APPLIED AND ENVIRONMENTAL MICROBIOLOGY, Feb. 1984, p. 239-2440099-2240/84/020239-06$02.00/0Copyright © 1984, American Society for Microbiology

Vol. 47, No. 2

Application of a Microcomputer-Based System to Control andMonitor Bacterial Growth

JEFFREY A. TITUS,t GREGORY W. LULI,t MICHAEL L. DEKLEVA, AND WILLIAM R. STROHL*

Department of Microbiology, The Ohio State University, Columbus, Ohio 43210

Received 12 September 1983/Accepted 7 November 1983

A modular microcomputer-based system was developed to control and monitor various modes ofbacterial growth. The control system was composed of an Apple II Plus microcomputer with 64-kilobyterandom-access memory; a Cyborg ISAAC model 91A multichannel analog-to-digital and digital-to-analogconverter; paired MRR-1 pH, P02, and foam control units; and in-house-designed relay, servo control, andturbidimetry systems. To demonstrate the flexibility of the system, we grew bacteria under variouscomputer-controlled and monitored modes of growth, including batch, turbidostat, and chemostat systems.The Apple-ISAAC system was programmed in Labsoft BASIC (extended Applesoft) with an average

control program using ca. 6 to 8 kilobytes of memory and up to 30 kilobytes for datum arrays. This modularmicrocomputer-based control system was easily coupled to laboratory scale fermentors for a variety offermentations.

A general philosophy for datum acquisition and analysisfrom computer-controlled fermentation systems was devel-oped ca. 10 years ago (10). Since then, the use of computersfor datum acquisition and control of fermentation processeshas increased rapidly, particularly in industry (2, 5). Recent-ly, several research (7, 9, 11, 12) and review (2, 3, 5, 13)articles have appeared which describe various computer-assisted fermentation control systems. Most of these sys-tems have involved minicomputers such as the Digital Elec-tronics Corp. PDP 11 series (2, 3, 5, 11) or combined micro-and minicomputer hierarchical systems (5, 12). These areexcellent for industry or laboratories with large budgets butoffer little to most university facilities with limited space,budgets, and electrical engineering expertise.The use of microcomputers to control fermentation pro-

cesses was first suggested at the Dijon Conference in 1973,although many doubts about their applicability were ex-pressed (6). Hampel (3) stated in 1979 that computer controlof fermentations in biology laboratories is very limitedbecause biologists lack expertise in advanced programmingskills and electrical engineering. Also in 1979, Jefferies et al.(6) developed a single-circuit board microcomputer for con-trol of a fermentor, exemplifying the potential simplicitypossible for microcomputer fermentation control. Since thattime, commercial microcomputers have become reasonablypriced, increasingly popular, and more useful in microbio-logical laboratories. Moreover, many microbiologists arenow mastering BASIC computer language, a higher-levellanguage which is relatively easy to learn. These factors,coupled with the recent increase in availability of lessexpensive analog-to-digital (A/D) and D/A converters on themarket, should make it possible for more microbiologists toutilize microcomputers to control various processes, includ-ing fermentation. Hatch (5) recently stated that "the use ofmicrocomputers for control of instruments and experimentsis now receiving intense scrutiny." The use of microcomput-ers in fermentation processes has been usually limited tocombined micro- and minicomputer hierarchical systems (5,

* Corresponding author.t Present address: Bristol Laboratories, Syracuse, NY 13221.t Present address: Battelle Columbus Laboratories, Columbus,

OH 43210.

12). Recently, an Apple microcomputer was used to controlan enzyme electrode system via a D/A-A/D converter sys-tem (7). Thus, the use of microcomputers for independentfermentation control seemed to be the next logical step. Wedescribe here a relatively simple and inexpensive microcom-puter-coupled fermentation system which has the flexibilityand power to simultaneously acquire data from and controldifferent types of fermentation processes.

