Effects of Low Temperature, Light and O2 on Chilling-sensitive and -resistant Strains in Chlorella ellipsoidea

A low-temperature sensitive strain, Chlorella ellipsoidea Gerneck(IAM C-102), lost its chilling sensitivity during preservation.Cells of the original strain (low-temperature sensitive) andthe variant (low-temperature resistant) were both synchronouslygrown under a 14-hr light-10-hr dark regime. In the originalstrain, cells at the D-L stage (transient phase) were most sensitiveto a low temperature, whereas the variant cells were not damagedat any stage. During low-temperature treatment, the viability of D-L cellsin the sensitive strain decreased after a lag period of 1 hr.The O₂-uptake activity (respiration) showed the same behavioras the viability, whereas the O₂-evolution activity (photosynthesis)decreased from the start of chilling. In the resistant strain,only O₂ evolution decreased. The decreased activity was restoredwhen the chilled cells were incubated at 25°C. This restorationwas inhibited by oligomycin. Lowering the light intensity or eliminating O2 diminished thechilling injury of the sensitive strain. The results indicatethat the chilling injury of Chlorella results from the combinedeffects of low temperature, light and O₂. (Received September 26, 1980; Accepted March 23, 1981)     

桃叶片抗冷性对光周期诱导休眠的响应

以6年生“春捷”桃树为试材,以自然生长的桃树为对照,研究了长日照和短日照的休眠诱导效应和休眠诱导进程中叶片抗冷性对光周期的响应.结果表明: 在逐渐降低的自然环境温度下,长日照和短日照处理树体均能进入休眠诱导期,其中长日照处理延后1周而短日照处理提前1周进入.随着休眠程度的加深,各处理叶片的总含水量、自由水含量降低,束缚水含量、束缚水/自由水比值升高.超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性在休眠诱导期内均呈单峰曲线,高峰值出现在休眠诱导期的后期,过氧化物酶(POD)活性进入休眠诱导期后迅速下降,后期回升形成小高峰.休眠诱导期内可溶性蛋白含量稳步下降,脯氨酸和丙二醛(MDA)含量持续升高,伤害率逐渐增大.长日照可显著提高SOD、CAT活性及脯氨酸含量,减缓POD活性和可溶性蛋白含量的降幅,降低MDA和伤害率的增幅.这表明长日照处理叶片受伤害程度更轻,而短日照处理相应指标的变化则不同,尤其诱导期后期叶片的伤害率显著高于对照,表现出较低的抗冷性.如果环境温度允许,实际生产中可以适当延长光照时间来提高叶片的抗冷性.     

Resistance to ciprofloxacin by enhancement of antioxidant defenses in biofilm and planktonic Proteus mirabilis

Antibiotic resistance and antioxidant defense were induced by ciprofloxacin in planktonic Proteus mirabilis and compared with the natural antibiotic resistance of biofilm. Resistant variants (1X and 1Y) were obtained from cultures of the sensitive wild type “wt” strain 1 in the presence of the antibiotic. Planktonic strain 1 exhibited oxidative stress with increases in the reactive oxygen species (ROS) and consumption of NO in the presence of ciprofloxacin, whereas 1X and 1Y suffered non-significant rises in ROS generation, but produced and consumed more NO than sensitive strain 1. The two resistant variants were more resistant to telluride than wt and showed increased levels of intracellular superoxide dismutase (SOD) and glutathione (GSH). However, ciprofloxacin did not stimulate oxidative stress in biofilm. The production of ROS and NO with or without ciprofloxacin was less significant in biofilms than in an equivalent number of planktonic bacteria; sensitive and resistant strains did not present differences. On the other hand, SOD and GSH were more elevated in the biofilm than in planktonic bacteria. In summary, these results indicate that ciprofloxacin can induce resistance by the enhancement of antioxidant defense in planktonic bacteria, similar to the natural resistance occurring in biofilm. This feature may be added to the factors that regulate the susceptibility to this antibiotic.     

