| Bacillariaceae Ehrenberg is a family which belongs to Bacillariophyta,Bacillariophycidae,Bacillariales.The Bacillariaceae is a very species-rich family of raphid diatoms.Traditionally,key features of this family were the possession of a central or eccentric raphe usually raised above the rest of the valve on a ridge referred to as the “keel” and subtended internally by rib-like or more substantial bridges of silica,called fibulae.The shape,decoration and raphe are often the main characters for identification.Based on our collections,severval species in this family were examined using LM and SEM to observe the morphological features,and isolated colony were cultured.Four genes SSU r DNA?LSU r DNA?rbc L and psb C were sequenced,and data was concatenated to construct phylogenetic trees using Maximum Likelihood and Bayesian Analysis techniques.The relationship between the genera and taxa within the genus were analysed.The main results are as follows:1.Thirty-two strains were isolated from more than 100 samples.These are identified as three families,five genera and seventeen taxa.2.The phylogenetic trees of different species of Bacillariaceae were constructed based on the SSU r DNA?LSU r DNA?rbc L and psb C sequences data using ML and BI methods.The main results are as follows:1)Molecular systems results showed that Bacillariaceae is monophyletic.The Bacillaria are located at the base of the phylogenetic tree,and several genera located in the middle as Hantzschia,Cylindrotheca,and Simonsenia,which fully supports their monophyletic origin.At the end of the phylogenetic tree is Tryblionella and Denticula.All the analyses recovered Nitzschia as non-monophyletic.2)The genus Nitzschia is non-monophyletic.Different branches are closely related to different morphological groups within the genus.Nitzschia species comprise all of clades.The N.Sect.Lanceolatae often clustered into two large branches.One Clade contains species of Nitzschia capitellata?Nitzschia palea,and N.Sect.Obtusae group species of Nitzschia clausii?N.Sect.Nitzschiellae group species of Nitzschia reversa?Nitzschia acicularis;Another Clade contains species of Nitzschia inconspicua and Nitzschia amphibia;Species of N.Section Sigmoideae and N.Sect.Dissipatae were gathered in a clade;N.Sect.Lineares group species of Nitzschia linearis ?N.Sect.Dubiae ? Bilobatae group species of Nitzschia commutate were gathered in a clade.3.Combined analysis of morphology and phylogeny,some species with special morphological characteristics are relatively conservative,and the valve morphology?raphe-keel system and number of keel are still the important characters for the classification of this family.Phylogenetic analysis showed its superiority at distinguish species with unclear morphology,and can better determine the evolutionary relationship of different genera and species.4.The biomass and neutral lipid fluorescence of each cultured strains were measured explore oil-producing potential.Comparison of these strains were concluded that five species strains Nitzschia palea ? Nitzschia amphibia ? Nitzschia gracilis ?Nitzschia fonticola ? Hantzschia amphioxys were showed good petenial which have rapid growth rate and high oil productivity.This study provides reference data for the taxonomic study of Bacillariaceae and the study of lipid-rich microalgae. |
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