Tolerance to antimicrobial agents and persistence of Escherichia coli and cyanobacteria

Bacterial persistence is the tolerance of a small part of a cell population to bactericidal agents, which is attained by a suppression of important cell functions and subsequent deceleration or cessation of cell division. The growth rate is the decisive factor in the transition of the cells to the persister state. A comparative study of quickly growing Escherichia coli K-12 strain MC 4100 and cyanobacteria Synechocystis sp. PCC 6803 and Anabaena variabilis ATCC 29413 growing slowly was performed. The cyanobacterial cells, like E. coli cells, differed in sensitivity to antimicrobial substances depending on the growth phase. Carbenicillin inhibiting the synthesis of peptidoglycan, a component of the bacterial cell wall, and lincomycin inhibiting the protein synthesis gave rise to nucleoid decay in cells from exponential cultures of Synechocystis 6803 and did not influence the nucleoids in cells from stationary cultures. Carbenicillin suppressed the growth of exponential cultures and had no effect on cyanobacterial stationary cultures. A suppression of Synechocystis 6803 growth in the exponential phase by lincomycin was stronger than in the stationary phase. Similar data were obtained with cyanobacterial cells under the action of H2O2 or menadione, an inducer of reactive oxygen species production. Slowly growing cyanobacteria were similar to quickly growing E. coli in their characteristics. Persistence is a characteristic feature of cyanobacteria.     

Elemental and macromolecular plasticity of Chlamydomonas reinhardtii (Chlorophyta) in response to resource limitation and growth rate

With the ongoing differential disruption of the biogeochemical cycles of major elements that are essential for all life (carbon, nitrogen, and phosphorus), organisms are increasingly faced with a heterogenous supply of these elements in nature. Given that photosynthetic primary producers form the base of aquatic food webs, impacts of changed elemental supply on these organisms are particularly important. One way that phytoplankton cope with the differential availability of nutrients is through physiological changes, resulting in plasticity in macromolecular and elemental biomass composition. Here, we assessed how the green alga Chlamydomonas reinhardtii adjusts its macromolecular (e.g., carbohydrates, lipids, and proteins) and elemental (C, N, and P) biomass pools in response to changes in growth rate and the modification of resources (nutrients and light). We observed that Chlamydomonas exhibits considerable plasticity in elemental composition (e.g., molar ratios ranging from 124 to 971 for C:P, 4.5 to 25.9 for C:N, and 15.1 to 61.2 for N:P) under all tested conditions, pointing to the adaptive potential of Chlamydomonas in a changing environment. Exposure to low light modified the elemental and macromolecular composition of cells differently than limitation by nutrients. These observed differences, with potential consequences for higher trophic levels, included smaller cells, shifts in C:N and C:P ratios (due to proportionally greater N and P contents), and differential allocation of C among macromolecular pools (proportionally more lipids than carbohydrates) with different energetic value. However, substantial pools of N and P remained unaccounted for, especially at fast growth, indicating accumulation of N and P in forms we did not measure.     

The effect of alterations in the physical state of the membrane lipids on the ability of Acholeplasma laidlawii B to grow at various temperatures

The physical state of the membrane lipids, as determined by fatty acid composition and environmental temperature, has a marked effect on both the temperature range within which Acholeplasma laidlawii B cells can grow and on growth rates within the permissible temperature ranges. The minimum growth temperature of 8 °C is not defined by the fatty acid composition of the membrane lipids when cells are enriched in fatty acids giving rise to gel to liquid-crystalline membrane lipid phase transitions occurring below this temperature. The elevated minimum growth temperatures of cells enriched in fatty acids giving rise to lipid phase transitions occurring at higher temperatures, however, are clearly defined by the fatty acid composition of the membrane lipids. The optimum and maximum growth temperatures are also influenced indirectly by the physical state of the membrane lipids, being significantly reduced for cells supplemented with lower melting, unsaturated fatty acids. The temperature coefficient of growth at temperatures near or above the midpoint of the lipid phase transition is 16 to 18 $\text{kcal}\text{mol}$, but this value increases abruptly to 40 to 45 $\text{kcal}\text{mol}$ at temperatures below the phase transition midpoint. Both the absolute rates and temperature coefficients of cell growth are similar for cells whose membrane lipids exist entirely or predominantly in the liquid-crystalline state, but absolute growth rates decline rapidly and temperature coefficients increase at temperatures where more than half of the membrane lipids become solidified. Cell growth ceases when the conversion of the membrane lipid to the gel state approaches completion, but growth and replication can continue at temperatures where less than one tenth of the total lipid remains in the fluid state. An appreciable heterogeneity in the physical state of the membrane lipids can apparently be tolerated by this organism without a detectable loss of membrane function.     

