Phycospheric Native Bacteria Pelagibaca bermudensis and Stappia sp. Ameliorate Biomass Productivity of Tetraselmis striata (KCTC1432BP) in Co-cultivation System through Mutualistic Interaction

Abstract

Effective sustainable algal cultivation techniques are essential for mass production of the marine microalga Tetraselmis for biofuel and array of co-products. The phycospheric communities affect the microalgal growth and metabolism through various allelochemical and nutrient interactions; hence, their potential to affect the quantity and quality of both biomass and bioproducts is significant. In the present study, we have screened the phycospheric communities of biofuel producing Tetraselmis striata (KCTC1432BP). A total of 26 bacterial strains were isolated and identified from the phycosphere of T. striata mass culture. Then, each bacterial strain was tested in co-cultivation conditions with T. striata for evaluating its growth promoting and inhibitory effects. Among these all strains, two promising strains (Pelagibaca bermudensis KCTC 13073BP and Stappia sp. KCTC 13072BP) were selected because of their maximum growth promoting effects and mutualistic interactions. The growth rate, biomass productivity, lipid contents, and fatty acids were analyzed during their combined growth in O3 media and compared with axenic growth of T. striata. Later, growth promoting mechanisms in the co-cultivation environment were investigated for these promising bacterial strains under replete and limited conditions of nutrients (nitrate, phosphate, and vitamin B12). The growth promoting potential of P. bermudensis was illustrated by the two fold enhancement in biomass productivity. These bacteria are promising for microalgal cultivation without any negative effects on the native seawater bacterial communities, as revealed by next generation sequencing analysis. This study represents, to date, the first report highlighting the role of phycospheric growth promoting bacteria of promising biofuel feedstock T. striata.

Tetraselmis suecica F&M‐M33 growth is influenced by its associated bacteria

“…Park et al . (2017) found a similar growth of T. striata in cultures grown with normal and limiting concentration of vitamin B 12 . In this work, the presence of the whole bacterial community (LAB), as well as the addition of the single bacteria, led to similar T. suecica F&M‐M33 growth with or without vitamins except for Leeuwenhoekiella sp.…”

“…most effective in promoting T. striata growth. P. bermudensis was more effective than Stappia in algal growth stimulation (Park et al ., 2017). …”

“…The Roseobacter ‐clade bacteria are aerobic anoxygenic phototrophs (which also include Porphyrobacter ) that can use energy from light while growing on organic substances as carbon source (Koblížek, 2015). Members of this clade are reported to favour algal growth (Grossart and Simon, 2007; Seyedsayamdost et al ., 2011; Luo and Moran, 2014; Park et al ., 2017), although some representatives are able to turn the mutualistic relationship into a parasitic one, lysing algal cells to feed on the intracellular substances, when molecules signalling algal cell ageing are released (Seyedsayamdost et al ., 2011). A stimulating effect of the Roseobacter ‐clade representative Pelagibaca bermudensis on T. striata growth was reported under P‐limitation, possibly implying a P recycling activity of this bacterium (Park et al ., 2017).…”

“…Members of this clade are reported to favour algal growth (Grossart and Simon, 2007; Seyedsayamdost et al ., 2011; Luo and Moran, 2014; Park et al ., 2017), although some representatives are able to turn the mutualistic relationship into a parasitic one, lysing algal cells to feed on the intracellular substances, when molecules signalling algal cell ageing are released (Seyedsayamdost et al ., 2011). A stimulating effect of the Roseobacter ‐clade representative Pelagibaca bermudensis on T. striata growth was reported under P‐limitation, possibly implying a P recycling activity of this bacterium (Park et al ., 2017). Grossart and Simon (2007) reported growth stimulation of Thalassiosira rotula by a Roseobacter ‐clade isolate in F/2 medium and inhibition in the more oligotrophic F/10, which is not in accordance with the behaviour shown by our isolates on T. suecica F&M‐M33; however, our cultures were performed at very high cell density (about 10 g l −1 at the end of the trials).…”

“…This may occur through different mechanisms, among which nutrient regeneration, release of trace elements and vitamins (particularly vitamin B 12 ) or of stimulatory compounds, enrichment of CO 2 and consumption of excess O 2 , or scavenging of reactive oxygen species in the algal microenvironment (Mouget et al ., 1995; Croft et al ., 2005; Hünken et al ., 2008; Natrah et al ., 2014; Cooper and Smith, 2015; Fuentes et al ., 2016; Park et al ., 2017). Addition of selected bacterial strains in mass cultures has been shown to have a stabilizing effect, improving microalgal production reliability (Fukami et al ., 1997).…”