Analysis of growth phase regulated KatA and CatE and their physiological roles in determining hydrogen peroxide resistance in Agrobacterium tumefaciens

Agrobacterium tumefaciens possesses two catalases, a bifunctional catalase-peroxidase, KatA and a homologue of a growth phase regulated monofunctional catalase, CatE. In stationary phase cultures and in cultures entering stationary phase, total catalase activity increased 2-fold while peroxidase activity declined. katA and catE were found to be independently regulated in a growth phase dependent manner. KatA levels were highest during exponential phase and declined as cells entered stationary phase, while CatE was detectable at early exponential phase and increased during stationary phase. Only small increases in H2O2 resistance levels were detected as cells entering stationary phase. The katA mutant was more sensitive to H2O2 than the parental strain during both exponential and stationary phase. Inactivation of catE alone did not significantly change the level of H2O2 resistance. However, the katA catE double mutant was more sensitive to H2O2 during both exponential and stationary phase than either of the single catalase mutants. The data indicated that KatA plays the primary role and CatE acts synergistically in protecting A. tumefaciens from H2O2 toxicity during all phases of growth. Catalase-peroxidase activity (KatA) was required for full H2O2 resistance. The expression patterns of the two catalases in A. tumefaciens reflect their physiological roles in the protection against H2O2 toxicity, which are different from other bacteria.     

Some growth and metabolic characteristics of monensin-sensitive and monensin-resistant strains of Prevotella (Bacteroides) ruminicola.

New strains with enhanced resistance to monensin were developed from Prevotella (Bacteroides) ruminicola subsp. ruminicola 23 and P. ruminicola subsp. brevis GA33 by stepwise exposure to increasing concentrations of monensin. The resulting resistant strains (23MR2 and GA33MR) could initiate growth in concentrations of monensin which were 4 to 40 times greater than those which inhibited the parental strains. Resistant strains also showed enhanced resistance to nigericin and combinations of monensin and nigericin but retained sensitivity to lasalocid. Glucose utilization in cultures of the monensin-sensitive strains (23 and GA33) and one monensin-resistant strain (23MR2) was retarded but not completely inhibited when logarithmic cultures were challenged with monensin (10 mg/liter). Monensin challenge of cultures of the two monensin-sensitive strains (23 and GA33) was characterized by 78 and 51% decreases in protein yield (milligrams of protein per mole of glucose utilized), respectively. Protein yields in cultures of resistant strain 23MR2 were decreased by only 21% following monensin challenge. Cell yields and rates of glucose utilization by resistant strains GA33MR were not decreased by challenge with 10 mg of monensin per liter. Resistant strains produced greater relative proportions of propionate and less acetate than the corresponding sensitive strains. The relative amounts of succinate produced were greater in cultures of strains 23, GA33, and 23MR2 following monensin challenge. However, only minor changes in end product formation were associate with monensin challenge of resistant strain GA33MR. These results suggest that monensin has significant effects on both the growth characteristics and metabolic activities of these predominant, gram-negative ruminal bacteria.     

Some growth and metabolic characteristics of monensin-sensitive and monensin-resistant strains of Prevotella (Bacteroides) ruminicola.

New strains with enhanced resistance to monensin were developed from Prevotella (Bacteroides) ruminicola subsp. ruminicola 23 and P. ruminicola subsp. brevis GA33 by stepwise exposure to increasing concentrations of monensin. The resulting resistant strains (23MR2 and GA33MR) could initiate growth in concentrations of monensin which were 4 to 40 times greater than those which inhibited the parental strains. Resistant strains also showed enhanced resistance to nigericin and combinations of monensin and nigericin but retained sensitivity to lasalocid. Glucose utilization in cultures of the monensin-sensitive strains (23 and GA33) and one monensin-resistant strain (23MR2) was retarded but not completely inhibited when logarithmic cultures were challenged with monensin (10 mg/liter). Monensin challenge of cultures of the two monensin-sensitive strains (23 and GA33) was characterized by 78 and 51% decreases in protein yield (milligrams of protein per mole of glucose utilized), respectively. Protein yields in cultures of resistant strain 23MR2 were decreased by only 21% following monensin challenge. Cell yields and rates of glucose utilization by resistant strains GA33MR were not decreased by challenge with 10 mg of monensin per liter. Resistant strains produced greater relative proportions of propionate and less acetate than the corresponding sensitive strains. The relative amounts of succinate produced were greater in cultures of strains 23, GA33, and 23MR2 following monensin challenge. However, only minor changes in end product formation were associate with monensin challenge of resistant strain GA33MR. These results suggest that monensin has significant effects on both the growth characteristics and metabolic activities of these predominant, gram-negative ruminal bacteria.     

