The effect of using light emitting diodes and fluorescent lamps as different light sources in growth inhibition tests of green alga, diatom, and cyanobacteria

Aquatic organisms have been used to investigate the safety of chemicals worldwide. One such assessment is an algal growth inhibition test. Algal growth inhibition tests are commonly performed using a growth chamber with fluorescent lamps as the lighting source, as test guidelines require continuous uniform fluorescent illumination. However, fluorescent lamps contain mercury, which has been identified as hazardous to humans and other organisms. The Minamata Convention (adopted in 2013) requires reduction or prohibition of products containing mercury. On the other hand, light-emitting diodes do not contain mercury and provide a photosynthetically effective wavelength range of 400–700 nm which is an adequate light intensity for algal growth. Light-emitting diodes are thus preferable to fluorescent lamps as a potential light source in algal growth inhibition tests. In this study, we investigated if light-emitting diodes could be substituted for fluorescent lamps in growth inhibition studies with green alga (Pseudokirchneriella subcapitata), diatom (Navicula pelliculosa), and cyanobacteria (Anabaena flos-aquae). Algal growth inhibition tests were performed using five different chemicals known to have different modes of action and are assigned as reference substances in the test guidelines. The results of each algal test showed similar values between light-emitting diodes and fluorescent lamps in terms of conditions for the growth inhibition rate and percent inhibition in yield of each chemical. It was therefore concluded that using light-emitting diodes instead of fluorescent lamps as a lighting source had no effect on the algal growth inhibition test results.

Comparative genome analysis of test algal strain NIVA-CHL1 (Raphidocelis subcapitata) maintained in microalgal culture collections worldwide

Raphidocelis subcapitata is one of the most frequently used species for algal growth inhibition tests. Accordingly, many microalgal culture collections worldwide maintain R. subcapitata for distribution to users. All R. subcapitata strains maintained in these collections are derived from the same cultured strain, NIVA-CHL1. However, considering that 61 years have passed since this strain was isolated, we suspected that NIVA-CHL1 in culture collections might have acquired various mutations. In this study, we compared the genome sequences among NIVA-CHL1 from 8 microalgal culture collections and one laboratory in Japan to evaluate the presence of mutations. We found single-nucleotide polymorphisms or indels at 19,576 to 28,212 sites per strain in comparison with the genome sequence of R. subcapitata NIES-35, maintained at the National Institute for Environmental Studies, Tsukuba, Japan. These mutations were detected not only in non-coding but also in coding regions; some of the latter mutations may affect protein function. In growth inhibition test with 3,5-dichlorophenol, EC50 values varied 2.6-fold among the 9 strains. In the ATCC 22662–2 and CCAP 278/4 strains, we also detected a mutation in the gene encoding small-conductance mechanosensitive ion channel, which may lead to protein truncation and loss of function. Growth inhibition test with sodium chloride suggested that osmotic regulation has changed in ATCC 22662–2 and CCAP 278/4 in comparison with NIES-35.

Lemna minor Bioassay Evaluation Using Computer Image Analysis

This article deals with using computer vision in the evaluation of the Lemna minor bioassay. According to the conventional method, the growth of Lemna minor mass is determined from the number of leaves grown. In this work, instead of counting individual leaves, we propose measuring the area occupied by the leaves using computer vision and compare the new approach with the conventional one. The bioassay is performed according to the ISO 20079 standard as a 168 h growth inhibition test; the aim of the experiment was to quantify the negative effects on the vegetative growth using two parameters—the number of leaves and the area occupied by the leaves. The method based on image processing was faster and also more precise since it enabled us to detect the negative effect of the tested substance on leave size, not only on their number. It can be concluded that the toxic effect has shown to be more significant when considering the leaves area rather than the number of leaves. Moreover, mistakes caused by human factor during leaves counting are eliminated using the computer vision based method.

Isolation and Phylogenetic Analysis of Avian Mycoplasmas from Poultry Affected with Respiratory Infections in India

Mycoplasma gallisepticum (MG) and Mycoplasma synoviae (MS) are the two most pathogenic avian mycoplasmas. In the present study, examination of 92 pooled tissue samples from broiler chicken of 92 different poultry flocks of Haryana (India) exhibiting respiratory infections resulted in isolation of 13 (14%) Mollicutes. Based on biochemical reactions, growth inhibition test, PCR and/or sequencing, 8 (8.6%) isolates could be characterized as MG, 1 (1.08%) as MS, 3 (3.24%) as M. gallinarum and 1 (1.08%) as Acholeplasma laidlawii. The phylogenetic analysis using Intergenic spacer region (IGSR) of these MG isolates revealed that they clustered with USA strain whereas the vaccine strains were in different clade. Single locus sequence typing (SLST) revealed considerable nucleotides variation between 8 MG isolates and vaccine strains. Conclusively, Sequencing of IGSR region of MG can be used as a valuable epidemiological investigation tool for the differentiation of wild-type MG strains from vaccine strains.