Biogeochemical processes in the algal-bacterial mats of the Urinskii alkaline hot spring

The structure and production characteristics of microbial communities from the Urinskii alkaline hot spring (Buryat Republic, Russia) have been investigated. A distinctive characteristic of this hot spring is the lack of sulfide in the issuing water. The water temperature near the spring vents ranged from 69 to 38.5°C and pH values ranged from 8.8 to 9.2. The total mineralization of water was less than 0.1 g/liter. Temperature has a profound effect on the species composition and biogeochemical processes occurring in the algal-bacterial mats of the Urinskii hot spring. The maximum diversity of the phototrophic community was observed at the temperatures 40 and 46°C. A total of 12 species of cyanobacteria, 4 species of diatoms, and one species of thermophilic anoxygenic phototrophic bacteria, Chloroflexus aurantiacus, have been isolated from mat samples. At temperatures above 40°C, the filamentous cyanobacterium Phormidium laminosum was predominant; its cell number and biomass concentration comprised 95.1 and 63.9%, respectively. At lower temperatures, the biomass concentrations of the cyanobacterium Oscillatoria limosa and diatoms increased (50.2 and 36.4%, respectively). The cyanobacterium Mastigocladus laminosus, which is normally found in neutral or slightly acidic hydrothermal systems, was detected in microbial communities. As the diatom concentration increases, so does the dry matter concentration in mats, while the content of organic matter decreases. The concentrations of proteins and carbohydrates reached their maximum levels at 45–50°C. The maximum average rate of oxygenic photosynthesis [2.1 g C/(m² day)], chlorophyll a content (343.4 mg/m²), and cell number of phototrophic microorganisms were observed at temperatures from 45 to 50°C. The peak mass of bacterial mats (56.75 g/m²) occurred at a temperature of 65–60°C. The maximum biomass concentration of phototrophs (414.63 × 10^?6 g/ml) and the peak rate of anoxygenic photosynthesis [0.42 g C/(m² day)] were observed at a temperature of 35–40°C.     

Functional and structural response of the methanogenic microbial community in rice field soil to temperature change

The microbial community in anoxic rice field soil produces CH₄ over a wide temperature range up to 55°C. However, at temperatures higher than about 40°C, the methanogenic path changes from CH₄ production by hydrogenotrophic plus acetoclastic methanogenesis to exclusively hydrogenotrophic methanogenesis and simultaneously, the methanogenic community consisting of Methanosarcinaceae, Methanoseataceae, Methanomicrobiales, Methanobacteriales and Rice Cluster I (RC‐1) changes to almost complete dominance of RC‐1. We studied changes in structure and function of the methanogenic community with temperature to see whether microbial members of the community were lost or their function impaired by exposure to high temperature. We characterized the function of the community by the path of CH₄ production measuring δ¹³C in CH₄ and CO₂ and calculating the apparent fractionation factor (α_app) and the structure of the community by analysis of the terminal restriction fragment length polymorphism (T‐RFLP) of the microbial 16S rRNA genes. Shift of the temperature from 45°C to 35°C resulted in a corresponding shift of function and structure, especially when some 35°C soil was added to the 45°C soil. The bacterial community (T‐RFLP patterns), which was much more diverse than the archaeal community, changed in a similar manner upon temperature shift. Incubation of a mixture of 35°C and 50°C pre‐incubated methanogenic rice field soil at different temperatures resulted in functionally and structurally well‐defined communities. Although function changed from a mixture of acetoclastic and hydrogenotrophic methanogenesis to exclusively hydrogenotrophic methanogenesis over a rather narrow temperature range of 42–46°C, each of these temperatures also resulted in only one characteristic function and structure. Our study showed that temperature conditions defined structure and function of the methanogenic microbial community.     

