Bacteria-mediated aggregation of the marine phytoplankton Thalassiosira weissflogii and Nannochloropsis oceanica

© 2020, The Author(s). The ecological relationships between heterotrophic bacteria and marine phytoplankton are complex and multifaceted, and in some instances include the bacteria-mediated aggregation of phytoplankton cells. It is not known to what extent bacteria stimulate aggregation of marine phytoplankton, the variability in aggregation capacity across different bacterial taxa or the potential role of algogenic exopolymers in this process. Here we screened twenty bacterial isolates, spanning nine orders, for their capacity to stimulate aggregation of two marine phytoplankters, Thalassiosira weissflogii and Nannochloropsis oceanica. In addition to phytoplankton aggregation efficiency, the production of exopolymers was measured using Alcian Blue. Bacterial isolates from the Rhodobacterales, Flavobacteriales and Sphingomonadales orders stimulated the highest levels of cell aggregation in phytoplankton cultures. When co-cultured with bacteria, exopolymer concentration accounted for 34.1% of the aggregation observed in T. weissflogii and 27.7% of the aggregation observed in N. oceanica. Bacteria-mediated aggregation of phytoplankton has potentially important implications for mediating vertical carbon flux in the ocean and in extracting phytoplankton cells from suspension for biotechnological applications

Photosynthetic carbon uptake induces autoflocculation of the marine microalga Nannochloropsis oculata

© 2017 Elsevier B.V. Microalgal biomass has been used to produce biofuels, aquaculture feed, high-value chemicals such as pigments and antioxidants, and even human food. This study addresses one of the key bottlenecks to the commercialisation of microalgal bioproducts: the high energy and environmental cost of harvesting microalgal cells out of suspension. An innovative and sustainable autoflocculation procedure was developed to pre-concentrate microalgal biomass for easier harvesting. Microalgal cell agglomeration by autoflocculation at high pH was induced for the first time, without the addition of a chemical flocculant, in the commercially-relevant microalga Nannochloropsis oculata. Photosynthetic inorganic carbon uptake, in the absence of carbon dioxide supply by mass transfer, was used to raise the culture pH. Autoflocculation started at pH 9.5 and reached a maximum flocculation efficiency of 90% at pH 10.4. Microalgal surface charge-neutralisation by calcium cations, and sweep flocculation by calcium carbonate and calcium phosphate precipitates were identified as the dominant flocculation mechanisms. This was also the first study to measure changes in bacterial community composition under autoflocculation. There was a clear shift from free-living bacteria in suspension to attached bacteria during autoflocculation, with Flavobacteriales becoming the dominant order of bacteria. This highlights the influential role of attached bacteria and bacteria-produced extracellular polymeric substances in microalgal flocculation. This study shows that regulating carbon dioxide supply is a promising green alternative to traditional microalgal flocculation processes as it alleviates the requirement for costly and harmful chemical flocculants and brings us closer to sustainable microalgal bioproducts

Regulation of cell delamination during cortical neurodevelopment and implication for brain disorders

Cortical development is dependent on key processes that can influence apical progenitor cell division and progeny. Pivotal among such critical cellular processes is the intricate mechanism of cell delamination. This indispensable cell detachment process mainly entails the loss of apical anchorage, and subsequent migration of the mitotic derivatives of the highly polarized apical cortical progenitors. Such apical progenitor derivatives are responsible for the majority of cortical neurogenesis. Many factors, including transcriptional and epigenetic/chromatin regulators, are known to tightly control cell attachment and delamination tendency in the cortical neurepithelium. Activity of these molecular regulators principally coordinate morphogenetic cues to engender remodeling or disassembly of tethering cellular components and external cell adhesion molecules leading to exit of differentiating cells in the ventricular zone. Improper cell delamination is known to frequently impair progenitor cell fate commitment and neuronal migration, which can cause aberrant cortical cell number and organization known to be detrimental to the structure and function of the cerebral cortex. Indeed, some neurodevelopmental abnormalities, including Heterotopia, Schizophrenia, Hydrocephalus, Microcephaly, and Chudley-McCullough syndrome have been associated with cell attachment dysregulation in the developing mammalian cortex. This review sheds light on the concept of cell delamination, mechanistic (transcriptional and epigenetic regulation) nuances involved, and its importance for corticogenesis. Various neurodevelopmental disorders with defective (too much or too little) cell delamination as a notable etiological underpinning are also discussed