MATERIALS AND METHODSBacteria and media. Vibrio natriegens ATCC 14048 and

Bacillus thuringiensis DM-1 were used in this study. V.natriegens was grown at 37°C in a modification of M9medium (8) containing 1 or 10 mM glucose as the carbonsource. The medium was modified by the addition of 1.5%NaCl and filter-sterilized vitamins as follows (in microgramsliter-1): biotin, 130; folic acid, 130; pyridoxine, 665; thia-mine, 330; p-aminobenzoic acid, 330; riboflavin, 330; nico-tinic acid, 330; pantothenic acid, 330; vitamin B12, 330; andlipoic acid, 130. B. thuringiensis was grown at 32°C intryptose-phosphate broth consisting of the following (ingrams liter- ): tryptose (Difco Laboratories, Detroit,Mich.), 20; glucose, 2; NaCl, 5; and Na2HPO4, 2.5.

Fermentation hardware systems. Figure 1 shows the hard-ware setup for the microcomputer-assisted fermentationsystem. The central system consisted of an Apple II Plusmicrocomputer (64 K random-access memory) with a moni-tor (cathode ray tube) and dual disk drives and a CyborgISAAC model 91A multichannel A/D and D/A converter.ISAAC contains 16 channels of A/D input, 4 channels of D/Aoutput, 16 bits of binary input-output (digital I/O), and fourisolated Schmitt trigger switches. Four channels of D/Aoutput were added to expansion slot no. 7 of ISAAC,yielding eight total output channels. This gave the Apple-ISAAC system the capability to control, with feedback,eight analog systems, plus up to six binary (on-off) systems.The ISAAC system also contained 5-V (transistor-transistorlogic level) and 12-V outputs which could be used as powersources for certain functions or devices. Because ISAAC putout a latched 5-V signal on binary demand, a relay box wasconstructed containing eight separate optically isolated 5-Vrelays which opened or closed 115-V alternating current linevoltage. The relay box could be used for any control feature

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A C D

FIG. 1. Diagram of the microcomputer control hardware (not drawn to scale). The Braun MRR-1 fermentation control system included aP02 amplifier and controller (A), a foam controller (B), a pH amplifier and controller (C), and digital and strip chart displays (D). The Apple IIPlus microcomputer, cathode ray tube (CRT) monitor, disk drives 1 and 2, and ISAAC D/A-A/D converter were connected to thefermentation system via a junction box (E). Binary outputs (Ea) were used to activate 115-V alternating current circuits via the relay controlbox (F) to operate pumping systems (G) for the turbidostat. Analog outputs (Eb) were used to override various functions of the MRR-1 controlunit (top of figure) and operate the servo controller (H) of the agitation potentiometer. Various feedback parameters, such as the ICtemperature probe (1), the PO2 probe (J), the agitation feedback DC motor (K), the pH probe (L), and the CdS turbidimeter (M), wereconnected to the analog input channels of the junction box (Ec). These were sent to ISAAC for conversion to digital signals. A peristalticpump (N) provided the turbidimeter with a closed culture loop for continuous measurement of turbidity.

requiring the turning on and off of pumps, switches, orvalves.

Paired MRR-1 fermentation control units (B. Braun, Inc.,Burlingame, Calif.), each containing a strip chart recorderand PO2, pH, and foam controls, were connected to theApple-ISAAC system via the analog inputs. The MRR-1 pHand P02 control modules were overridden by the computerD/A output system according to the instruction manual forthe MRR-1 fermentation control units. To obtain the desiredcontrol sensitivity in the P02 module, the inputs and outputsof the P02 system were inverted to 0 to +5 V for use withISAAC (R. Bailey, B. Braun Instruments, Inc., personalcommunication). Ingold autoclavable dissolved oxygen po-tentiometric electrodes mounted in each fermentation vesselwere connected to the MRR-1 P02 controller to measuredissolved oxygen. Nonautoclavable Cple-Palmer sealed ep-oxy body pH electrodes (0.6 by 22 cm) were sterilized byovernight immersion in Chlorox solution (Chlorox Co.,Oakland, Calif.). Before they were mounted in the fermen-tors, the electrodes were aseptically washed with sterilewater. The pH electrodes were then mounted in 20-mlsyringe barrels that were fitted with rubber stoppers into thetop plates of the fermentor vessels (Fig. 1). Holes were cutthrough the syringes and their plunger seals to accommodatethe pH probes and hold them tightly in place. This was foundto adequately seal the assembly and fermentors againstcontamination. The pH and oxygen control systems of theMRR-1 fermentation control units shared a common ground