外源水杨酸对低温下杏花抗氧化酶和CBF转录因子表达的影响

为探讨水杨酸（SA）对杏花抗寒性的影响机制,以早熟品种‘骆驼黄’杏的显蕾期花枝为试材,分析–2℃的低温下适宜浓度SA及其抑制剂ABT和PAC对杏花MDA、抗氧化酶和CBF转录因子的影响。结果表明,–2℃低温条件下,对照和2个SA抑制剂处理的杏花细胞膜系统均受到严重伤害,CAT、POD和SOD等抗氧化酶活性降低,MDA含量明显升高。而SA预处理的杏花在低温胁迫期间抗氧化酶活性增强,MDA含量比对照和抑制剂处理的有明显降低且相对稳定。通过荧光定量检测CBF转录因子的表达水平,表明SA能诱导杏花CBF基因的表达,尤其在低温处理3 h时,SA预处理的杏花中CBF的表达量明显高于对照和SA抑制剂处理。由此认为,适宜浓度的外源SA可能是通过调控低温下杏花中CBF转录因子的表达、增强细胞的抗氧化酶活性,减轻低温造成的膜脂过氧化伤害,从而在一定程度上增强了杏花的抗寒性。     

The role of surface polysaccharide in determining the resistance of Serratia marcescens to serum killing

Two O14:H12 strains of Serratia marcescens with different sensitivities to killing by normal pooled human serum were investigated. Complement binding, studied by measuring hydrophobicity and using rocket immunoelectrophoresis with anti-human C3, showed the sensitive cells (S1220) rapidly bound and fixed complement whereas the resistant cells (4444-60) bound less C3b. The strains had identical membrane protein composition. Crossed immunoelectrophoresis suggested that in S1220 cells the polysaccharide material including LPS was less antigenic and present in smaller amounts than in 4444-60 cells. This was confirmed by examining extracted polysaccharide material chemically and by SDS-PAGE. The resistant strain had 33% more phenol-extractable polysaccharide material than the sensitive strain, possibly comprising LPS with longer O antigen chain lengths, or a microcapsule of O antigen polysaccharide. Extra polysaccharide material on the surface of the resistant strain prevents complement components binding and reaching the hydrophobic membrane where lytic lesions occur.     

Growth on ethanol results in co-ordinated Saccharomyces cerevisiae response to inactivation of genes encoding superoxide dismutases

Superoxide dismutase (SOD) is an essential enzyme protecting cells against oxidative stress. However, its specific role under different conditions is not clear. To study the possible role of SOD in the cell during respiration, Saccharomyces cerevisiae single and double mutants with inactivated SOD1 and/or SOD2 genes growing on ethanol as an energy and carbon source were used. Activities of antioxidant and associated enzymes as well as the level of protein carbonyls were measured. SOD activity was significantly higher in a Mn-SOD deficient strain than that in the wild-type parental strain, but significantly lower in a Cu, Zn-SOD mutant. A strong positive correlation between SOD and catalase activities (R(2) = 0.99) shows possible protection of catalase by SOD from inactivation in vivo and/or decrease in catalase activity because of lower H(2)O(2) formation in the mutant cells. SOD deficiency resulted in a malate dehydrogenase activity increase, whereas glucose-6-phosphate dehydrogenase (G6PDH) activity was lower in SOD-deficient strains. Linear and non-linear positive correlations between SOD and isocitrate dehydrogenase activities are discussed. No changes in the activity of glutathione reductase and protein carbonyl levels support the idea that SOD-deficient cells are not exposed to strong oxidative stress during exponential growth of yeast cultures on ethanol.     

Effect of Cold Temperatures on the Viability of Chromobacterium violaceum

The effect of low, nonfreezing temperatures on the viability of five strains of Chromobacterium violaceum was studied. The viability of cultures grown at 30 C was determined after exposure to various diluents held at 0 to 2 C. A culture diluted at its growth temperature served as the control. Cells of strain N were most sensitive in the early part of the exponential phase of growth. Cells of strains 252 and 341 were most sensitive in the late exponential, early stationary phase of growth. Cells of strain 9 showed greatest loss of viability during the maximal stationary phase. Strain 69 was completely resistant throughout its growth cycle to cold injury. Cell viability was much greater in buffered salts solution than in distilled water, broth, or physiological saline, whether cultures were diluted at room temperature or in the cold. The proportion of cells surviving after exposure to cold, however, was the same regardless of the composition of the diluent. Loss of viability was progressive at 0 to 2 C and reached a maximum after 2 hr. There was no loss of viability of cells exposed to 20 C, but there was some loss at 12 C. Strain 341 cultivated at 15 C was much less sensitive to 0 to 2 C than when it was cultivated at 30 C. The composition of the growth medium seemed to have no effect on the survival of cells exposed to cold. The polyamines, spermine and trimethylenediamine, as well as erythritol and sucrose, exerted some protective action against the effects of cold but not uniformly for all strains studied.     

