Karl-Johan Bergstrand

Impact of light quality on biomass production and fatty acid content in the microalga Chlorella vulgaris

In this study, the green microalga Chlorella vulgaris was exposed to monochromatic light at six different wavelengths in order to study the effect on biomass productivity and fatty acid content. A significantly higher amount of biomass by produced in the treatments with yellow, red and white light compared with blue, green and purple light. There were also significant differences in total lipid content and fatty acid profile between the treatments. The green light regime gave the lowest concentration of lipids, but increased the concentration of polyunsaturated fatty acids. Thus it can be concluded that light quality significantly affects biomass productivity, total lipid concentration and fatty acid profile in the microalga C. vulgaris.

Characterization of biosurfactant-producing strains of fluorescent pseudomonads in a soilless cultivation system.

The use of biosurfactants is a promising alternative in biological control of zoospore-producing plant pathogens. In the present study, biosurfactant production by the indigenous population of fluorescent pseudomonads in a soilless plant cultivation system was studied during the growing season. A total of 600 strains was screened and of these 18.5% were observed to produce biosurfactants. Production of both antibiotics and biosurfactant was uncommon among the isolated strains. A selective effect of the cultivation system filter was observed on the biosurfactant-producing strains and these strains were only occasionally observed after the filter, despite having a significantly higher motility than the nonbiosurfactant-producing strains. The majority of biosurfactant-producing strains were isolated from the filter skin, which suggests that this is a suitable surface for inoculation with biocontrol strains.

Production of biosurfactants and antibiotics by fluorescent pseudomonads isolated from a closed hydroponic system equipped with a slow filter

The presence of antibiotic- and biosurfactant-producing strains of fluorescent pseudomonads in a closed hydroponic system equipped with a slow filter was investigated. A total of 271 strains of pseudomonads were isolated before the filter, from the filter skin and from the effluent. Production of biosurfactants was determined using the drop-collapse method. The ability of the strains to inhibit the growth of the plant pathogens Pythium ultimum, Phytophthora cryptogea and Fusarium oxysporum was determined using dual culture plating. The influence of carbon sources on production was determined for selected strains, which also were identified to species level. Production of antibiotics or biosurfactants was observed to be a common trait among the fluorescent pseudomonads within the closed hydroponic system and it was affected by the filter. Pythium ultimum was the pathogen that was most sensitive to antibiotics produced by the fluorescent pseudomonads. The results indicated a strong influence of nutritional resources on antibiotic and biosurfactant production.

Light spectrum modifies the utilization pattern of energy sources in Pseudomonas sp. DR 5-09

Despite the overruling impact of light in the phyllosphere, little is known regarding the influence of light spectra on non-phototrophic bacteria colonizing the leaf surface. We developed an in vitro method to study phenotypic profile responses of bacterial pure cultures to different bands of the visible light spectrum using monochromatic (blue: 460 nm; red: 660 nm) and polychromatic (white: 350–990 nm) LEDs, by modification and optimization of a protocol for the Phenotype MicroArray™ technique (Biolog Inc., CA, USA). The new protocol revealed high reproducibility of substrate utilization under all conditions tested. Challenging the non-phototrophic bacterium Pseudomonas sp. DR 5–09 with white, blue, and red light demonstrated that all light treatments affected the respiratory profile differently, with blue LED having the most decisive impact on substrate utilization by impairing respiration of 140 substrates. The respiratory activity was decreased on 23 and 42 substrates under red and white LEDs, respectively, while utilization of one, 16, and 20 substrates increased in the presence of red, blue, and white LEDs, respectively. Interestingly, on four substrates contrasting utilization patterns were found when the bacterium was exposed to different light spectra. Although non-phototrophic bacteria do not rely directly on light as an energy source, Pseudomonas sp. DR 5–09 changed its respiratory activity on various substrates differently when exposed to different lights. Thus, ability to sense and distinguish between different wavelengths even within the visible light spectrum must exist, and leads to differential regulation of substrate usage. With these results, we hypothesize that different light spectra might be a hitherto neglected key stimulus for changes in microbial lifestyle and habits of substrate usage by non-phototrophic phyllospheric microbiota, and thus might essentially stratify leaf microbiota composition and diversity.