with the ISAAC A/D converter. For calibration of the pHand P02 controller systems of the computer program withthe MRR-1 fermentation control unit, values above andbelow the desired set point values were put into the comput-er before the fermentation run to set up standard curves. Theprogram contained algorithms to initiate and save the stan-dard calibration curves for each parameter and to computeobtained input values with them.A Harvard model 1203 peristaltic pump (Harvard Apparat-

us Co., South Natick, Mass.) was used for medium inlets tothe fermentors. Because the Harvard pumps are highlyaccurate and linearly calibrated, no direct feedback wasrequired on the pumping system. The pump was connectedto the relay box in which 5-V optically isolated relays,triggered by the 5-V binary outputs of ISAAC, were housed.The pump speed could be set at a given dilution rate, or ifsemicontinuous additions were desired, the changes couldbe made by altering the frequency of the pumping actionwith the binary output via the relay box. The number oftimes that the pump was turned on was recorded and savedin a special datum file by a counter function written into theLabsoft BASIC program.The primary control for dissolved oxygen, as monitored

by the computer via the MRR-1 P02 amplifier and controlmodules, was by the adjustment of agitation speeds between150 and 350 rpm. The agitation rate was controlled by servocontrollers (pulse width comparator motors used for radiocontrol models and available at local hobby stores; 0 to 1200

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turning radius over 2.5 to S V) attached to the agitationcontrol potentiometer. The analog- to-pulse width conver-sion for the servo control was based on the circuit describedby Wolfe (14). To provide feedback of the agitation rate, adirect current (DC) motor (Radio Shack no. 273-208) wasmechanically attached to the drive shaft of each fermentor.These DC motors generated an analog signal of ca. 0 to + 1 Vfor 0 to 500 rpm which was put into the Apple-ISAACsystem. The agitation feedback DC voltage to the computerwas calibrated against several mechanically determined agi-tation rates. Likewise, the servo controllers on the agitationpotentiometers were calibrated to between 50 and 500 rpmso that a certain voltage (analog) output from the computerwas reliably translated into the proper degree of turn for thedesired agitation rate. The secondary P02 control (althoughnever required for the runs shown here) was the airflow rate.This was regulated by a servo-controlled needle valve in theMRR-1 P02 module on command from the computer.Fermentor temperatures were monitored by a tempera-

ture-sensing integrated circuit (IC) probe (LM334; RadioShack no. 276-1734) which took a 12-V output voltage fromISAAC and a series of two resistors, a 220-f adjustableresistor which connected back to the IC, and a 10,000-flresistor connected to a ground according to instructionsprovided with the temperature sensor. The IC was coatedwith a silicone glue and was placed in an external tempera-ture well. The signal from the IC was connected to an A/Dinput channel of ISAAC and precalibrated against knowntemperatures of between 20 and 45°C.

Turbidity was measured either by a continuous flow cellused with a Spectronic 21 spectrophotometer (Bausch &Lomb, Inc., Rochester, N.Y.) or by a special laboratory-constructed turbidirieter. The turbidimeter worked by con-tinuously pumping culturd- through closed loops which ranthrough a dark box containing a 6-V light bulb and twoisolated CdS photoresistors (Radio Shack no. 276-116). Aglass tube (inside diameter, 10 mm) connected to the fermen-tor and pump via standd hosing was positioned betweenthe light and the CdS detector. A 5-V signal powered theCdS detector which essdntially acted as a variable resistor.As the cultures increased in density (thus diminishing theamount of light the CdS detector received), the resistanceincreased and the voltage decreased. Thus, the voltage inputto the computer was inversely related to the optical density.Standard curves also have been constructed to relate analogoutput from the CdS detectors to optical density.