红酵母的抗氧化机制与高产类胡萝卜素菌株的筛选*

通过聚丙烯酰胺凝胶电泳(PAGE)和超氧化物歧化酶(SOD)的鉴别性定位染色分析,表明红酵母Rhodotorula sp.仅存在线粒体中的Mn-SOD。在类胡萝卜素含量较高的时期(培养5d),红酵母SOD活力下降, 过氧化氢酶(CAT)活力升高,而此时它对外界O2-. 和H2O2的抗性均明显高于类胡萝卜素含量较低的时期(培养2d)。以上结果表明红酵母胞质中的抗氧化作用已主要由类胡萝卜素来承担,类胡萝卜素含量越高,红酵母抗氧化能力越强。由此,利用产生的O2-. 试剂TBO处理红酵母,可筛选出稳定高产的类胡萝卜素菌株,其中以培养2d的红酵母作为筛选对象更佳,所筛菌落类胡萝卜素含量可高达1740.9~2039.2g/g干重,比未处理的对照增加了28.2%~50.1%。     

Virulence and resistance to superoxide, low pH and hydrogen peroxide among strains of Mycobacterium tuberculosis.

Six strains of Mycobacterium tuberculosis of different virulence in guinea-pigs were compared with regard to their resistance to low pH, to hydrogen peroxide (H2O2) at different pH values and to superoxide (O2-). Low virulence was associated with susceptibility to H2O2 in native and isoniazid-resistant strains but not in laboratory-attenuated strain H37Ra. H2O2 resistance was only partly related to catalase content. Low virulence was not associated with susceptibility to an acid environment but the tuberculocidal effect of H2O2 was significantly increased at low pH. The strains were uniformly resistant to O2- and contained similar amounts of superoxide dismutase. The implications of these observations are discussed in the context of mechanisms of host defence in tuberculosis.     

Rhizobium japonicum mutants that are hypersensitive to repression of H2 uptake by oxygen.

The synthesis of an H2 oxidation system in free-living Rhizobium japonicum wild-type strain SR is repressed by oxygen. Maximal H2 uptake rates were obtained in strain SR after derepression in 11 microM or less dissolved oxygen. Oxygen levels above 45 microM completely repressed H2 uptake in strain SR. Five R. japonicum mutant strains that are hypersensitive to repression or H2 oxidation by oxygen were derived from strain SR. The mutants were obtained by screening H2 uptake-negative mutants that retained the ability to oxidize H2 as bacteroids from soybean nodules. As bacteroids, the five mutant strains were capable of H2 oxidation rates comparable to that of the wild type. The mutants did not take up H2 when derepressed in 22 microM dissolved oxygen, whereas strain SR had substantial activity at this oxygen concentration. The O2 repression of H2 uptake in both the wild-type and two mutant strains, SR174 and SR200, was rapid and was similar to the effect of inhibiting synthesis of H2 uptake system components with rifampin. None of the mutant strains was able to oxidize H2 when the artificial electron acceptors methylene blue or phenazine methosulfate were provided. The mutant strains were not sensitive to killing by oxygen, they took up O2 at rates similar to strain SR, and they did not produce an H2 uptake system that was oxygen labile. Cyclic AMP levels were comparable in strain SR and the five mutant strains after subjection of the cultures to the derepression conditions.     

