Background: The nematode infraorder Tylenchomorpha (Class Chromadorea) includes plant parasites that are of agricultural and economic importance, as well as insect-associates and fungal feeding species. Among tylenchomorph plant parasites, members of the superfamily Tylenchoidea, such as root-knot nematodes, have great impact on agriculture. Of the five superfamilies within Tylenchomorpha, one (Aphelenchoidea) includes mainly fungal-feeding species, but also some damaging plant pathogens, including certain Bursaphelenchus spp. The evolutionary relationships of tylenchoid and aphelenchoid nematodes have been disputed based on classical morphological features and molecular data. For example, similarities in the structure of the stomatostylet suggested a common evolutionary origin. In contrast, phylogenetic hypotheses based on nuclear SSU ribosomal DNA sequences have revealed paraphyly of Aphelenchoidea, with, for example, fungal-feeding Aphelenchus spp. within Tylenchomorpha, but Bursaphelenchus and Aphelenchoides spp. more closely related to infraorder Panagrolaimomorpha. We investigated phylogenetic relationships of plant-parasitic tylenchoid and aphelenchoid species in the context of other chromadorean nematodes based on comparative analysis of complete mitochondrial genome data, including two newly sequenced genomes from Bursaphelenchus xylophilus (Aphelenchoidea) and Pratylenchus vulnus (Tylenchoidea). Results: The complete mitochondrial genomes of B. xylophilus and P. vulnus are 14,778 bp and 21,656 bp, respectively, and identical to all other chromadorean nematode mtDNAs in that they contain 36 genes (lacking atp8) encoded in the same direction. Their mitochondrial protein-coding genes are biased toward use of amino acids encoded by T-rich codons, resulting in high A+T richness. Phylogenetic analyses of both nucleotide and amino acid sequence datasets using maximum likelihood and Bayesian methods did not support B. xylophilus as most closely related to Tylenchomorpha (Tylenchoidea). Instead, B. xylophilus, was nested within a strongly supported clade consisting of species from infraorders Rhabditomorpha, Panagrolaimomorpha, Diplogasteromorpha, and Ascaridomorpha. The clade containing sampled Tylenchoidea (P. vulnus, H. glycines, and R. similis) was sister to all analyzed chromadoreans. Comparison of gene arrangement data was also consistent with the phylogenetic relationships as inferred from sequence data. Alternative tree topologies depicting a monophyletic grouping of B. xylophilus (Aphelenchoidea) plus Tylenchoidea, Tylenchoidea plus Diplogasteromorpha (Pristionchus pacificus), or B. xylophilus plus Diplogasteromorpha were significantly worse interpretations of the mtDNA data. Conclusions: Phylogenetic trees inferred from nucleotide and amino acid sequences of mtDNA coding genes are in agreement that B. xylophilus (the single representative of Aphelenchoidea) is not closely related to Tylenchoidea, indicating that these two groups of plant parasites do not share an exclusive most recent common ancestor, and that certain morphological similarities between these stylet-bearing nematodes must result from convergent evolution. In addition, the exceptionally large mtDNA genome size of P. vulnus, which is the largest among chromadorean nematode mtDNAs sequenced to date, results from lengthy repeated segments in non-coding regions.

Inflammation mediated by the innate immune system is an organism's protective mechanism against infectious environmental risk factors. It is also a driver of the pathogeneses of various human diseases, including cancer development and progression. Microalgae are increasingly being focused on as sources of bioactive molecules with therapeutic potential against various diseases. Furthermore, the antioxidant, anti-inflammatory, and anticancer potentials of microalgae and their secondary metabolites have been widely reported. However, the underlying mechanisms remain to be elucidated. Therefore, in this study, we investigated the molecular mechanisms underlying the anti-inflammatory and anticancer activities of the ethanol extract of the Antarctic freshwater microalga Micractinium sp. (ETMI) by several in vitro assays using RAW 264.7 macrophages and HCT116 human colon cancer cells. ETMI exerted its anti-inflammatory activity by modulating the main inflammatory indicators such as cyclooxygenase (COX)-2, interleukin (IL)-6, inducible nitric oxide synthase (iNOS), tumor necrosis factor (TNF)-α, and nitric oxide (NO) in a dose-dependent manner. In addition, ETMI exerted cytotoxic activity against HCT116 cells in a dose-dependent manner, leading to significantly reduced cancer cell proliferation. Further, it induced cell cycle arrest in the G1 phase through the regulation of hallmark genes of the G1/S phase transition, including CDKN1A, and cyclin-dependent kinase 4 and 6 (CDK4 and CDK6, respectively). At the transcriptional level, the expression of CDKN1A gradually increased in response to ETMI treatment while that of CDK4 and CDK6 decreased. Taken together, our findings suggest that the anti-inflammatory and anticancer activities of the Antarctic freshwater microalga, Micractinium sp., and ETMI may provide a new clue for understanding the molecular link between inflammation and cancer and that ETMI may be a potential anticancer agent for targeted therapy of colorectal cancer.

Inflammation triggered by the innate immune system is a strategy to protect organisms from the risk of environmental infection. However, it has recently become clear that inflammation can cause a variety of human diseases, including cancer. In this study, we investigated the effects of an ethanol extract of the Antarctic freshwater microalgae, Chloromonas reticulata (ETCH), on inflammation and carcinogenesis in RAW 264.7 macrophages and HCT116 human colon cancer cells, respectively. ETCH exhibited significant anti-inflammatory activity through the dose-dependent modulation of major inflammatory markers such as COX-2, IL-6, iNOS, TNF-α, and NO production. For example, ETCH reduced LPS-induced upregulation of COX-2, IL-6, iNOS, and TNF- alpha mRNA levels, leading to a significant decrease in the levels of LPS-stimulated NO and IL-6 as well as TNF-alpha products. In contract, ETCH exhibited dose-dependent cytotoxic activity against HCT116 cells, yielding a profound reduction in the proliferation of the cancer cells. Furthermore, ETCH induced G2 phase cell cycle arrest by transcriptionally regulating of genes involved in G2 / M transition including p21 (CDKN1A), cyclin B1 (CCNB1), and CDK1; CDKN1A mRNA levels were upregulated in response to ETCH, whereas CCNB1 and CDK1 were downregulated. This study reports for the first time anti-inflammatory and anti-cancer effects of, C. reticulata and provides new insights into the molecular mechanisms of the linkage between inflammation and cancer.