Thermoacidophilic microbial community oxidizing the gold-bearing flotation concentrate of a pyrite-arsenopyrite ore

An aboriginal community of thermophilic acidophilic chemolithotrophic microorganisms (ACM) was isolated from a sample of pyrite gold-bearing flotation concentrate at 45–47°C and pH 1.8–2.0. Compared to an experimental thermoacidophilic microbial consortium formed in the course of cultivation in parallel bioreactors, it had lower rates of iron leaching and oxidation, while its rate of sulfur oxidation was higher. A new thermophilic acidophilic microbial community was obtained by mutual enrichment with the microorganisms from the experimental and aboriginal communities during the oxidation of sulfide ore flotation concentrate at 47°C. The dominant bacteria of this new ACM community were Acidithiobacillus caldus (the most active sulfur oxidize) and Sulfobacillus thermotolerans (active oxidizer of both iron and sulfur), while iron-oxidizing archaea of the family Ferroplasmaceae and heterotrophic bacteria Alicyclobacillus tolerans were the minor components. The new ACM community showed promise for leaching/oxidation of sulfides from flotation concentrate at high pulp density (S : L = 1 : 4).     

Sulfidic acetate mineralization at 45°C by an aquifer microbial community: key players and effects of heat changes on activity and community structure

High-Temperature Aquifer Thermal Energy Storage (HT-ATES) is a sustainable approach for integrating thermal energy from various sources into complex energy systems. Temperatures ≥45°C, which are relevant in impact zones of HT-ATES systems, may dramatically influence the structure and activities of indigenous aquifer microbial communities. Here, we characterized an acetate-mineralizing, sulfate-reducing microbial community derived from an aquifer and adapted to 45°C. Acetate mineralization was strongly inhibited at temperatures ≤25°C and 60°C. Prolonged incubation at 12°C and 25°C resulted in acetate mineralization recovery after 40–80 days whereas acetate was not mineralized at 60°C within 100 days. Cultures pre-grown at 45°C and inhibited for 28 days by incubation at 12°C, 25°C, or 60°C recovered quickly after changing the temperature back to 45°C. Phylotypes affiliated to the order Spirochaetales and to endospore-forming sulfate reducers of the order Clostridiales were highly abundant in microcosms being active at 45°C highlighting their key role. In summary, prolonged incubation at 45°C resulted in active microbial communities mainly consisting of organisms adapted to temperatures between the typical temperature range of mesophiles and thermophiles and being resilient to temporary heat changes.     

Biodiversity of the microbial mat of the Garga hot spring

Background

Microbial mats are a good model system for ecological and evolutionary analysis of microbial communities. There are more than 20 alkaline hot springs on the banks of the Barguzin river inflows. Water temperature reaches 75 °C and pH is usually 8.0–9.0. The formation of microbial mats is observed in all hot springs. Microbial communities of hot springs of the Baikal rift zone are poorly studied. Garga is the biggest hot spring in this area.

Results

In this study, we investigated bacterial and archaeal diversity of the Garga hot spring (Baikal rift zone, Russia) using 16S rRNA metagenomic sequencing. We studied two types of microbial communities: (i) small white biofilms on rocks in the points with the highest temperature (75 °C) and (ii) continuous thick phototrophic microbial mats observed at temperatures below 70 °C. Archaea (mainly Crenarchaeota; 19.8% of the total sequences) were detected only in the small biofilms. The high abundance of Archaea in the sample from hot springs of the Baikal rift zone supplemented our knowledge of the distribution of Archaea. Most archaeal sequences had low similarity to known Archaea. In the microbial mats, primary products were formed by cyanobacteria of the genus Leptolyngbya. Heterotrophic microorganisms were mostly represented by Actinobacteria and Proteobacteria in all studied samples of the microbial mats. Planctomycetes, Chloroflexi, and Chlorobi were abundant in the middle layer of the microbial mats, while heterotrophic microorganisms represented mostly by Firmicutes (Clostridia, strict anaerobes) dominated in the bottom part. Besides prokaryotes, we detect some species of Algae with help of detection their chloroplasts 16 s rRNA.

Conclusions

High abundance of Archaea in samples from hot springs of the Baikal rift zone supplemented our knowledge of the distribution of Archaea. Most archaeal sequences had low similarity to known Archaea. Metagenomic analysis of microbial communities of the microbial mat of Garga hot spring showed that the three studied points sampled at 70 °C, 55 °C, and 45 °C had similar species composition. Cyanobacteria of the genus Leptolyngbya dominated in the upper layer of the microbial mat. Chloroflexi and Chlorobi were less abundant and were mostly observed in the middle part of the microbial mat. We detected domains of heterotrophic organisms in high abundance (Proteobacteria, Firmicutes, Verrucomicrobia, Planctomicetes, Bacteroidetes, Actinobacteria, Thermi), according to metabolic properties of known relatives, which can form complete cycles of carbon, sulphur, and nitrogen in the microbial mat. The studied microbial mats evolved in early stages of biosphere formation. They can live autonomously, providing full cycles of substances and preventing live activity products poisoning.

