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While microalgae are a promising feedstock for production of fuels and other chemicals, a challenge for the algal bioproducts industry is obtaining consistent, robust algae growth. Algal cultures include complex bacterial communities and can be difficult to manage because specific bacteria can promote or reduce algae growth. To overcome bacterial contamination, algae growers may use closed photobioreactors designed to reduce the number of contaminant organisms. Even with closed systems, bacteria are known to enter and cohabitate, but little is known about these communities. Therefore, the richness, structure, and composition of bacterial communities were characterized in closed photobioreactor cultivations of Nannochloropsis salina in F/2 medium at different scales, across nine months spanning late summer-early spring, and during a sequence of serially inoculated cultivations. Using 16S rRNA sequence data from 275 samples, bacterial communities in small, medium, and large cultures were shown to be significantly different. Larger systems contained richer bacterial communities compared to smaller systems. Relationships between bacterial communities and algae growth were complex. On one hand, blooms of a specific bacterial type were observed in three abnormal, poorly performing replicate cultivations, while on the other, notable changes in the bacterial community structures were observed in a series of serial large-scale batch cultivations that had similar growth rates. Bacteria common to the majority of samples were identified, including a single OTU within the class Saprospirae that was found in all samples. This study contributes important information for crop protection in algae systems, and demonstrates the complex ecosystems that need to be understood for consistent, successful industrial algae cultivation. This is the first study to profile bacterial communities during the scale-up process of industrial algae systems.

The study of the interactions between plants and their microbial communities in the rhizosphere is important for developing sustainable management practices and agricultural products such as biofertilizers and biopesticides. Plant roots release a broad variety of chemical compounds to attract and select microorganisms in the rhizosphere. In turn, these plant-associated microorganisms, via different mechanisms, influence plant health and growth. In this review, we summarize recent progress made in unraveling the interactions between plants and rhizosphere microbes through plant root exudates, focusing on how root exudate compounds mediate rhizospheric interactions both at the plant-microbe and plant-microbiome levels. We also discuss the potential of root exudates for harnessing rhizospheric interactions with microbes that could lead to sustainable agricultural practices. Key words: rhizosphere, root exudates, microbial communities, plant-microbe interactions, plant-microbiome interactions. L'etude des interactions entre les plantes et leurs communautes microbiennes dans la rhizosphere est importante pour developper de pratiques de gestion durable et de produits agricoles comme les fertilisants et les pesticides biologiques. Les racines d'une plante liberent une grande variete de composes chimiques afin d'attirer et selectionner les microorganismes dans la rhizosphere. A leur tour, les microorganismes associes aux plantes, par l'intermediaire de differents mecanismes, influencent la sante et la croissance de la plante. Dans cet article de revue, nous resumons les progres realises recemment dans l'etude des interactions entre les plantes et les microbes de la rhizosphere a travers les exsudats des racines, en se concentrant sur la maniere par laquelle les composes de l'exsudat agissent comme intermediaries des interactions rhizospheriques a l'echelle plante-microbe et plante-microbiome. Nous discutons aussi du potentiel des exsudats de racines a maitriser les interactions rhizospheriques avec les microbes, ce qui pourrait conduire a des pratiques agricoles durables. [Traduit par la Redaction] Mots-cles: rhizosphere, exsudats de racines, communautes microbiennes, interactions plante-microbe, interactions plantemicrobiome., Introduction The amount of microbial species in the rhizosphere may fluctuate from thousands to millions (Nihorimbere et al. 2011), and accordingly, the interactions between roots and soil microbes are often [...]

The conversion of carbohydrates in biomass via fermentation is an important component of an overall strategy to decarbonize the production of fuels and chemicals. Owing to the cost and resources required to produce biomass hydrolysates, the economic and environmental sustainability of these fermentation processes requires that they operate with high yields, sugar conversion, and productivity. Immobilized‐cell technology in a continuous bioprocess can achieve significantly higher volumetric productivities than is possible from standard batch fermentation using free cells. Here, we demonstrate approaches for improvement of ethanol yield from algal hydrolysates and a mock hydrolysate medium. Saccharomyces cerevisiae was immobilized in alginate and incorporated into a two‐column immobilized cell reactor system. Furthermore, the yeast quorum‐sensing molecule, 2‐phenylethanol, was added to improve ethanol yield by restricting growth and diverting sugar to ethanol. The bioreactor system could achieve high ethanol volumetric productivity (>20 g/Lreactor·h) and high glucose conversion (>99%) in mock hydrolysate, while the addition of 0.2% 2‐phenylethanol resulted in 4.9% higher ethanol yield. With an algal hydrolysate of <10 g/L sugar, the ethanol volumetric productivity reached 9.8 g/Lreactor·h, and the addition of 0.2% 2‐phenylethanol increased the ethanol yield by up to 7.4%. These results demonstrate the feasibility of novel strategies to achieve sustainability goals in biomass conversions. [ABSTRACT FROM AUTHOR]