotating-wall bioreactor

Glucose interference in production of microcin B17 by Escherichia coli ZK650 was decreased sevenfold by growth in a ground-based rotating-wall bioreactor operated in the simulated microgravity mode as compared with growth in flasks. When cells were grown in the bioreactor in the normal gravity mode, relief from glucose interference was even more dramatic, amounting to a decrease in glucose interference of over 100-fold.

NASA Discipline Environmental Health↗
NASA NTRS2000

Growth of Streptomyces Hygroscopicus in Rotating-Wall Bioreactor Under Simulated Microgravity Inhibits Rapamycin Production

Growth of Streptomyces hygroscopicus under conditions of simulated microgravity in a rotating-wall bioreactor resulted in a pellet form of growth, lowered dry cell weight, and inhibition of rapamycin production. With the addition of Teflon beads to the bioreactor, growth became much less pelleted, dry cell weight increased but rapamycin production was still markedly inhibited. Growth under simulated microgravity favored extracellular production of rapamycin in contrast to a greater percentage of cell-bound rapamycin observed under normal gravity conditions.

Fang, A.↗
NASA NTRS1997

Effect of simulated microgravity and shear stress on microcin B17 production by Escherichia coli and on its excretion into the medium

Production of the antibacterial polypeptide microcin B17 (MccB17) by Escherichia coli ZK650 was inhibited by simulated microgravity. The site of MccB17 accumulation was found to be different, depending on whether the organism was grown in shaking flasks or in rotating bioreactors designed to establish a simulated microgravity environment. In flasks, the accumulation was cellular, but in the reactors, virtually all the microcin was found in the medium. The change from a cellular site to an extracellular one was apparently not a function of gravity, since extracellular production occurred in these bioreactors, irrespective of whether they were operated in the simulated microgravity or normal gravity mode. More probably, excretion is due to the much lower degree of shear stress in the bioreactors. Addition of even a single glass bead to the 50-ml medium volume in the bioreactor created enough shear to change the site of MccB17 accumulation from the medium to the cells.

NASA Center JSC↗
NASA NTRS1997

Gramicidin S production by Bacillus brevis in simulated microgravity

In a continuing study of microbial secondary metabolism in simulated microgravity, we have examined gramicidin S (GS) production by Bacillus brevis strain Nagano in NASA High Aspect Rotating Vessels (HARVs), which are designed to simulate some aspects of microgravity. Growth and GS production were found to occur under simulated microgravity. When performance under simulated microgravity was compared with that under normal gravity conditions in the bioreactors, GS production was found to be unaffected by simulated microgravity. The repressive effect of glycerol in flask fermentations was not observed in the HARV. Thus the negative effect of glycerol on specific GS formation is dependent on shear and/or vessel geometry, not gravity.

NASA Discipline Number 04-10↗
NASA NTRS1997

Secondary metabolism in simulated microgravity: beta-lactam production by Streptomyces clavuligerus

Rotating bioreactors designed at NASA's Johnson Space Center were used to simulate a microgravity environment in which to study secondary metabolism. The system examined was beta-lactam antibiotic production by Streptomyces clavuligerus. Both growth and beta-lactam production occurred in simulated microgravity. Stimulatory effects of phosphate and L-lysine, previously detected in normal gravity, also occurred in simulated microgravity. The degree of beta-lactam antibiotic production was markedly inhibited by simulated microgravity.

NASA Discipline Environmental Health↗