     

Prosopis chilensis is a plant highly tolerant to heat shock

At temperatures between 25 and 35°C, 100% of Prosopis chilensis seeds germinated within 24 h. At higher temperatures, the germination rate was reduced; at 50°C, seeds did not germinate. After germination at 25°C, the optimal temperature for seedling growth was 35°C and the seedlings did not grow at a temperature of 50°C. However, when germination was at 35°C, the optimal temperature for seedling growth was 40°C and some seedlings grew at 50°C, suggesting that thermotolerance was induced during seed germination at 35°C. Further thermotolerance can be induced in seedlings germinated at 35°C, by exposing them to 40°C for 2h. Under these conditions, seedlings exhibited increased growth rate at 45 and 50°C. Fluorography of SDS-polyacrylamide gel electrophoresis of the proteins synthesized and accumulated during 2 h at temperatures of 35, 40, 45 and 50°C in the presence of [³⁵S]methionine revealed the expression of 11 proteins not detectable at 35°C. Most of the proteins present at 35°C also increased in expression. The temperature for maximal expression of these proteins was 45°C.     

Temperature impacts on anaerobic biotransformation of LNAPL and concurrent shifts in microbial community structure

Thermally-enhanced bioremediation is a promising treatment approach for petroleum contamination; however, studies examining temperature effects on anaerobic biodegradation in zones containing light non-aqueous phase liquids (LNAPLs) are lacking. Herein, laboratory microcosm studies were conducted for a former refinery to evaluate LNAPL transformation, sulfate reduction, and methane generation over a one-year period for temperatures ranging from 4 to 40 °C, and microbial community shifts were characterized. Temperatures of 22 and 30 °C significantly increased total biogas generation compared to lower (4 and 9 °C) and higher temperatures (35 and 40 °C; p < 0.1). Additionally, at 22 and 30 °C methane generation commenced ~6 months earlier than for 35 and 40 °C. Statistically significant biodegradation of benzene, toluene and xylenes was observed at elevated temperatures but not at lower temperatures (p < 0.1). Additionally, a novel differential chromatogram approach was developed to overcome challenges associated with resolving losses in complex mixtures of hydrocarbons, and application of this method revealed greater losses of hydrocarbons at 22 and 30 °C as compared to lower and higher temperatures. Finally, molecular biology assays revealed that the composition and activity of microbial communities shifted in a temperature-dependent manner. Collectively, results demonstrated that anaerobic biodegradation processes can be enhanced by increasing the temperature of LNAPL-containing soils, but biodegradation does not simply increase as temperature increases likely due to a lack of microorganisms that thrive at temperatures well above the historical high temperatures for a site. Rather, optimal degradation is achieved by holding soils at the high end of, or slightly higher than, their natural range.     

The effects of temperature and light intensity on growth,reproduction and EPS synthesis of a thermophilic strain related to the genus Graesiella

Tunisian microalgae are diverse and rarely been studied. This study reports a first investigation of thermophile Chlorophyta isolated from mats community colonizing the geothermal springs in the north of Tunisia at water temperature 60 °C. In the study, the combined effect of temperature and light intensity was investigated on the cell growth, the mother and daughter cells abundance and the extracellular polymeric substances synthesis in batch culture of the isolated species. Three levels were tested for each factor, 20, 30, 40 °C for temperature; and 20, 70, 120 μmol photons m^?2 s^?1 for light intensity, using full factorial design and response surface methodology. The thermophile strain was identified as a genus Graesiella and showed 99.8 % similarity with two Graesiella species: Graesiella emersonii and Graesiella vacuolata based on the 18S rDNA molecular identification. The optimal growth condition was found at 30 °C and 120 µmol photons m^?2 s^?1 (7 MC mL^?1 day^?1), with the abundance of vegetative cells (daughter cells). In contrast, the number of mother cells increased significantly as the growth decreased; consequently, the highest ratio of auto spore mother cells versus daughter cells (19.4) was obtained at 20 °C and 20 µmol photons m^?2 s^?1. The highest yield of EPS production (11.7 mg L^?1 day^?1) was recorded at the highest temperature (40 °C) and lowest light intensity (20 µmol photons m^?2s^?1). These results revealed how the species respond to high and low temperatures and suggest that the species should be considered as facultative thermophile.     