Oxidative stress induced by ciprofloxacin in Staphylococcus aureus

Staphylococcus aureus with multiple sensitivity to ciprofloxacin, was investigated to detect alterations in the production of superoxide anion (O(2)(-)), other reactive oxidant species (ROS), and superoxide dismutase (SOD), and to relate them with ciprofloxacin accumulation and sensitivity. Oxidative stress was studied by means of Nitroblue Tetrazolium reaction (NBT) and chemiluminescence (CL); lucigenin was employed to detect O(2)(-), and luminol was used to measure other ROS. Sensitive strains exhibited higher intracellular O(2)(-) increase than resistant ones when incubated with ciprofloxacin. SOD was determined in normal conditions and induction was investigated in the presence of ciprofloxacin. These assays demonstrated that resistant and sensitive strains exported a great amount of SOD and that the induction of SOD intracellular was insufficient to counteract the augment of O(2)(-) in the cytoplasm of sensitive strains. Accumulation of ciprofloxacin, researched by spectrofluorometry, showed high levels of antibiotic in sensitive strains which increased the O(2)(-) causing more oxidative stress than in resistant S. aureus.     

Iron Superoxide Dismutase Protects against Chilling Damage in the Cyanobacterium Synechococcus species PCC7942

A strain of Synechococcus sp. PCC7942 lacking functional Fe superoxide dismutase (SOD), designated sodB⁻, was characterized by its growth rate, photosynthetic pigments, inhibition of photosynthetic electron transport activity, and total SOD activity at 0°C, 10°C, 17°C, and 27°C in moderate light. At 27°C, the sodB⁻ and wild-type strains had similar growth rates, chlorophyll and carotenoid contents, and cyclic photosynthetic electron transport activity. The sodB⁻ strain was more sensitive to chilling stress at 17°C than the wild type, indicating a role for FeSOD in protection against photooxidative damage during moderate chilling in light. However, both the wild-type and sodB⁻ strains exhibited similar chilling damage at 0°C and 10°C, indicating that the FeSOD does not provide protection against severe chilling stress in light. Total SOD activity was lower in the sodB⁻ strain than in the wild type at 17°C and 27°C. Total SOD activity decreased with decreasing temperature in both strains but more so in the wild type. Total SOD activity was equal in the two strains when assayed at 0°C.     

Stomatal behaviour and cuticular properties of maize leaves of different chilling-resistance during cold treatment

Stomatal behaviour and the amount and synthesis of epicuticular waxes were studied in maize leaves of various degrees of chilling resistance in order to investigate the rapid desiccation characteristic of chilling injury. In contrast to the resistant variety (KSC 360), the sensitive line (Lye) failed to close the stomata during chilling treatment. Both, the amount of epicuticular waxes and their degree of labeling by 1-14C-acetate were much higher in the resistant than in the sensitive leaves. Chilling-sensitivity was also related to a suppressed conversion of free fatty acids into free primary alcohols.     

Evaluation of the pH-dependent,stationary-phase acid tolerance in Listeria monocytogenes and Salmonella Typhimurium DT104 induced by culturing in media with 1% glucose: a comparative study with Escherichia coli O157:H7

AIMS: To comparatively evaluate the adaptive stationary-phase acid tolerance response (ATR) in food-borne pathogens induced by culturing in glucose-containing media, as affected by strain variability and antibiotic resistance, growth temperature, challenge pH and type of acidulant. METHODS AND RESULTS: Antibiotic resistant or sensitive strains of Listeria monocytogenes, Salmonella including S. Typhimurium DT104, and Escherichia coli O157:H7 were cultured (30 degrees C for 24 h; 10 degrees C for up to 14 days) in trypticase soya broth with yeast extract (TSBYE) with 1% or without glucose to induce or prevent acid adaptation, respectively. Cultures were subsequently exposed to pH 3.5 or 3.7 with lactic or acetic acid at 25 degrees C for 120 min. Acid-adapted cultures were more acid tolerant than nonadapted cultures, particularly those of L. monocytogenes and Salmonella. No consistent, positive or negative, influence of antibiotic resistance on the pH-inducible ATR or acid resistance (AR) was observed. Compared with 30 degrees C cultures, growth and acid adaptation of L. monocytogenes and S. Typhimurium DT104 at 10 degrees C markedly reduced their ATR and AR in stationary phase. E. coli O157:H7 had the greatest AR, relying less on acid adaptation. A 0.2 unit difference in challenge pH (3.5-3.7) caused great variations in survival of acid-adapted and nonadapted cells. CONCLUSIONS: Culturing L. monocytogenes and Salmonella to stationary phase in media with 1% glucose induces a pH-dependent ATR and enhances their survival to organic acids; thus, this method is suitable for producing acid-adapted cultures for use in food challenge studies. SIGNIFICANCE AND IMPACT OF THE STUDY: Bacterial pathogens may become acid-adapted in foods containing glucose or other fermentable carbohydrates. Low storage temperatures may substantially decrease the stationary-phase ATR of L. monocytogenes and S. Typhimurium DT104, but their effect on ATR of E. coli O157:H7 appears to be far less dramatic.     

