Screening and selection of growth-promoting bacteria for Dunaliella cultures

Abstract

Previous studies have demonstrated that bacteria influence microalgal metabolism, suggesting that the selection and characterization of growth-promoting bacteria should offer a new strategy for improving industrial algal cultivation. In the present study, 48 cultivable bacteria were isolated from marine microalgae species and identified using 16S rRNA phylogenetic analysis. The recovered bacteria were found to be members of the α-and γ-Proteobacteria, Cytophaga-Flavobacterium-Bacteroides (CFB) and gram-positive monophyletic clusters. To address the effect of these bacteria on the growth of Dunaliella sp. individually, an experimental high-throughput tool was developed to simultaneously compare replicated associations. A two-step approach was used to monitor growth rate and biomass accumulation of Dunaliella sp. in mixed culture with bacteria, which proved the highthroughput device to be an efficient tool for the selection of growth-promoting bacteria. Depending on the bacterial strain involved, inhibitory effects were recorded for maximal microalgal growth rate, whereas inhibitory and stimulating effects were registered on microalgal biomass accumulation and nitrogen incorporation. Organic nitrogen remineralization by Alteromonas sp. SY007 and Muricauda sp. SY244 is discussed to explain the higher biomass and ammonium incorporation of Dunaliella sp. obtained under nitrogen-limited conditions. These bacteria could be considered as helpers for N accumulation in Dunaliella sp. cells.

Effect of bacteria on growth and biochemical composition of two benthic diatoms Halamphora coffeaeformis and Entomoneis paludosa

“…It is currently accepted that bacteria can positively or negatively affect microalgal growth performance (Cole, 1982;Le Chevanton et al, 2013;Natrah et al, 2014;Park et al, 2008). In the present study, both higher diatoms growth rates and cell division were related to the highest bacterial abundance, a positive interaction already observed for Thalassiosira rotula (Grossart and Simon, 2007) and Skeletonema costatum (Grossart et al, 2006b) in culture.…”

“…Some species of Rhodobacteraceae also have been described with negative effects on microalgae. They decreased both growth and maximal biomass of Dunaliella in culture (Le Chevanton et al, 2013), but in this later case, bacterial strains were distinct from those of Dunaliella's assemblage, isolated from some other microalgae (E. huxleyi and diatoms) culture media. Their action could be thus considered as exogenous factor on the microalgae biology, a situation that does not correspond to the present study where bacterial strains have been harboured for a long time with the two diatoms in culture.…”

“…Alteromonas sp., Muricauda sp.) can also convert some nitrogen compounds into chemical forms subsequently assimilated by microalgae (Le Chevanton et al, 2013;Tai et al, 2009). Other improvement of the microalgal growth are made by hormones, such as indole-3-acetic acid by Azospirillum spp.…”

“…Pseudomonas sp., Halomonas sp.) can have a negative impact on growth and development of microalgal species (Le Chevanton et al, 2013). A competition can occur between the two groups for the use of resources such as inorganic nutrients (nitrate, phosphate), especially under limiting conditions (Guerrini et al, 1998;Joint et al, 2002;Rhee, 1972).…”

“…Pseudomonas sp., Halomonas sp.) on microalgal growth performance (Le Chevanton et al, 2013). Heterotrophic bacteria phyla commonly associated to diatom cultures are Proteobacteria and Bacteroidetes (Schäfer et al, 2002) and the main species belong to Alteromonas, Flavobacterium, Roseobacter, and Sulfitobacter genera (Grossart et al, 2005;Hunken et al, 2008;Kaczmarska et al, 2005;Sapp et al, 2007a;Sapp et al, 2007b;Sapp et al, 2007c).…”