Characterisation of bacteria from the cultures of a Chlorella strain isolated from textile wastewater and their growth enhancing effects on the axenic cultures of Chlorella vulgaris in low nutrient media

There is increasing interest in the use of microalgae grown on wastewater to provide useful metabolites. Several bacteria have been shown to affect the growth rate and quality of the algae, but it is not clear if this is specific to a particular group of bacteria or if nutrient conditions can also influence this interaction. The bacterial community associated with a freshwater Chlorella sp. isolated from open pond textile factory wastewater was characterised and a diverse group of bacteria isolated. We provide evidence that nutrient concentrations affect bacterial community composition. When grown in BG11 medium, the community was dominated by Pseudomonas sp., but when grown in Chu 10 medium (which contains lower nitrogen and phosphorus), the relative abundance of a Brevundimonas spp. increased. Several of the bacteria isolated were able to influence the growth of an axenic Chlorella vulgaris culture. The Pseudomonas sp. had a negative effect in all media tested whereas several isolates enhanced C. vulgaris growth, but only in Chu 10 medium. This supports the theory that bacterial stimulation of algal growth is not limited to species-specific interactions but is influenced by environmental conditions. In low nutrient conditions, Chlorella sp. may be increasingly dependent on bacteria for growth

Modulation of Polar Lipid Profiles in Chlorella sp. in Response to Nutrient Limitation

We evaluate the effects of nutrient limitation on cellular composition of polar lipid classes/species in Chlorella sp. using modern polar lipidomic profiling methods (Liquid Chromatography-Tandem Mass Spectrometry; LC-MS/MS). Total polar lipid concentration was highest in nutrient-replete (HN) cultures with a significant reduction in monogalactosyldiacylglycerol (MGDG), phosphatidylglycerol (PG), phosphatidylcholine (PC) and phosphatidylethanolamine (PE) class concentrations for nutrient-deplete (LN) cultures. Moreover, reductions in the abundance of MGDG relative to total polar lipids versus an increase in the relative abundance of digalactosyldiacylglycerol (DGDG) were recorded in LN cultures. In HN cultures, polar lipid species composition remained relatively constant throughout culture with high degrees of unsaturation associated with acyl moieties. Conversely, in LN cultures lipid species composition shifted towards greater saturation of acyl moieties. Multivariate analyses revealed that changes in the abundance of a number of species contributed to the dissimilarity between LN and HN cultures but with dominant effects from certain species e.g. reduction in MGDG 34:7 (18:3/16:4). Results demonstrate that Chlorella sp. significantly alters its polar lipidome in response to nutrient limitation and this is discussed in terms of physiological significance and polar lipids production for applied microalgal production systems

Dip in the gene pool: metagenomic survey of natural coccolithovirus communities

Despite the global oceanic distribution and recognised biogeochemical impact of coccolithoviruses (EhV), their diversity remains poorly understood. Here we employed a metagenomic approach to study the occurrence and progression of natural EhV community genomic variability. Analysis of EhV metagenomes from the early and late stages of an induced bloom led to three main discoveries. First, we observed resilient and specific genomic signatures in the EhV community associated with the Norwegian coast, which reinforce the existence of limitations to the capacity of dispersal and genomic exchange among EhV populations. Second, we identified a hyper-variable region (approximately 21kbp long) in the coccolithovirus genome. Third, we observed a clear trend for EhV relative amino-acid diversity to reduce from early to late stages of the bloom. This study validated two new methodological combinations, and proved very useful in the discovery of new genomic features associated with coccolithovirus natural communities