Eubacteria have 3 growth modes keyed to nutrient flow

Aerobic growth of Escherichia coli and Paracoccus denitrificans has been studied in chemostat, fed batch, and recycling fermentor modes under carbon and energy limitation. Two abrupt drops or discontinuities in molar growth yield, Y, have been found that occur over relatively short ranges in the value of specific growth rate.Before the first discontinuity, Y is constant and maximal. After the first discontinuity, at a doubling time of 33 h, Y becomes constant again and independent of until the second discontinuity appears at a doubling time of about 50 h, corresponding to a of about 0.014. At this point, Y drops to a lower value that is constant at doubling times longer than 100 h, corresponding to a of about 0.007.The second discontinuity is associated in Paracoccus with elevated levels of guanosine tetraphosphate (ppGpp) that impose stringent regulation as has been found previously with Bacillus and Escherichia species. It is thus likely that the stringent response generally occurs in bacteria in vivo at a doubling time of about 50 h. The cause of the first discontinuity is unknown. All experiments indicate that Pirt-type calculations relating , Y, and maintenance energy demand are no longer valid. In chemostat experiments, the intercept of the relationship between specific substrate utilization and specific growth rate is defined as maintenance. However, this intercept most probably is caused by stringent regulation at low dilution rates. Three regions of bacterial growth rates are defined by this study, corresponding to doubling times of 0.5 to 15 h, 33 to 50 h, and >100 h. Some growth behavior in each region is unique to that region.Abbreviations ppGpp guanosine 5 diP 3 diP - pppGpp guanosine 5 triP 3 diP - SPR substrate provision rate (mol/l h)     

A fluid dynamic study of the retrofitting of large agitated bioreactors: Turbulent flow

Studies were conducted in three 19-m(3) fermentors (14 m(3) working volume, aspect ratio = 3:1), one fitted with four Rushton turbines (D/T = 0.35), one with three Lightnin' A315 hydrofoil impellers (D/T = 0.46). The power drawn under the same aerated conditions relative to the unaerated ones was always greater with the hydrofoils, which gives them the potential for enhanced mass transfer rates under practical operating conditions. However, the power draw was also sensitive to the magnitude of the unaerated power. Indeed, at low unaerated specific power ( approximately 0.6 W-kg) and high air flow rates ( approximately 1vvm), the relative power draw with the hydrofoils could be even greater than 1. The hold-up with each of the impellers was broadly similar at the same aeration rate and power input, though the later had a much smaller impact in these large vessels than has been reported in the literature based on smaller scale work. As usual, repressed coalescence caused increased hold-up, and, with the hydrofoils, this increase was associated with a lower power draw. Because of the greater mechanical vibration of the reactors with the hydrofoils, vibration characteristics of the vessels were measured and they were very similar. The results showed that provided care is taken in the mechanical design of the system, such impellers can operate reliably in large-scale fermentations with the potential for enhanced biological performance. (c) 1994 John Wiley & Sons, Inc.     

Very slow growth of Bacillus polymyxa: Stringent response and maintenance energy

Bacillus polymyxa grown in a recycling fermentor shows the same behavior previously observed with Escherichia coli: 3 successive growth phases. In the last 2 phases the growth rate is linear and the apparent maintenance energy demand rate and the molar growth yield are both independent of the specific growth rate, , and of the cells mass. The final phase of very slow growth is an indefinitely prolonged state of strong, stringent control, the regulatory system based on guanosine 3-diphosphate 5-diphosphate, and guanosine 3-diphosphate 5-triphosphate. The maximum cost of this stringent response is calculated to be 9% of the energy available to these energy-limited cells. There is a further energy cost contained in substantial amounts of DNA, RNA, and protein released from the cells during the latter 2 growth phases. The cost of production of these extra cellular anabolites ranges from 8–11% of the available energy.After a carbon-energy upshift in phase 3, the population growth rate immediately returned to that of early phase 2 growth, 50 h or more earlier.If maintenance energy is considered as energy expended by cells to maintain homeostasis, catabolic capacity, or anabolic potential, then the cost of stringent control — which preserves the fidelity of protein synthesis in slowly growing cells — must be considered a maintenance energy cost.Abbreviations GPR glucose provision rate - F_R medium flow rate - S_R substrate concentration - V_F fermentor volume - F_S filtrate removal rate - ppGpp guanosine 3-diphosphate 5-diphosphate - pppGpp guanosine 3-diphosphate 5-triphosphate     

Composition of in vitro denture plaque biofilms and susceptibility to antifungals

The aim of this study was to investigate the composition of microcosm denture plaque biofilms and the susceptibility of Candida spp. within these biofilms to antifungal agents. An in vitro model was employed to grow oral biofilms derived from denture associated stomatitis (DAS) patient samples to assess fungal growth in the presence and absence of antifungal agents. The compositions of genera present in vitro were found to be similar to those exhibited on the mucosa and denture fitting surfaces of DAS samples. Exposure to single agents, e.g., miconazole, fluconazole or chlorhexidine did not inhibit growth of Candida spp. when used in clinically relevant doses. Combinations of miconazole and chlorhexidine, pulsed into the system to mimic patient use, did reduce bacterial and candidal growth for several days. Hence, the use of dual-therapy appeared to be useful in reducing the number of viable organisms within denture plaque grown in vitro although resistance to these agents was also evident.     

