Vince Ördög

Auxin and cytokinin relationships in 24 microalgal strains1

Endogenous auxins and cytokinins were quantitated in 24 axenic microalgal strains from the Chlorophyceae, Trebouxiophyceae, Ulvophyceae, and Charophyceae. These strains were in an exponential growth phase, being harvested on day 4. Acutodesmus acuminatus Mosonmagyaróvár Algal Culture Collection‐41 (MACC) produced the highest biomass and Chlorococcum ellipsoideum MACC‐712 the lowest biomass. The auxins, indole‐3‐acetic acid (IAA) and indole‐3‐acetamide (IAM) were present in all microalgal strains. No other auxin conjugates were detected. IAA and IAM concentrations varied greatly, ranging from 0.50 to 71.49 nmol IAA · g−1 DW and 0.18 to 99.83 nmol IAM · g−1 DW, respectively. In 19 strains, IAA occurred in higher concentrations than IAM. Nineteen cytokinins were identified in the microalgal strains. Total cytokinin concentrations varied, ranging from 0.29 nmol · g−1 DW in Klebsormidium flaccidum MACC‐692 to 21.40 nmol · g−1 DW in Stigeoclonium nanum MACC‐790. The general trend was that cis‐zeatin types were the predominant cytokinins; isopentenyladenine‐type cytokinins were present in moderate concentrations, while low levels of trans‐zeatin‐type and very low levels of dihydrozeatin‐type cytokinins were detected. Ribotides were generally the main cytokinin conjugate forms present with the cytokinin free bases and ribosides present in similar but moderate levels. The levels of O‐glucosides were low. Only one N‐glucoside was detected, being present in nine strains in very low concentrations. In 15 strains, the auxin content was 2‐ to 4‐fold higher than the cytokinin content.

Bacterial symbionts enhance photo-fermentative hydrogen evolution of Chlamydomonas algae

The green algae Chlamydomonas sp. MACC-549 and Chlamydomonas reinhardtii cc124 were investigated for their hydrogen-evolution capability in mixed algal–bacterial cultures. Stable bacterial contaminations were identified during the cultivation of Chlamydomonas sp. 549. The bacterial symbionts belonged to various genera, mostly Brevundimonas, Rhodococcus, and Leifsonia, each of which enhanced the algal hydrogen production. This phenomenon was not limited to natural associations. Increased algal hydrogen evolution was achieved by simple artificial algal–bacterial communities as well. Algal–bacterial cocultures were designed and tested in hydrogen evolution experiments. The highest hydrogen yields were obtained when hydrogenase-deficient Escherichia coli was used as a symbiotic bacterium (Chlamydomonas sp. 549 generated 1196.06 ± 4.42 μL H2 L−1, while C. reinhardtii cc124 produced 5800.54 ± 65.73 μL H2 L−1). The results showed that oxygen elimination is the most crucial factor for algal hydrogen production and that efficient bacterial respiration is essential for the activation of algal Fe-hydrogenase. The algae-based hydrogen evolution method described represents a novel combination of fermentative and photolytic hydrogen generation processes. Active photosynthesis was maintained during the entire hydrogen evolution process, which contributes to the sustainability of hydrogen production.

Biostimulant properties of cyanobacterial hydrolysate related to polyamines

Developing new and natural sources of plant growth promotors is essential to ensure the safe and sustainable production of vegetables for human consumption. In recent years, the potential of microalgae as plant biostimulants has been investigated. Arthrospira platensis (Spirulina platensis) biomass is a recognized protein source and its enzymatic hydrolysis contains molecules such as polyamines with potential to promote plant growth. Therefore, the aim of the present study was to investigate the biostimulant properties of hydrolyzed biomass of A. platensis. Bioassays were performed to determine auxin-like and cytokinin-like bioactivity of the hydrolysates. In addition, its effect on lettuce seedling growth was investigated and an organic system field trail performed where yield and free polyamine levels in leaves quantified. The hydrolysates had a cytokinin-like effect in the bioassay. Foliar applications promoted the growth of lettuce seedlings with the 4-h reaction hydrolysate (Sph4) being the most effective at promoting growth and increasing the spermine content by 64% in the lettuce leaves. The polyamine concentration was also compared in non-hydrolyzed A. platensis and Sph4. Hydrolysis resulted in a 34% increase in spermine content. It was concluded that Sph4 is a natural plant growth promoter that can be used as a raw material for biostimulants, and spermine could be an active compound and a metabolic indicator of Sph4 bioactivity.

Endogenous brassinosteroids in microalgae exposed to salt and low temperature stress

ABSTRACT Brassinosteroids are part of the hormonal network that regulates growth processes and stress responses in plants. There is evidence for a similar hormonal network in microalgae. In the present study, six microalgae (Chlorococcum ellipsoideum, Gyoerffyana humicola, Nautococcus mamillatus, Acutodesmus acuminatus, Protococcus viridis and Chlorella vulgaris) were subjected to salt and low temperature stress with the addition of 36 g l–1 NaCl and transfer from 25°C to 15°C. There was a rapid response to salt stress with the brassinosteroid content (mainly castasterone with lower amounts of brassinolide, homocastasterone and typhasterol) increasing within 30 min of the salt treatment and remaining at these elevated levels after 7 h. The decrease in temperature had little effect on the brassinosteroid content. This was the first study to show that endogenous brassinosteroids increase in response to abiotic stress in a number of microalgae species.

A Chlamydomonas zöldalga nemzetség algáinak szerepe a biotechnológiában és helyük a zöldalgák rendszerében

Összefoglalás: A Chlamydomonas az egyik legnagyobb zöldalga nemzetség több mint 800 leírt fajjal. Megközelítőleg 400 törzsük áll rendelkezésre törzsgyűjteményekben és alkalmazható kutatási célokra. A Chlamydomonas nemzetség sokoldalú gyakorlati jelentőségére utal, hogy modellszervezetként olyan tudományterületeken alkalmazzák, mint a fotoszintézis kutatás, a genetika, az UV-rezisztencia kérdései, a biogázés biodízel-termelés lehetőségei, a hormonkutatás, a mezőgazdaság és a gyógyszerkutatás. A Chlamydomonas taxonokat hagyományosan életciklusuk vegetatív szakaszában, morfológiai jellemzőik szerint osztályozzák. Az egysejtű szervezeteket magába foglaló nemzetség alapvető jellemzője a két egyenlő hosszúságú ostor és a sejt térfogatának mintegy felét kitevő kloroplasztisz, amely egy vagy több pirenoidot tartalmaz. Az 1990-es évek óta, a molekuláris markerek fi logenetikai elemzésben való alkalmazása bebizonyította, hogy a morfológiai megközelítés nem kielégítő a legtöbb zöldalga, így a Chlamydomonas nemzetség esetében sem. Napjainkra kiderült, hogy a nemzetség polifi letikus, ezért alapos felülvizsgálatra van szükség, amelyre a legújabb irányvonal, a polifázikus megközelítés kínál lehetőséget. Utóbbi olyan különböző eljárásokat egyesít magában, mint a morfológiai, citológiai, ultrastrukturális és molekuláris biológiai elemzések. A hagyományos taxonómiát alkalmazó morfológusok több mint 800 Chlamydomonas fajt jegyeznek, de a polifázikus megközelítés alkalmazásával ez a szám minden bizonnyal a töredékére, 100–150 taxonra fog csökkenni.