Biology subjects

Halim, R.

Publications and source records attributed to Halim, R..

3 recordsLinked to original sources

bioRxiv2025

Protease secreting Nannochloropsis limnetica can valorise invasive plants through circular water-use and accumulate neutral lipids

AO_SCPLOWBSTRACTC_SCPLOWNannochloropsis limnetica can be cultivated on a wide range of effluents and generate high value lipids. Using a fed-batch system, this microalgae was used to demonstrate circular reuse of water to valorise protein depleted fractions (PDF) generated from Gorse leaf protein concentrate (LPC) production. Protein, phenolics and sugar content in the PDF was measured over seven days and corresponding microalgal lipid content was profiled. Extracellular protease activity was also screened to understand how N. limnetica digests and utilises proteins in the medium. A signal peptide-based approach predicted seven proteases expected to be secreted. N. limnetica could rapidly deplete nutrients (ksugar=0.20 {+/-} 0.06 day-1 and kproteins=0.17 {+/-} 0.04 day-1) from the wastewater which could be reused for subsequent LPC extraction processes without any impact on recovery or purity. Phenolics levels remained unaffected during microalgal growth and accumulated in the water across each extraction cycle. Microalgal neutral lipid content ([~]132.8 mglipid g-1 ) was higher in the effluent compared to standard BBM ([~]114.5 mglipid g-1 ). Casein agar plates and 1D zymogram confirmed extracellular protease production by N. limnetica, although their identities remains unclear owing to conflicting / fragmented data from the LC/MS analysis. This work shows that N. limnetica is able to secrete proteases to digest and utilise residual proteins in the medium, and can be employed to valorise agricultural wastewater. Identification of the proteases will require further investigation. HighlightsO_LIN. limnetica can rapidly deplete residual nutrients from LPC effluents. C_LIO_LIN. limnetica accumulates higher neutral lipids with LPC effluents versus BBM. C_LIO_LIN. limnetica secretes extracellular proteases to digest proteins in the medium. C_LIO_LIWater can be circularly reused between LPC production and N. limnetica cultivation. C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=108 SRC="FIGDIR/small/691304v2_ufig1.gif" ALT="Figure 1"> View larger version (34K): org.highwire.dtl.DTLVardef@1524de0org.highwire.dtl.DTLVardef@76cea1org.highwire.dtl.DTLVardef@1f7ad4aorg.highwire.dtl.DTLVardef@191f929_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2025

Using network component analysis to study axenisation strategies for phototrophic eukaryotic microalgae

BackgroundThe axenisation of phototrophic eukaryotic microalgae has been studied for over a century, with antibiotics commonly employed to achieve axenic cultures. However, this approach often yields inconsistent outcomes and may contribute to the emergence of antibiotic-resistant microbes. A comprehensive review of microalgal species and the methods used to achieve axeny could provide insights into potentially effective workflows and identify gaps for future exploration. MethodsScholarly databases were systematically searched, supplemented by citation network analysis and AI-assisted tools, to collect studies on achieving axenic phototrophic eukaryotic microalgae cultures. Data about microalgal species, axenisation workflows, outcomes, and related factors (e.g., sampling locations, axenisation confirmation methods) were summarised. Network component analysis was used to identify clusters of commonly reported methods for diatoms, dinoflagellates, and green algae. A scoring framework was developed to assess the quality and reliability of evidence presented in the studies. ResultsPromising workflows circumventing the use of antibiotics appear to be filtration {leftrightarrow} washing {leftrightarrow} micropicking for diatoms, micropicking {leftrightarrow} subculturing {leftrightarrow} flow cytometry for dinoflagellates, and anoxy {leftrightarrow} photosensitisation {leftrightarrow} streak plating for green algae. Evidence from the literature indicates that a combination of microscopy (e.g., epifluorescence), cell counting (e.g., agar plating), and sequencing (16S and/or 18S) could enhance confidence in confirming axeny. ConclusionMore systematic and high quality primary research is required to identify effective workflows for other microalgal divisions and fortify / contradict the ones proposed herein based on network component analysis.

microbiology↗

bioRxiv2024

Axenisation of oleaginous microalgal cultures via anoxic photosensitisation.

Growing interest in sustainable biofuel research has necessitated high quality axenic oleaginous microalgal strains. Unfortunately, most strains available in culture banks contain commensal microbes such as bacteria and the default decontamination method involves antibiotic treatment which has begun to exacerbate the emergence of antibiotic resistance. To overcome this problem, anoxic photosensitisation was investigated as an alternate approach. Four oleaginous microalgal species (Tetradesmus obliquus, Desmodesmus armatus, Chlorella vulgaris and Nannochloropsis limnetica) were incubated in varying concentrations of Rose Bengal (0 {micro}M, 1 {micro}M, 3 {micro}M and 9 {micro}M) either in normal (oxic) or anoxic conditions, for 72 h under light (8.85 {+/-} 0.40 W m-2) in a specially designed heterotrophic growth complex (HGC) medium, followed by 72 h in standard Bolds Basal Medium (BBM). Commonly used antibiotics-based protocol was used as the control method. Post treatment, cell numbers and percentage populations were counted with Flow cytometry, and viability was tested using standard plating methods using BBM and LB. Additionally, the contaminating microbes in the cultures were profiled using 16s rRNA sequencing. Anoxic conditions were able to significantly decrease bacterial content, albeit with an equally detrimental effect on the microalgal population. Although the responses differed between the microalgae, anoxic incubation along with Rose Bengal at 3 {micro}M was able to completely decontaminate N. limnetica and C. vulgaris, while D. armatus and T. obliquus could be decontaminated with an additional streak-plating step. None of the cultures could be decontaminated using antibiotics treatment owing to the presence of gram-negative, multi-drug resistant bacteria such as S. maltophilia, M. foliorum and S. chilensis. These results suggest that decontamination of xenic microalgal cultures was largely due to anoxy, that was synergistically enhanced by Rose Bengal at a concentration of [≥]3 {micro}M. HighlightsO_LIRose Bengal at 3 {micro}M in anoxic conditions can help achieve axenic microalgal cultures. C_LIO_LIStandard antibiotics were unable to decontaminate any of the cultures owing to the presence of multi-drug resistant bacteria. C_LIO_LIStandard antibiotics treatment was deleterious to D. armatus cultures. C_LIO_LIStreak plating may be required for D. armatus and T. obliquus after anoxic Rose Bengal treatment to obtain individual colonies for further inoculation. C_LI

microbiology↗