Biofilm Formation by Chlorella vulgaris is Affected by Light Quality

Abstract Formation of biofilm on surfaces is a common feature in aquatic environments. Major groups of inhabitants in conditions where light is present are photoautotrophic microorganisms, such as cyanobacteria and microalgae. This study examined the effect of light quality on growth and biofilm formation of the microalgal species Chlorella vulgaris. Dense biofilm formation and aggregated growth of cells were observed in treatments exposed to blue, purple and white light. Less dense biofilm formation and solitary growth of cells were observed in treatments exposed to red, yellow or green light. Microalgal biofilms are of high importance in many respects, not least from an economic perspective. One example is the intense efforts undertaken to control biofilm formation on technical surfaces such as ship hulls. The present study suggests that light quality plays a role in biofilm formation and that blue-light receptors may be involved.

Cross Response of Slow Filters to Dual Pathogen Inoculation in ClosedHydroponic Growing Systems

The efficacy of slow filters for horticultural purposes is suggested to be the result of multiple factors. Physical and biological properties of the filter column and the nutrient solution are likely to influence on filter performance. It has previously been shown that enzyme activity on the filter skin is a main parameter which will explain roughly 50% of filter efficacy. Since enzyme activity is enhanced by the addition of fungal cell walls to the filter skin, presence of a fungal root pathogen might affect enzyme activity and filter efficacy. In this study, slow filters integrated into closed NFT systems with a tomato crop were inoculated with mycelia from Pythium aphanidermatum. Enzyme activity, microbial colonisation, polysaccharide content and DNA content of the filter skin as well as microbial flora and total organic carbon in the nutrient solution were monitored. Tests of filter efficacy against Fusarium oxysporum f.sp. cyclaminis showed no significant influence on filter efficacy by the addition of P. aphanidermatum. Enzyme activities in the filter skin were not affected by the addition of P. aphanidermatum. A negative correlation was found between biofilm polysaccharide content and activity of xylanase activity on the filter skin. Filter efficacy was high (>99.9%) throughout the study. No damage to the crop as effect of pathogenic fungi was seen. We concluded that abundance of an oomycete pathogen in a closed hydroponic system does not affect filter efficacy, and that the filter skin microflora function, but not composition, is affected by this pathogen.

Dynamics of nitrogen availability in pot grown crops with organic fertilization

ABSTRACT Pot grown herbs are often cultivated as certified organic products, and there is an increasing demand for organically certified ornamental plants. Supplying the required nutrients using organic fertilizers is a challenge with respect to matching the mineralization and thus the availability of dissolved nutrients in the growing medium with plant demand. In experiments, sweet basil and Pelargonium × hortorum were cultivated using two different organic fertilizer strategies and controlled-release mineral nutrients as control treatment. The two organic strategies were, i) blood meal + Baralith® Enslow (a plant-based organic fertilizer), and ii) poultry manure. The availability of dissolved nitrogen was monitored during the crop cycle by under-pressure lysimeter sampling. Plant development parameters were measured along with chlorophyll fluorescence and chlorophyll concentration of leaves. For both organic treatments, nitrate-N availability was low at the beginning of the experiment, whereas ammonium-N was high. During the experiment, ammonium availability decreased at the same time as nitrate availability increased after a few weeks and then declined again by the end of the experiment. The blood meal + Enslow treatment caused poor germination and slow growth in basil. Plant height and fresh weight was also affected by this treatment for basil but not for Pelargonium. Chlorophyll concentration was affected by treatment, with also visually detectable paler leaves in the treatment with poultry manure. There were no differences in chlorophyll fluorescence (Fv/Fm) between treatments, indicating that plants were not stressed in any of the treatments.