Production of ferulic acid from lignocellulolytic agricultural biomass by Thermobifida fusca thermostable esterase produced in Yarrowia lipolytica transformant

A gene (axe) encoding the AXE thermostable esterase in Thermobifida fusca NTU22 was cloned into a Yarrowia lipolytica P01g host strain. Recombinant expression resulted in extracellular esterase production at levels as high as 70.94 U/ml in Hinton flask culture broth, approximately 140 times higher than observed in a Pichia pastoris expression system. After 72 h of fermentation by the Y. lipolytica transformant in the fed-batch fermentor, the fermentation broth accumulated 41.11 U/ml esterase activity. Rice bran, wheat bran, bagasse and corncob were used as hydrolysis substrates for the esterase, with corncob giving the best ferulic acid yield. The corncob was incubated with T. fusca xylanase (Tfx) for 12 h and then with the AXE esterase for an additional 12 h. Ferulic acid accumulated to 396 μM in the culture broth, a higher concentration than with esterase alone or with Tfx and esterase together for 24 h.     

Production of poly(3-hydroxybutyrate) from whey by fed-batch culture of recombinant Escherichia coli in a pilot-scale fermenter

Production of poly(3-hydroxybutyrate) [P(3HB)] from wheyby fed-batch culture of recombinant Escherichia coli CGSC 4401 harboring a plasmid containing the Alcaligenes latus polyhydroxyalkanoate (PHA) biosynthesis genes was examined in a 30 l fermenter supplying air only. With lactose below 2 g l^–1, cells grew to 12 g dry cell l^–1 with 9% (w/w) P(3HB) content. Accumulation of P(3HB) could be triggered by increasing lactose to 20 g l^–1. By employing this strategy, 51 g dry cell l^–1 was obtained with a 70% (w/w) P(3HB) content after 26 h. The productivity was 1.35 g P(3HB) l^–1 h^–1. The same fermentation strategy was used in a 300 l fermenter, and 30 g dry cell l^–1 with 67% (w/w) P(3HB) content was obtained in 20 h.     

Pilot scale production of poly(3-hydroxybutyrate-co-3-hydroxy-valerate) by fed-batch culture of recombinantEscherichia coli

Production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB/V)], by fed-batch culture of recombinantEscherichia coli harboring a plasmid containing theAlcaligenes latus polyhydroxyalkanoate (PHA) biosynthesis genes, was examined in two pilot-scale fermentors with air supply only. In a 30 L fermentor having aK _La value of 0.11 s⁻¹, the final P(3HB/V) concentration and the P(3HB/V) content obtained were 29.6 g/L and 70.1 wt%, respectively, giving a productivity of 1.37 g P(3HB/V)/L-h. In a 300 L fermentor having aK _La of 0.03 s⁻¹, the P(3HB/V) concentration and the P(3HB/V) content were 20.4 g/L and 69 wt%, respectively, giving a productivity of 1.06 g P(3HB/V)/L-h. These results suggest that economical production of P(3HB/V) is possible by fed-batch culture of recombinantE. coli in a large-scale fermentor having lowK _La value.     

多抗霉素染菌发酵罐批中分离抗杂菌高产菌株

探讨从多抗霉素染菌罐批中分离抗杂菌高产菌株的方法。经分离选育出抗杂菌高产株211^#、221^#两株。通过20吨级发酵罐实践表明：211^#、221^#菌株在正常罐批的发酵单位比对照分别提高12％和33％,在染茵罐批的发酵单位比对照分别提高14％和29％。     

脱色希瓦氏菌(Shewanella decolorationis) S12还原不同电子受体的厌氧发酵罐培养方法

脱色希瓦氏菌Shewanella decolorationisS12在厌氧环境下能够使用多种电子受体进行厌氧呼吸。为了取得足够的细胞量用于膜蛋白质组学等科学研究的需要,本研究选取无机小分子(硝酸钠)、金属离子(柠檬酸铁)和有机大分子(偶氮染料苋菜红)作为电子受体,在使用确定成分的无机盐培养基条件下,使用不同浓度的电子供体和碳源对S12进行厌氧条件下静置和发酵罐的优化培养,采用连续补充电子受体的培养方式,确认了电子供体和碳源的合适浓度,建立了S12厌氧发酵罐培养方法。相比传统的静置厌氧培养,厌氧发酵罐培养方法在保证了严格厌氧条件下高效率还原电子受体的同时,还极大的提高了细胞生长密度。连续补充电子受体的厌氧发酵罐培养的S12最大细胞密度最大分别可达到静置厌氧培养细胞密度的325,304,369倍,而生长时间也比静置厌氧培养分别缩短了26.5%,17.6%,7.5%。这为需要大量细胞和蛋白的细菌厌氧呼吸生长实验建立了可行方法,对于进行兼性厌氧呼吸的微生物的大规模厌氧培养具有借鉴意义。     

菊糖芽孢乳杆菌DS2-18中试规模的D-乳酸发酵研究

研究了菊糖芽孢乳杆茵DS2的突变株DS2-18在中试规模的D-乳酸发酵.在容积为300L自控发酵罐中,DS2-18茵在合适的发酵条件下,即培养基组成(g/L):葡萄糖120,玉米浆8,蛋白胨6,豆粕水解液100,接种量8%(v/v),发酵温度40℃,以轻质碳酸钙作为中和剂调pH 5～6,发酵期间交替不通气和通气,发酵6...