The effect of temperature on growth and lipid and fatty acid composition on marine microalgae used for biodiesel production

Cultivation temperature is one of the major factors affecting the growth and lipid accumulation of microalgae. In this study, the effects of temperature on the growth, lipid content, fatty acid composition and biodiesel properties of the marine microalgae Chaetoceros sp. FIKU035, Tetraselmis suecica FIKU032 and Nannochloropsis sp. FIKU036 were investigated. These species were cultured at different temperatures (25, 30, 35 and 40 °C). The results showed that the specific growth rate, biomass and lipid content of all microalgae decreased with increasing temperature. With regards to fatty acids, the presence of saturated fatty acids (SFAs) in T. suecica FIKU032 and Nannochloropsis sp. FIKU036 decreased with increasing temperature, in contrast with polyunsaturated fatty acids (PUFAs). Moreover, Chaetoceros sp. FIKU035 was the only species that could grow at 40 °C. The highest lipid productivity was observed in Chaetoceros sp. FIKU035 when cultivated at 25 °C (66.73 ± 1.34 mg L^?1 day^?1) and 30 °C (61.35 ± 2.89 mg L^?1 day^?1). Moreover, the biodiesel properties (cetane number, cold filter plugging point, kinematic viscosity and density) of the lipids obtained from this species were in accordance with biodiesel standards. This study indicated that Chaetoceros sp. FIKU035 can be considered as a suitable species for biodiesel production in outdoor cultivation.     

Photosynthetic and respiratory responses of Gracilaria parvispora from the southeastern Gulf of California

Photosynthetic and respiratory responses (P–E curves) of Gracilaria parvispora from the southeast Gulf of California were studied at four temperatures (20, 25, 30, 35 °C) and salinity (25, 30, 35, 40 psu) combinations. The alga showed acclimation in its photosynthetic and respiratory responses to tropical temperature as well as to oceanic salinity. A positive effect of temperature on photosynthetic rate (P _max) was observed for all salinities. Photosynthetic rates for treatments at 20 and 25 °C were lower (<9.2 mg O₂?g dry weight (dw)^?1?h^?1) than for treatments at 30 and 35 °C (>12 mg O₂ g dw^?1?h^?1). G. parvispora showed limited tolerance to low salinities (25 psu) and low temperatures (20 °C) and the interaction between temperature and salinity was significant (analysis of variance, P?<?0.05). Responses to salinity indicated adaptation to oceanic salinity. Photosynthetic responses were lower at 25 psu than at higher salinities. The lowest P _max values (6.2–8.2 mg O₂?g dw^?1?h^?1) were observed at the lowest salinity (25 psu) regardless of temperature. Compensation and saturation irradiances (26–170 and 57–149 μmol photons m^?2?s^?1, respectively) indicate adaptation to lower irradiances in shallow (1–2 m depth) habitats, where turbidity can be high, and the capacity of shade adaptation has been developed. Results suggest distribution of this species is mainly related to salinity or temperature. The potential mariculture efforts of G. parvispora would be limited by low temperatures in winter, and indicate that this species will probably not be able to spread further due to low temperatures (<15 °C) in the upper part of the Gulf of California.     

Effect of culture conditions of Kluyveromyces marxianus on its autolysis, and process optimization

Cultivation of the lactose-metabolizing yeast Kluyveromyces marxianus var. marxianus (formerly K.?fragilis) on supplemented whey permeate resulted in cellular yield little affected by culture conditions in the ranges pH?=?2.3–5 and T?=?30–40?°C. When autolysis was induced only by energy source deficiency and thermal shock, cellular material solubilization depended slightly on autolysis temperature in the range T?=?45–60?°C. On the contrary, the process was under tight control of culture conditions; when autolysis was carried out at 50?°C with an initial dry cellular concentration of 50?g l^?1, a clear optimum was observed for cells cultivated at pH?=?4.5 and T?=?35?°C. So the critical step of the autolytic process consisted in biosynthesis of lytic enzymes (during cell growth) rather than enzymatic progress (during autolysis). These results were compatible with a model previously proposed for Saccharomyces cerevisiae [1].     

