Enhanced performance of the microalga Chlorella sorokiniana remotely induced by the plant growth-promoting bacteria Azospirillum brasilense and Bacillus pumilus

Abstract

Remote effects (occurring without physical contact) of two plant growth-promoting bacteria (PGPB)Azospirillum brasilense Cd and Bacilus pumilus ES4 on growth of the green microalga Chlorella sorokiniana UTEX 2714 were studied. The two PGPB remotely enhanced the growth of the microalga, up to six-fold, and its cell volume by about three-fold. In addition to phenotypic changes, both bacteria remotely induced increases in the amounts of total lipids, total carbohydrates, and chlorophyll a in the cells of the microalga, indicating an alteration of the microalga's physiology. The two bacteria produced large amounts of volatile compounds, including CO 2 , and the known plant growth-promoting volatile 2,3-butanediol and acetoin. Several other volatiles having biological functions in other organisms, as well as numerous volatile compounds with undefined biological roles, were detected. Together, these bacteria-derived volatiles can positively affect growth and metabolic parameters in green microalgae without physical attachment of the bacteria to the microalgae. This is a new paradigm on how PGPB promote growth of microalgae which may serve to improve performance of Chlorella spp. for biotechnological applications.In vitro culturing at laboratory or mass industrial scales is the most common way by which the biotechnological industry is producing products from microalgae 1,2 and inoculants of plant growth-promoting bacteria (PGPB) for agricultural and environmental applications 3 . The current paradigm of how PGPB enhance plant growth is through attachment of the bacteria to plant roots. PGPB first establish a stable physical interaction with its host and subsequently colonize the root system, which results in beneficial effects on plants 4,5 When the PGPB move toward its host before attachment, the chances of successful colonization improve 6 . In the absence of attachment and colonization to plant surface, no effect of PGPB on higher plants are recorded 7 . Attachment of the PGPB Azospirillum spp. to roots of many plant species has been demonstrated since the emergence of the field some 40 years ago 4,[8][9][10][11][12] . A. brasilense has also been observed to attach to, and form stable aggregates with, the microalga Chlorella vulgaris 13 . Similar interactions have also been proposed for Gram-positive bacteria, such as Bacillus spp.14 . While attachment to roots has been documented as the major requirement for a beneficial association of PGPB with plants 7 , it is also well documented that the PGPB

Plant Growth-Promoting Methylobacteria Selectively Increase the Biomass of Biotechnologically Relevant Microalgae

“…Algae were shown to benefit from micro-and macronutrients provided by bacteria, and in return, release dissolved organic carbon into their surroundings. Efforts have been made in identifying bacteria that positively contribute to the algal fitness; especially nitrogenfixing bacteria of the genera Azospirillum, Rhizobium, and Bacillus, known for their beneficial effect on plants, are promising candidates (Gonzalez and Bashan, 2000;de-Bashan et al, 2008;Hernandez et al, 2009;de-Bashan and Bashan, 2010;Kim et al, 2014;Amavizca et al, 2017). While binary algaebacteria interactions were explored in the past, little is known about the algae-associated microbiota as well as potentially beneficial algae-microbe interactions with distinct members of the plant microbiota.…”

“…Mutualistic inter-kingdom symbioses are not only limited to land plants, but also extend to green algae (Xie et al, 2013;Hom et al, 2015). Following the same principles of plant growth-promoting rhizobacteria, algae-associated bacteria harbor potential to stimulate growth and morphogenesis of algae by releasing essential minerals, vitamins, auxins and quorum sensing signaling molecules (Joint et al, 2002;Croft et al, 2006;Goecke et al, 2010;Amavizca et al, 2017). The equivalent to the rhizosphere -the immediate surrounding of roots with increased biological and chemical activity in soil -is the phycoscphere, which is the area surrounding a phytoplankton cell, rich in dissolved organic matter and metabolites exuded by the cell in the surrounding water and stimulating the growth of heterotrophic bacteria (Seymour et al, 2017).…”

Smells from the desert: Microbial volatiles that affect plant growth and development of native and non‐native plant species

“…Esters such as methyl isobutyrate, EI, methyl 2‐methylbutanoate, and methyl 3‐methylbutanoate are emitted by Actynomycetes and Streptomyces (Schöller, Gürtler, Pedersen, Molin, & Wilkins, ; Schulz & Dickschat, ). IA, among several other volatiles, was produced by Azospirillum brasilense , Bacillus pumilus , and Escherichia coli in interaction with the microalga Chlorella sorokiniana , enhancing its performance (Amavizca et al, ). EV has been reported both in bacteria and fungi.…”

Biomass Production and Nutrient Removal through Cultivation of <i>Euglena gracilis</i> in Domestic Wastewater

“…5. These data refer to the wastewater treatment performance promoting microalgal growth through providing nutrients, vitamins, phytohormones, chelators, or volatile organic compounds 12)- 16) , or by creating a favorable microenvironment 17) . Some previous studies have demonstrated through the cultivation of E. gracilis.…”