Temperature dependence on the delayed fluorescence of chlorophyll a in blue-green algae.

1. The delayed fluorescence of chlorophyll a was measured with a phosphoroscope by changing the temperature in a range of room temperatures in intact cells of blue-green algae, Anacystis nidulans, two strains of Anabaena variabilis and Plectonema boryanum, and other kinds of algae, Cyanidium caldarium and Chlorella pyrenoidosa. The induction of delayed fluorescence remarkably depended on the temperature of measurment. Nevertheless, the induction pattern was characterized by three levels of intensity; the initial rise level at the onset of excitation light, the maximum level after a period of excitation and the steady-state level after 10 min of excitation. 2. In A. nidulans and a strain of A. variabilis grown at various temperatures, close relationship was found between the phase transition of membrane lipids and the initial rise and the steady-state levels of delayed fluorescence. The initial rise level showed the maximum at the temperature of phase transition between the liquid crystalline and the mixed solid-liquid crystalline states, The steady-state levels showed a remarkable change from a high in the liquid crystalline state to a low level in the mixed solid-liquid crystalline state. 3. The millisecond decay kinetics of the delayed fluorescence measured at the steady-state level in A. nidulans grown at 38 degrees C consisted of two components with different decay rates. The half-decay time of the fast component was about 0.17 ms and was constant throughout the temperature range of measurement. The half decay time of slow component ranged from 0.6 to 1.5 ms, depending on the temperature of measurment.     

Effects of temperature acclimation on Neurospora phospholipids. Fatty acid desaturation appears to be a key element in modifying phospholipid fluid properties

Experiments were conducted on the effect of growth temperature on phospholipids of Neurospora. Strains grown at high (37 degrees C) and low (15 degrees C) temperatures show large differences in the proportions of phospholipid fatty acid alpha-linolenate (18 : 3) which can vary by 10-fold over this temperature range. Changes in the phospholipid base composition are less dramatic; the most significant is an increase in phosphatidylethanolamines at low temperatures accompanied by a concomitant decrease in phosphatidylcholine. It appears that phospholipid fatty acid desaturation is closely regulated with respect to growth temperature. Over the 37 to 15 degrees C growth temperature range there appear to be at least two desaturase systems in Neurospora which are under different controls. Production of 18 : 1 and 18 : 2 species appears to occur at high levels over the entire temperature range, whereas the production of 18 : 3 seems to be inversely related to growth temperature. Shifting 37 degrees C-acclimated cultures to 15 degrees C produces a growth lag period of approximately 3 h, during which the level of 18 : 3 increases markedly. Differential scanning calorimetry of phospholipids from 37 degrees C cells shows a phase transition at -22 degrees C while lipids from 15 degrees C cultures exhibit a phase transition with reduced enthalpy at about -41 degrees C. The data are consistent with the idea that phospholipid composition in Neurospora is under strict control and suggest that membrane fluidity is regulated with respect to growth temperature through changes in membrane lipid composition.     

Growth and stoichiometry of a Catharanthus roseus cell suspension culture grown under nitrogen-limiting conditions

The uptake of carbohydrate and nitrate by Catharanthus roseus cell suspension cultures was studied in relation to biomass production in shake flasks. Biomass production was similar when using either 6, 12, 18, or 24 mM nitrate as the nitrogen source and 20 g L(-1) sucrose as the carbon source. In all cases, maximum biomass production was reached when carbohydrates were entirely consumer by the cells. Apparent biomass yields, Y(X/S) and Y(X/N) were 0.49 g biomass g(-1) glucose equivalent and 0.23 g biomass mmol(-1) nitrate, respectively. The determination of the cellular carbon-to-nitrogen ration (C/N ration) resulted in the identification of three district growth phases: an active growth phase, and accumulation phase, and a biomass decline phase (endogenous metabolism). The onset of the last two phases was correlated with nitrate and sugar of the last two phases was correlated with nitrate and sugar exhaustion, respectively. Balanced stoichiometric equations describing the active growth and accumulation phases were proposed based on elemental composition and ash content of the biomass. The stoichiometric equation related to the accumulation phase predicts that the available sugars are stored as starch- and lipid-like materials.     