Software system. The programming language used wasLabsoft, an extension of Applesoft BASIC, which wassupplied with ISAAC. The Labsoft software, containingunique commands differentiated from Applesoft by a preced-ing anipersand, was loaded into the Apple-ISAAC systembefore the actual fermentation program. The fermentationprogram, developed in our laboratory, is outlined by the flowdiagram in Fig. 2. Analog inputs from the various sensingdevices were fed into ISAAC via a junction box and wereconverted to digital values that were read by the Apple-ISAAC system. The Apple-ISAAC system was programmedto collect these values, log them in sequential datum files,and make decisions based upon them. Data were acquiredand saved by a series of averaging loops. The Apple-ISAACsystem took ca. 200 readings per s for each input sensor,averaged them, and checked the average against the pre-setpoint limits. If corrective measures were required, theproper D/A outputs were activated and the parameter wascorrected to pre-set point limits. The entire loop took ca. 10s, and those averages were constantly shown and updated

after each 10-s loop on the cathode ray tube monitor. After10 passes through the averaging loop (ca. 1.5-min total), the10 values were averaged, stored in a datum array, andconsidered as a datum point. Each datum point thus repre-sented the average of ca. 2,000 readings. The datum pointsfor each sensor were graphed on an NEC PC-8023A-C dotmatrix printer. The Apple-ISAAC system was programmedto accumulate 50 datum points for each of 10 functions andthen save them (ca. once every 76 min) on a datum file disk.It took the disk operating system ca. 2 min to save the 500datum points in 10 separate files, during which time thefermentors were not under computer control. This wasfound to be the best compromise which allowed both aminimum of lost control time and a maximum efficiency fordatum collection. The datum averaging and saving systemdescribed above was designed to accommodate both shortfermentation runs (i.e., <12 h) and long runs (>10 days) by avariable which changed the datum point times according tothe length of the run. The values shown were for a 48-h run.The data were later retrieved from the datum file disk withan in-house-modified Scientific Plotter (InteractiveMicroware, Inc., State College, Pa.) plotting program. Thus,the program was written so that the data could be viewed inthree ways. (i) They were continuously displayed and updat-ed every 10 s on the cathode ray tube monitor for aninstantaneous examination of the fermentation progress. (ii)They were printed every few minutes on a hard copy tofollow the progress of, and the changes in, the fermentationruns. (iii) They were stored on a standard 5.25-in. (ca. 13-cm)floppy disk for future retrieval and analysis.

Fermentation runs. For the experiments shown in Fig. 3,computer-controlled versus uncontrolled batch growth of B.thuringiensis was carried out in paired 14-liter (10-literworking volume) New Brunswick fermentors. These experi-ments tested the computer monitoring of temperature main-tenance at 32°C, P02 control by alteration of the agitationrate, pH control in both directions, foam control by theMRR-1 fermentation control units, and continuous monitor-ing of turbidity by a flow-through cell hooked to a Spectronic21 spectrophotometer set at 550 nm.The chemostat versus turbidostat experiments shown in

Fig. 4 were run with paired 1-liter (500-ml working volume)glass jar fermentors maintained at 37°C by a circulationwater bath. Agitation of the fermentors was carried out bystirring each sample with 1.5-in. (ca. 4-cm) stir bars, and theairflow rate was computer controlled via the MRR-1 P02controller. The Vibrio cultures were grown in monitored butuncontrolled batch culture to the mid-log phase. Then flowrate control (chemostat) versus turbidity feedback control(turbidostat) was initiated. The chemostat culture contained1 mM glucose for carbon limitation, and the turbidostatculture contained 10 mM glucose for excess carbon.