Short-term effects of temperature upon the growth of intertidal fucales

The growth rate of five species of intertidal Fucales (Pelvetia canaliculata (L.) Dec. et Thur., Fucus spiralis L., Fucus vesiculosus L., Fucus serratus L., Ascophyllum nodosum (L.) Le Jolis) was measured at temperatures from 2.5 to 35 °C. An increase in temperature immediately causes a high growth rate, and during the first hour it increases linearly with temperature; at 35 °C it is 20 times the control at 7 °C. This acceleration of growth is based mainly on stored photosynthate. After the first few hours the growth rate decreases rapidly, particularly at the highest temperatures. After 2–3 weeks a temperature optimum below 17.5 °C is indicated. High temperatures, 30–35 °C, were lethal to all species, with a survival time corresponding to their vertical zonation in the natural habitat.     

Differential protein expression for geothermal Agrostis scabra and turf-type Agrostis stolonifera differing in heat tolerance

Heat stress is a major factor limiting the growth of cool-season grasses in warm climatic regions by affecting many physiological processes, including protein metabolism. Protein degradation often occurs with increasing temperatures, but certain specific proteins such as heat shock proteins (HSPs) may be induced or enhanced in their expression under supraoptimal temperatures. The objectives of this study were to determine the critical temperature that causes protein induction or degradation in two Agrostis grass species differing in heat tolerance and to compare protein profiles between the two species under different temperature regimes. Plants of heat-tolerant Agrostis scabra and two cultivars of heat-sensitive Agrostis stolonifera (‘L-93’ and ‘Penncross’) were exposed to constant day/night temperatures of 20, 30, 35, 40, or 45 °C for 14 d. Leaf photochemical efficiency (Fv/Fm), chlorophyll and carotenoid contents, and soluble protein content declined with increasing temperatures. The decreases were the least severe for A. scabra, intermediate for ‘L-93’, and the most severe for ‘Penncross’, indicating interspecific and intraspecific variations in heat tolerance in Agrostis species. Protein degradation was observed at 30–45 °C in both cultivars of A. stolonifera, and at 40–45 °C in A. scabra.HSPs were induced or enhanced at 35–45 °C in ‘L-93’ and A. scabra, and at 40–45 °C in ‘Penncross’. Immunoblotting also revealed stronger expressions of HSP60 and HSP70 in A. scabra or ‘L-93’ than in ‘Penncross’ at 35–45 °C after 3 d. The results suggested the superior heat tolerance of Agrostis grass species and cultivars could be attributed to the early induction of HSPs, particularly small molecular weight (23 kDa), at a lower level of heat stress and the maintenance of protein thermostability, particularly high-molecular weight proteins (83 kDa and large units of Rubisco).     

A comparative study of development and demographic parameters of <Emphasis Type="Italic">Tetranychus merganser</Emphasis> and <Emphasis Type="Italic">Tetranychus kanzawai</Emphasis> (Acari: Tetranychidae) at different temperatures

We investigated the effect of temperature on development and demographic parameters such as the intrinsic rate of natural increase (r _m) of the two spider mite species Tetranychus merganser Boudreaux and T. kanzawai Kishida at eleven constant temperatures ranging from 15 to 40°C at intervals of 2.5°C. Both male and female T. merganser and T. kanzawai completed development from egg to adult at temperatures ranging from 15 to 37.5°C. The longest developmental duration of immature stages was found at 15°C and the shortest developmental duration was found at 35°C for both species. Using linear and non-linear developmental rate models, the lower thermal thresholds for egg-to-adult (female and male) and egg-to-egg development were estimated as 12.2–12.3°C for T. merganser and as 10.8°C for T. kanzawai. The highest developmental rates were observed at around 35°C, whereas the upper developmental thresholds were around 40°C for both species. In fact, at 40°C, a few eggs of either species hatched, but no larvae reached the next stage. The r _m-values of T. merganser ranged from 0.072 (15°C) to 0.411 day⁻¹ (35°C), whereas those of T. kanzawai ranged from 0.104 (15°C) to 0.399 (30°C). The r _m-values were higher for T. kanzawai than for T. merganser at temperatures from 15 to 30°C, but not at 35°C (0.348 day⁻¹). Total fecundity of T. merganser was also higher than that of T. kanzawai at 35°C. These results indicate that higher temperatures favor T. merganser more than T. kanzawai.     