The effect of growth temperature on the bioenergetics of photosynthetic algal cultures

Two photosynthetic algal cultures, one Chlorella vulgaris, and the other a Chlorogonium sp., were cultured under light limitations in chemostats. The effects of growth temperature on their energy yield and maintenance energy requirement were studied. It was observed that a lowering in temperature resulted in a lower maximum growth yield from the light energy, Y(G). This was attributed to two reasons. First, at low temperatures there was a change in the algal cell composition with more energy being expended to synthesize a higher biomass protein content. Secondly, at low temperatures, a cyanide-resistant respiratory pathway became operative which led to a decrease in the number of ATP being generated. The maintenance energy coefficient was a function of temperature increasing with decreasing temperature. This might reflect energy wastage by the cell at low temperatures. The maximum specific growth rate dropped with decreasing temperature, and can be described by an Arrhenius type rate-temperature model up to the optimal temperature for growth; i.e., activation energy remained constant.     

Influence of Temperature and Methyl Jasmonate on Scenedesmus Incrassulatus

The effect of the methyl ester of jasmonic acid (MeJA) in 10 M concentration was studied on the development of the bacterial contaminants and on the content of some metabolites in Scenedesmus incrassulatus cultivated at temperatures 15, 20, 25, 30, and 36 °C. The number of bacteria on algae cells increased with the rise in temperature. Application of MeJA into nutrient medium inhibited the development of bacterial pathogens more than 3 times at 20 °C, 2.3 times at 30 °C, and 2.6 times at 36 °C without changing the species composition. MeJA caused an increase of the protein content in algae cells. The contents of palmitic and linoleic acids increased with the rise of temperature from 15 to 36 °C. At the same time the contents of linolenic and oleic acid decreased. At low temperatures, cultivation with MeJA induced more significant changes in the composition of C18 acids while at high temperature the changes were more pronounced in C16 acids. Treatment with MeJA decreased the activity of glutamate dehydrogenase at optimal and suboptimal temperatures and increased it at superoptimal temperature. Hence MeJA jasmonate had a positive effect on the tolerance of S. incrassulatus to stress temperatures, which was also demonstrated by better growth.     

Enriching Rotifers with “Premium” Microalgae. Nannochloropsis gaditana

The nutritive quality of Nannochloropsis gaditana cultured semicontinuously with different daily renewal rates was tested as a diet for short-term enrichment of the rotifer Brachionus plicatilis. After 24 h, dramatic differences in the survival, dry weight, and biochemical composition of the rotifers depending on the renewal rate of microalgal cultures were observed. Survival after the feeding period increased with increasing renewal rates. Rotifers fed microalgae from low renewal rate, nutrient-deficient cultures showed low dry weight and organic contents very similar to those of the initial rotifers that were starved for 12 h before the start of the feeding period. On the contrary, rotifers fed nutrient-sufficient microalgal cells underwent up to twofold increases of dry weight and protein, lipid, and carbohydrate contents with regard to rotifers fed nutrient-depleted N. gaditana. Consequently, feed conversion rate decreased in these conditions, indicating a better assimilation of the microalgal biomass obtained at high renewal rates. No single microalgal biochemical parameter among those studied can explain the response of the filter feeder. Similarly to gross composition, EPA and n-3 contents in rotifers fed microalgae from nutrient-sufficient cultures were double than the contents found in rotifers fed nutrient-limited microalgae. In addition, very high positive correlations between the contents of EPA and n-3 in N. gaditana and B. plicatilis were observed. These results demonstrate that selecting the appropriate conditions of semicontinuous culture can strongly enhance the nutritional value of microalgae that is reflected in the growth and biochemical composition of the filter-feeder even in short exposure periods.     