RESULTS AND DISCUSSION

Figure 3 shows results obtained from the modular micro-computer system for computer-monitored and -controlledversus computer-monitored (only) batch growth of B. thurin-giensis in paired 10-liter fermentors. These runs were typicalof several B. thuringiensis growth experiments performedwith this system in which the results were very reproducible.The optical densities of B. thuringiensis in the computer-controlled and uncontrolled vessels, as monitored by a

laboratory-constructed flow-through cell with the Spectronic21 spectrophotometer, were identical and reached finaldensities of ca. 0.43 absorbance unit after 21 h of fermenta-tion. In the computer-controlled vessel, the servo control on

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FIG. 2. Flow diagram of the fermentation control program. Control set points were entered by floppy disks or keyboard. The initial controlset points were saved on the file disk and used throughout the fermentation runs. During each command loop the data were stored in files ac-cording to the total elapsed time. A series of decision control loops then were accessed to control each parameter within the set point values.Each sensor was read and fed back to the computer via ISAAC for simple decisions. Changes made to the cultures (i.e., acid and baseadditions) were incremented by a program-internal increment counter. Cascade control is exemplified by the computer operation of the servosvia analog-to-pulse width (A-PW) converters to turn servos for agitation control.

the agitation potentiometer increased the agitation from aninitial set point of 150 rpm to a final rate of ca. 325 rpm tomaintain P02 above 50% of saturation. Because the agitationrate did not exceed the preset limit of 350 rpm, the airflowrate was not increased. Thus, the cascade control of dis-solved oxygen by agitation was sufficient to maintain the P02above the set point. Other experiments have shown that thesecondary p02-controlling mechanism, airflow, was activat-ed once the maximum preset agitation rate was achieved.The dissolved oxygen of the uncontrolled vessel declinedrapidly to 0% of saturation after ca. 8 h offermentation. Theagitation of the uncontrolled vessel was not altered but wasmonitored at a constant 200 rpm via the DC voltage-generating feedback motor. The pH of the uncontrolledvessel declined to 5.9, whereas the pH in the computer-controlled vessel was properly maintained between 7.0 and7.4 by base and acid additions, respectively. This demon-strated the ability of the on-line system to control and alterdissolved oxygen and pH while collecting, saving, printingout, and displaying the data. The temperature of both vesselswas measured and plotted by the computer at a constant 320Cvia the temperature-sensitive IC but was controlled externallyby the built-in heat exchanger of the 14-liter New Brunswickfermentation units. Although not shown in this study, thetemperature could be controlled for temperature shift experi-ments by attaching the servo control system described herein

to the potentiometer of the heat exchanger system.V. natriegens was grown in monitored but uncontrolled

defined medium batch cultures for ca. 5 h (Fig. 4). Thecomputer control was then initiated (first arrow, Fig. 4), andthe vibrios were subsequently grown in chemostat versusturbidostat cultures. The cultures responded to the set pointcommands given by the computer, and the chemostatreached the steady state after 10 to 12 h. The dilution rate ofthe chemostat was set at D = 0.48 h-'; thus, it took thevibrios about five to six residence times to reach the steadystate. The flow rate of the turbidostat was calculated to be350 ml/h, so Dturb = 0.7 h-1. The turbidostat did not reachthe steady state until ca. 25 h after the control was started(second arrow, Fig. 4). This may have been due to thechanges in dissolved oxygen which eventually stabilized.The dissolved oxygen lower limits for the chemostat andturbidostat were set at 80% of saturation, and the controlwas by MRR-1-regulated airflow. Enough growth occurredin the turbidostat to force control of the dissolved oxygen bythe MRR-1 airflow system (Fig. 4). Growth in the glucose-limited chemostat, however, was at a low enough level thatthe dissolved oxygen remained above 95% of saturation. ThepH of both the chemostat and the turbidostat was maintainedbetween the set points of 6.9 and 7.0. These experimentsdemonstrated that the simple and inexpensive turbidimetrysystem was sensitive enough to feedback control the turbi-

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TIME (hours)FIG. 3. Batch growth of B. thuringiensis in tryptose-phosphate

medium in fermentors with a 10-liter working volume. In one vesselthe following parameters were only monitored at preset values:dissolved oxygen (DO-U), agitation (RPM-U), and pH (pH-U). Thesecond vessel was computer controlled at 50% dissolved oxygen(DO-C) by increasing the agitation rate based on PO2 (RPM-C). ThepH (pH-C) was controlled via acid or base additions. Temperature(T) and culture turbidities (OD, optical density) were monitored (andwere identical) for both vessels.

