Biology subjects

Saurav, K.

Publications and source records attributed to Saurav, K..

3 recordsLinked to original sources

bioRxiv2025

The Maculalactone Biosynthetic Gene Cluster, a Cryptic Furanolide Pathway Revealed in Nodularia sp. NIES-3585

Cyanobacteria have long been recognised as a prolific source of bioactive natural products (NPs). Among these are the furanolides, a structurally diverse class of compounds first discovered in the 1980s. Furanolides are characterised by a {gamma} -butyrolactone core bearing aromatic or aliphatic substituents at the - and {beta} -positions and an aromatic substituent at the {gamma} -position. Recent advances in understanding the genetic basis of furanolide biosynthesis has enabled genome mining approaches to discover related cryptic furanolide biosynthetic gene clusters (BGCs). In this work, we identified and cloned a cryptic BGC (15.5 kb) from Nodularia sp. NIES-3585 using the Direct Pathway Cloning (DiPaC) strategy and heterologously expressed it in E. coli BAP1. Through isolation and structural elucidation, we characterised the known compounds maculalactone B and deoxyenhygrolide A and discovered the novel analogue maculalactone N, featuring a 4-hydroxyphenyl substituent at the{beta}position. Application of Global Natural Product Social Molecular Networking (GNPS) analysis of high-resolution LCMS data enabled the identification of 25 maculalactone-related molecules. Further, a MS/MS fragmentation rationale for furanolides was developed and used to probe for maculalactone-like molecules that were too low in abundance for isolation. The fragmentation analysis suggests the{beta} substituent displays remarkable diversity, accommodating aromatic, aliphatic, or indole moieties. Additionally, structural diversity appears through various hydroxylation patterns. These results demonstrate the substrate promiscuity of the maculalactone biosynthetic enzymes and their capacity to generate considerable structural diversity, while highlighting DiPaC as an effective strategy to access cyanobacterial NPs from cryptic BGCs.

synthetic biology↗

bioRxiv2021

Quorum sensing signals from epibiont mediate the induction of bioactive peptides in mat-forming cyanobacteria Nostoc

The regulation of oligopeptides production is essential in understanding their ecological role in complex microbial communities including harmful cyanobacterial blooms. The role of chemical communication between the cyanobacterium and the microbial community harboured as epibionts within its phycosphere is at an initial stage of research and little is understood about its specificity. Herein, we present insight into the role of a bacterial epibiont in regulating production of cyanobacterial oligopeptides microviridins, well-known elastase inhibitors with presumed anti-grazing effects, in an ecologically important cyanobacterial genus Nostoc. Heterologous expression and identification of specific signal molecules from the epibiont suggest the role of a quorum sensing-based interaction. Further, physiological experiments show an increase in microviridin production without affecting cyanobacterial growth and photosynthetic activity. Simultaneously, oligopeptides presenting a selective inhibition pattern provide support for their specific function in response to the presence of cohabitant epibionts. Thus, the chemical interaction revealed in our study provides an example of an interspecies signalling pathway monitoring the bacterial flora around the cyanobacterial filaments and induction of intrinsic species-specific metabolic responses. IMPORTANCEThe regulation of cyanopeptide production beyond microcystin is essential to understand their ecological role in complex microbial communities, e.g. harmful cyanobacterial blooms. The role of chemical communication between the cyanobacterium and the epibionts within its phycosphere is at an initial stage of research and little is understood about its specificity. The frequency of cyanopeptide occurrence also demonstrates the need to understand the contribution of cyanobacterial peptides to the overall biological impact of cyanopeptides on aquatic organisms and vertebrates including humans. Our results shed light on the epibiont control of cyanopeptide production via quorum sensing mechanisms and we posit that such mechanisms may be widespread in natural cyanobacterial bloom community regulation.

microbiology↗

bioRxiv2020

Microbial communities in an ultra-oligotrophic sea are more affected by season than by distancefrom shore

Marine microbial communities vary seasonally and spatially, but these two factors are rarely addressed together. We studied temporal and spatial patterns of the microbial community structure and activity along a coast to offshore transect from the Israeli coast of the Eastern Mediterranean Sea (EMS) over six cruises, in three seasons of two consecutive years. The ultra-oligotrophic status of the South Eastern Mediterranean Sea was reflected in the microbial community composition that was dominated by oligotrophic microbial groups such as SAR11 throughout the year, even at the most coastal station sampled. Seasons affected microbial communities much more than distance from shore explaining about half of the observed variability in the microbial community, compared to only about 6% that was explained by station. However, the most coastal site differed significantly in community structure and activity from the three further offshore stations in early winter and summer, but not in spring. Our data on the microbial community composition and its seasonality from a transect into the South Eastern Levantine basin support the notion that the EMS behaves similar to open gyres rather than an inland sea.

ecology↗