RESPONSE OF TRACHYDISCUS MINUTUS (XANTHOPHYCEAE) TO TEMPERATURE AND LIGHT1

The effects of different temperatures and light intensities on growth, pigments, sugars, lipids, and proteins, as well as on some antioxidant and proteolytic enzymes of Trachydiscus minutus (Bourr.) H. Ettl, were investigated. The optimum growth temperature and light intensity were 25°C and 2 × 132 μmol photons · m^?2 · s^?1, respectively. Under these conditions, proteins were the main biomass components (33.45% dry weight [dwt]), with high levels of carbohydrates (29% dwt) and lipids (21.77% dwt). T. minutus tolerated temperatures between 20°C and 32°C, with only moderate changes in cell growth and biochemical composition. Extremely low (15°C) and high (40°C) temperatures decreased chl and RUBISCO contents and inhibited cell growth. The biochemical response of the alga to both unfavorable conditions was an increase in lipid content (up to 35.19% dwt) and a decrease in carbohydrates (down to 13.64% dwt) with much less of a change in total protein content (in the range of 30.51%–38.13% dwt). At the same time, the defense system of T. minutus was regulated differently in response to heat or cold treatments. Generally, at 40°C, the activities of superoxide dismutase (SOD), catalase (CAT), and proteases were drastically elevated, and three polypeptides were overexpressed, whereas the glutathione reductase (GR) and peroxidase (POD) activities were reduced. In contrast, at 15°C, all these enzymes except GR were suppressed. The effect of light was to enhance or decrease the temperature stress responses, depending on intensity. Our studies demonstrate the broad temperature adaptability of T. minutus as well as the potential for the production of valuable algal biomass.     

养分异质条件下结缕草克隆分株生长、碳水化合物及可溶性蛋白的生理整合

通过对连接和断开的结缕草分株进行不同的养分处理,研究了养分异质条件下结缕草克隆分株生长、碳水化合物及可溶性蛋白含量的变化.结果表明: 在养分异质条件下,处于中、高养分水平的母株可以显著提高与其相连子株的地上、地下及总生物量,高养分下分别提高32.5%、22.1%和24.8%,降低根冠比、可溶性糖及非结构性碳水化合物(NSC)含量,高养分下分别降低7.7%、15.2%和13.1%,但是对淀粉、纤维素、可溶性蛋白含量无显著影响.处于中、高养分水平的子株对与其相连的母株生长、碳水化合物及可溶性蛋白含量没有显著影响.养分异质条件下结缕草母株对子株生物量、根冠比、可溶性糖及NSC含量有明显的生理整合,其整合强度与养分梯度呈正比,而对淀粉、纤维素及可溶性蛋白含量没有显现显著的生理整合效应.子株对母株各项指标都没有显著的生理整合,结缕草母株和子株间是一种单向的生理整合.     

Effect of growth temperature on lipid and fatty acid compositions in the blue-green algae, Anabaena variabilis and Anacystis nidulans.

The lipid composition was affected by growth temperature in Anacystis nidulans, but was not in Anabaena variabilis. A. variabilis contained fatty acids of 18 and 16 carbon atoms, which were localized at 1- and 2-positions, respectively, of the glycerol moiety of lipids. Desaturation of C18 acids was affected by the growth temperature. A. nidulans contained fatty acids of 14, 16 and 18 carbon atoms. Monounsaturated and saturated acids were esterified mainly to 1- and 2-position, respectively. Desaturation and chain length of fatty acids were influenced by the growth temperature. The variations in lipid and fatty acid compositions with the growth temperature are discussed in relation to the growth temperature-dependent shift of thermotropic phase transition temperature of the membrane lipids in the blue-green algae.     

六种固氮蓝藻提取液对玉米的促长作用和提取液成分比较

本文用六种固氮蓝藻的提取液处理玉米种子,同时对其提取液氨基酸组成和碳水化合物与维生素Ｂ１２的含量进行了分析。结果表明固氮鱼腥藻ＨＢ６８６（ＡｎａｂａｅｎａａｚｏｔｉｃａＨＢ６８６）、球孢鱼腥藻ＨＢ１０１７（Ａ．ｓｐｈａｅｒｉｃａＨＢ１０１７）、多变鱼腥藻ＨＢ１０５８（Ａ．ｖａｒｉａｂｉｌｉｓＨＢ１０５８）和小单歧藻ＨＢＴＴ（ＴｏｌｙｐｏｔｈｒｉｘｔｅｎｕｉｓＨＢＴＴ）的提取液中氨基酸、碳水化合物和维生素Ｂ１２的含量高于鱼腥藻ＳＰ．ＨＢ１０４２（Ａｎａｂａｅｎａｓｐ．ＨＢ１０４２）和繁育管链藻ＨＢ３８（ＡｕｌｏｓｉｒａｆｅｒｔｉｌｉｓｓｉｍａＨＢ３８）。同时,促进玉米种子萌发和幼苗生长的效果前四种藻较好,后两种则较差。     