dostat while simultaneously providing an on-line analysis ofthe steady state in both the chemostat and turbidostatsystems. The comparatively slow growth of the vibrio could

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TIME (hours)FIG. 4. V. natriegens was grown in modified M9 medium in

fermentors with a 500-ml working volume under batch conditions.Computer control for chemostat ( ) versus turbidostat (------)conditions was started after ca. 5 h of growth (small arrow). The pHfor both systems was controlled between 6.9 and 7.0. Culturedensities were monitored with CdS photoresistors and are repre-sented as arbitrary resistance units. The chemostat culture (OD-C)reached the steady state after ca. 15 h, whereas the turbidostatculture (OD-T) fluctuated with unstable dissolved oxygen conditions(DO-T) for ca. 20 h before entering steady-state conditions (largearrow).

probably be attributed to the defined medium in which it wasgrown.The power of the ISAAC-Apple system is that ISAAC

uses 12-bit D/A and A/D converters which give 4,096 digitalsteps over a 0- to 5-V analog signal. The analog parametersthus have a resolution of ca. 82 digital steps per every 100mV. Particularly when 0- to 1-V steps are used, such as withthe DC agitation feedback measurement, the resolutionoffered by the 12-bit converter is even more important.There are several inexpensive 8-bit converters available, butthey give a resolution equal to only 256 steps over either a 0-to 1- or 0- to 5-V analog signal. These converters would notoffer sufficient resolution to control fermentation processessuch as the types shown here.The microcomputer fermentation control package de-

scribed here obviously does not compete with the DEC PDP-11 series or any other mini- or combined micro- and mini-computer hierarchical fermentation control system. Instead,this system seems ideal for laboratories that are not able toafford or that do not require the power of a mini- or mainframe computer. We have shown microcomputer control ofthe basic functions needed to initiate process control onfer entations. The datum storage disks easily have enoughroon to save twice the maximum amount of data shownhere. The Apple-ISAAC system is also capable of handlingseveral more input-output variables than used here. Suchpossible functions could include substrate or product levelfeedback via enzyme electrodes (1) or exit gas analyses (4, 5,9, 11). These would allow for a more sophisticated level ofcontrol, i.e., material balances and respiratory quotient-typecontrol from on-line gas and substrate concentration mea-surements (13).Most of the control loops employed here were simple

algorithms in which the actual datum values were regularlychecked and updated against programmed set points. How-ever, one cascade loop, the control of dissolved oxygen viathe agitation rate (primary control) and then the airflow rate(secondary control), was included. This demonstrates thepotential for using the Apple-ISAAC system in severaldifferent types of fermentations. Moreover, the system isflexible enough that the algorithms and control loops couldbe used to control and monitor laboratory processes otherthan fermentations. The controlling modes used in this workwere of a relatively simple nature and demonstrated our firststeps toward microcomputer control of fermentation pro-cesses. We are now engaged in adding more high level-typecontrol processes, i.e., the controlled addition of mediumcomponents based on calculated values such as the respira-tory quotient or biomass balance as mentioned above. Oursystem would then meet criteria suggested by several inves-tigators for a "complete" computer-controlled fermentationlaboratory (4, 5, 13).One potential disadvantage of the Apple-ISAAC control

package is that programming is done with a BASIC interpret-er which results in slow program execution. Fermentationprocesses, however, require long time periods, and thespeed of BASIC execution has never been a factor in any ofour fermentation runs. The lack of problems with this isexemplified by the number of time-consuming averagingloops placed in the datum analysis and storage portion of theprogram. An advantage of the BASIC language is that manystudents and researchers already have acquired BASICprogramming skills or can learn them without difficulty.The Apple-ISAAC fermentation control package de-

scribed here offers a relatively inexpensive, reasonable, andrealistic alternative to small laboratories who wish to com-

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puter control fermentation processes. Although the systemhas certain limitations, particularly in datum storage, typicalfermentations such as those shown here offer no difficulties.We have also used this system to computer control longerand more complex antibiotic fermentations by certain strep-tomycetes, demonstrating once again its versatility at thelaboratory scale level. Furthermore, we have recentlylearned that other investigators are using the Apple-ISAACsystem for computer control of certain other fermentationsystems, such as the monitoring and set point control of gasadditions for anaerobic growth of Desulfovibrio sp. (D. J.Cork and F. K. Konan, Dev. Ind. Microbiol., in press).

