Chaetoceros muelleri is one of the most widely used microalgae species in aquaculture in northwestern Mexico as food for fish and crustaceans. Its importance is due to its fast growth, nutritional quality and lipid accumulation under nutrient-limiting conditions. However, the biochemical and molecular mechanisms of uptake of phosphorus (P) limiting conditions for this species is still unknown. This study aimed to analyze the growth and biochemical composition of C muelleri in response to different phosphorus concentrations. Four treatments under different phosphorus conditions were used: control (72 µM P), excess (144 µM P) and two treatments with phosphorus limitation, limited A (18 µM P) and limited B (7 µM P). The highest cell concentration was observed in control and excess of P (>3.4×10 6 cells mL -1 ). The highest dry mass concentration and chlorophyll-a content were found in control medium (72 µM P) whereas the highest total lipid (4.42%) was found in the lowest P-concentration medium (7 µM P). No significant differences were found in the total protein content, but we did find differences between the treatments with phosphorus limitation (7 and 18 µM P).

Diatoms are the most abundant group of phytoplankton, and their success lies in their significant adaptation ability to stress conditions, such as nutrient limitation. Phosphorus (P) is a key nutrient involved in the transfer of energy and the synthesis of several cellular components. Molecular and biochemical mechanisms related to how diatoms cope with P deficiency are not clear, and research into this has been limited to a few species. Among the molecular responses that have been reported in diatoms cultured under P deficient conditions is the upregulation of genes encoding enzymes related to the transport, assimilation, remobilization and recycling of this nutrient. Regarding biochemical responses, due to the reduction of the requirements for carbon structures for the synthesis of proteins and phospholipids, more CO2 is fixed than is consumed by the Calvin cycle. To deal with this excess, diatoms redirect the carbon flow toward the synthesis of storage compounds such as triacylglycerides and carbohydrates, which are excreted as extracellular polymeric substances. This review aimed to gather all current knowledge regarding the biochemical and molecular mechanisms of diatoms related to managing P deficiency in order to provide a wider insight into and understanding of their responses, as well as the metabolic pathways affected by the limitation of this nutrient.

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Plants belonging to genus Jatropha has arisen interest because of its high oil content that could be used to produce biodiesel. It is also widely reported that the main fatty acids in Jatropha oilseed are oleic and linoleic acids. However, there are scarce studies related to native species of Jatropha from Northwestern Mexico which are adapted to arid conditions, and the expression of genes involved in fatty acid synthesis for these species is still unknown. Therefore, the aim of this study was to analyze the expression of five genes, ACP1, KASII, D9SD, FAD2-1 and FAD2-2, which are involved in the oleic and linoleic acids synthesis in mature wild-seeds of Jatropha cinerea, a native species from Sonoran Desert, using semi-quantitative RT-PCR. The J. cinerea seeds were randomly collected in Bahía de Kino, Sonora (México) which is a region characterized by its harsh environments such as saline soils and extreme temperature changes and J. curcas mature seeds from a non-toxic variety from Veracruz, Mexico were used as a reference. The RT-PCR analysis of three biological replicates were considered to ensure data consistent. Our analysis showed a higher expression of KASII and FAD2-1 genes in J. cinerea seeds compared to J. curcas, meanwhile the expression of ACP1, D9SD and FAD2-2 were higher in J. curcas. Furthermore, Actin and FAD2-1 genes sequences here obtained are the first reported for J. cinerea, thus providing information to develop further studies.

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