Changes in Membrane Lipid Composition in Exponentially Growing Staphylococcus aureus During the Shift from 37 to 25 C

Lowering the temperature of growth of Staphylococcus aureus from 37 to 25 C decreased the growth rate and induced changes in the composition of the membrane lipids. Changes in lipid composition also occur in the transition between exponential and stationary growth phases at one temperature. To isolate the effects of lowering the temperature, exponentially growing S. aureus was abruptly switched from 37 to 25 C by transfer to cooler medium. Exponential growth continued at 25 C without a lag period but with a threefold increase in doubling time. In the period of exponential growth at suboptimal temperature, there was essentially no change in the fatty acid composition of the lipids, little change in the vitamin K(2) composition with perhaps a slight increase in the total level, and essentially no change in the phospholipid composition, but a marked stimulation of the synthesis of the rubixanthins. Growth of cells at 25 C was much more sensitive to the inhibition of rubixanthin formation by mixed-function oxidase inhibitors than cells growing at 37 C, suggesting some function for the rubixanthins at suboptimal temperatures. The striking increases in the proportions of monoenoic fatty acids observed at lowered growth temperatures in many biological systems are not detected in S. aureus.     

Elemental balancing of biomass and medium composition enhances growth capacity in high-density Chlorella vulgaris cultures

The basic requirements for high-density photoautotrophic microalgal cultures in enclosed photobioreactors are a powerful light source and proper distribution of light, efficient gas exchange, and suitable medium composition. This article introduces the concept of balancing the elemental composition of growth medium with biomass composition to obtain high-density cultures. N-8 medium, commonly used for culturing Chlorella vulgaris was evaluated for its capacity to support high-density cultures on the basis of elemental stoichiometric composition of C. vulgaris. This analysis showed that the N-8 medium is deficient in iron, magnesium, sulfur, and nitrogen at high cell densities. N-8 medium was redesigned to contain stoichiometrically balanced quantities of the four deficient elements to support a biomass concentration of 2% (v/v). The redesigned medium, called M-8 medium, resulted in up to three- to fivefold increase in total chlorophyll content per volume of culture as compared to N-8 medium. Further experiments showed that addition of each of the four elements separately to N-8 medium did not improve culture performance and that balanced supplementation of all four deficient elements was required to yield the improved performance. Long-term (24 d) C. vulgaris culture in M-8 medium showed continuous increase in chlorophyll content and biomass throughout the period of cultivation. In contrast, the increase in chlorophyll content and biomass ceased after 7 and 12 d, respectively in N-8 medium, demonstrating the higher capacity of M-8 medium to produce biomass. Thus, the performance of high cell density photobioreactors can be significantly enhanced by proper medium design. The elemental composition of the biomass generated is an appropriate basis for medium design.     

The effect of growth temperature on the thermotropic behavior of the membranes of a thermophilic Bacillus. Composition-structure-function relationships

The following study was carried out with the aim of widening our understanding of the thermoadaptive mechanisms of the membrane of thermophiles, using Bacillus stearothermophilus var. nondiastaticus as test-organism. The phospholipids and their acyl chain composition of this Bacillus studied in relation to the physical properties of its membrane from bacteria grown at various temperatures. Phospholipids account for 68-75 weight% of the total lipid in cells grown at 45, 55 or 65 degrees C. Phosphatidylglycerol and diphosphatidylglycerol constitute up to 90% of the total phospholipids; no amino phospholipids were found. Increasing the growth temperatures from 45 degrees to 65 degrees C caused an approximately 4-fold decrease in the proportion of the branched-chain fatty acids and a 2-fold increase in the amount of the saturated acyl chains. The reduced proportion of the branched fatty acids was mainly due to a decrease in their anteiso forms. Unsaturated fatty acids were not produced by cells grown at 65 degrees C. In accordance with the fatty acid composition, the molecular packing of phospholipids in monolayers was more expanded with phospholipids from 45 degrees C grown cells as compared with cultures grown at 55 degrees C. The thermotropic gel to liquid-crystalline phase transition of the membrane lipids was monitored by differential scanning calorimetry and fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene. With increase of the growth temperature the phase transition was progressively shifted to higher but narrower range of temperatures. Completion of the lipid melting occurred always at temperatures below those employed for growth. A constructed phase diagram enabled to relate the growth temperature, the fatty acid composition and the lipid apparent microviscosity at temperatures not used in the present study for growth of the thermophile. The minimum temperature for growth and the upper boundary temperature of the least saturated lipid crystallization were extrapolated in this manner; they correspond to the experimentally determined minimal growth temperature. The apparent microviscosity, a measure of membrane order, decreased gradually and conspicuously as the growth temperature was elevated. The delimiting apparent microviscosity values, at the maximal (65 degrees C) and minimal (41 degrees C) growth temperatures were 0.8 and 1.8 poise, respectively. This lack of rigorous homeostatic control of the bulk lipid viscosity prompted reevaluation of the physiological significance of 'homeoviscous adaptation' in Bacillus stearothermophilus.     