ACKNOWLEDGMENTSDevelopment of this system has been supported in part by several

sources, including The Ohio State University Departments of Mi-crobiology and Biochemistry and the College of Biological Sciencesand a grant (PCM-8204778) from the National Research Foundationto W.R.S.We thank J. I. Frea for his suggestions about the CdS sensors,

L. M. Khoury for assistance with the figures, and S. Schlasner foradvice in preparation of this manuscript. We especially thank R. M.Pfister for his encouragement, support, and thoughtful discussionswhich led to the development of this project and this manuscript.The fermentation software programs, schematics of the alterationsmade to existing equipment, and schematics of our in-house-builtrelay systems are available upon request from W.R.S.

LITERATURE CITED1. Barker, A. S., and P. J. Somers. 1978. Enzyme electrodes and

enzyme based sensors, p. 120-151. In A. Wiseman (ed.), Topicsin enzyme and fermentation biotechnology, vol. 2. HalstedPress, Chichester, England.

2. Dobry, D. D., and J. L. Jost. 1977. Computer applications tofermentation operations, p. 95-114. In D. Perlman (ed.), Annualreports on fermentation processes, vol. 1. Academic Press,Inc., New York.

3. Hampel, W. A. 1979. Application of microcomputers in thestudy of microbial processes. Adv. Biochem. Eng. 13:1-33.

4. Harmes, C. S., III. 1972. Design criteria of a fully computerizedfermentation system. Dev. Ind. Microbiol. 13:146-156.

5. Hatch, R. T. 1982. Computer applications for analysis andcontrol of fermentation. Annu. Rep. Ferm. Proc. 5:291-311.

6. Jefferies, R. P., III, S. S. Klein, and J. Drakeford. 1979. Single-board microcomputer for fermentation control. Biotechnol.Bioeng. Symp. 9:231-239.

7. Kernevez, J. P., L. M. Konate, and J. L. Romette. 1983. Deter-mination of substrate concentrations by a computerized enzymeelectrode. Biotechnol. Bioeng. 25:845-855.

8. Maniatis, T., E. F. Fritsch, and J. Sambrook. 1982. Molecularcloning, a laboratory manual. Cold Spring Harbor Laboratory,Cold Spring Harbor, N.Y.

9. Mohler, R. D., P. J. Hennigan, H. C. Lim, G. T. Tsao, andW. A. Weigand. 1979. Development of a computerized fermen-tation system having complete feedback capabilities for use in aresearch environment. Biotechnol. Bioeng. Symp. 9:257-268.

10. Nyiri, L. K. 1972. A philosophy of data acquisition, analysis,and computer control of fermentation processes. Dev. Ind.Microbiol. 13:136-145.

11. Park, S. H., K. T. Hong, J. H. Lee, and J. C. Bae. 1983. On-lineestimation of cell growth for glutamic acid fermentation system.Eur. J. Appl. Microbiol. Biotechnol. 17:168-172.

12. Rolf, M. J., P. J. Hennigan, R. D. Mohler, W. A. Weigand, andH. C. Lim. 1982. Development of a direct digital-controlledfermentor using a microminicomputer hierarchical system. Bio-technol. Bioeng. 24:1191-1210.

13. Weigand, W. A. 1978. Computer applications to fermentationprocesses. Annu. Rep. Ferm. Proc. 2:43-72.

14. Wolfe, G. W. 1982. Computer peripherals that you can build.TAB Books, Blue Ridge Summit, Pa.

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