Insights into the seasonal changes in the taxonomic and functional diversity of bacteria in the eastern Arabian Sea: Shotgun metagenomics approach.

The eastern Arabian Sea (EAS) is known for its unique oceanographic features such as the seasonal monsoonal winds, upwelling of nutrient-rich waters and a significant increase in primary productivity during the monsoon season. In this study, we utilised the shotgun metagenomics approach to determine the seasonal variations in bacterial taxonomic and functional profiles during the non-monsoon and monsoon seasons in the EAS. Significant seasonal variations in the bacterial community structure were observed at the phylum and genera levels. These findings also correspond with seasonal shifts in the functional profiles of the bacterial communities based on the variations of genes encoding enzymes associated with different metabolic pathways. Pronounced seasonal variation of bacterial taxa was evident with an increased abundance of Idiomarina, Marinobacter, Psychrobacter and Alteromonas of Proteobacteria, Bacillus and Staphylococcus of Firmicutes during the non-monsoon season. These taxa were linked to elevated nucleotide and amino acid biosynthesis, amino acid and lipid degradation. Conversely, during the monsoon, the taxa composition changed with Alteromonas, Candidatus Pelagibacter of Proteobacteria and Cyanobacteria Synechococcus; contributing largely to the amino acid and lipid biosynthesis, fermentation and inorganic nutrient metabolism which was evident from functional analysis. Regression analysis confirmed that increased seasonal primary productivity significantly influenced the abundance of genes associated with carbohydrate, protein and lipid metabolism. These highlight the pivotal role of seasonal changes in primary productivity in shaping the bacterial communities, their functional profiles and driving the biogeochemical cycling in the EAS.

Evaluating the Bacterial Diversity from the Southwest Coast of India Using Fatty Acid Methyl Ester Profiles.

The fatty acid composition of bacterial isolates remains stable under standardized culture conditions, which makes it a useful taxonomic marker. The present study aims to characterize the diversity and quantity of fatty acid methyl esters (FAME) profiles of cultivable bacterial isolates collected along the southwest coast of India. Based on the similarity indices (range > 0.3-0.7) of the FAME profiles, the isolates were aggregated into 10 families, 11 genera and 19 species of cultured isolates. The following classes of bacteria were found: Bacilli, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria and Actinobacteria, which also included a few pathogens such as Pseudomonas, Staphylococcus and Bacillus sp. The hydroxyl FAMEs 2-hydroxydodecanoic acid (C12:0 2OH), 2-hydroxypentadecanoic acid (C15:0 2OH),3-hydroxy 14-methylpentadecanoic acid (C16:0iso 3OH), 3 hydroxy hexadecenoic acid (C16:0 3OH) and 3-hydroxy 15-methylhexadecanoic acid (C17:0iso 3OH), as well as the unsaturated FAMEs (11Z)-11-hexadecenoic acid (C16:1 É·5c), were exclusively associated with the isolates from Mangalore samples. Similarly, FAMEs 2-hydroxydecanoic acid (C10:0 2OH), 9-methyldecanoic acid (C11:0iso), undecanoic acid (C11:0), tridecanoic acid (C13:0), 10-methylhexadecanoic acid (C16:0 10-CH3) and (7Z)-7-hexadecenoic acid (C16:1 É·9c) occurred only in the isolates from Trivandrum samples. However, the isolates from Goa did not possess a signature FAME profile. The reproducibility of the GC-MIDI bacterial identification system was evaluated using 16S rRNA gene sequencing techniques for selected isolates.