Continuous culture of Candida utilis: influence of medium nitrogen concentration

When Candida utilis was grown in continuous culture, decreasing the concentration of N in the medium affected cell composition, biomass yield, biomass productivity, maximal growth rate and cell morphology. When the dilution rate was low (0.1 h^-1), reducing N from 1100 to 100 mg/l led to a 40% decrease in RNA content of the cells. Nitrogen-limited growth, which occurred when N<420 mg/l, was associated with significant changes in cell-wall carbohydrates and a significant reduction in the glycogen content of the cells. A set of culture conditions was established which permitted maximal consumption of the main nutrients in the medium and the production of yeast biomass suitable as a source of single-cell protein.     

Effect of catholyte in culture media on cell growth at extreme temperatures]

The growth of Escherichia coli cells in media whose properties were changed by the action of direct current in the cathode compartment of a diaphragm electrolyzer was studied. For this purpose, the growth medium was preliminarily treated using different method of medium preparation under different treatment conditions. The biological activity of medium was estimated by measuring the effect of these solutions on cell growth. Cells were cultivated under extremal temperature conditions, 20 degrees C and 42 degrees C (optimal temperature 37 degrees C). It was shown that at low temperatures, the cell growth considerably increases as compared to control. At elevated temperatures, the acceleration of cell death occurred, whereas in the control the deceleration of cell growth and partial cell death were observed.     

Optimal conditions for the expression of a single-chain antibody (scFv) gene in Pichia pastoris

A Pichia pastoris system was used to express a single-chain antibody (scFv) targeted against Mamestra configurata (bertha armyworm) serpins. To improve scFv production we examined parameters such as proteinase activity, temperature, cell density, osmotic stress, medium composition, pH, and reiterative induction. P. pastoris was found to express several proteases; however, adjustment of medium pH to limit their activity did not correlate with increased scFv recovery. Induction medium pH values of 6.5-8.0 were most conducive to scFv production, despite significant differences in cell growth rates. Increasing inoculum density limited growth potential but gave rise to higher levels of scFv production. Three factors, medium composition, pre-induction osmotic stress, and temperature, had the greatest effects on protein production. Supplementation of the induction medium with arganine, casamino acids, or EDTA increased scFv production several fold, as did cultivation under osmotic stress conditions during pre-induction biomass accumulation. Incubation at 15 versus 30 degrees C extended the period whereby cells were capable of producing scFv from 1 to 7 days. Under optimal conditions, yeast cultures yielded 25 mg/L of functional scFv and could be subject to five reiterative inductions.     

Rapid algal culture diagnostics for open ponds using multispectral image analysis

This article presents a multispectral image analysis approach for probing the spectral backscattered irradiance from algal cultures. It was demonstrated how this spectral information can be used to measure algal biomass concentration, detect invasive species, and monitor culture health in real time. To accomplish this, a conventional RGB camera was used as a three band photodetector for imaging cultures of the green alga Chlorella sp. and the cyanobacterium Anabaena variabilis. A novel floating reference platform was placed in the culture, which enhanced the sensitivity of image color intensity to biomass concentration. Correlations were generated between the RGB color vector of culture images and the biomass concentrations for monocultures of each strain. These correlations predicted the biomass concentrations of independently prepared cultures with average errors of 22 and 14%, respectively. Moreover, the difference in spectral signatures between the two strains was exploited to detect the invasion of Chlorella sp. cultures by A. variabilis. Invasion was successfully detected for A. variabilis to Chlorella sp. mass ratios as small as 0.08. Finally, a method was presented for using multispectral imaging to detect thermal stress in A. variabilis. These methods can be extended to field applications to provide delay free process control feedback for efficient operation of large scale algae cultivation systems. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 30:233–240, 2014