Biofilm formation by Escherichia coli O157:H7 on stainless steel: effect of exopolysaccharide and Curli production on its resistance to chlorine

The resistance of Escherichia coli O157:H7 strains ATCC 43895-, 43895-EPS (an exopolysaccharide [EPS]-overproducing mutant), and ATCC 43895+ (a curli-producing mutant) to chlorine, a sanitizer commonly used in the food industry, was studied. Planktonic cells of strains 43895-EPS and/or ATCC 43895+ grown under conditions supporting EPS and curli production, respectively, showed the highest resistance to chlorine, indicating that EPS and curli afford protection. Planktonic cells (ca. 9 log(10) CFU/ml) of all strains, however, were killed within 10 min by treatment with 50 microg of chlorine/ml. Significantly lower numbers of strain 43895-EPS, compared to those of strain ATCC 43895-, attached to stainless steel coupons, but the growth rate of strain 43895-EPS on coupons was not significantly different from that of strain ATCC 43895-, indicating that EPS production did not affect cell growth during biofilm formation. Curli production did not affect the initial attachment of cells to coupons but did enhance biofilm production. The resistance of E. coli O157:H7 to chlorine increased significantly as cells formed biofilm on coupons; strain ATCC 43895+ was the most resistant. Population sizes of strains ATCC 43895+ and ATCC 43895- in biofilm formed at 12 degrees C were not significantly different, but cells of strain ATCC 43895+ showed significantly higher resistance than did cells of strain ATCC 43895-. These observations support the hypothesis that the production of EPS and curli increase the resistance of E. coli O157:H7 to chlorine.     

Survival of subsurface microorganisms exposed to UV radiation and hydrogen peroxide.

Aerobic and microaerophilic subsurface bacteria were screened for resistance to UV light. Contrary to the hypothesis that subsurface bacteria should be sensitive to UV light, the organisms studied exhibited resistance levels as efficient as those of surface bacteria. A total of 31% of the aerobic subsurface isolates were UV resistant, compared with 26% of the surface soil bacteria that were tested. Several aerobic, gram-positive, pigmented, subsurface isolates exhibited greater resistance to UV light than all of the reference bacterial strains tested except Deinococcus radiodurans. None of the microaerophilic, gram-negative, nonpigmented, subsurface isolates were UV resistant; however, these isolates exhibited levels of sensitivity similar to those of the gram-negative reference bacteria Escherichia coli B and Pseudomonas fluorescens. Photoreactivation activity was detected in three subsurface isolates, and strain UV3 exhibited a more efficient mechanism than E. coli B. The peroxide resistance of four subsurface isolates was also examined. The aerobic subsurface bacteria resistant to UV light tolerated higher levels of H2O2 than the microaerophilic organisms. The conservation of DNA repair pathways in subsurface microorganisms may be important in maintaining DNA integrity and in protecting the organisms against chemical insults, such as oxygen radicals, during periods of slow growth.     

Development of resistance in slow-growing rhizobia to 1-naphthyl-N-methyl carbamate (sevin)

Summary Different strains of rhizobia (isolated fromLotus corniculatus andVigna unguiculata) andRhizobium meliloti adapt to sevin (50 g/ml). The number of transfers (20–31) and days of incubation (80–130) during which different strains of rhizobia develop resistance varied. The results of reversion of resistance to sevin, experiments showed that the resistance developed was stable. Rate of growth was faster in resistant strains but their final cell numbers were less than those of sensitive strains. Dehydrogenase activity increased with the development of resistance to sevin, except in strain D-467. With the development of resistance to sevin, total lipids and phospholipids decreased, glycolipids increased and neutral lipids varied. Presence of glycerol, sodium oleate and sodium acetate (known to stimulate lipid production) and flavin mononucleotide and wheat germ lipases (known to decrease lipid production) in the culture medium did not change the growth pattern and lipids of the sevin resistant and sensitive strains of rhizobia.