Influence of temperature on process efficiency and microbial community response during the biological removal of chlorophenols in a packed-bed bioreactor

Two reactors, initially operated at 14 and 23±1°C (RA and RB, respectively), were inoculated with a bacterial consortium enriched and acclimatized to the respective temperatures over 4 months. The biofilms, formed in the reactors, were studied using scanning electron microscopy, cultivation of the biofilm microflora, and physiological analysis of the isolates. Two bacteria able to mineralize chlorophenols under a large range of temperature (10–30°C) were isolated from the biofilm communities of reactors RA and RB and characterized as Alcaligenaceae bacterium R14C4 and Cupriavidus basilensis R25C6, respectively. When temperature was decreased by 10°C, the chlorophenols removal capacity was reduced from 51.6 to 22.8 mg l⁻¹ h⁻¹ in bioreactor RA (from 14 to 4°C) and from 59.3 to 34.7 mg l⁻¹ h⁻¹ in bioreactor RB (from 23±1 to 14°C). Fluorescence in situ hybridization (FISH) of the biofilm communities showed that, in all temperatures tested, the β-proteobacteria were the major bacterial community (35–47%) followed by the γ-proteobacteria (12.0–6.5%). When the temperature was decreased by 10°C, the proportions of γ-proteobacteria and Pseudomonas species increased significantly in both microbial communities.     

Effects of dual stress (high salt and high temperature) on the photochemical efficiency of wheat leaves (Triticum aestivum)

In this study, we have focused on those components of Photosystem (PS) II which are significantly affected by dual stress (high salt and temperature) on wheat as measured by Plant Efficiency Analyser (PEA). It was observed that some of the chlorophyll a fluorescence parameters were temperature dominated, while some other parameters were salt dominated. We have also observed additive effects for parameters like antenna size heterogeneity. An important observation was that in high temperature alone, the K-step was observed at 40 °C, while in case of dual stress, the K-step was observed at 45 °C, while the Chl a fluorescence transient of 40 °C?+?0.5 M?NaCl was quite similar to 35 °C transient curve. In the presence of salt, K-step was observed at higher temperature suggesting a protection of OEC by salt. Plants are under dual stress, but effect of temperature stress is less severe in presence of salt stress. Thus, we can say that salt stress caused partial prevention from high temperature stress but it did not cause complete protection of PS II.     

Hyperproduction of phenylalanine by Escherichia coli: application of a temperature-controllable expression vector carrying the repressor-promoter system of bacteriophage lambda

For the high production of phenylalanine by Escherichia coli, we cloned the pheA^FR and aroF^FR genes (FR = feedback resistant), which encoded chorismate mutase P-prephenate dehydratase and 3-deoxy-d-arabinoheptulosonate-7-phosphate synthase that are feedback inhibition-free as to the endproducts, into a temperature-controllable expression vector composed of the P_R and P_L promoter and a temperature sensitive repressor, cI₈₅₇, of bacteriophage lambda. The plasmid obtained was designated as pSY130-14, and the temperature dependency of expression of the cloned genes and of phenylalanine production was investigated at different temperatures between 30 and 42°C using the strain AT2471 harbouring the plasmid. Above 35°C, the pheA^FR gene and aroF^FR gene expressions, and activities of both enzymes continued to increase up to 42°C. The cell concentration remained constant up to 38.5°C, but started to decrease sharply above 40°C, while the cell concentration of the host strain, AT2471, remained constant at all temperatures tested. The concentration of phenylalanine also depended on the temperature, and the highest production of phenylalanine, 18.6 g l⁻¹, was obtained from glucose at 38.5°C in a 2.5 1 reactor.     

