As the most recognizable natural secondary carotenoid astaxanthin producer, the green microalga Haematococcus pluvialis cultivation is performed via a two-stage process. The first is dedicated to biomass accumulation under growth-favoring conditions (green stage), and the second stage is for astaxanthin evolution under various stress conditions (red stage). This mini-review discusses the further improvement made on astaxanthin production by providing an overview of recent works on H. pluvialis, including the valuable ideas for bioprocess optimization on cell growth, and the current stress-exerting strategies for astaxanthin pigment production. The effects of nutrient constituents, especially nitrogen and carbon sources, and illumination intensity are emphasized during the green stage. On the other hand, the significance of the nitrogen depletion strategy and other exogenous factors comprising salinity, illumination, and temperature are considered for the astaxanthin inducement during the red stage. In short, any factor that interferes with the cellular processes that limit the growth or photosynthesis in the green stage could trigger the encystment process and astaxanthin formation during the red stage. This review provides an insight regarding the parameters involved in bioprocess optimization for high-value astaxanthin biosynthesis from H. pluvialis.

Here, we report the complete genome sequence of Paenibacillus durus type strain ATCC 35681, which can fix atmospheric nitrogen even in the presence of nitrate.

Methylobacterium sp. are pink-pigmented facultative methylotrophs (PPFMs) that can promote plant’s growth due to several physiological characteristics such as the ability to produce phytohormone namely indole acetic acid (IAA) and effective roles in phosphate solubilization and nitrogen fixation process. Members of this genus are ubiquitous in the environment and characterized by its ability to utilize single C compound such as methanol as its energy source. These characteristics made Methylobacterium sp. as potential candidates for biofertilizer. In this study, Methylobacterium sp. were isolated from the leaves of paddy and palm oil tree using Ammonia Mineral Salt (AMS) agar supplemented with methanol. Nine isolates were selected based on the appearance of pink colonies on AMS agar. Several analyses were conducted to evaluate plant growth-promoting activities of the selected isolates. The production of IAA was quantified spectrophotometrically using Salkowski’s reagent, and solubilization of inorganic phosphate was determined using vanadate molybdate assay. The results showed that, all the isolates are capable to produce IAA and solubilize inorganic phosphate. As for nitrogen fixation, the lack/poor growth of the isolates on two nitrogen-free media, namely Burks’s and Jensen media manifested the absence or weak nitrogen fixing activity. Findings from these qualitative and quantitative analyses are vital and it will serve as preliminary data for the future exploration of Methylobacterium sp. as biofertilizer.

In this post genomic era, there are a great number of in silico annotated hypothetical genes. However, experimental validation of the functionality of these genes remains tentative. Two of the major challenges faced by researcher are whether these hypothetical genes are protein-coding genes and whether their corresponding predicted translational start codons are correct. In this report, we demonstrate a convenient procedure to validate the presence of a hypothetical gene product of BPSS1356 from Burkholderia pseudomallei as well as its start codon. It was done by integration of a His-Tag coding sequence into C-terminal end of BPSS1356 gene via homologous recombination. We then purified the native protein using affinity chromatography. The genuine start codon of BPSS1356 was then determined by protein N-terminal sequencing.

Burkholderia pseudomallei is an opportunistic pathogen and the causative agent of melioidosis. It is able to adapt to harsh environments and can live intracellularly in its infected hosts. In this study, identification of transcriptional factors that associate with the β′ subunit (RpoC) of RNA polymerase was performed. The N-terminal region of this subunit is known to trigger promoter melting when associated with a sigma factor. A pull-down assay using histidine-tagged B. pseudomallei RpoC N-terminal region as bait showed that a hypothetical protein BPSS1356 was one of the proteins bound. This hypothetical protein is conserved in all B. pseudomallei strains and present only in the Burkholderia genus. A BPSS1356 deletion mutant was generated to investigate its biological function. The mutant strain exhibited reduced biofilm formation and a lower cell density during the stationary phase of growth in LB medium. Electron microscopic analysis revealed that the ΔBPSS1356 mutant cells had a shrunken cytoplasm indicative of cell plasmolysis and a rougher surface when compared to the wild type. An RNA microarray result showed that a total of 63 genes were transcriptionally affected by the BPSS1356 deletion with fold change values of higher than 4. The expression of a group of genes encoding membrane located transporters was concurrently down-regulated in ΔBPSS1356 mutant. Amongst the affected genes, the putative ion transportation genes were the most severely suppressed. Deprivation of BPSS1356 also down-regulated the transcriptions of genes for the arginine deiminase system, glycerol metabolism, type III secretion system cluster 2, cytochrome bd oxidase and arsenic resistance. It is therefore obvious that BPSS1356 plays a multiple regulatory roles on many genes.