Action spectra of oxygen production and chlorophyll a fluorescence in the green microalga Nannochloropsis oculata

The first complete action spectrum of oxygen evolution and chlorophyll a fluorescence was measured for the biofuel candidate alga Nannochloropsis oculata. A novel analytical procedure was used to generate a representative and reproducible action spectrum for microalgal cultures. The action spectrum was measured at 14 discrete wavelengths across the visible spectrum, at an equivalent photon flux density of 60μmolphotonsm-2s-1. Blue light (~414nm) was absorbed more efficiently and directed to photosystem II more effectively than red light (~679nm) at light intensities below the photosaturation limit. Conversion of absorbed photons into photosynthetic oxygen evolution was maximised at 625nm; however, this maximum is unstable since neighbouring wavelengths (646nm) resulted in the lowest photosystem II operating efficiency. Identifying the wavelength-dependence of photosynthesis has clear implications to optimising growth efficiency and hence important economic implications to the algal biofuels and bioproducts industries. © 2014 Elsevier Ltd

Proteomic and biophysical analyses reveal a metabolic shift in nitrogen deprived Nannochloropsis oculata

© 2016. The microalga Nannochloropsis oculata is a model organism for understanding intracellular lipid production, with potential benefits to the biofuel, aquaculture and nutraceutical industries. It is well known that nitrogen deprivation increases lipid accumulation in microalgae but the underlying processes are not fully understood. In this study, detailed proteomic and biophysical analyses were used to describe mechanisms that regulate carbon partitioning in nitrogen-deplete N. oculata. The alga selectively up- or down-regulated proteins to shift its metabolic flux in order to compensate for deficits in nitrate availability. Under nitrogen deprivation, proteins involved in photosynthesis, carbon fixation and chlorophyll biosynthesis were all down-regulated, and this was reflected in reduced cell growth and chlorophyll content. Protein content was reduced 4.9-fold in nitrogen-deplete conditions while fatty acid methyl esters increased by 60%. Proteomic analysis revealed that organic carbon and nitrogen from the breakdown of proteins and pigments is channeled primarily into fatty acid synthesis. As a result, the fatty acid concentration increased and the fatty acid profile became more favorable for algal biodiesel production. This advancement in microalgal proteomic analysis will help inform lipid accumulation strategies and optimum cultivation conditions for overproduction of fatty acids in N. oculata

Emerging role of m6Am^{6}A methylome in brain development

Dynamic modification of RNA affords proximal regulation of gene expression triggered by non-genomic or environmental changes. One such epitranscriptomic alteration in RNA metabolism is the installation of a methyl group on adenosine [$N^{6}$-methyladenosine ($m^{6}A$)] known to be the most prevalent modified state of messenger RNA (mRNA) in the mammalian cell. The methylation machinery responsible for the dynamic deposition and recognition of $m^{6}A$ on mRNA is composed of subunits that play specific roles, including reading, writing, and erasing of $m^{6}A$ marks on mRNA to influence gene expression. As a result, peculiar cellular perturbations have been linked to dysregulation of components of the mRNA methylation machinery or its cofactors. It is increasingly clear that neural tissues/cells, especially in the brain, make the most of $m^{6}A$ modification in maintaining normal morphology and function. Neurons in particular display dynamic distribution of $m^{6}A$ marks during development and in adulthood. Interestingly, such dynamic $m^{6}A$ patterns are responsive to external cues and experience. Specific disturbances in the neural $m^{6}A$ landscape lead to anomalous phenotypes, including aberrant stem/progenitor cell proliferation and differentiation, defective cell fate choices, and abnormal synaptogenesis. Such $m^{6}A$-linked neural perturbations may singularly or together have implications for syndromic or non-syndromic neurological diseases, given that most RNAs in the brain are enriched with $m^{6}A$ tags. Here, we review the current perspectives on the $m^{6}A$ machinery and function, its role in brain development and possible association with brain disorders, and the prospects of applying the clustered regularly interspaced short palindromic repeats (CRISPR)–dCas13b system to obviate $m^{6}A$-related neurological anomalies