The effect of simulated copper stress on genes associated with the metabolism of polyphosphates and polyhydroxyalkanoates in Bacillus thuringiensis Y1

Aims@#Bacillus thuringiensis Y1 is a copper-tolerant bacterium that can serve as a model for the elucidation of the mechanism of energy metabolism under simulated copper stress. This study aimed to elucidate the effects of simulated copper stress on the genes associated with the biosynthesis of polyhydroxyalkanoates (PAH) and the metabolism of polyphosphates (PP).@*Methodology and results @#The gene expression study involved the growth of the bacterium in nutrient broth supplemented with two concentrations of copper sulphate (0.4 mM and 0.8 mM), followed by RNA extraction and quantification of four and 11 genes associated with the metabolism of polyphosphate (PP) and polyhydroxyalkanoates (PAHs) respectively, using reverse transcription quantitative polymerase chain reaction (RT-qPCR). Three genes associated with polyphosphate metabolism, which are polyphosphate kinase (ppk), exopolyphosphatase (ppx) and NAD kinase (ppnk), were all shown to be upregulated by both 0.4 mM and 0.8 mM copper, except for the 5’-nucleotidase (surE) gene that was downregulated under the second treatment. Among the 11 genes associated with the metabolism of polyhydroxyalkanoates, only the 3-ketoacyl-CoA-thiolase (phaA) gene was upregulated in both treatments and highly expressed in the second treatment; the majority were downregulated and repressed.@*Conclusion, significance and impact of study @#The study demonstrated that copper induces the metabolism of polyphosphates in B. thuringiensis Y1 that serve as an alternative source of energy under copper stress. This model can be extended to the study of other species of Bacillus under environmental stress.

Bacterial community associated with Pyrodinium bahamense var. compressum during late exponential growth phase based on 16S rRNA gene sequence analysis

Aims@#Pyrodinium bahamense var. compressum is one of the principal causal agents of harmful algal blooms (HABs) in the coastal waters of Sabah, Malaysia. Seafood and aquaculture products tainted with lethal concentrations of the principal neurotoxin, saxitoxin, have been implicated in mortality and morbidity. The bacteria-algae association may play a key role in paralytic shellfish toxin (PST) production during a toxic bloom event. The production of PST during a harmful bloom is unclear and research on the bacterial diversity associated with Sabah P. bahamense is scarce. The present study examined the cultivable bacteria diversity associated with P. bahamense through 16S ribosomal RNA (rRNA) gene sequence analysis.@*Methodology and results@#The V3-V4 region of the 16S rRNA gene sequence was amplified and used to identify bacterial populations associated with P. bahamense var. compressum. A total of 62 isolates were successfully isolated, belonging to three different phyla, which were Proteobacteria; 55 (89%), Bacteroidetes; 6 (10%) and Actinobacteria; 1 (1%). Out of 55 Proteobacteria, 27 isolates were gamma-Proteobacteria (Marinobacter salsuginis) and 28 of the isolates were alpha-Proteobacteria; Mameliella atlantica (13), Roseibium denhamense (10) and Roseibium hamelinense (5). The remaining bacteria isolates from the phyla Bacteroidetes and Actinobacteria were identified as Muricauda lutimaris (6) and Micrococcus luteus (1), respectively.@*Conclusion, significance and impact of study@#The analysis of the bacterial 16S rRNA gene revealed multiple bacterial taxa associated with the toxic P. bahamense var. compressum bloom. The findings of the present work will pave the way for further studies aimed at isolating and characterizing genes involved in the saxitoxin biosynthesis in the associated bacteria.

Enhanced microbial biomass and lipid production through co-cultivation of yeast Rhodotorula toruloides and microalga Chaetoceros muelleri

Aims@#The synergistic bio-activity between oleaginous yeast and microalga has been recognized, which would enhance lipid production as biodiesel feedstock. Nevertheless, yeast and microalga require different conditions for optimal growth. In this study, the locally isolated oleaginous yeast Rhodotorula toruloides and microalga Chaetoceros muelleri were co-cultivated to enhance biomass and lipid production.@*Methodology and results@#The growth characteristics of both yeast and microalga monocultures were initially determined prior to optimizing the co-cultivation conditions. The biomass and lipid productivity of the co-culture were investigated and compared to their monocultures. The results showed that R. toruloides grew actively within 3 days while C. muelleri exhibited more prolonged cultivation, up to 21 days. The co-cultivation could be carried out optimally using growth media at pH 6, light intensity of 15,000 lux and yeast/microalga ratio of 1:2, yielding the highest biomass productivity determined at 0.18 g/l/day and lipid production of 17%. The lipid productivity of the co-culture increased by 42% and 75% as compared to monocultures of yeast and microalga, respectively. Furthermore, the biomass productivity was also higher than the monoculture, about 1.2-fold for the yeast and 13-fold for the microalga.@*Conclusion, significance and impact of study@#The findings revealed that co-cultivation of yeast and microalga is a viable technique for long-term microbial oil production.

Bacterial diversity of the abandoned Mamut Copper Mine in Sabah, Malaysia and its correlation with copper contamination

Aims@#The former Mamut Copper Mine, acid mine drainage site represents an anthropogenic altered landscape characterized by its acidic topsoil which is contaminated primarily with copper. Even though the mining operation was ceased at 1999, the bacterial diversity in this area has never been investigated. This study was conducted to ascertain the bacterial diversity of this abandoned copper mine and correlate it to the copper concentration in the soil. @*Methodology and results@#Soil samples were collected from 7 sites near the mine pit and the vicinity. Soil samples were assessed for soil copper elemental concentration using inductively coupled plasma optical emission spectrometry and bacteria were isolated via serial dilution followed by culture on nutrient agar plates. Phylogenetic analysis was done based on the full-length sequences of 16S rRNA gene. Twenty-four phylotypes were obtained from the 7 locations which originated from the phyla Firmicutes, Actinobacteria, Bacteroidetes and Proteobacteria. The results of the study indicated that site 2 (6.030223°; 116.658030°), located in between the mine pit and the mine factory with a copper concentration of 88.96 ppm, possessed the most diverse bacterial community with a Shannon diversity index (H) of 1.68, evenness (EH) of 0.94 and richness (S) of 6. @*Conclusion, significance and impact of study@#Current study revealed that there was a positive correlation between the copper concentration and the H index and the richness, but this was not reflected in the evenness. This is the first report of bacterial diversity from the former Mamut Copper Mine site. The data provided a valuable insight for the future monitoring of the bacterial community in this ecologically important niche.