Effect of physical factors on the production of bacteriocin from Pediococcus acidilactici ITV 26

The effect of pH, temperature and agitation on growth and bacteriocin production by Pediococcus acidilactici ITV 126 was investigated. Experiments were made in flasks containing MRS medium at 30 to 40°C, pH 5 to 7 and agitation 0 to 200 rpm. Factor levels were arranged in a 2³ factorial design with central and axial points. Anova and Tukey paired comparison tests showed that a temperature of 35°C favored bacteriocin production, whereas 40°C was best for cell growth. A statistical interaction of temperature and agitation was observed affecting microbial growth. pH 5 favored both cell growth and bacteriocin production. Journal of Industrial Microbiology & Biotechnology (2001) 26, 191–195. Received 30 October 1999/ Accepted in revised form 31 January 2001     

The growth of four species of Azolla as affected by temperature

The growth of 22 strains of Azolla pinnata R. Br., 3 strains of A. filiculoides Lam. and one strain each of A. mexicana Presl and A. caroliniana Willd. was tested separately in liquid culture media kept in controlled, artificial light (30 klux) growth cabinets. Three temperature levels were used: 33°C (37/29°C day/night), 29°C (33/25°C) and 22°C (26/18°C)/ Photoperiod was 12 h a day.For most A. pinnata strains (except three) and an A. mexicana strain the maximum weekly relative growth rate was higher at 33°C than at 22°C, but not for A. filiculoides and A. caroliniana. The highest value of maximum relative growth rate corresponded to 1.9 doubling days and in most strains this occurred in the first week. As the plants grew, the growth rate slowed down more severely at higher temperatures. The maximum biomass was higher at 22°C than at 33°C in all strains. At 22°C, it took 30–50 days to attain maximum biomass and the highest value was 14 g N m^?2 or 320 g dry m^?2 by A. caroliniana, followed by 12 g N m^?2 or 290 g dry wt. m^?2 by one strain of A. filiculoides. At 29°C, the maximum biomass was attained in 20–35 days. The highest value was 6.3 g N m^?2 or 154 g dry wt. m^?2 by A. caroliniana. At 33°C, most A. pinnata strains gave a maximum biomass of less than 4 g N m^?2 after 13–23 days, while some strains grew up to 30 days, resulting in a higher maximum biomass. The highest maximum biomass at 33°C was 5.5 g N m^?2 or 140 g m^?2 dry wt. by A. pinnata from Cheng Mai while the maximum biomass of A. filiculoides and A. caroliniana was much less. Azolla filiculoides requires lower temperature than other species for its growth. Azolla pinnata has the best tolerance to high temperatures among the four species. Azolla mexicana could not be discriminated from A. pinnata in its response to temperature. Azolla caroliniana may keep an intermediate position between A. filiculoides and A. pinnata in temperature response.The formation of ammonia in the medium was examined and it occurred mostly under stationary growth conditions, but, at 33°C, some strains of A. pinnata and A. mexicana released or formed ammonia at 0.3–0.8 μg N ml^?1 per week during their initial exponential growth stage.     

Life history parameters for Nesidiocoris tenuis (Reuter) (Het., Miridae) under different temperature regimes

The development time for eggs and nymphs and female fertility were determined for Nesidiocoris tenuis Reuter (Het., Miridae: Dicyphini) at 15, 20, 25, 30, 35 and 40 ± 1°C, using tomato, Solanum esculentum (Miller), as substrate and eggs of Ephestia kuehniella Zeller as substitute prey. At 40°C, N. tenuis was unable to develop and barely reproduced. Egg development ranged from 30.8 days at 15°C to 6.3 days at 35°C. The cumulative thermal requirements for the eggs were 148.6 degree days (°d) and the lower thermal threshold, 10.3°C. The duration of the nymphal instar decreased from 55.9 days at 15°C to 8.6 days at 35°C. The thermal constant for the nymphs was 182.3 °d and the lower thermal threshold 11.7°C. No nymphs survived at 40°C, and the highest mortalities were at extreme temperatures (15 and 35°C). Female and male weights were influenced significantly by temperature. The fertility of N. tenuis females was reduced greatly at 15 and 40°C. The highest fertility during an observation period of 18 days following female emergence (79.5–60.0 nymphs per female) was within the temperature range of 20 to 35°C. Fertility was related directly to female weight and temperature (r² = 0.932). Based on development, reproduction data and thermal requirements, the optimum temperature range for N. tenuis was established as being between 20 and 30°C. Overall, N. tenuis is the most thermophilous of all dicyphines from vegetable crops in the Mediterranean area studied so far.